class-wp-sqlite-translator.php

<?php
/**
 * The queries translator.
 *
 * @package wp-sqlite-integration
 * @see https://github.com/phpmyadmin/sql-parser
 */

/**
 * The queries translator class.
 */
class WP_SQLite_Translator {

	const SQLITE_BUSY   = 5;
	const SQLITE_LOCKED = 6;

	const DATA_TYPES_CACHE_TABLE = '_mysql_data_types_cache';

	const CREATE_DATA_TYPES_CACHE_TABLE = 'CREATE TABLE IF NOT EXISTS _mysql_data_types_cache (
		`table` TEXT NOT NULL,
		`column_or_index` TEXT NOT NULL,
		`mysql_type` TEXT NOT NULL,
		PRIMARY KEY(`table`, `column_or_index`)
	);';

	/**
	 * We use the ASCII SUB character to escape LIKE literal _ and %
	 */
	const LIKE_ESCAPE_CHAR = "\x1a";

	/**
	 * Class variable to reference to the PDO instance.
	 *
	 * @access private
	 *
	 * @var PDO object
	 */
	private $pdo;

	/**
	 * The database version.
	 *
	 * This is used here to avoid PHP warnings in the health screen.
	 *
	 * @var string
	 */
	public $client_info = '';

	/**
	 * How to translate field types from MySQL to SQLite.
	 *
	 * @var array
	 */
	private $field_types_translation = array(
		'bit'                => 'integer',
		'bool'               => 'integer',
		'boolean'            => 'integer',
		'tinyint'            => 'integer',
		'smallint'           => 'integer',
		'mediumint'          => 'integer',
		'int'                => 'integer',
		'integer'            => 'integer',
		'bigint'             => 'integer',
		'float'              => 'real',
		'double'             => 'real',
		'decimal'            => 'real',
		'dec'                => 'real',
		'numeric'            => 'real',
		'fixed'              => 'real',
		'date'               => 'text',
		'datetime'           => 'text',
		'timestamp'          => 'text',
		'time'               => 'text',
		'year'               => 'text',
		'char'               => 'text',
		'varchar'            => 'text',
		'binary'             => 'integer',
		'varbinary'          => 'blob',
		'tinyblob'           => 'blob',
		'tinytext'           => 'text',
		'blob'               => 'blob',
		'text'               => 'text',
		'mediumblob'         => 'blob',
		'mediumtext'         => 'text',
		'longblob'           => 'blob',
		'longtext'           => 'text',
		'geomcollection'     => 'text',
		'geometrycollection' => 'text',
	);

	/**
	 * The MySQL to SQLite date formats translation.
	 *
	 * Maps MySQL formats to SQLite strftime() formats.
	 *
	 * For MySQL formats, see:
	 * * https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_date-format
	 *
	 * For SQLite formats, see:
	 * * https://www.sqlite.org/lang_datefunc.html
	 * * https://strftime.org/
	 *
	 * @var array
	 */
	private $mysql_date_format_to_sqlite_strftime = array(
		'%a' => '%D',
		'%b' => '%M',
		'%c' => '%n',
		'%D' => '%jS',
		'%d' => '%d',
		'%e' => '%j',
		'%H' => '%H',
		'%h' => '%h',
		'%I' => '%h',
		'%i' => '%M',
		'%j' => '%z',
		'%k' => '%G',
		'%l' => '%g',
		'%M' => '%F',
		'%m' => '%m',
		'%p' => '%A',
		'%r' => '%h:%i:%s %A',
		'%S' => '%s',
		'%s' => '%s',
		'%T' => '%H:%i:%s',
		'%U' => '%W',
		'%u' => '%W',
		'%V' => '%W',
		'%v' => '%W',
		'%W' => '%l',
		'%w' => '%w',
		'%X' => '%Y',
		'%x' => '%o',
		'%Y' => '%Y',
		'%y' => '%y',
	);

	/**
	 * Number of rows found by the last SELECT query.
	 *
	 * @var int
	 */
	private $last_select_found_rows;

	/**
	 * Number of rows found by the last SQL_CALC_FOUND_ROW query.
	 *
	 * @var int integer
	 */
	private $last_sql_calc_found_rows = null;

	/**
	 * The query rewriter.
	 *
	 * @var WP_SQLite_Query_Rewriter
	 */
	private $rewriter;

	/**
	 * Last executed MySQL query.
	 *
	 * @var string
	 */
	public $mysql_query;

	/**
	 * A list of executed SQLite queries.
	 *
	 * @var array
	 */
	public $executed_sqlite_queries = array();

	/**
	 * The affected table name.
	 *
	 * @var array
	 */
	private $table_name = array();

	/**
	 * The type of the executed query (SELECT, INSERT, etc).
	 *
	 * @var array
	 */
	private $query_type = array();

	/**
	 * The columns to insert.
	 *
	 * @var array
	 */
	private $insert_columns = array();

	/**
	 * Class variable to store the result of the query.
	 *
	 * @access private
	 *
	 * @var array reference to the PHP object
	 */
	private $results = null;

	/**
	 * Class variable to check if there is an error.
	 *
	 * @var boolean
	 */
	public $is_error = false;

	/**
	 * Class variable to store the file name and function to cause error.
	 *
	 * @access private
	 *
	 * @var array
	 */
	private $errors;

	/**
	 * Class variable to store the error messages.
	 *
	 * @access private
	 *
	 * @var array
	 */
	private $error_messages = array();

	/**
	 * Class variable to store the affected row id.
	 *
	 * @var int integer
	 * @access private
	 */
	private $last_insert_id;

	/**
	 * Class variable to store the number of rows affected.
	 *
	 * @var int integer
	 */
	private $affected_rows;

	/**
	 * Class variable to store the queried column info.
	 *
	 * @var array
	 */
	private $column_data;

	/**
	 * Variable to emulate MySQL affected row.
	 *
	 * @var integer
	 */
	private $num_rows;

	/**
	 * Return value from query().
	 *
	 * Each query has its own return value.
	 *
	 * @var mixed
	 */
	private $return_value;

	/**
	 * Variable to keep track of nested transactions level.
	 *
	 * @var int
	 */
	private $transaction_level = 0;

	/**
	 * Value returned by the last exec().
	 *
	 * @var mixed
	 */
	private $last_exec_returned;

	/**
	 * The PDO fetch mode passed to query().
	 *
	 * @var mixed
	 */
	private $pdo_fetch_mode;

	/**
	 * The last reserved keyword seen in an SQL query.
	 *
	 * @var mixed
	 */
	private $last_reserved_keyword;

	/**
	 * True if a VACUUM operation should be done on shutdown,
	 * to handle OPTIMIZE TABLE and similar operations.
	 *
	 * @var bool
	 */
	private $vacuum_requested = false;

	/**
	 * True if the present query is metadata
	 *
	 * @var bool
	 */
	private $is_information_schema_query = false;

	/**
	 * True if a GROUP BY clause is detected.
	 *
	 * @var bool
	 */
	private $has_group_by = false;

	/**
	 * 0 if no LIKE is in progress, otherwise counts nested parentheses.
	 *
	 * @todo A generic stack of expression would scale better. There's already a call_stack in WP_SQLite_Query_Rewriter.
	 * @var int
	 */
	private $like_expression_nesting = 0;

	/**
	 * 0 if no LIKE is in progress, otherwise counts nested parentheses.
	 *
	 * @var int
	 */
	private $like_escape_count = 0;

	/**
	 * Associative array with list of system (non-WordPress) tables.
	 *
	 * @var array  [tablename => tablename]
	 */
	private $sqlite_system_tables = array();

	/**
	 * The last error message from SQLite.
	 *
	 * @var string
	 */
	private $last_sqlite_error;

	/**
	 * Constructor.
	 *
	 * Create PDO object, set user defined functions and initialize other settings.
	 * Don't use parent::__construct() because this class does not only returns
	 * PDO instance but many others jobs.
	 *
	 * @param PDO $pdo The PDO object.
	 */
	public function __construct( $pdo = null ) {
		if ( ! $pdo ) {
			if ( ! is_file( FQDB ) ) {
				$this->prepare_directory();
			}

			$locked      = false;
			$status      = 0;
			$err_message = '';
			do {
				try {
					$options = array(
						PDO::ATTR_ERRMODE           => PDO::ERRMODE_EXCEPTION,
						PDO::ATTR_STRINGIFY_FETCHES => true,
						PDO::ATTR_TIMEOUT           => 5,
					);

					$dsn = 'sqlite:' . FQDB;
					$pdo = new PDO( $dsn, null, null, $options ); // phpcs:ignore WordPress.DB.RestrictedClasses
				} catch ( PDOException $ex ) {
					$status = $ex->getCode();
					if ( self::SQLITE_BUSY === $status || self::SQLITE_LOCKED === $status ) {
						$locked = true;
					} else {
						$err_message = $ex->getMessage();
					}
				}
			} while ( $locked );

			if ( $status > 0 ) {
				$message                = sprintf(
					'<p>%s</p><p>%s</p><p>%s</p>',
					'Database initialization error!',
					"Code: $status",
					"Error Message: $err_message"
				);
				$this->is_error         = true;
				$this->error_messages[] = $message;
				return;
			}
		}

		new WP_SQLite_PDO_User_Defined_Functions( $pdo );

		// MySQL data comes across stringified by default.
		$pdo->setAttribute( PDO::ATTR_STRINGIFY_FETCHES, true ); // phpcs:ignore WordPress.DB.RestrictedClasses.mysql__PDO
		$pdo->query( WP_SQLite_Translator::CREATE_DATA_TYPES_CACHE_TABLE );

		/*
		 * A list of system tables lets us emulate information_schema
		 * queries without returning extra tables.
		 */
		$this->sqlite_system_tables ['sqlite_sequence']              = 'sqlite_sequence';
		$this->sqlite_system_tables [ self::DATA_TYPES_CACHE_TABLE ] = self::DATA_TYPES_CACHE_TABLE;

		$this->pdo = $pdo;

		// Fixes a warning in the site-health screen.
		$this->client_info = SQLite3::version()['versionString'];

		register_shutdown_function( array( $this, '__destruct' ) );

		// WordPress happens to use no foreign keys.
		$statement = $this->pdo->query( 'PRAGMA foreign_keys' );
		// phpcs:ignore Universal.Operators.StrictComparisons.LooseEqual
		if ( $statement->fetchColumn( 0 ) == '0' ) {
			$this->pdo->query( 'PRAGMA foreign_keys = ON' );
		}
		$this->pdo->query( 'PRAGMA encoding="UTF-8";' );
	}

	/**
	 * Destructor
	 *
	 * If SQLITE_MEM_DEBUG constant is defined, append information about
	 * memory usage into database/mem_debug.txt.
	 *
	 * This definition is changed since version 1.7.
	 */
	public function __destruct() {
		if ( defined( 'SQLITE_MEM_DEBUG' ) && SQLITE_MEM_DEBUG ) {
			$max = ini_get( 'memory_limit' );
			if ( is_null( $max ) ) {
				$message = sprintf(
					'[%s] Memory_limit is not set in php.ini file.',
					gmdate( 'Y-m-d H:i:s', $_SERVER['REQUEST_TIME'] )
				);
				error_log( $message );
				return;
			}
			if ( stripos( $max, 'M' ) !== false ) {
				$max = (int) $max * MB_IN_BYTES;
			}
			$peak = memory_get_peak_usage( true );
			$used = round( (int) $peak / (int) $max * 100, 2 );
			if ( $used > 90 ) {
				$message = sprintf(
					"[%s] Memory peak usage warning: %s %% used. (max: %sM, now: %sM)\n",
					gmdate( 'Y-m-d H:i:s', $_SERVER['REQUEST_TIME'] ),
					$used,
					$max,
					$peak
				);
				error_log( $message );
			}
		}
	}

	/**
	 * Get the PDO object.
	 *
	 * @return PDO
	 */
	public function get_pdo() {
		return $this->pdo;
	}

	/**
	 * Method to return inserted row id.
	 */
	public function get_insert_id() {
		return $this->last_insert_id;
	}

	/**
	 * Method to return the number of rows affected.
	 */
	public function get_affected_rows() {
		return $this->affected_rows;
	}

	/**
	 * This method makes database directory and .htaccess file.
	 *
	 * It is executed only once when the installation begins.
	 */
	private function prepare_directory() {
		global $wpdb;
		$u = umask( 0000 );
		if ( ! is_dir( FQDBDIR ) ) {
			if ( ! @mkdir( FQDBDIR, 0704, true ) ) {
				umask( $u );
				wp_die( 'Unable to create the required directory! Please check your server settings.', 'Error!' );
			}
		}
		if ( ! is_writable( FQDBDIR ) ) {
			umask( $u );
			$message = 'Unable to create a file in the directory! Please check your server settings.';
			wp_die( $message, 'Error!' );
		}
		if ( ! is_file( FQDBDIR . '.htaccess' ) ) {
			$fh = fopen( FQDBDIR . '.htaccess', 'w' );
			if ( ! $fh ) {
				umask( $u );
				echo 'Unable to create a file in the directory! Please check your server settings.';

				return false;
			}
			fwrite( $fh, 'DENY FROM ALL' );
			fclose( $fh );
		}
		if ( ! is_file( FQDBDIR . 'index.php' ) ) {
			$fh = fopen( FQDBDIR . 'index.php', 'w' );
			if ( ! $fh ) {
				umask( $u );
				echo 'Unable to create a file in the directory! Please check your server settings.';

				return false;
			}
			fwrite( $fh, '<?php // Silence is gold. ?>' );
			fclose( $fh );
		}
		umask( $u );

		return true;
	}

	/**
	 * Method to execute query().
	 *
	 * Divide the query types into seven different ones. That is to say:
	 *
	 * 1. SELECT SQL_CALC_FOUND_ROWS
	 * 2. INSERT
	 * 3. CREATE TABLE(INDEX)
	 * 4. ALTER TABLE
	 * 5. SHOW VARIABLES
	 * 6. DROP INDEX
	 * 7. THE OTHERS
	 *
	 * #1 is just a tricky play. See the private function handle_sql_count() in query.class.php.
	 * From #2 through #5 call different functions respectively.
	 * #6 call the ALTER TABLE query.
	 * #7 is a normal process: sequentially call prepare_query() and execute_query().
	 *
	 * #1 process has been changed since version 1.5.1.
	 *
	 * @param string $statement          Full SQL statement string.
	 * @param int    $mode               Not used.
	 * @param array  ...$fetch_mode_args Not used.
	 *
	 * @see PDO::query()
	 *
	 * @throws Exception    If the query could not run.
	 * @throws PDOException If the translated query could not run.
	 *
	 * @return mixed according to the query type
	 */
	public function query( $statement, $mode = PDO::FETCH_OBJ, ...$fetch_mode_args ) { // phpcs:ignore WordPress.DB.RestrictedClasses
		$this->flush();
		if ( function_exists( 'apply_filters' ) ) {
			/**
			 * Filters queries before they are translated and run.
			 *
			 * Return a non-null value to cause query() to return early with that result.
			 * Use this filter to intercept queries that don't work correctly in SQLite.
			 *
			 * From within the filter you can do
			 *  function filter_sql ($result, $translator, $statement, $mode, $fetch_mode_args) {
			 *     if ( intercepting this query  ) {
			 *       return $translator->execute_sqlite_query( $statement );
			 *     }
			 *     return $result;
			 *   }
			 *
			 * @param null|array $result Default null to continue with the query.
			 * @param object     $translator The translator object. You can call $translator->execute_sqlite_query().
			 * @param string     $statement The statement passed.
			 * @param int        $mode Fetch mode: PDO::FETCH_OBJ, PDO::FETCH_CLASS, etc.
			 * @param array      $fetch_mode_args Variable arguments passed to query.
			 *
			 * @returns null|array Null to proceed, or an array containing a resultset.
			 * @since 2.1.0
			 */
			$pre = apply_filters( 'pre_query_sqlite_db', null, $this, $statement, $mode, $fetch_mode_args );
			if ( null !== $pre ) {
				return $pre;
			}
		}
		$this->pdo_fetch_mode = $mode;
		$this->mysql_query    = $statement;
		if (
			preg_match( '/^\s*START TRANSACTION/i', $statement )
			|| preg_match( '/^\s*BEGIN/i', $statement )
		) {
			return $this->begin_transaction();
		}
		if ( preg_match( '/^\s*COMMIT/i', $statement ) ) {
			return $this->commit();
		}
		if ( preg_match( '/^\s*ROLLBACK/i', $statement ) ) {
			return $this->rollback();
		}

		try {
			// Perform all the queries in a nested transaction.
			$this->begin_transaction();

			do {
				$error = null;
				try {
					$this->execute_mysql_query(
						$statement
					);
				} catch ( PDOException $error ) {
					if ( $error->getCode() !== self::SQLITE_BUSY ) {
						throw $error;
					}
				}
			} while ( $error );

			/**
			 * Notifies that a query has been translated and executed.
			 *
			 * @param string $query          The executed SQL query.
			 * @param string $query_type     The type of the SQL query (e.g. SELECT, INSERT, UPDATE, DELETE).
			 * @param string $table_name     The name of the table affected by the SQL query.
			 * @param array  $insert_columns The columns affected by the INSERT query (if applicable).
			 * @param int    $last_insert_id The ID of the last inserted row (if applicable).
			 * @param int    $affected_rows  The number of affected rows (if applicable).
			 *
			 * @since 0.1.0
			 */
			do_action(
				'sqlite_translated_query_executed',
				$this->mysql_query,
				$this->query_type,
				$this->table_name,
				$this->insert_columns,
				$this->last_insert_id,
				$this->affected_rows
			);

			// Commit the nested transaction.
			$this->commit();

			return $this->return_value;
		} catch ( Exception $err ) {
			// Rollback the nested transaction.
			$this->rollback();
			if ( defined( 'PDO_DEBUG' ) && PDO_DEBUG === true ) {
				throw $err;
			}
			return $this->handle_error( $err );
		}
	}

	/**
	 * Method to return the queried column names.
	 *
	 * These data are meaningless for SQLite. So they are dummy emulating
	 * MySQL columns data.
	 *
	 * @return array|null of the object
	 */
	public function get_columns() {
		if ( ! empty( $this->results ) ) {
			$primary_key = array(
				'meta_id',
				'comment_ID',
				'link_ID',
				'option_id',
				'blog_id',
				'option_name',
				'ID',
				'term_id',
				'object_id',
				'term_taxonomy_id',
				'umeta_id',
				'id',
			);
			$unique_key  = array( 'term_id', 'taxonomy', 'slug' );
			$data        = array(
				'name'         => '', // Column name.
				'table'        => '', // Table name.
				'max_length'   => 0,  // Max length of the column.
				'not_null'     => 1,  // 1 if not null.
				'primary_key'  => 0,  // 1 if column has primary key.
				'unique_key'   => 0,  // 1 if column has unique key.
				'multiple_key' => 0,  // 1 if column doesn't have unique key.
				'numeric'      => 0,  // 1 if column has numeric value.
				'blob'         => 0,  // 1 if column is blob.
				'type'         => '', // Type of the column.
				'int'          => 0,  // 1 if column is int integer.
				'zerofill'     => 0,  // 1 if column is zero-filled.
			);
			$table_name  = '';
			$sql         = '';
			$query       = end( $this->executed_sqlite_queries );
			if ( $query ) {
				$sql = $query['sql'];
			}
			if ( preg_match( '/\s*FROM\s*(.*)?\s*/i', $sql, $match ) ) {
				$table_name = trim( $match[1] );
			}
			foreach ( $this->results[0] as $key => $value ) {
				$data['name']  = $key;
				$data['table'] = $table_name;
				if ( in_array( $key, $primary_key, true ) ) {
					$data['primary_key'] = 1;
				} elseif ( in_array( $key, $unique_key, true ) ) {
					$data['unique_key'] = 1;
				} else {
					$data['multiple_key'] = 1;
				}
				$this->column_data[] = json_decode( json_encode( $data ) );

				// Reset data for next iteration.
				$data['name']         = '';
				$data['table']        = '';
				$data['primary_key']  = 0;
				$data['unique_key']   = 0;
				$data['multiple_key'] = 0;
			}

			return $this->column_data;
		}
		return null;
	}

	/**
	 * Method to return the queried result data.
	 *
	 * @return mixed
	 */
	public function get_query_results() {
		return $this->results;
	}

	/**
	 * Method to return the number of rows from the queried result.
	 */
	public function get_num_rows() {
		return $this->num_rows;
	}

	/**
	 * Method to return the queried results according to the query types.
	 *
	 * @return mixed
	 */
	public function get_return_value() {
		return $this->return_value;
	}

	/**
	 * Executes a MySQL query in SQLite.
	 *
	 * @param string $query The query.
	 *
	 * @throws Exception If the query is not supported.
	 */
	private function execute_mysql_query( $query ) {
		$tokens           = ( new WP_SQLite_Lexer( $query ) )->tokens;
		$this->rewriter   = new WP_SQLite_Query_Rewriter( $tokens );
		$this->query_type = $this->rewriter->peek()->value;

		switch ( $this->query_type ) {
			case 'ALTER':
				$this->execute_alter();
				break;

			case 'CREATE':
				$this->execute_create();
				break;

			case 'SELECT':
				$this->execute_select();
				break;

			case 'INSERT':
			case 'REPLACE':
				$this->execute_insert_or_replace();
				break;

			case 'UPDATE':
				$this->execute_update();
				break;

			case 'DELETE':
				$this->execute_delete();
				break;

			case 'CALL':
			case 'SET':
				/*
				 * It would be lovely to support at least SET autocommit,
				 * but I don't think that is even possible with SQLite.
				 */
				$this->results = 0;
				break;

			case 'TRUNCATE':
				$this->execute_truncate();
				break;

			case 'BEGIN':
			case 'START TRANSACTION':
				$this->results = $this->begin_transaction();
				break;

			case 'COMMIT':
				$this->results = $this->commit();
				break;

			case 'ROLLBACK':
				$this->results = $this->rollback();
				break;

			case 'DROP':
				$this->execute_drop();
				break;

			case 'SHOW':
				$this->execute_show();
				break;

			case 'DESCRIBE':
				$this->execute_describe();
				break;

			case 'CHECK':
				$this->execute_check();
				break;

			case 'OPTIMIZE':
			case 'REPAIR':
			case 'ANALYZE':
				$this->execute_optimize( $this->query_type );
				break;

			default:
				throw new Exception( 'Unknown query type: ' . $this->query_type );
		}
	}

	/**
	 * Executes a MySQL CREATE TABLE query in SQLite.
	 *
	 * @throws Exception If the query is not supported.
	 */
	private function execute_create_table() {
		$table = $this->parse_create_table();

		$definitions = array();
		foreach ( $table->fields as $field ) {
			/*
			 * Do not include the inline PRIMARY KEY definition
			 * if there is more than one primary key.
			 */
			if ( $field->primary_key && count( $table->primary_key ) > 1 ) {
				$field->primary_key = false;
			}
			if ( $field->auto_increment && count( $table->primary_key ) > 1 ) {
				throw new Exception( 'Cannot combine AUTOINCREMENT and multiple primary keys in SQLite' );
			}

			$definitions[] = $this->make_sqlite_field_definition( $field );
			$this->update_data_type_cache(
				$table->name,
				$field->name,
				$field->mysql_data_type
			);
		}

		if ( count( $table->primary_key ) > 1 ) {
			$definitions[] = 'PRIMARY KEY ("' . implode( '", "', $table->primary_key ) . '")';
		}

		$create_query = (
			$table->create_table .
			'"' . $table->name . '" (' . "\n" .
			implode( ",\n", $definitions ) .
			')'
		);
		$this->execute_sqlite_query( $create_query );
		$this->results      = $this->last_exec_returned;
		$this->return_value = $this->results;

		foreach ( $table->constraints as $constraint ) {
			$index_type = $this->mysql_index_type_to_sqlite_type( $constraint->value );
			$unique     = '';
			if ( 'UNIQUE INDEX' === $index_type ) {
				$unique = 'UNIQUE ';
			}
			$index_name = "{$table->name}__{$constraint->name}";
			$this->execute_sqlite_query(
				"CREATE $unique INDEX \"$index_name\" ON \"{$table->name}\" (\"" . implode( '", "', $constraint->columns ) . '")'
			);
			$this->update_data_type_cache(
				$table->name,
				$index_name,
				$constraint->value
			);
		}
	}

	/**
	 * Parse the CREATE TABLE query.
	 *
	 * @return stdClass Structured data.
	 */
	private function parse_create_table() {
		$this->rewriter       = clone $this->rewriter;
		$result               = new stdClass();
		$result->create_table = null;
		$result->name         = null;
		$result->fields       = array();
		$result->constraints  = array();
		$result->primary_key  = array();

		/*
		 * The query starts with CREATE TABLE [IF NOT EXISTS].
		 * Consume everything until the table name.
		 */
		while ( true ) {
			$token = $this->rewriter->consume();
			if ( ! $token ) {
				break;
			}
			// The table name is the first non-keyword token.
			if ( WP_SQLite_Token::TYPE_KEYWORD !== $token->type ) {
				// Store the table name for later.
				$result->name = $this->normalize_column_name( $token->value );

				// Drop the table name and store the CREATE TABLE command.
				$this->rewriter->drop_last();
				$result->create_table = $this->rewriter->get_updated_query();
				break;
			}
		}

		/*
		 * Move to the opening parenthesis:
		 * CREATE TABLE wp_options (
		 *   ^ here.
		 */
		$this->rewriter->skip(
			array(
				'type'  => WP_SQLite_Token::TYPE_OPERATOR,
				'value' => '(',
			)
		);

		/*
		 * We're in the table definition now.
		 * Read everything until the closing parenthesis.
		 */
		$declarations_depth = $this->rewriter->depth;
		do {
			/*
			 * We want to capture a rewritten line of the query.
			 * Let's clear any data we might have captured so far.
			 */
			$this->rewriter->replace_all( array() );

			/*
			 * Decide how to parse the current line. We expect either:
			 *
			 * Field definition, e.g.:
			 *     `my_field` varchar(255) NOT NULL DEFAULT 'foo'
			 * Constraint definition, e.g.:
			 *      PRIMARY KEY (`my_field`)
			 *
			 * Lexer does not seem to reliably understand whether the
			 * first token is a field name or a reserved keyword, so
			 * instead we'll check whether the second non-whitespace
			 * token is a data type.
			 */
			$second_token = $this->rewriter->peek_nth( 2 );

			if ( $second_token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_DATA_TYPE
			) ) {
				$result->fields[] = $this->parse_mysql_create_table_field();
			} else {
				$result->constraints[] = $this->parse_mysql_create_table_constraint();
			}

			/*
			 * If we're back at the initial depth, we're done.
			 * Also, MySQL supports a trailing comma – if we see one,
			 * then we're also done.
			 */
		} while (
			$token
			&& $this->rewriter->depth >= $declarations_depth
			&& $this->rewriter->peek()->token !== ')'
		);

		// Merge all the definitions of the primary key.
		foreach ( $result->constraints as $k => $constraint ) {
			if ( 'PRIMARY' === $constraint->value ) {
				$result->primary_key = array_merge(
					$result->primary_key,
					$constraint->columns
				);
				unset( $result->constraints[ $k ] );
			}
		}

		// Inline primary key in a field definition.
		foreach ( $result->fields as $k => $field ) {
			if ( $field->primary_key ) {
				$result->primary_key[] = $field->name;
			} elseif ( in_array( $field->name, $result->primary_key, true ) ) {
				$field->primary_key = true;
			}
		}

		// Remove duplicates.
		$result->primary_key = array_unique( $result->primary_key );

		return $result;
	}

	/**
	 * Parses a CREATE TABLE query.
	 *
	 * @throws Exception If the query is not supported.
	 *
	 * @return stdClass
	 */
	private function parse_mysql_create_table_field() {
		$result                   = new stdClass();
		$result->name             = '';
		$result->sqlite_data_type = '';
		$result->not_null         = false;
		$result->default          = null;
		$result->auto_increment   = false;
		$result->primary_key      = false;

		$field_name_token = $this->rewriter->skip(); // Field name.
		$this->rewriter->add( new WP_SQLite_Token( "\n", WP_SQLite_Token::TYPE_WHITESPACE ) );
		$result->name = $this->normalize_column_name( $field_name_token->value );

		$definition_depth = $this->rewriter->depth;

		$skip_mysql_data_type_parts = $this->skip_mysql_data_type();
		$result->sqlite_data_type   = $skip_mysql_data_type_parts[0];
		$result->mysql_data_type    = $skip_mysql_data_type_parts[1];

		// Look for the NOT NULL and AUTO_INCREMENT flags.
		while ( true ) {
			$token = $this->rewriter->skip();
			if ( ! $token ) {
				break;
			}
			if ( $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_RESERVED,
				array( 'NOT NULL' )
			) ) {
				$result->not_null = true;
				continue;
			}

			if ( $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_RESERVED,
				array( 'PRIMARY KEY' )
			) ) {
				$result->primary_key = true;
				continue;
			}

			if ( $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				null,
				array( 'AUTO_INCREMENT' )
			) ) {
				$result->primary_key    = true;
				$result->auto_increment = true;
				continue;
			}

			if ( $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_FUNCTION,
				array( 'DEFAULT' )
			) ) {
				$result->default = $this->rewriter->consume()->token;
				continue;
			}

			if ( $this->is_create_table_field_terminator( $token, $definition_depth ) ) {
				$this->rewriter->add( $token );
				break;
			}
		}

		return $result;
	}

	/**
	 * Translate field definitions.
	 *
	 * @param stdClass $field Field definition.
	 *
	 * @return string
	 */
	private function make_sqlite_field_definition( $field ) {
		$definition = '"' . $field->name . '" ' . $field->sqlite_data_type;
		if ( $field->auto_increment ) {
			$definition .= ' PRIMARY KEY AUTOINCREMENT';
		} elseif ( $field->primary_key ) {
			$definition .= ' PRIMARY KEY ';
		}
		if ( $field->not_null ) {
			$definition .= ' NOT NULL';
		}
		if ( null !== $field->default ) {
			$definition .= ' DEFAULT ' . $field->default;
		}

		/*
		 * In MySQL, text fields are case-insensitive by default.
		 * COLLATE NOCASE emulates the same behavior in SQLite.
		 */
		if ( 'text' === $field->sqlite_data_type ) {
			$definition .= ' COLLATE NOCASE';
		}
		return $definition;
	}

	/**
	 * Parses a CREATE TABLE constraint.
	 *
	 * @throws Exception If the query is not supported.
	 *
	 * @return stdClass
	 */
	private function parse_mysql_create_table_constraint() {
		$result          = new stdClass();
		$result->name    = '';
		$result->value   = '';
		$result->columns = array();

		$definition_depth = $this->rewriter->depth;
		$constraint       = $this->rewriter->peek();
		if ( ! $constraint->matches( WP_SQLite_Token::TYPE_KEYWORD ) ) {
			/*
			 * Not a constraint declaration, but we're not finished
			 * with the table declaration yet.
			 */
			throw new Exception( 'Unexpected token in MySQL query: ' . $this->rewriter->peek()->value );
		}

		$result->value = $this->normalize_mysql_index_type( $constraint->value );
		if ( $result->value ) {
			$this->rewriter->skip(); // Constraint type.
			if ( 'PRIMARY' !== $result->value ) {
				$result->name = $this->rewriter->skip()->value;
			}

			$constraint_depth = $this->rewriter->depth;
			$this->rewriter->skip(); // `(`
			do {
				$result->columns[] = $this->normalize_column_name( $this->rewriter->skip()->value );
				$paren_maybe       = $this->rewriter->peek();
				if ( $paren_maybe && '(' === $paren_maybe->token ) {
					$this->rewriter->skip();
					$this->rewriter->skip();
					$this->rewriter->skip();
				}
				$this->rewriter->skip(); // `,` or `)`
			} while ( $this->rewriter->depth > $constraint_depth );
		}

		do {
			$token = $this->rewriter->skip();
		} while ( ! $this->is_create_table_field_terminator( $token, $definition_depth ) );

		return $result;
	}

	/**
	 * Checks if the current token is the terminator of a CREATE TABLE field.
	 *
	 * @param WP_SQLite_Token $token            The current token.
	 * @param int             $definition_depth The initial depth.
	 * @param int|null        $current_depth    The current depth.
	 *
	 * @return bool
	 */
	private function is_create_table_field_terminator( $token, $definition_depth, $current_depth = null ) {
		if ( null === $current_depth ) {
			$current_depth = $this->rewriter->depth;
		}
		return (
			// Reached the end of the query.
			null === $token

			// The field-terminating ",".
			|| (
				$current_depth === $definition_depth &&
				WP_SQLite_Token::TYPE_OPERATOR === $token->type &&
				',' === $token->value
			)

			// The definitions-terminating ")".
			|| $current_depth === $definition_depth - 1

			// The query-terminating ";".
			|| (
				WP_SQLite_Token::TYPE_DELIMITER === $token->type &&
				';' === $token->value
			)
		);
	}

	/**
	 * Executes a DELETE statement.
	 *
	 * @throws Exception If the table could not be found.
	 */
	private function execute_delete() {
		$this->rewriter->consume(); // DELETE.

		// Process expressions and extract bound parameters.
		$params = array();
		while ( true ) {
			$token = $this->rewriter->peek();
			if ( ! $token ) {
				break;
			}

			$this->remember_last_reserved_keyword( $token );

			if (
				$this->extract_bound_parameter( $token, $params )
				|| $this->translate_expression( $token )
			) {
				continue;
			}

			$this->rewriter->consume();
		}
		$this->rewriter->consume_all();

		$updated_query = $this->rewriter->get_updated_query();

		// Perform DELETE-specific translations.

		// Naive rewriting of DELETE JOIN query.
		// @TODO: Actually rewrite the query instead of using a hardcoded workaround.
		if ( str_contains( $updated_query, ' JOIN ' ) ) {
			$table_prefix = isset( $GLOBALS['table_prefix'] ) ? $GLOBALS['table_prefix'] : 'wp_';
			$this->execute_sqlite_query(
				"DELETE FROM {$table_prefix}options WHERE option_id IN (SELECT MIN(option_id) FROM {$table_prefix}options GROUP BY option_name HAVING COUNT(*) > 1)"
			);
			$this->set_result_from_affected_rows();
			return;
		}

		$rewriter = new WP_SQLite_Query_Rewriter( $this->rewriter->output_tokens );

		$comma = $rewriter->peek(
			array(
				'type'  => WP_SQLite_Token::TYPE_OPERATOR,
				'value' => ',',
			)
		);
		$from  = $rewriter->peek(
			array(
				'type'  => WP_SQLite_Token::TYPE_KEYWORD,
				'value' => 'FROM',
			)
		);
		// The DELETE query targets a single table if there's no comma before the FROM.
		if ( ! $comma || ! $from || $comma->position >= $from->position ) {
			$this->execute_sqlite_query(
				$updated_query,
				$params
			);
			$this->set_result_from_affected_rows();
			return;
		}

		// The DELETE query targets multiple tables – rewrite it into a
		// SELECT to fetch the IDs of the rows to delete, then delete them
		// using a separate DELETE query.

		$this->table_name = $rewriter->skip()->value;
		$rewriter->add( new WP_SQLite_Token( 'SELECT', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ) );

		/*
		 * Get table name.
		 */
		$from  = $rewriter->peek(
			array(
				'type'  => WP_SQLite_Token::TYPE_KEYWORD,
				'value' => 'FROM',
			)
		);
		$index = array_search( $from, $rewriter->input_tokens, true );
		for ( $i = $index + 1; $i < $rewriter->max; $i++ ) {
			// Assume the table name is the first token after FROM.
			if ( ! $rewriter->input_tokens[ $i ]->is_semantically_void() ) {
				$this->table_name = $rewriter->input_tokens[ $i ]->value;
				break;
			}
		}
		if ( ! $this->table_name ) {
			throw new Exception( 'Could not find table name for dual delete query.' );
		}

		/*
		 * Now, let's figure out the primary key name.
		 * This assumes that all listed table names are the same.
		 */
		$q       = $this->execute_sqlite_query( 'SELECT l.name FROM pragma_table_info("' . $this->table_name . '") as l WHERE l.pk = 1;' );
		$pk_name = $q->fetch()['name'];

		/*
		 * Good, we can finally create the SELECT query.
		 * Let's rewrite DELETE a, b FROM ... to SELECT a.id, b.id FROM ...
		 */
		$alias_nb = 0;
		while ( true ) {
			$token = $rewriter->consume();
			if ( WP_SQLite_Token::TYPE_KEYWORD === $token->type && 'FROM' === $token->value ) {
				break;
			}

			/*
			 * Between DELETE and FROM we only expect commas and table aliases.
			 * If it's not a comma, it must be a table alias.
			 */
			if ( ',' !== $token->value ) {
				// Insert .id AS id_1 after the table alias.
				$rewriter->add_many(
					array(
						new WP_SQLite_Token( '.', WP_SQLite_Token::TYPE_OPERATOR, WP_SQLite_Token::FLAG_OPERATOR_SQL ),
						new WP_SQLite_Token( $pk_name, WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_KEY ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( 'AS', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( 'id_' . $alias_nb, WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_KEY ),
					)
				);
				++$alias_nb;
			}
		}
		$rewriter->consume_all();

		// Select the IDs to delete.
		$select = $rewriter->get_updated_query();
		$stmt   = $this->execute_sqlite_query( $select );
		$stmt->execute( $params );
		$rows          = $stmt->fetchAll();
		$ids_to_delete = array();
		foreach ( $rows as $id ) {
			$ids_to_delete[] = $id['id_0'];
			$ids_to_delete[] = $id['id_1'];
		}

		$query = (
		count( $ids_to_delete )
			? "DELETE FROM {$this->table_name} WHERE {$pk_name} IN (" . implode( ',', $ids_to_delete ) . ')'
			: "DELETE FROM {$this->table_name} WHERE 0=1"
		);
		$this->execute_sqlite_query( $query );
		$this->set_result_from_affected_rows(
			count( $ids_to_delete )
		);
	}

	/**
	 * Executes a SELECT statement.
	 */
	private function execute_select() {
		$this->rewriter->consume(); // SELECT.

		$params                  = array();
		$table_name              = null;
		$has_sql_calc_found_rows = false;

		// Consume and record the table name.
		while ( true ) {
			$token = $this->rewriter->peek();
			if ( ! $token ) {
				break;
			}

			$this->remember_last_reserved_keyword( $token );

			if ( ! $table_name ) {
				$this->table_name = $this->peek_table_name( $token );
				$table_name       = $this->peek_table_name( $token );
			}

			if ( $this->skip_sql_calc_found_rows( $token ) ) {
				$has_sql_calc_found_rows = true;
				continue;
			}

			if (
				$this->extract_bound_parameter( $token, $params )
				|| $this->translate_expression( $token )
			) {
				continue;
			}

			$this->rewriter->consume();
		}
		$this->rewriter->consume_all();

		$updated_query = $this->rewriter->get_updated_query();

		if ( $table_name && str_starts_with( strtolower( $table_name ), 'information_schema' ) ) {
			$this->is_information_schema_query = true;
			$updated_query                     = $this->get_information_schema_query( $updated_query );
			$params                            = array();
		} elseif (
			strpos( $updated_query, '@@SESSION.sql_mode' ) !== false
			|| strpos( $updated_query, 'CONVERT( ' ) !== false
		) {
			/*
			 * If the query contains a function that is not supported by SQLite,
			 * return a dummy select. This check must be done after the query
			 * has been rewritten to use parameters to avoid false positives
			 * on queries such as `SELECT * FROM table WHERE field='CONVERT('`.
			 */
			$updated_query = 'SELECT 1=0';
			$params        = array();
		} elseif ( $has_sql_calc_found_rows ) {
			// Emulate SQL_CALC_FOUND_ROWS for now.
			$query = $updated_query;
			// We make the data for next SELECT FOUND_ROWS() statement.
			$unlimited_query = preg_replace( '/\\bLIMIT\\s\d+(?:\s*,\s*\d+)?$/imsx', '', $query );
			$stmt            = $this->execute_sqlite_query( $unlimited_query );
			$stmt->execute( $params );
			$this->last_sql_calc_found_rows = count( $stmt->fetchAll() );
		}

		// Emulate FOUND_ROWS() by counting the rows in the result set.
		if ( strpos( $updated_query, 'FOUND_ROWS(' ) !== false ) {
			$last_found_rows = ( $this->last_sql_calc_found_rows ? $this->last_sql_calc_found_rows : 0 ) . '';
			$updated_query   = "SELECT {$last_found_rows} AS `FOUND_ROWS()`";
		}

		$stmt = $this->execute_sqlite_query( $updated_query, $params );
		if ( $this->is_information_schema_query ) {
			$this->set_results_from_fetched_data(
				$this->strip_sqlite_system_tables(
					$stmt->fetchAll( $this->pdo_fetch_mode )
				)
			);
		} else {
			$this->set_results_from_fetched_data(
				$stmt->fetchAll( $this->pdo_fetch_mode )
			);
		}
	}

	/**
	 * Executes a TRUNCATE statement.
	 */
	private function execute_truncate() {
		$this->rewriter->skip(); // TRUNCATE.
		if ( 'TABLE' === strtoupper( $this->rewriter->peek()->value ) ) {
			$this->rewriter->skip(); // TABLE.
		}
		$this->rewriter->add( new WP_SQLite_Token( 'DELETE', WP_SQLite_Token::TYPE_KEYWORD ) );
		$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
		$this->rewriter->add( new WP_SQLite_Token( 'FROM', WP_SQLite_Token::TYPE_KEYWORD ) );
		$this->rewriter->consume_all();
		$this->execute_sqlite_query( $this->rewriter->get_updated_query() );
		$this->results      = true;
		$this->return_value = true;
	}

	/**
	 * Executes a DESCRIBE statement.
	 *
	 * @throws PDOException When the table is not found.
	 */
	private function execute_describe() {
		$this->rewriter->skip();
		$this->table_name = $this->rewriter->consume()->value;
		$stmt             = $this->execute_sqlite_query(
			"SELECT
				`name` as `Field`,
				(
					CASE `notnull`
					WHEN 0 THEN 'YES'
					WHEN 1 THEN 'NO'
					END
				) as `Null`,
				IFNULL(
					d.`mysql_type`,
					(
						CASE `type`
						WHEN 'INTEGER' THEN 'int'
						WHEN 'TEXT' THEN 'text'
						WHEN 'BLOB' THEN 'blob'
						WHEN 'REAL' THEN 'real'
						ELSE `type`
						END
					)
				) as `Type`,
				TRIM(`dflt_value`, \"'\") as `Default`,
				'' as Extra,
				(
					CASE `pk`
					WHEN 0 THEN ''
					ELSE 'PRI'
					END
				) as `Key`
				FROM pragma_table_info(\"$this->table_name\") p
				LEFT JOIN " . self::DATA_TYPES_CACHE_TABLE . " d
				ON d.`table` = \"$this->table_name\"
				AND d.`column_or_index` = p.`name`
				;
			"
		);
		$this->set_results_from_fetched_data(
			$stmt->fetchAll( $this->pdo_fetch_mode )
		);
		if ( ! $this->results ) {
			throw new PDOException( 'Table not found' );
		}
	}

	/**
	 * Executes an UPDATE statement.
	 */
	private function execute_update() {
		$this->rewriter->consume(); // Update.

		$params = array();
		while ( true ) {
			$token = $this->rewriter->peek();
			if ( ! $token ) {
				break;
			}

			// Record the table name.
			if (
				! $this->table_name &&
				! $token->matches(
					WP_SQLite_Token::TYPE_KEYWORD,
					WP_SQLite_Token::FLAG_KEYWORD_RESERVED
				)
			) {
				$this->table_name = $token->value;
			}

			$this->remember_last_reserved_keyword( $token );

			if (
				$this->extract_bound_parameter( $token, $params )
				|| $this->translate_expression( $token )
			) {
				continue;
			}

			$this->rewriter->consume();
		}
		$this->rewriter->consume_all();

		$updated_query = $this->rewriter->get_updated_query();
		$this->execute_sqlite_query( $updated_query, $params );
		$this->set_result_from_affected_rows();
	}

	/**
	 * Executes a INSERT or REPLACE statement.
	 */
	private function execute_insert_or_replace() {
		$params                  = array();
		$is_in_duplicate_section = false;

		$this->rewriter->consume(); // INSERT or REPLACE.

		// Consume the query type.
		if ( 'IGNORE' === $this->rewriter->peek()->value ) {
			$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
			$this->rewriter->add( new WP_SQLite_Token( 'OR', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ) );
			$this->rewriter->consume(); // IGNORE.
		}

		// Consume and record the table name.
		$this->insert_columns = array();
		$this->rewriter->consume(); // INTO.
		$this->table_name = $this->rewriter->consume()->value; // Table name.

		/*
		 * A list of columns is given if the opening parenthesis
		 * is earlier than the VALUES keyword.
		 */
		$paren  = $this->rewriter->peek(
			array(
				'type'  => WP_SQLite_Token::TYPE_OPERATOR,
				'value' => '(',
			)
		);
		$values = $this->rewriter->peek(
			array(
				'type'  => WP_SQLite_Token::TYPE_KEYWORD,
				'value' => 'VALUES',
			)
		);
		if ( $paren && $values && $paren->position <= $values->position ) {
			$this->rewriter->consume(
				array(
					'type'  => WP_SQLite_Token::TYPE_OPERATOR,
					'value' => '(',
				)
			);
			while ( true ) {
				$token = $this->rewriter->consume();
				if ( $token->matches( WP_SQLite_Token::TYPE_OPERATOR, null, array( ')' ) ) ) {
					break;
				}
				if ( ! $token->matches( WP_SQLite_Token::TYPE_OPERATOR ) ) {
					$this->insert_columns[] = $token->value;
				}
			}
		}

		while ( true ) {
			$token = $this->rewriter->peek();
			if ( ! $token ) {
				break;
			}

			$this->remember_last_reserved_keyword( $token );

			if (
				( $is_in_duplicate_section && $this->translate_values_function( $token ) )
				|| $this->extract_bound_parameter( $token, $params )
				|| $this->translate_expression( $token )
			) {
				continue;
			}

			if ( $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				null,
				array( 'DUPLICATE' )
			)
			) {
				$is_in_duplicate_section = true;
				$this->translate_on_duplicate_key( $this->table_name );
				continue;
			}

			$this->rewriter->consume();
		}

		$this->rewriter->consume_all();

		$updated_query = $this->rewriter->get_updated_query();
		$this->execute_sqlite_query( $updated_query, $params );
		$this->set_result_from_affected_rows();
		$this->last_insert_id = $this->pdo->lastInsertId();
		if ( is_numeric( $this->last_insert_id ) ) {
			$this->last_insert_id = (int) $this->last_insert_id;
		}
		$this->last_insert_id = apply_filters( 'sqlite_last_insert_id', $this->last_insert_id, $this->table_name );
	}

	/**
	 * Preprocesses a string literal.
	 *
	 * @param string $value The string literal.
	 *
	 * @return string The preprocessed string literal.
	 */
	private function preprocess_string_literal( $value ) {
		/*
		 * The code below converts the date format to one preferred by SQLite.
		 *
		 * MySQL accepts ISO 8601 date strings:        'YYYY-MM-DDTHH:MM:SSZ'
		 * SQLite prefers a slightly different format: 'YYYY-MM-DD HH:MM:SS'
		 *
		 * SQLite date and time functions can understand the ISO 8601 notation, but
		 * lookups don't. To keep the lookups working, we need to store all dates
		 * in UTC without the "T" and "Z" characters.
		 *
		 * Caveat: It will adjust every string that matches the pattern, not just dates.
		 *
		 * In theory, we could only adjust semantic dates, e.g. the data inserted
		 * to a date column or compared against a date column.
		 *
		 * In practice, this is hard because dates are just text – SQLite has no separate
		 * datetime field. We'd need to cache the MySQL data type from the original
		 * CREATE TABLE query and then keep refreshing the cache after each ALTER TABLE query.
		 *
		 * That's a lot of complexity that's perhaps not worth it. Let's just convert
		 * everything for now. The regexp assumes "Z" is always at the end of the string,
		 * which is true in the unit test suite, but there could also be a timezone offset
		 * like "+00:00" or "+01:00". We could add support for that later if needed.
		 */
		if ( 1 === preg_match( '/^(\d{4}-\d{2}-\d{2})T(\d{2}:\d{2}:\d{2})Z$/', $value, $matches ) ) {
			$value = $matches[1] . ' ' . $matches[2];
		}

		/*
		 * Mimic MySQL's behavior and truncate invalid dates.
		 *
		 * "2020-12-41 14:15:27" becomes "0000-00-00 00:00:00"
		 *
		 * WARNING: We have no idea whether the truncated value should
		 * be treated as a date in the first place.
		 * In SQLite dates are just strings. This could be a perfectly
		 * valid string that just happens to contain a date-like value.
		 *
		 * At the same time, WordPress seems to rely on MySQL's behavior
		 * and even tests for it in Tests_Post_wpInsertPost::test_insert_empty_post_date.
		 * Let's truncate the dates for now.
		 *
		 * In the future, let's update WordPress to do its own date validation
		 * and stop relying on this MySQL feature,
		 */
		if ( 1 === preg_match( '/^(\d{4}-\d{2}-\d{2}) (\d{2}:\d{2}:\d{2})$/', $value, $matches ) ) {
			/*
			 * Calling strtotime("0000-00-00 00:00:00") in 32-bit environments triggers
			 * an "out of integer range" warning – let's avoid that call for the popular
			 * case of "zero" dates.
			 */
			if ( '0000-00-00 00:00:00' !== $value && false === strtotime( $value ) ) {
				$value = '0000-00-00 00:00:00';
			}
		}
		return $value;
	}

	/**
	 * Preprocesses a LIKE expression.
	 *
	 * @param WP_SQLite_Token $token The token to preprocess.
	 * @return string
	 */
	private function preprocess_like_expr( &$token ) {
		/*
		 * This code handles escaped wildcards in LIKE clauses.
		 * If we are within a LIKE experession, we look for \_ and \%, the
		 * escaped LIKE wildcards, the ones where we want a literal, not a
		 * wildcard match. We change the \ escape for an ASCII \x1a (SUB) character,
		 * so the \ characters won't get munged.
		 * These \_ and \% escape sequences are in the token name, because
		 * the lexer has already done stripcslashes on the value.
		 */
		if ( $this->like_expression_nesting > 0 ) {
			/* Remove the quotes around the name. */
			$unescaped_value = mb_substr( $token->token, 1, -1, 'UTF-8' );
			if ( str_contains( $unescaped_value, '\_' ) || str_contains( $unescaped_value, '\%' ) ) {
				++$this->like_escape_count;
				return str_replace(
					array( '\_', '\%' ),
					array( self::LIKE_ESCAPE_CHAR . '_', self::LIKE_ESCAPE_CHAR . '%' ),
					$unescaped_value
				);
			}
		}
		return $token->value;
	}
	/**
	 * Translate CAST() function when we want to cast to BINARY.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_cast_as_binary( $token ) {
		if ( ! $token->matches(
			WP_SQLite_Token::TYPE_KEYWORD,
			WP_SQLite_Token::FLAG_KEYWORD_DATA_TYPE,
			array( 'BINARY' )
		)
		) {
			return false;
		}

		$call_parent = $this->rewriter->last_call_stack_element();
		if (
			! $call_parent
			|| 'CAST' !== $call_parent['function']
		) {
			return false;
		}

		// Rewrite AS BINARY to AS BLOB inside CAST() calls.
		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( 'BLOB', $token->type, $token->flags ) );
		return true;
	}

	/**
	 * Translates an expression in an SQL statement if the token is the start of an expression.
	 *
	 * @param WP_SQLite_Token $token The first token of an expression.
	 *
	 * @return bool True if the expression was translated successfully, false otherwise.
	 */
	private function translate_expression( $token ) {
		return (
			$this->skip_from_dual( $token )
			|| $this->translate_concat_function( $token )
			|| $this->translate_concat_comma_to_pipes( $token )
			|| $this->translate_function_aliases( $token )
			|| $this->translate_cast_as_binary( $token )
			|| $this->translate_date_add_sub( $token )
			|| $this->translate_date_format( $token )
			|| $this->translate_interval( $token )
			|| $this->translate_regexp_functions( $token )
			|| $this->capture_group_by( $token )
			|| $this->translate_ungrouped_having( $token )
			|| $this->translate_like_escape( $token )
			|| $this->translate_left_function( $token )
		);
	}

	/**
	 * Skips the `FROM DUAL` clause in the SQL statement.
	 *
	 * @param WP_SQLite_Token $token The token to check for the `FROM DUAL` clause.
	 *
	 * @return bool True if the `FROM DUAL` clause was skipped, false otherwise.
	 */
	private function skip_from_dual( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_RESERVED,
				array( 'FROM' )
			)
		) {
			return false;
		}
		$from_table = $this->rewriter->peek_nth( 2 )->value;
		if ( 'DUAL' !== strtoupper( $from_table ) ) {
			return false;
		}

		// FROM DUAL is a MySQLism that means "no tables".
		$this->rewriter->skip();
		$this->rewriter->skip();
		return true;
	}

	/**
	 * Peeks at the table name in the SQL statement.
	 *
	 * @param WP_SQLite_Token $token The token to check for the table name.
	 *
	 * @return string|bool The table name if it was found, false otherwise.
	 */
	private function peek_table_name( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_RESERVED,
				array( 'FROM' )
			)
		) {
			return false;
		}
		$table_name = $this->rewriter->peek_nth( 2 )->value;
		if ( 'dual' === strtolower( $table_name ) ) {
			return false;
		}
		return $table_name;
	}

	/**
	 * Skips the `SQL_CALC_FOUND_ROWS` keyword in the SQL statement.
	 *
	 * @param WP_SQLite_Token $token The token to check for the `SQL_CALC_FOUND_ROWS` keyword.
	 *
	 * @return bool True if the `SQL_CALC_FOUND_ROWS` keyword was skipped, false otherwise.
	 */
	private function skip_sql_calc_found_rows( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				null,
				array( 'SQL_CALC_FOUND_ROWS' )
			)
		) {
			return false;
		}
		$this->rewriter->skip();
		return true;
	}

	/**
	 * Remembers the last reserved keyword encountered in the SQL statement.
	 *
	 * @param WP_SQLite_Token $token The token to check for the reserved keyword.
	 */
	private function remember_last_reserved_keyword( $token ) {
		if (
			$token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_RESERVED
			)
		) {
			$this->last_reserved_keyword = $token->value;
		}
	}

	/**
	 * Extracts the bound parameter from the given token and adds it to the `$params` array.
	 *
	 * @param WP_SQLite_Token $token The token to extract the bound parameter from.
	 * @param array           $params An array of parameters to be bound to the SQL statement.
	 *
	 * @return bool True if the parameter was extracted successfully, false otherwise.
	 */
	private function extract_bound_parameter( $token, &$params ) {
		if ( ! $token->matches(
			WP_SQLite_Token::TYPE_STRING,
			WP_SQLite_Token::FLAG_STRING_SINGLE_QUOTES
		)
			|| 'AS' === $this->last_reserved_keyword
		) {
			return false;
		}

		$param_name            = ':param' . count( $params );
		$value                 = $this->preprocess_like_expr( $token );
		$value                 = $this->preprocess_string_literal( $value );
		$params[ $param_name ] = $value;
		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( $param_name, WP_SQLite_Token::TYPE_STRING, WP_SQLite_Token::FLAG_STRING_SINGLE_QUOTES ) );
		$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
		return true;
	}

	/**
	 * Translate CONCAT() function.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_concat_function( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_FUNCTION,
				array( 'CONCAT' )
			)
		) {
			return false;
		}

		/*
		 * Skip the CONCAT function but leave the parentheses.
		 * There is another code block below that replaces the
		 * , operators between the CONCAT arguments with ||.
		 */
		$this->rewriter->skip();
		return true;
	}

	/**
	 * Translate CONCAT() function arguments.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_concat_comma_to_pipes( $token ) {
		if ( ! $token->matches(
			WP_SQLite_Token::TYPE_OPERATOR,
			WP_SQLite_Token::FLAG_OPERATOR_SQL,
			array( ',' )
		)
		) {
			return false;
		}

		$call_parent = $this->rewriter->last_call_stack_element();
		if (
			! $call_parent
			|| 'CONCAT' !== $call_parent['function']
		) {
			return false;
		}

		// Rewrite commas to || in CONCAT() calls.
		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( '||', WP_SQLite_Token::TYPE_OPERATOR ) );
		return true;
	}

	/**
	 * Translate DATE_ADD() and DATE_SUB() functions.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_date_add_sub( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_FUNCTION,
				array( 'DATE_ADD', 'DATE_SUB' )
			)
		) {
			return false;
		}

		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( 'DATETIME', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_FUNCTION ) );
		return true;
	}

	/**
	 * Translate the LEFT() function.
	 *
	 * > Returns the leftmost len characters from the string str, or NULL if any argument is NULL.
	 *
	 * https://dev.mysql.com/doc/refman/8.3/en/string-functions.html#function_left
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_left_function( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_FUNCTION,
				array( 'LEFT' )
			)
		) {
			return false;
		}

		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( 'SUBSTRING', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_FUNCTION ) );
		$this->rewriter->consume(
			array(
				'type'  => WP_SQLite_Token::TYPE_OPERATOR,
				'value' => ',',
			)
		);
		$this->rewriter->add( new WP_SQLite_Token( 1, WP_SQLite_Token::TYPE_NUMBER ) );
		$this->rewriter->add( new WP_SQLite_Token( ',', WP_SQLite_Token::TYPE_OPERATOR ) );
		return true;
	}

	/**
	 * Convert function aliases.
	 *
	 * @param object $token The current token.
	 *
	 * @return bool False when no match, true when this function consumes the token.
	 *
	 * @todo LENGTH and CHAR_LENGTH aren't always the same in MySQL for utf8 characters. They are in SQLite.
	 */
	private function translate_function_aliases( $token ) {
		if ( ! $token->matches(
			WP_SQLite_Token::TYPE_KEYWORD,
			WP_SQLite_Token::FLAG_KEYWORD_FUNCTION,
			array( 'SUBSTRING', 'CHAR_LENGTH' )
		)
		) {
			return false;
		}
		switch ( $token->value ) {
			case 'SUBSTRING':
				$name = 'SUBSTR';
				break;
			case 'CHAR_LENGTH':
				$name = 'LENGTH';
				break;
			default:
				$name = $token->value;
				break;
		}
		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( $name, $token->type, $token->flags ) );

		return true;
	}

	/**
	 * Translate VALUES() function.
	 *
	 * @param WP_SQLite_Token $token                   The token to translate.
	 *
	 * @return bool
	 */
	private function translate_values_function( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_FUNCTION,
				array( 'VALUES' )
			)
		) {
			return false;
		}

		/*
		 * Rewrite:  VALUES(`option_name`)
		 * to:       excluded.option_name
		 */
		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( 'excluded', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_KEY ) );
		$this->rewriter->add( new WP_SQLite_Token( '.', WP_SQLite_Token::TYPE_OPERATOR ) );

		$this->rewriter->skip(); // Skip the opening `(`.
		// Consume the column name.
		$this->rewriter->consume(
			array(
				'type'  => WP_SQLite_Token::TYPE_OPERATOR,
				'value' => ')',
			)
		);
		// Drop the consumed ')' token.
		$this->rewriter->drop_last();
		return true;
	}

	/**
	 * Translate DATE_FORMAT() function.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @throws Exception If the token is not a DATE_FORMAT() function.
	 *
	 * @return bool
	 */
	private function translate_date_format( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_FUNCTION,
				array( 'DATE_FORMAT' )
			)
		) {
			return false;
		}

		// Rewrite DATE_FORMAT( `post_date`, '%Y-%m-%d' ) to STRFTIME( '%Y-%m-%d', `post_date` ).

		// Skip the DATE_FORMAT function name.
		$this->rewriter->skip();
		// Skip the opening `(`.
		$this->rewriter->skip();

		// Skip the first argument so we can read the second one.
		$first_arg = $this->rewriter->skip_and_return_all(
			array(
				'type'  => WP_SQLite_Token::TYPE_OPERATOR,
				'value' => ',',
			)
		);

		// Make sure we actually found the comma.
		$comma = array_pop( $first_arg );
		if ( ',' !== $comma->value ) {
			throw new Exception( 'Could not parse the DATE_FORMAT() call' );
		}

		// Skip the second argument but capture the token.
		$format     = $this->rewriter->skip()->value;
		$new_format = strtr( $format, $this->mysql_date_format_to_sqlite_strftime );
		if ( ! $new_format ) {
			throw new Exception( "Could not translate a DATE_FORMAT() format to STRFTIME format ($format)" );
		}

		/*
		 * MySQL supports comparing strings and floats, e.g.
		 *
		 * > SELECT '00.42' = 0.4200
		 * 1
		 *
		 * SQLite does not support that. At the same time,
		 * WordPress likes to filter dates by comparing numeric
		 * outputs of DATE_FORMAT() to floats, e.g.:
		 *
		 *     -- Filter by hour and minutes
		 *     DATE_FORMAT(
		 *         STR_TO_DATE('2014-10-21 00:42:29', '%Y-%m-%d %H:%i:%s'),
		 *         '%H.%i'
		 *     ) = 0.4200;
		 *
		 * Let's cast the STRFTIME() output to a float if
		 * the date format is typically used for string
		 * to float comparisons.
		 *
		 * In the future, let's update WordPress to avoid comparing
		 * strings and floats.
		 */
		$cast_to_float = '%H.%i' === $format;
		if ( $cast_to_float ) {
			$this->rewriter->add( new WP_SQLite_Token( 'CAST', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_FUNCTION ) );
			$this->rewriter->add( new WP_SQLite_Token( '(', WP_SQLite_Token::TYPE_OPERATOR ) );
		}

		$this->rewriter->add( new WP_SQLite_Token( 'STRFTIME', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_FUNCTION ) );
		$this->rewriter->add( new WP_SQLite_Token( '(', WP_SQLite_Token::TYPE_OPERATOR ) );
		$this->rewriter->add( new WP_SQLite_Token( "'$new_format'", WP_SQLite_Token::TYPE_STRING ) );
		$this->rewriter->add( new WP_SQLite_Token( ',', WP_SQLite_Token::TYPE_OPERATOR ) );

		// Add the buffered tokens back to the stream.
		$this->rewriter->add_many( $first_arg );

		// Consume the closing ')'.
		$this->rewriter->consume(
			array(
				'type'  => WP_SQLite_Token::TYPE_OPERATOR,
				'value' => ')',
			)
		);

		if ( $cast_to_float ) {
			$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
			$this->rewriter->add( new WP_SQLite_Token( 'as', WP_SQLite_Token::TYPE_OPERATOR ) );
			$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
			$this->rewriter->add( new WP_SQLite_Token( 'FLOAT', WP_SQLite_Token::TYPE_KEYWORD ) );
			$this->rewriter->add( new WP_SQLite_Token( ')', WP_SQLite_Token::TYPE_OPERATOR ) );
		}

		return true;
	}

	/**
	 * Translate INTERVAL keyword with DATE_ADD() and DATE_SUB().
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_interval( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				null,
				array( 'INTERVAL' )
			)
		) {
			return false;
		}
		// Skip the INTERVAL keyword from the output stream.
		$this->rewriter->skip();

		$num  = $this->rewriter->skip()->value;
		$unit = $this->rewriter->skip()->value;

		/*
			* In MySQL, we say:
			*     DATE_ADD(d, INTERVAL 1 YEAR)
			*     DATE_SUB(d, INTERVAL 1 YEAR)
			*
			* In SQLite, we say:
			*     DATE(d, '+1 YEAR')
			*     DATE(d, '-1 YEAR')
			*
			* The sign of the interval is determined by the date_* function
			* that is closest in the call stack.
			*
			* Let's find it.
			*/
		$interval_op = '+'; // Default to adding.
		for ( $j = count( $this->rewriter->call_stack ) - 1; $j >= 0; $j-- ) {
			$call = $this->rewriter->call_stack[ $j ];
			if ( 'DATE_ADD' === $call['function'] ) {
				$interval_op = '+';
				break;
			}
			if ( 'DATE_SUB' === $call['function'] ) {
				$interval_op = '-';
				break;
			}
		}

		$this->rewriter->add( new WP_SQLite_Token( "'{$interval_op}$num $unit'", WP_SQLite_Token::TYPE_STRING ) );
		return true;
	}

	/**
	 * Translate REGEXP and RLIKE keywords.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_regexp_functions( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				null,
				array( 'REGEXP', 'RLIKE' )
			)
		) {
			return false;
		}
		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( 'REGEXP', WP_SQLite_Token::TYPE_KEYWORD ) );

		$next = $this->rewriter->peek();

		/*
		 * If the query says REGEXP BINARY, the comparison is byte-by-byte
		 * and letter casing matters – lowercase and uppercase letters are
		 * represented using different byte codes.
		 *
		 * The REGEXP function can't be easily made to accept two
		 * parameters, so we'll have to use a hack to get around this.
		 *
		 * If the first character of the pattern is a null byte, we'll
		 * remove it and make the comparison case-sensitive. This should
		 * be reasonably safe since PHP does not allow null bytes in
		 * regular expressions anyway.
		 */
		if ( $next->matches( WP_SQLite_Token::TYPE_KEYWORD, null, array( 'BINARY' ) ) ) {
			// Skip the "BINARY" keyword.
			$this->rewriter->skip();
			// Prepend a null byte to the pattern.
			$this->rewriter->add_many(
				array(
					new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
					new WP_SQLite_Token( 'char', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_FUNCTION ),
					new WP_SQLite_Token( '(', WP_SQLite_Token::TYPE_OPERATOR ),
					new WP_SQLite_Token( '0', WP_SQLite_Token::TYPE_NUMBER ),
					new WP_SQLite_Token( ')', WP_SQLite_Token::TYPE_OPERATOR ),
					new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
					new WP_SQLite_Token( '||', WP_SQLite_Token::TYPE_OPERATOR ),
					new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
				)
			);
		}
		return true;
	}

	/**
	 * Detect GROUP BY.
	 *
	 * @todo edgecase Fails on a statement with GROUP BY nested in an outer HAVING without GROUP BY.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function capture_group_by( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_RESERVED,
				array( 'GROUP' )
			)
		) {
			return false;
		}
		$next = $this->rewriter->peek_nth( 2 )->value;
		if ( 'BY' !== strtoupper( $next ) ) {
			return false;
		}

		$this->has_group_by = true;

		return false;
	}

	/**
	 * Translate WHERE something HAVING something to WHERE something AND something.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_ungrouped_having( $token ) {
		if (
			! $token->matches(
				WP_SQLite_Token::TYPE_KEYWORD,
				WP_SQLite_Token::FLAG_KEYWORD_RESERVED,
				array( 'HAVING' )
			)
		) {
			return false;
		}
		if ( $this->has_group_by ) {
			return false;
		}
		$this->rewriter->skip();
		$this->rewriter->add( new WP_SQLite_Token( 'AND', WP_SQLite_Token::TYPE_KEYWORD ) );

		return true;
	}

	/**
	 * Rewrite LIKE '\_whatever' as LIKE '\_whatever' ESCAPE '\' .
	 *
	 * We look for keyword LIKE. On seeing it we set a flag.
	 * If the flag is set, we emit ESCAPE '\' before the next keyword.
	 *
	 * @param WP_SQLite_Token $token The token to translate.
	 *
	 * @return bool
	 */
	private function translate_like_escape( $token ) {

		if ( 0 === $this->like_expression_nesting ) {
			$is_like = $token->matches( WP_SQLite_Token::TYPE_KEYWORD, null, array( 'LIKE' ) );
			/* is this the LIKE keyword? If so set the flag. */
			if ( $is_like ) {
				$this->like_expression_nesting = 1;
			}
		} else {
			/* open parenthesis during LIKE parameter, count it. */
			if ( $token->matches( WP_SQLite_Token::TYPE_OPERATOR, null, array( '(' ) ) ) {
				++$this->like_expression_nesting;

				return false;
			}

			/* close parenthesis matching open parenthesis during LIKE parameter, count it. */
			if ( $this->like_expression_nesting > 1 && $token->matches( WP_SQLite_Token::TYPE_OPERATOR, null, array( ')' ) ) ) {
				--$this->like_expression_nesting;

				return false;
			}

			/* a keyword, a commo, a semicolon, the end of the statement, or a close parenthesis */
			$is_like_finished = $token->matches( WP_SQLite_Token::TYPE_KEYWORD )
					|| $token->matches( WP_SQLite_Token::TYPE_DELIMITER, null, array( ';' ) ) || ( WP_SQLite_Token::TYPE_DELIMITER === $token->type && null === $token->value )
					|| $token->matches( WP_SQLite_Token::TYPE_OPERATOR, null, array( ')', ',' ) );

			if ( $is_like_finished ) {
				/*
				 * Here we have another keyword encountered with the LIKE in progress.
				 * Emit the ESCAPE clause.
				 */
				if ( $this->like_escape_count > 0 ) {
					/* If we need the ESCAPE clause emit it. */
					$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_DELIMITER ) );
					$this->rewriter->add( new WP_SQLite_Token( 'ESCAPE', WP_SQLite_Token::TYPE_KEYWORD ) );
					$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_DELIMITER ) );
					$this->rewriter->add( new WP_SQLite_Token( "'" . self::LIKE_ESCAPE_CHAR . "'", WP_SQLite_Token::TYPE_STRING ) );
					$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_DELIMITER ) );
				}
				$this->like_escape_count       = 0;
				$this->like_expression_nesting = 0;
			}
		}

		return false;
	}

	/**
	 * Rewrite a query from the MySQL information_schema.
	 *
	 * @param string $updated_query The query to rewrite.
	 *
	 * @return string The query for use by SQLite
	 */
	private function get_information_schema_query( $updated_query ) {
		// @TODO: Actually rewrite the columns.
		$normalized_query = preg_replace( '/\s+/', ' ', strtolower( $updated_query ) );
		if ( str_contains( $normalized_query, 'bytes' ) ) {
			// Count rows per table.
			$tables =
				$this->execute_sqlite_query( "SELECT name as `table_name` FROM sqlite_master WHERE type='table' ORDER BY name" )->fetchAll();
			$tables = $this->strip_sqlite_system_tables( $tables );

			$rows = '(CASE ';
			foreach ( $tables as $table ) {
				$table_name = $table['table_name'];
				$count      = $this->execute_sqlite_query( "SELECT COUNT(1) as `count` FROM $table_name" )->fetch();
				$rows      .= " WHEN name = '$table_name' THEN {$count['count']} ";
			}
			$rows         .= 'ELSE 0 END) ';
			$updated_query =
				"SELECT name as `table_name`, $rows as `rows`, 0 as `bytes` FROM sqlite_master WHERE type='table' ORDER BY name";
		} elseif ( str_contains( $normalized_query, 'count(*)' ) && ! str_contains( $normalized_query, 'table_name =' ) ) {
			// @TODO This is a guess that the caller wants a count of tables.
			$list = array();
			foreach ( $this->sqlite_system_tables as $system_table => $name ) {
				$list [] = "'" . $system_table . "'";
			}
			$list          = implode( ', ', $list );
			$sql           = "SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND name NOT IN ($list)";
			$table_count   = $this->execute_sqlite_query( $sql )->fetch();
			$updated_query = 'SELECT ' . $table_count[0] . ' AS num';

			$this->is_information_schema_query = false;
		} else {
			$updated_query =
				"SELECT name as `table_name`, 'myisam' as `engine`, 0 as `data_length`, 0 as `index_length`, 0 as `data_free` FROM sqlite_master WHERE type='table' ORDER BY name";
		}

		return $updated_query;
	}

	/**
	 * Remove system table rows from resultsets of information_schema tables.
	 *
	 * @param array $tables The result set.
	 *
	 * @return array The filtered result set.
	 */
	private function strip_sqlite_system_tables( $tables ) {
		return array_values(
			array_filter(
				$tables,
				function ( $table ) {
					$table_name = false;
					if ( is_array( $table ) ) {
						if ( isset( $table['Name'] ) ) {
							$table_name = $table['Name'];
						} elseif ( isset( $table['table_name'] ) ) {
							$table_name = $table['table_name'];
						}
					} elseif ( is_object( $table ) ) {
						$table_name = property_exists( $table, 'Name' )
							? $table->Name // phpcs:ignore WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
							: $table->table_name;
					}

					return $table_name && ! array_key_exists( $table_name, $this->sqlite_system_tables );
				},
				ARRAY_FILTER_USE_BOTH
			)
		);
	}

	/**
	 * Translate the ON DUPLICATE KEY UPDATE clause.
	 *
	 * @param string $table_name The table name.
	 *
	 * @return void
	 */
	private function translate_on_duplicate_key( $table_name ) {
		/*
		 * Rewrite:
		 *     ON DUPLICATE KEY UPDATE `option_name` = VALUES(`option_name`)
		 * to:
		 *     ON CONFLICT(ip) DO UPDATE SET option_name = excluded.option_name
		 */

		// Find the conflicting column.
		$pk_columns = array();
		foreach ( $this->get_primary_keys( $table_name ) as $row ) {
			$pk_columns[] = $row['name'];
		}

		$unique_columns = array();
		foreach ( $this->get_keys( $table_name, true ) as $row ) {
			foreach ( $row['columns'] as $column ) {
				$unique_columns[] = $column['name'];
			}
		}

		// Guess the conflict column based on the query details.

		// 1. Listed INSERT columns that are either PK or UNIQUE.
		$conflict_columns = array_intersect(
			$this->insert_columns,
			array_merge( $pk_columns, $unique_columns )
		);
		// 2. Composite Primary Key columns.
		if ( ! $conflict_columns && count( $pk_columns ) > 1 ) {
			$conflict_columns = $pk_columns;
		}
		// 3. The first unique column.
		if ( ! $conflict_columns && count( $unique_columns ) > 0 ) {
			$conflict_columns = array( $unique_columns[0] );
		}
		// 4. Regular Primary Key column.
		if ( ! $conflict_columns ) {
			$conflict_columns = $pk_columns;
		}

		/*
		 * If we still haven't found any conflict column, we
		 * can't rewrite the ON DUPLICATE KEY statement.
		 * Let's default to a regular INSERT to mimic MySQL
		 * which would still insert the row without throwing
		 * an error.
		 */
		if ( ! $conflict_columns ) {
			// Drop the consumed "ON".
			$this->rewriter->drop_last();
			// Skip over "DUPLICATE", "KEY", and "UPDATE".
			$this->rewriter->skip();
			$this->rewriter->skip();
			$this->rewriter->skip();
			while ( $this->rewriter->skip() ) {
				// Skip over the rest of the query.
			}
			return;
		}

		// Skip over "DUPLICATE", "KEY", and "UPDATE".
		$this->rewriter->skip();
		$this->rewriter->skip();
		$this->rewriter->skip();

		// Add the CONFLICT keyword.
		$this->rewriter->add( new WP_SQLite_Token( 'CONFLICT', WP_SQLite_Token::TYPE_KEYWORD ) );

		// Add "( <columns list> ) DO UPDATE SET ".
		$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
		$this->rewriter->add( new WP_SQLite_Token( '(', WP_SQLite_Token::TYPE_OPERATOR ) );

		$max = count( $conflict_columns );
		foreach ( $conflict_columns as $i => $conflict_column ) {
			$this->rewriter->add( new WP_SQLite_Token( '"' . $conflict_column . '"', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_KEY ) );
			if ( $i !== $max - 1 ) {
				$this->rewriter->add( new WP_SQLite_Token( ',', WP_SQLite_Token::TYPE_OPERATOR ) );
				$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
			}
		}
		$this->rewriter->add( new WP_SQLite_Token( ')', WP_SQLite_Token::TYPE_OPERATOR ) );
		$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
		$this->rewriter->add( new WP_SQLite_Token( 'DO', WP_SQLite_Token::TYPE_KEYWORD ) );
		$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
		$this->rewriter->add( new WP_SQLite_Token( 'UPDATE', WP_SQLite_Token::TYPE_KEYWORD ) );
		$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
		$this->rewriter->add( new WP_SQLite_Token( 'SET', WP_SQLite_Token::TYPE_KEYWORD ) );
		$this->rewriter->add( new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ) );
	}

	/**
	 * Get the primary keys for a table.
	 *
	 * @param string $table_name Table name.
	 *
	 * @return array
	 */
	private function get_primary_keys( $table_name ) {
		$stmt = $this->execute_sqlite_query( 'SELECT * FROM pragma_table_info(:table_name) as l WHERE l.pk > 0;' );
		$stmt->execute( array( 'table_name' => $table_name ) );
		return $stmt->fetchAll();
	}

	/**
	 * Get the keys for a table.
	 *
	 * @param string $table_name Table name.
	 * @param bool   $only_unique Only return unique keys.
	 *
	 * @return array
	 */
	private function get_keys( $table_name, $only_unique = false ) {
		$query   = $this->execute_sqlite_query( 'SELECT * FROM pragma_index_list("' . $table_name . '") as l;' );
		$indices = $query->fetchAll();
		$results = array();
		foreach ( $indices as $index ) {
			if ( ! $only_unique || '1' === $index['unique'] ) {
				$query     = $this->execute_sqlite_query( 'SELECT * FROM pragma_index_info("' . $index['name'] . '") as l;' );
				$results[] = array(
					'index'   => $index,
					'columns' => $query->fetchAll(),
				);
			}
		}
		return $results;
	}

	/**
	 * Get the CREATE TABLE statement for a table.
	 *
	 * @param string $table_name Table name.
	 *
	 * @return string
	 */
	private function get_sqlite_create_table( $table_name ) {
		$stmt = $this->execute_sqlite_query( 'SELECT sql FROM sqlite_master WHERE type="table" AND name=:table' );
		$stmt->execute( array( ':table' => $table_name ) );
		$create_table = '';
		foreach ( $stmt->fetchAll() as $row ) {
			$create_table .= $row['sql'] . "\n";
		}
		return $create_table;
	}

	/**
	 * Translate ALTER query.
	 *
	 * @throws Exception If the subject is not 'table', or we're performing an unknown operation.
	 */
	private function execute_alter() {
		$this->rewriter->consume();
		$subject = strtolower( $this->rewriter->consume()->token );
		if ( 'table' !== $subject ) {
			throw new Exception( 'Unknown subject: ' . $subject );
		}

		$this->table_name = $this->normalize_column_name( $this->rewriter->consume()->token );
		do {
			/*
			 * This loop may be executed multiple times if there are multiple operations in the ALTER query.
			 * Let's reset the initial state on each pass.
			 */
			$this->rewriter->replace_all(
				array(
					new WP_SQLite_Token( 'ALTER', WP_SQLite_Token::TYPE_KEYWORD ),
					new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
					new WP_SQLite_Token( 'TABLE', WP_SQLite_Token::TYPE_KEYWORD ),
					new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
					new WP_SQLite_Token( $this->table_name, WP_SQLite_Token::TYPE_KEYWORD ),
				)
			);
			$op_type          = strtoupper( $this->rewriter->consume()->token );
			$op_subject       = strtoupper( $this->rewriter->consume()->token );
			$mysql_index_type = $this->normalize_mysql_index_type( $op_subject );
			$is_index_op      = (bool) $mysql_index_type;

			if ( 'ADD' === $op_type && 'COLUMN' === $op_subject ) {
				$column_name = $this->rewriter->consume()->value;

				$skip_mysql_data_type_parts = $this->skip_mysql_data_type();
				$sqlite_data_type           = $skip_mysql_data_type_parts[0];
				$mysql_data_type            = $skip_mysql_data_type_parts[1];

				$this->rewriter->add(
					new WP_SQLite_Token(
						$sqlite_data_type,
						WP_SQLite_Token::TYPE_KEYWORD,
						WP_SQLite_Token::FLAG_KEYWORD_DATA_TYPE
					)
				);
				$this->update_data_type_cache(
					$this->table_name,
					$column_name,
					$mysql_data_type
				);
			} elseif ( 'DROP' === $op_type && 'COLUMN' === $op_subject ) {
				$this->rewriter->consume_all();
			} elseif ( 'CHANGE' === $op_type && 'COLUMN' === $op_subject ) {
				// Parse the new column definition.
				$from_name        = $this->normalize_column_name( $this->rewriter->skip()->token );
				$new_field        = $this->parse_mysql_create_table_field();
				$alter_terminator = end( $this->rewriter->output_tokens );
				$this->update_data_type_cache(
					$this->table_name,
					$new_field->name,
					$new_field->mysql_data_type
				);

				/*
				 * In SQLite, there is no direct equivalent to the CHANGE COLUMN
				 * statement from MySQL. We need to do a bit of work to emulate it.
				 *
				 * The idea is to:
				 * 1. Get the existing table schema.
				 * 2. Adjust the column definition.
				 * 3. Copy the data out of the old table.
				 * 4. Drop the old table to free up the indexes names.
				 * 5. Create a new table from the updated schema.
				 * 6. Copy the data from step 3 to the new table.
				 * 7. Drop the old table copy.
				 * 8. Restore any indexes that were dropped in step 4.
				 */

				// 1. Get the existing table schema.
				$old_schema  = $this->get_sqlite_create_table( $this->table_name );
				$old_indexes = $this->get_keys( $this->table_name, false );

				// 2. Adjust the column definition.

				// First, tokenize the old schema.
				$tokens       = ( new WP_SQLite_Lexer( $old_schema ) )->tokens;
				$create_table = new WP_SQLite_Query_Rewriter( $tokens );

				// Now, replace every reference to the old column name with the new column name.
				while ( true ) {
					$token = $create_table->consume();
					if ( ! $token ) {
						break;
					}
					if ( WP_SQLite_Token::TYPE_STRING !== $token->type
						|| $from_name !== $this->normalize_column_name( $token->value ) ) {
						continue;
					}

					// We found the old column name, let's remove it.
					$create_table->drop_last();

					// If the next token is a data type, we're dealing with a column definition.
					$is_column_definition = $create_table->peek()->matches(
						WP_SQLite_Token::TYPE_KEYWORD,
						WP_SQLite_Token::FLAG_KEYWORD_DATA_TYPE
					);
					if ( $is_column_definition ) {
						// Skip the old field definition.
						$field_depth = $create_table->depth;
						do {
							$field_terminator = $create_table->skip();
						} while (
							! $this->is_create_table_field_terminator(
								$field_terminator,
								$field_depth,
								$create_table->depth
							)
						);

						// Add an updated field definition.
						$definition = $this->make_sqlite_field_definition( $new_field );
						// Technically it's not a token, but it's fine to cheat a little bit.
						$create_table->add( new WP_SQLite_Token( $definition, WP_SQLite_Token::TYPE_KEYWORD ) );
						// Restore the terminating "," or ")" token.
						$create_table->add( $field_terminator );
					} else {
						// Otherwise, just add the new name in place of the old name we dropped.
						$create_table->add(
							new WP_SQLite_Token(
								"`$new_field->name`",
								WP_SQLite_Token::TYPE_KEYWORD
							)
						);
					}
				}

				// 3. Copy the data out of the old table
				$cache_table_name = "_tmp__{$this->table_name}_" . rand( 10000000, 99999999 );
				$this->execute_sqlite_query(
					"CREATE TABLE `$cache_table_name` as SELECT * FROM `$this->table_name`"
				);

				// 4. Drop the old table to free up the indexes names
				$this->execute_sqlite_query( "DROP TABLE `$this->table_name`" );

				// 5. Create a new table from the updated schema
				$this->execute_sqlite_query( $create_table->get_updated_query() );

				// 6. Copy the data from step 3 to the new table
				$this->execute_sqlite_query( "INSERT INTO {$this->table_name} SELECT * FROM $cache_table_name" );

				// 7. Drop the old table copy
				$this->execute_sqlite_query( "DROP TABLE `$cache_table_name`" );

				// 8. Restore any indexes that were dropped in step 4
				foreach ( $old_indexes as $row ) {
					/*
					 * Skip indexes prefixed with sqlite_autoindex_
					 * (these are automatically created by SQLite).
					 */
					if ( str_starts_with( $row['index']['name'], 'sqlite_autoindex_' ) ) {
						continue;
					}

					$columns = array();
					foreach ( $row['columns'] as $column ) {
						$columns[] = ( $column['name'] === $from_name )
							? '`' . $new_field->name . '`'
							: '`' . $column['name'] . '`';
					}

					$unique = '1' === $row['index']['unique'] ? 'UNIQUE' : '';

					/*
					 * Use IF NOT EXISTS to avoid collisions with indexes that were
					 * a part of the CREATE TABLE statement
					 */
					$this->execute_sqlite_query(
						"CREATE $unique INDEX IF NOT EXISTS `{$row['index']['name']}` ON $this->table_name (" . implode( ', ', $columns ) . ')'
					);
				}

				if ( ',' === $alter_terminator->token ) {
					/*
					 * If the terminator was a comma,
					 * we need to continue processing the rest of the ALTER query.
					 */
					$comma = true;
					continue;
				}
				// We're done.
				break;
			} elseif ( 'ADD' === $op_type && $is_index_op ) {
				$key_name          = $this->rewriter->consume()->value;
				$sqlite_index_type = $this->mysql_index_type_to_sqlite_type( $mysql_index_type );
				$sqlite_index_name = "{$this->table_name}__$key_name";
				$this->rewriter->replace_all(
					array(
						new WP_SQLite_Token( 'CREATE', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( $sqlite_index_type, WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( "\"$sqlite_index_name\"", WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_KEY ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( 'ON', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( '"' . $this->table_name . '"', WP_SQLite_Token::TYPE_STRING, WP_SQLite_Token::FLAG_STRING_DOUBLE_QUOTES ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( '(', WP_SQLite_Token::TYPE_OPERATOR ),
					)
				);
				$this->update_data_type_cache(
					$this->table_name,
					$sqlite_index_name,
					$mysql_index_type
				);

				$token = $this->rewriter->consume(
					array(
						WP_SQLite_Token::TYPE_OPERATOR,
						null,
						'(',
					)
				);
				$this->rewriter->drop_last();

				// Consume all the fields, skip the sizes like `(20)` in `varchar(20)`.
				while ( true ) {
					$token = $this->rewriter->consume();
					if ( ! $token ) {
						break;
					}
					// $token is field name.
					if ( ! $token->matches( WP_SQLite_Token::TYPE_OPERATOR ) ) {
						$token->token = '`' . $this->normalize_column_name( $token->token ) . '`';
						$token->value = '`' . $this->normalize_column_name( $token->token ) . '`';
					}

					/*
					 * Optionally, it may be followed by a size like `(20)`.
					 * Let's skip it.
					 */
					$paren_maybe = $this->rewriter->peek();
					if ( $paren_maybe && '(' === $paren_maybe->token ) {
						$this->rewriter->skip();
						$this->rewriter->skip();
						$this->rewriter->skip();
					}
					if ( ')' === $token->value ) {
						break;
					}
				}
			} elseif ( 'DROP' === $op_type && $is_index_op ) {
				$key_name = $this->rewriter->consume()->value;
				$this->rewriter->replace_all(
					array(
						new WP_SQLite_Token( 'DROP', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( 'INDEX', WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_RESERVED ),
						new WP_SQLite_Token( ' ', WP_SQLite_Token::TYPE_WHITESPACE ),
						new WP_SQLite_Token( "\"{$this->table_name}__$key_name\"", WP_SQLite_Token::TYPE_KEYWORD, WP_SQLite_Token::FLAG_KEYWORD_KEY ),
					)
				);
			} else {
				throw new Exception( 'Unknown operation: ' . $op_type );
			}
			$comma = $this->rewriter->consume(
				array(
					'type'  => WP_SQLite_Token::TYPE_OPERATOR,
					'value' => ',',
				)
			);
			$this->rewriter->drop_last();
			$this->execute_sqlite_query(
				$this->rewriter->get_updated_query()
			);
		} while ( $comma );

		$this->results      = 1;
		$this->return_value = $this->results;
	}

	/**
	 * Translates a CREATE query.
	 *
	 * @throws Exception If the query is an unknown create type.
	 */
	private function execute_create() {
		$this->rewriter->consume();
		$what = $this->rewriter->consume()->token;

		/**
		 * Technically it is possible to support temporary tables as follows:
		 *    ATTACH '' AS 'tempschema';
		 *    CREATE TABLE tempschema.<name>(...)...;
		 * However, for now, let's just ignore the TEMPORARY keyword.
		 */
		if ( 'TEMPORARY' === $what ) {
			$this->rewriter->drop_last();
			$what = $this->rewriter->consume()->token;
		}

		switch ( $what ) {
			case 'TABLE':
				$this->execute_create_table();
				break;

			case 'PROCEDURE':
			case 'DATABASE':
				$this->results = true;
				break;

			default:
				throw new Exception( 'Unknown create type: ' . $what );
		}
	}

	/**
	 * Translates a DROP query.
	 *
	 * @throws Exception If the query is an unknown drop type.
	 */
	private function execute_drop() {
		$this->rewriter->consume();
		$what = $this->rewriter->consume()->token;

		/*
		 * Technically it is possible to support temporary tables as follows:
		 *   ATTACH '' AS 'tempschema';
		 *   CREATE TABLE tempschema.<name>(...)...;
		 * However, for now, let's just ignore the TEMPORARY keyword.
		 */
		if ( 'TEMPORARY' === $what ) {
			$this->rewriter->drop_last();
			$what = $this->rewriter->consume()->token;
		}

		switch ( $what ) {
			case 'TABLE':
				$this->rewriter->consume_all();
				$this->execute_sqlite_query( $this->rewriter->get_updated_query() );
				$this->results = $this->last_exec_returned;
				break;

			case 'PROCEDURE':
			case 'DATABASE':
				$this->results = true;
				return;

			default:
				throw new Exception( 'Unknown drop type: ' . $what );
		}
	}

	/**
	 * Translates a SHOW query.
	 *
	 * @throws Exception If the query is an unknown show type.
	 */
	private function execute_show() {
		$this->rewriter->skip();
		$what1 = $this->rewriter->consume()->token;
		$what2 = $this->rewriter->consume()->token;
		$what  = $what1 . ' ' . $what2;
		switch ( $what ) {
			case 'CREATE PROCEDURE':
				$this->results = true;
				return;

			case 'GRANTS FOR':
				$this->set_results_from_fetched_data(
					array(
						(object) array(
							'Grants for root@localhost' => 'GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, RELOAD, SHUTDOWN, PROCESS, FILE, REFERENCES, INDEX, ALTER, SHOW DATABASES, SUPER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, REPLICATION SLAVE, REPLICATION CLIENT, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, EVENT, TRIGGER, CREATE TABLESPACE, CREATE ROLE, DROP ROLE ON *.* TO `root`@`localhost` WITH GRANT OPTION',
						),
					)
				);
				return;

			case 'FULL COLUMNS':
				$this->rewriter->consume();
				// Fall through.
			case 'COLUMNS FROM':
				$table_name = $this->rewriter->consume()->token;
				$stmt       = $this->execute_sqlite_query(
					"PRAGMA table_info(\"$table_name\");"
				);
				/* @todo we may need to add the Extra column if anybdy needs it. 'auto_increment' is the value */
				$name_map = array(
					'name'       => 'Field',
					'type'       => 'Type',
					'dflt_value' => 'Default',
					'cid'        => null,
					'notnull'    => null,
					'pk'         => null,
				);
				$columns  = $stmt->fetchAll( $this->pdo_fetch_mode );
				$columns  = array_map(
					function ( $row ) use ( $name_map ) {
						$new       = array();
						$is_object = is_object( $row );
						$row       = $is_object ? (array) $row : $row;
						foreach ( $row as $k => $v ) {
							$k = array_key_exists( $k, $name_map ) ? $name_map [ $k ] : $k;
							if ( $k ) {
								$new[ $k ] = $v;
							}
						}
						if ( array_key_exists( 'notnull', $row ) ) {
							$new['Null'] = ( '1' === $row ['notnull'] ) ? 'NO' : 'YES';
						}
						if ( array_key_exists( 'pk', $row ) ) {
							$new['Key'] = ( '1' === $row ['pk'] ) ? 'PRI' : '';
						}
						return $is_object ? (object) $new : $new;
					},
					$columns
				);
				$this->set_results_from_fetched_data( $columns );
				return;

			case 'INDEX FROM':
				$table_name = $this->rewriter->consume()->token;
				$results    = array();

				foreach ( $this->get_primary_keys( $table_name ) as $row ) {
					$results[] = array(
						'Table'       => $table_name,
						'Non_unique'  => '0',
						'Key_name'    => 'PRIMARY',
						'Column_name' => $row['name'],
					);
				}
				foreach ( $this->get_keys( $table_name ) as $row ) {
					foreach ( $row['columns'] as $k => $column ) {
						$results[] = array(
							'Table'       => $table_name,
							'Non_unique'  => '1' === $row['index']['unique'] ? '0' : '1',
							'Key_name'    => $row['index']['name'],
							'Column_name' => $column['name'],
						);
					}
				}
				for ( $i = 0;$i < count( $results );$i++ ) {
					$sqlite_key_name = $results[ $i ]['Key_name'];
					$mysql_key_name  = $sqlite_key_name;

					/*
					 * SQLite automatically assigns names to some indexes.
					 * However, dbDelta in WordPress expects the name to be
					 * the same as in the original CREATE TABLE. Let's
					 * translate the name back.
					 */
					if ( str_starts_with( $mysql_key_name, 'sqlite_autoindex_' ) ) {
						$mysql_key_name = substr( $mysql_key_name, strlen( 'sqlite_autoindex_' ) );
						$mysql_key_name = preg_replace( '/_[0-9]+$/', '', $mysql_key_name );
					}
					if ( str_starts_with( $mysql_key_name, "{$table_name}__" ) ) {
						$mysql_key_name = substr( $mysql_key_name, strlen( "{$table_name}__" ) );
					}

					$mysql_type = $this->get_cached_mysql_data_type( $table_name, $sqlite_key_name );
					if ( 'FULLTEXT' !== $mysql_type && 'SPATIAL' !== $mysql_type ) {
						$mysql_type = 'BTREE';
					}

					$results[ $i ] = (object) array_merge(
						$results[ $i ],
						array(
							'Seq_in_index'  => 0,
							'Key_name'      => $mysql_key_name,
							'Index_type'    => $mysql_type,

							/*
							 * Many of these details are not available in SQLite,
							 * so we just shim them with dummy values.
							 */
							'Collation'     => 'A',
							'Cardinality'   => '0',
							'Sub_part'      => null,
							'Packed'        => null,
							'Null'          => '',
							'Comment'       => '',
							'Index_comment' => '',
						)
					);
				}
				$this->set_results_from_fetched_data(
					$results
				);

				return;

			case 'TABLE STATUS':  // FROM `database`.
				$this->rewriter->skip();
				$database_expression = $this->rewriter->skip();
				$stmt                = $this->execute_sqlite_query(
					"SELECT name as `Name`, 'myisam' as `Engine`, 0 as `Data_length`, 0 as `Index_length`, 0 as `Data_free` FROM sqlite_master WHERE type='table' ORDER BY name"
				);

				$tables = $this->strip_sqlite_system_tables( $stmt->fetchAll( $this->pdo_fetch_mode ) );
				foreach ( $tables as $table ) {
					$table_name  = $table->Name; // phpcs:ignore WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
					$stmt        = $this->execute_sqlite_query( "SELECT COUNT(1) as `Rows` FROM $table_name" );
					$rows        = $stmt->fetchall( $this->pdo_fetch_mode );
					$table->Rows = $rows[0]->Rows; // phpcs:ignore WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
				}

				$this->set_results_from_fetched_data(
					$this->strip_sqlite_system_tables( $tables )
				);

				return;

			case 'TABLES LIKE':
				$table_expression = $this->rewriter->skip();
				$stmt             = $this->execute_sqlite_query(
					"SELECT `name` as `Tables_in_db` FROM `sqlite_master` WHERE `type`='table' AND `name` LIKE :param;",
					array(
						':param' => $table_expression->value,
					)
				);
				$this->set_results_from_fetched_data(
					$stmt->fetchAll( $this->pdo_fetch_mode )
				);
				return;

			default:
				switch ( $what1 ) {
					case 'TABLES':
						$stmt = $this->execute_sqlite_query(
							"SELECT name FROM sqlite_master WHERE type='table'"
						);
						$this->set_results_from_fetched_data(
							$stmt->fetchAll( $this->pdo_fetch_mode )
						);
						return;

					case 'VARIABLE':
					case 'VARIABLES':
						$this->results = true;
						return;

					default:
						throw new Exception( 'Unknown show type: ' . $what );
				}
		}
	}

	/**
	 * Consumes data types from the query.
	 *
	 * @throws Exception If the data type cannot be translated.
	 *
	 * @return array The data types.
	 */
	private function skip_mysql_data_type() {
		$type = $this->rewriter->skip();
		if ( ! $type->matches(
			WP_SQLite_Token::TYPE_KEYWORD,
			WP_SQLite_Token::FLAG_KEYWORD_DATA_TYPE
		) ) {
			throw new Exception( 'Data type expected in MySQL query, unknown token received: ' . $type->value );
		}

		$mysql_data_type = strtolower( $type->value );
		if ( ! isset( $this->field_types_translation[ $mysql_data_type ] ) ) {
			throw new Exception( 'MySQL field type cannot be translated to SQLite: ' . $mysql_data_type );
		}

		$sqlite_data_type = $this->field_types_translation[ $mysql_data_type ];

		// Skip the length, e.g. (10) in VARCHAR(10).
		$paren_maybe = $this->rewriter->peek();
		if ( $paren_maybe && '(' === $paren_maybe->token ) {
			$mysql_data_type .= $this->rewriter->skip()->token;
			$mysql_data_type .= $this->rewriter->skip()->token;
			$mysql_data_type .= $this->rewriter->skip()->token;
		}

		// Skip the int keyword.
		$int_maybe = $this->rewriter->peek();
		if ( $int_maybe && $int_maybe->matches(
			WP_SQLite_Token::TYPE_KEYWORD,
			null,
			array( 'UNSIGNED' )
		)
		) {
			$mysql_data_type .= ' ' . $this->rewriter->skip()->token;
		}
		return array(
			$sqlite_data_type,
			$mysql_data_type,
		);
	}

	/**
	 * Updates the data type cache.
	 *
	 * @param string $table           The table name.
	 * @param string $column_or_index The column or index name.
	 * @param string $mysql_data_type The MySQL data type.
	 *
	 * @return void
	 */
	private function update_data_type_cache( $table, $column_or_index, $mysql_data_type ) {
		$this->execute_sqlite_query(
			'INSERT INTO ' . self::DATA_TYPES_CACHE_TABLE . ' (`table`, `column_or_index`, `mysql_type`)
				VALUES (:table, :column, :datatype)
				ON CONFLICT(`table`, `column_or_index`) DO UPDATE SET `mysql_type` = :datatype
			',
			array(
				':table'    => $table,
				':column'   => $column_or_index,
				':datatype' => $mysql_data_type,
			)
		);
	}

	/**
	 * Gets the cached MySQL data type.
	 *
	 * @param string $table           The table name.
	 * @param string $column_or_index The column or index name.
	 *
	 * @return string The MySQL data type.
	 */
	private function get_cached_mysql_data_type( $table, $column_or_index ) {
		$stmt       = $this->execute_sqlite_query(
			'SELECT d.`mysql_type` FROM ' . self::DATA_TYPES_CACHE_TABLE . ' d
			WHERE `table`=:table
			AND `column_or_index` = :index',
			array(
				':table' => $table,
				':index' => $column_or_index,
			)
		);
		$mysql_type = $stmt->fetchColumn( 0 );
		if ( str_ends_with( $mysql_type, ' KEY' ) ) {
			$mysql_type = substr( $mysql_type, 0, strlen( $mysql_type ) - strlen( ' KEY' ) );
		}
		return $mysql_type;
	}

	/**
	 * Normalizes a column name.
	 *
	 * @param string $column_name The column name.
	 *
	 * @return string The normalized column name.
	 */
	private function normalize_column_name( $column_name ) {
		return trim( $column_name, '`\'"' );
	}

	/**
	 * Normalizes an index type.
	 *
	 * @param string $index_type The index type.
	 *
	 * @return string|null The normalized index type, or null if the index type is not supported.
	 */
	private function normalize_mysql_index_type( $index_type ) {
		$index_type = strtoupper( $index_type );
		$index_type = preg_replace( '/INDEX$/', 'KEY', $index_type );
		$index_type = preg_replace( '/ KEY$/', '', $index_type );
		if (
			'KEY' === $index_type
			|| 'PRIMARY' === $index_type
			|| 'UNIQUE' === $index_type
			|| 'FULLTEXT' === $index_type
			|| 'SPATIAL' === $index_type
		) {
			return $index_type;
		}
		return null;
	}

	/**
	 * Converts an index type to a SQLite index type.
	 *
	 * @param string|null $normalized_mysql_index_type The normalized index type.
	 *
	 * @return string|null The SQLite index type, or null if the index type is not supported.
	 */
	private function mysql_index_type_to_sqlite_type( $normalized_mysql_index_type ) {
		if ( null === $normalized_mysql_index_type ) {
			return null;
		}
		if ( 'PRIMARY' === $normalized_mysql_index_type ) {
			return 'PRIMARY KEY';
		}
		if ( 'UNIQUE' === $normalized_mysql_index_type ) {
			return 'UNIQUE INDEX';
		}
		return 'INDEX';
	}

	/**
	 * Executes a CHECK statement.
	 */
	private function execute_check() {
		$this->rewriter->skip();  // CHECK.
		$this->rewriter->skip();  // TABLE.
		$table_name = $this->rewriter->consume()->value;  // Τable_name.

		$tables =
			$this->execute_sqlite_query(
				"SELECT name as `table_name` FROM sqlite_master WHERE type='table' AND name = :table_name ORDER BY name",
				array( $table_name )
			)->fetchAll();

		if ( is_array( $tables ) && 1 === count( $tables ) && $table_name === $tables[0]['table_name'] ) {

			$this->set_results_from_fetched_data(
				array(
					(object) array(
						'Table'    => $table_name,
						'Op'       => 'check',
						'Msg_type' => 'status',
						'Msg_text' => 'OK',
					),
				)
			);
		} else {

			$this->set_results_from_fetched_data(
				array(
					(object) array(
						'Table'    => $table_name,
						'Op'       => 'check',
						'Msg_type' => 'Error',
						'Msg_text' => "Table '$table_name' doesn't exist",
					),
					(object) array(
						'Table'    => $table_name,
						'Op'       => 'check',
						'Msg_type' => 'status',
						'Msg_text' => 'Operation failed',
					),
				)
			);
		}
	}

	/**
	 * Handle an OPTIMIZE / REPAIR / ANALYZE TABLE statement, by using VACUUM just once, at shutdown.
	 *
	 * @param string $query_type The query type.
	 */
	private function execute_optimize( $query_type ) {
		// OPTIMIZE TABLE tablename.
		$this->rewriter->skip();
		$this->rewriter->skip();
		$table_name = $this->rewriter->skip()->value;
		$status     = '';

		if ( ! $this->vacuum_requested ) {
			$this->vacuum_requested = true;
			if ( function_exists( 'add_action' ) ) {
				$status = "SQLite does not support $query_type, doing VACUUM instead";
				add_action(
					'shutdown',
					function () {
						$this->execute_sqlite_query( 'VACUUM' );
					}
				);
			} else {
				/* add_action isn't available in the unit test environment, and we're deep in a transaction. */
				$status = "SQLite unit testing does not support $query_type.";
			}
		}
		$resultset = array(
			(object) array(
				'Table'    => $table_name,
				'Op'       => strtolower( $query_type ),
				'Msg_type' => 'note',
				'Msg_text' => $status,
			),
			(object) array(
				'Table'    => $table_name,
				'Op'       => strtolower( $query_type ),
				'Msg_type' => 'status',
				'Msg_text' => 'OK',
			),
		);

		$this->set_results_from_fetched_data( $resultset );
	}

	/**
	 * Error handler.
	 *
	 * @param Exception $err Exception object.
	 *
	 * @return bool Always false.
	 */
	private function handle_error( Exception $err ) {
		$message = $err->getMessage();
		$this->set_error( __LINE__, __FUNCTION__, $message );
		$this->return_value = false;
		return false;
	}

	/**
	 * Method to format the error messages and put out to the file.
	 *
	 * When $wpdb::suppress_errors is set to true or $wpdb::show_errors is set to false,
	 * the error messages are ignored.
	 *
	 * @param string $line          Where the error occurred.
	 * @param string $function_name Indicate the function name where the error occurred.
	 * @param string $message       The message.
	 *
	 * @return boolean|void
	 */
	private function set_error( $line, $function_name, $message ) {
		$this->errors[]         = array(
			'line'     => $line,
			'function' => $function_name,
		);
		$this->error_messages[] = $message;
		$this->is_error         = true;
	}

	/**
	 * PDO has no explicit close() method.
	 *
	 * This is because PHP may choose to reuse the same
	 * connection for the next request. The PHP manual
	 * states the PDO object can only be unset:
	 *
	 * https://www.php.net/manual/en/pdo.connections.php#114822
	 */
	public function close() {
		$this->pdo = null;
	}

	/**
	 * Method to return error messages.
	 *
	 * @throws Exception If error is found.
	 *
	 * @return string
	 */
	public function get_error_message() {
		if ( count( $this->error_messages ) === 0 ) {
			$this->is_error       = false;
			$this->error_messages = array();
			return '';
		}

		if ( false === $this->is_error ) {
			return '';
		}

		$output  = '<div style="clear:both">&nbsp;</div>' . PHP_EOL;
		$output .= '<div class="queries" style="clear:both;margin-bottom:2px;border:red dotted thin;">' . PHP_EOL;
		$output .= '<p>MySQL query:</p>' . PHP_EOL;
		$output .= '<p>' . $this->mysql_query . '</p>' . PHP_EOL;
		$output .= '<p>Queries made or created this session were:</p>' . PHP_EOL;
		$output .= '<ol>' . PHP_EOL;
		foreach ( $this->executed_sqlite_queries as $q ) {
			$message = "Executing: {$q['sql']} | " . ( $q['params'] ? 'parameters: ' . implode( ', ', $q['params'] ) : '(no parameters)' );

			$output .= '<li>' . htmlspecialchars( $message ) . '</li>' . PHP_EOL;
		}
		$output .= '</ol>' . PHP_EOL;
		$output .= '</div>' . PHP_EOL;
		foreach ( $this->error_messages as $num => $m ) {
			$output .= '<div style="clear:both;margin-bottom:2px;border:red dotted thin;" class="error_message" style="border-bottom:dotted blue thin;">' . PHP_EOL;
			$output .= sprintf(
				'Error occurred at line %1$d in Function %2$s. Error message was: %3$s.',
				(int) $this->errors[ $num ]['line'],
				'<code>' . htmlspecialchars( $this->errors[ $num ]['function'] ) . '</code>',
				$m
			) . PHP_EOL;
			$output .= '</div>' . PHP_EOL;
		}

		try {
			throw new Exception();
		} catch ( Exception $e ) {
			$output .= '<p>Backtrace:</p>' . PHP_EOL;
			$output .= '<pre>' . $e->getTraceAsString() . '</pre>' . PHP_EOL;
		}

		return $output;
	}

	/**
	 * Executes a query in SQLite.
	 *
	 * @param mixed $sql The query to execute.
	 * @param mixed $params The parameters to bind to the query.
	 * @throws PDOException If the query could not be executed.
	 * @return object {
	 *     The result of the query.
	 *
	 *     @type PDOStatement $stmt The executed statement
	 *     @type * $result The value returned by $stmt.
	 * }
	 */
	public function execute_sqlite_query( $sql, $params = array() ) {
		$this->executed_sqlite_queries[] = array(
			'sql'    => $sql,
			'params' => $params,
		);

		$stmt = $this->pdo->prepare( $sql );
		if ( false === $stmt || null === $stmt ) {
			$this->last_exec_returned = null;
			$info                     = $this->pdo->errorInfo();
			$this->last_sqlite_error  = $info[0] . ' ' . $info[2];
			throw new PDOException( implode( ' ', array( 'Error:', $info[0], $info[2], 'SQLite:', $sql ) ), $info[1] );
		}
		$returned                 = $stmt->execute( $params );
		$this->last_exec_returned = $returned;
		if ( ! $returned ) {
			$info                    = $stmt->errorInfo();
			$this->last_sqlite_error = $info[0] . ' ' . $info[2];
			throw new PDOException( implode( ' ', array( 'Error:', $info[0], $info[2], 'SQLite:', $sql ) ), $info[1] );
		}

		return $stmt;
	}

	/**
	 * Method to set the results from the fetched data.
	 *
	 * @param array $data The data to set.
	 */
	private function set_results_from_fetched_data( $data ) {
		if ( null === $this->results ) {
			$this->results = $data;
		}
		if ( is_array( $this->results ) ) {
			$this->num_rows               = count( $this->results );
			$this->last_select_found_rows = count( $this->results );
		}
		$this->return_value = $this->results;
	}

	/**
	 * Method to set the results from the affected rows.
	 *
	 * @param int|null $override Override the affected rows.
	 */
	private function set_result_from_affected_rows( $override = null ) {
		/*
		 * SELECT CHANGES() is a workaround for the fact that
		 * $stmt->rowCount() returns "0" (zero) with the
		 * SQLite driver at all times.
		 * Source: https://www.php.net/manual/en/pdostatement.rowcount.php
		 */
		if ( null === $override ) {
			$this->affected_rows = (int) $this->execute_sqlite_query( 'select changes()' )->fetch()[0];
		} else {
			$this->affected_rows = $override;
		}
		$this->return_value = $this->affected_rows;
		$this->num_rows     = $this->affected_rows;
		$this->results      = $this->affected_rows;
	}

	/**
	 * Method to clear previous data.
	 */
	private function flush() {
		$this->mysql_query                 = '';
		$this->results                     = null;
		$this->last_exec_returned          = null;
		$this->table_name                  = null;
		$this->last_insert_id              = null;
		$this->affected_rows               = null;
		$this->insert_columns              = array();
		$this->column_data                 = array();
		$this->num_rows                    = null;
		$this->return_value                = null;
		$this->error_messages              = array();
		$this->is_error                    = false;
		$this->executed_sqlite_queries     = array();
		$this->like_expression_nesting     = 0;
		$this->like_escape_count           = 0;
		$this->is_information_schema_query = false;
		$this->has_group_by                = false;
	}

	/**
	 * Begin a new transaction or nested transaction.
	 *
	 * @return boolean
	 */
	public function begin_transaction() {
		$success = false;
		try {
			if ( 0 === $this->transaction_level ) {
				$this->execute_sqlite_query( 'BEGIN' );
			} else {
				$this->execute_sqlite_query( 'SAVEPOINT LEVEL' . $this->transaction_level );
			}
			$success = $this->last_exec_returned;
		} finally {
			if ( $success ) {
				++$this->transaction_level;
				/**
				 * Notifies that a transaction-related query has been translated and executed.
				 *
				 * @param string $command       The SQL statement (one of "START TRANSACTION", "COMMIT", "ROLLBACK").
				 * @param bool   $success       Whether the SQL statement was successful or not.
				 * @param int    $nesting_level The nesting level of the transaction.
				 *
				 * @since 0.1.0
				 */
				do_action( 'sqlite_transaction_query_executed', 'START TRANSACTION', (bool) $this->last_exec_returned, $this->transaction_level - 1 );
			}
		}
		return $success;
	}

	/**
	 * Commit the current transaction or nested transaction.
	 *
	 * @return boolean True on success, false on failure.
	 */
	public function commit() {
		if ( 0 === $this->transaction_level ) {
			return false;
		}

		--$this->transaction_level;
		if ( 0 === $this->transaction_level ) {
			$this->execute_sqlite_query( 'COMMIT' );
		} else {
			$this->execute_sqlite_query( 'RELEASE SAVEPOINT LEVEL' . $this->transaction_level );
		}

		do_action( 'sqlite_transaction_query_executed', 'COMMIT', (bool) $this->last_exec_returned, $this->transaction_level );
		return $this->last_exec_returned;
	}

	/**
	 * Rollback the current transaction or nested transaction.
	 *
	 * @return boolean True on success, false on failure.
	 */
	public function rollback() {
		if ( 0 === $this->transaction_level ) {
			return false;
		}

		--$this->transaction_level;
		if ( 0 === $this->transaction_level ) {
			$this->execute_sqlite_query( 'ROLLBACK' );
		} else {
			$this->execute_sqlite_query( 'ROLLBACK TO SAVEPOINT LEVEL' . $this->transaction_level );
		}
		do_action( 'sqlite_transaction_query_executed', 'ROLLBACK', (bool) $this->last_exec_returned, $this->transaction_level );
		return $this->last_exec_returned;
	}
}