Caret behavior by single tap in Cupertino textfields

compose/foundation/foundation/src/skikoMain/kotlin/androidx/compose/foundation/text/CupertionTextFieldPointerModifier.skiko.kt → compose/foundation/foundation/src/skikoMain/kotlin/androidx/compose/foundation/text/CupertinoTextFieldPointerModifier.skiko.kt

@@ -97,29 +97,39 @@ private fun getTapHandlerModifier(
     return Modifier.pointerInput(interactionSource) {
         detectRepeatingTapGestures(
             onTap = { touchPointOffset ->
-                tapTextFieldToFocus(
-                    currentState,
-                    currentFocusRequester,
-                    !currentReadOnly
-                )
                 if (currentState.hasFocus) {
                     if (currentState.handleState != HandleState.Selection) {
                         currentState.layoutResult?.let { layoutResult ->
-                            TextFieldDelegate.setCursorOffset(
-                                touchPointOffset,
-                                layoutResult,
-                                currentState.processor,
-                                currentOffsetMapping,
-                                currentState.onValueChange
+                            TextFieldDelegate.cupertinoSetCursorOffsetFocused(
+                                position = touchPointOffset,
+                                textLayoutResult = layoutResult,
+                                editProcessor = currentState.processor,
+                                offsetMapping = currentOffsetMapping,
+                                showContextMenu = {},
+                                onValueChange = currentState.onValueChange
                             )
-                            // Won't enter cursor state when text is empty.
-                            if (currentState.textDelegate.text.isNotEmpty()) {
-                                currentState.handleState = HandleState.Cursor
-                            }
                         }
                     } else {
                         currentManager.deselect(touchPointOffset)
                     }
+                } else {
+                    tapTextFieldToFocus(
+                        currentState,
+                        currentFocusRequester,
+                        !currentReadOnly
+                    )
+                    currentState.layoutResult?.let { layoutResult ->
+                        TextFieldDelegate.setCursorOffset(
+                            touchPointOffset,
+                            layoutResult,
+                            currentState.processor,
+                            currentOffsetMapping,
+                            currentState.onValueChange
+                        )
+                    }
+                }
+                if (currentState.textDelegate.text.isNotEmpty()) {
+                    currentState.handleState = HandleState.Cursor
                 }
             },
             onDoubleTap = {
@@ -149,7 +159,10 @@ private fun getSelectionModifier(manager: TextFieldSelectionManager): Modifier {
     }
 }
 
-private fun TextFieldSelectionManager.doRepeatingTapSelection(touchPointOffset: Offset, selectionAdjustment: SelectionAdjustment) {
+private fun TextFieldSelectionManager.doRepeatingTapSelection(
+    touchPointOffset: Offset,
+    selectionAdjustment: SelectionAdjustment
+) {
     if (value.text.isEmpty()) return
     enterSelectionMode()
     state?.layoutResult?.let { layoutResult ->

compose/foundation/foundation/src/skikoMain/kotlin/androidx/compose/foundation/text/StringHelpers.skiko.kt

@@ -28,4 +28,157 @@ internal actual fun String.findFollowingBreak(index: Int): Int {
     val it = BreakIterator.makeCharacterInstance()
     it.setText(this)
     return it.following(index)
+}
+
+// TODO Remove once it's available in common stdlib https://youtrack.jetbrains.com/issue/KT-23251
+internal typealias CodePoint = Int
+
+/**
+ * Converts a surrogate pair to a unicode code point.
+ */
+private fun Char.Companion.toCodePoint(high: Char, low: Char): CodePoint =
+    (((high - MIN_HIGH_SURROGATE) shl 10) or (low - MIN_LOW_SURROGATE)) + 0x10000
+
+/**
+ * The minimum value of a supplementary code point, `\u0x10000`.
+ */
+private const val MIN_SUPPLEMENTARY_CODE_POINT: Int = 0x10000
+
+internal fun CodePoint.charCount(): Int = if (this >= MIN_SUPPLEMENTARY_CODE_POINT) 2 else 1
+
+internal val String.codePoints
+    get() = sequence {
+        var index = 0
+        while (index < length) {
+            val codePoint = codePointAt(index)
+            yield(codePoint)
+            index += codePoint.charCount()
+        }
+    }
+
+/**
+ * Returns the character (Unicode code point) at the specified index.
+ */
+internal fun String.codePointAt(index: Int): CodePoint {
+    val high = this[index]
+    if (high.isHighSurrogate() && index + 1 < this.length) {
+        val low = this[index + 1]
+        if (low.isLowSurrogate()) {
+            return Char.toCodePoint(high, low)
+        }
+    }
+    return high.code
+}
+
+
+/**
+ * Finds the offset of the next non-whitespace symbols subsequence (word) in the given text
+ * starting from the specified caret offset.
+ *
+ * @param offset The offset where to start looking for the next word.
+ * @param currentText The current text in which to search for the next word.
+ * @return The offset of the next non-whitespace symbols subsequence (word), or the end of the string
+ *         if no such word is found.
+ */
+internal fun findNextNonWhitespaceSymbolsSubsequenceStartOffset(
+    offset: Int,
+    currentText: String
+): Int {
+    /* Assume that next non whitespaces symbols subsequence (word) is when current char is whitespace and next character is not.
+     * Emoji (compound incl.) should be treated as a new word.
+     */
+    val charIterator =
+        BreakIterator.makeCharacterInstance() // wordInstance doesn't consider symbols sequence as word
+    charIterator.setText(currentText)
+
+    var currentOffset: Int
+    var nextOffset = charIterator.next()
+    while (nextOffset < offset) {
+        nextOffset = charIterator.next()
+    }
+    currentOffset = nextOffset
+
+    while (nextOffset != BreakIterator.DONE) {
+        nextOffset = charIterator.next()
+        if (currentText.codePointAt(currentOffset).isWhitespace() && !currentText.codePointAt(
+                nextOffset
+            ).isWhitespace()
+        ) {
+            return currentOffset
+        } else {
+            currentOffset = nextOffset
+        }
+    }
+    return currentOffset
+}
+
+/**
+ * Determines whether the character at the specified offset in the string is a whitespace Unicode character.
+ *
+ * @param offset The index of the character to check.
+ * @return `true` if the character at the specified offset is a whitespace character, `false` otherwise.
+ */
+internal fun String.isWhitespace(offset: Int): Boolean {
+    return this.codePointAt(offset).isWhitespace()
+}
+
+/**
+ * Checks if the character at the specified offset in the string is a punctuation Unicode character.
+ *
+ * @param offset The offset of the character to check.
+ * @return true if the character at the specified offset is a punctuation character, false otherwise.
+ */
+internal fun String.isPunctuation(offset: Int): Boolean {
+    return this.codePointAt(offset).isPunctuation()
+}
+
+internal fun String.halfSymbolsOffset(): Int {
+    val symbolsCount = this.codePoints.count()
+    val charIterator = BreakIterator.makeCharacterInstance()
+    charIterator.setText(this)
+    var currentOffset = 0
+    for (i in 0..symbolsCount / 2) {
+        currentOffset = charIterator.next()
+    }
+    return currentOffset
+}
+
+/**
+ * Checks if the given Unicode code point is a whitespace character.
+ *
+ * @return `true` if the code point is a whitespace character, `false` otherwise.
+ */
+private fun CodePoint.isWhitespace(): Boolean {
+    // TODO: Extend this behavior when (if) Unicode will have compound whitespace characters.
+    if (this.charCount() != 1) {
+        return false
+    }
+    return this.toChar().isWhitespace()
+}
+
+/**
+ * Checks if the given Unicode code point is a punctuation character.
+ *
+ * @return 'true' if the CodePoint is a punctuation character, 'false' otherwise.
+ */
+private fun CodePoint.isPunctuation(): Boolean {
+    // TODO: Extend this behavior when (if) Unicode will have compound punctuation characters.
+    if (this.charCount() != 1) {
+        return false
+    }
+    val punctuationSet = setOf(
+        CharCategory.DASH_PUNCTUATION,
+        CharCategory.START_PUNCTUATION,
+        CharCategory.END_PUNCTUATION,
+        CharCategory.CONNECTOR_PUNCTUATION,
+        CharCategory.OTHER_PUNCTUATION,
+        CharCategory.INITIAL_QUOTE_PUNCTUATION,
+        CharCategory.FINAL_QUOTE_PUNCTUATION
+    )
+    punctuationSet.forEach {
+        if (it.contains(this.toChar())) {
+            return true
+        }
+    }
+    return false
 }

compose/foundation/foundation/src/skikoMain/kotlin/androidx/compose/foundation/text/TextFieldDelegate.skiko.kt

@@ -0,0 +1,144 @@
+/*
+ * Copyright 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.compose.foundation.text
+
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Rect
+import androidx.compose.ui.text.TextRange
+import androidx.compose.ui.text.input.EditProcessor
+import androidx.compose.ui.text.input.OffsetMapping
+import androidx.compose.ui.text.input.TextFieldValue
+
+/**
+ * Sets and adjusts the cursor offset when the TextField is focused in a Cupertino style.
+ * Cursor final offset depends on position of the cursor and content of the textfield.
+ *
+ * See **determineCursorDesiredPosition()** for more details.
+ * @param position The position of the cursor in the TextField.
+ * @param textLayoutResult The TextLayoutResultProxy object that contains the layout information of the TextField text.
+ * @param editProcessor The EditProcessor object that manages the editing operations of the TextField.
+ * @param offsetMapping The OffsetMapping object that maps the transformed offset to the original offset.
+ * @param showContextMenu The function that displays the context menu at the given rectangular area.
+ * @param onValueChange The function that is called when the TextField value changes.
+ */
+internal fun TextFieldDelegate.Companion.cupertinoSetCursorOffsetFocused(
+    position: Offset,
+    textLayoutResult: TextLayoutResultProxy,
+    editProcessor: EditProcessor,
+    offsetMapping: OffsetMapping,
+    showContextMenu: (Rect) -> Unit,
+    onValueChange: (TextFieldValue) -> Unit
+) {
+    val offset =
+        offsetMapping.transformedToOriginal(textLayoutResult.getOffsetForPosition(position))
+    val currentValue = editProcessor.toTextFieldValue()
+    val currentText = currentValue.text
+
+    val cursorDesiredOffset = determineCursorDesiredOffset(
+        offset,
+        currentValue,
+        textLayoutResult,
+        currentText
+    )
+
+    if (cursorDesiredOffset == offset) {
+        showContextMenu(textLayoutResult.value.getCursorRect(offset))
+    }
+    onValueChange(
+        editProcessor.toTextFieldValue().copy(selection = TextRange(cursorDesiredOffset))
+    )
+}
+
+/**
+ * Determines the desired cursor position based on the given parameters.
+ *
+ * The rules for determining position of the caret are as follows:
+ * - When you make a single tap on a word, the caret moves to the end of this word.
+ * - If there’s a punctuation mark after the word, the caret is between the word and the punctuation mark.
+ * - If you tap on a whitespace, the caret is placed before the word. Same for many whitespaces in a row. (and punctuation marks)
+ * - If there’s a punctuation mark before the word, the caret is between the punctuation mark and the word.
+ * - When you make a single tap on the first half of the word, the caret is placed before this word.
+ * - If you tap on the left edge of the TextField, the caret is placed before the first word on this line. The same is for the right edge.
+ * - If you tap at the caret, that is placed in the middle of the word, it will jump to the end of the word.
+ * @param offset The current offset position.
+ * @param currentValue The current TextFieldValue.
+ * @param textLayoutResult The TextLayoutResultProxy representing the layout of the text.
+ * @param currentText The current text in the TextField.
+ * @return The desired cursor position after evaluating the given parameters.
+ */
+internal fun determineCursorDesiredOffset(
+    offset: Int,
+    currentValue: TextFieldValue,
+    textLayoutResult: TextLayoutResultProxy,
+    currentText: String
+): Int {
+    val caretOffsetPosition: Int
+    val previousCaretPosition = currentValue.selection.start
+    if (offset == previousCaretPosition) {
+        caretOffsetPosition = offset
+    } else if (textLayoutResult.isLeftEdgeTapped(offset)) {
+        val lineNumber = textLayoutResult.value.getLineForOffset(offset)
+        caretOffsetPosition = textLayoutResult.value.getLineStart(lineNumber)
+    } else if (textLayoutResult.isRightEdgeTapped(offset)) {
+        val lineNumber = textLayoutResult.value.getLineForOffset(offset)
+        caretOffsetPosition = textLayoutResult.value.getLineEnd(lineNumber)
+    } else if (isPunctuationOrSpaceTapped(offset, currentText)) {
+        val nextWordStartOffset =
+            findNextNonWhitespaceSymbolsSubsequenceStartOffset(offset, currentText)
+        caretOffsetPosition = nextWordStartOffset
+    } else if (textLayoutResult.isFirstHalfOfWordTapped(offset, currentText)) {
+        val wordBoundary = textLayoutResult.value.getWordBoundary(offset)
+        caretOffsetPosition = wordBoundary.start
+    } else {
+        val wordBoundary = textLayoutResult.value.getWordBoundary(offset)
+        caretOffsetPosition = wordBoundary.end
+    }
+    return caretOffsetPosition
+}
+
+private fun isPunctuationOrSpaceTapped(
+    caretOffset: Int,
+    currentText: String
+): Boolean {
+    /* From TextLayoutResultProxy.value.getWordBoundary(caretOffset) it is clear
+    * that for whitespace or punctuation mark method will return empty range.
+    * caretOffset can be between 0...currentText.length, so it should be somewhere between words.
+    * */
+    return currentText.isPunctuation(caretOffset) || currentText.isWhitespace(caretOffset)
+}
+
+private fun TextLayoutResultProxy.isFirstHalfOfWordTapped(
+    caretOffset: Int,
+    currentText: String
+): Boolean {
+    val wordBoundary = value.getWordBoundary(caretOffset)
+    val word = currentText.substring(wordBoundary.start, wordBoundary.end)
+    val middleIndex = wordBoundary.start + word.halfSymbolsOffset()
+    return caretOffset < middleIndex
+}
+
+private fun TextLayoutResultProxy.isLeftEdgeTapped(caretOffset: Int): Boolean {
+    val lineNumber = value.getLineForOffset(caretOffset)
+    val lineStartOffset = value.getLineStart(lineNumber)
+    return lineStartOffset == caretOffset
+}
+
+private fun TextLayoutResultProxy.isRightEdgeTapped(caretOffset: Int): Boolean {
+    val lineNumber = value.getLineForOffset(caretOffset)
+    val lineEndOffset = value.getLineEnd(lineNumber)
+    return lineEndOffset == caretOffset
+}