process._prompt for asking questions on the command line

[coolaj86]

I'm not quite sure this is the implementation, but probably something close to this.

I'd actually much prefer to have inline autocomplete, like fish, but I've done that before and it's no small feat - certainly outside of the "almost bare metal" approach of AjScript.

/**
 * @param {String} query
 * @param {Object} options
 * @param {Array<String>} [options.choices]
 * @param {Boolean} [options.mask]
 */
process._prompt = async function (query, options) {
  let Readline = require("readline");

  let completer;
  if (options?.choices) {
    /**
     * @param {String} line
     */
    completer = function (line) {
      let completions = options.choices || [];
      let hits = completions.filter(function (c) {
        return c.startsWith(line);
      });
      if (!hits.length) {
        hits = completions;
      }
      return [hits, line];
    };
  }

  let rl = Readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    completer,
  });

  if (options?.mask) {
    rl.input.on("keypress", function (_char, _modifiers) {
      // _char = "e"
      // _modifiers = { sequence: 'e', name: 'e', ctrl: false, meta: false, shift: false }
      let len = rl.line.length;
      // place cursor at the beginning of the prompt
      Readline.moveCursor(rl.output, -len, 0);
      // clear right of the cursor / prompt
      Readline.clearLine(rl.output, 1);
      // mask with "*"
      rl.output.write("*".repeat(len));
    });
  }

  let answer = await new Promise(function (resolve) {
    return rl.question(query ?? "", resolve);
  });

  // TODO what if we need control over closing?
  // ex: Promise.race([getPrompt, getFsEvent, getSocketEvent]);
  rl.close();
  return answer;
};

Inspired by https://github.com/google/zx/blob/51fb6d5d710fcd0bfcc7bc905066ac0fa042467c/index.mjs#L143.