packages/flutter/lib/src/services/text_editing_delta.dart - external/github.com/flutter/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'dart:ui' show TextRange;

 import 'package:flutter/foundation.dart';

 import 'text_editing.dart';
 import 'text_input.dart' show TextEditingValue;

 export 'dart:ui' show TextRange;

 export 'text_editing.dart' show TextSelection;
 export 'text_input.dart' show TextEditingValue;

 TextAffinity? _toTextAffinity(String? affinity) {
   switch (affinity) {
     case 'TextAffinity.downstream':
       return TextAffinity.downstream;
     case 'TextAffinity.upstream':
       return TextAffinity.upstream;
   }
   return null;
 }

 /// Replaces a range of text in the original string with the text given in the
 /// replacement string.
 String _replace(String originalText, String replacementText, int start, int end) {
   final String textStart = originalText.substring(0, start);
   final String textEnd = originalText.substring(end, originalText.length);
   final String newText = textStart + replacementText + textEnd;
   return newText;
 }

 /// A structure representing a granular change that has occurred to the editing
 /// state as a result of text editing.
 ///
 /// See also:
 ///
 ///  * [TextEditingDeltaInsertion], a delta representing an insertion.
 ///  * [TextEditingDeltaDeletion], a delta representing a deletion.
 ///  * [TextEditingDeltaReplacement], a delta representing a replacement.
 ///  * [TextEditingDeltaNonTextUpdate], a delta representing an update to the
 ///    selection and/or composing region.
 ///  * [TextInputConfiguration], to opt-in your [DeltaTextInputClient] to receive
 ///    [TextEditingDelta]'s you must set [TextInputConfiguration.enableDeltaModel]
 ///    to true.
 abstract class TextEditingDelta {
   /// Creates a delta for a given change to the editing state.
   ///
   /// {@template flutter.services.TextEditingDelta}
   /// The [oldText], [selection], and [composing] arguments must not be null.
   /// {@endtemplate}
   const TextEditingDelta({
     required this.oldText,
     required this.selection,
     required this.composing,
   }) : assert(oldText != null),
        assert(selection != null),
        assert(composing != null);

   /// Creates an instance of this class from a JSON object by inferring the
   /// type of delta based on values sent from the engine.
   factory TextEditingDelta.fromJSON(Map<String, dynamic> encoded) {
     // An insertion delta is one where replacement destination is collapsed.
     //
     // A deletion delta is one where the replacement source is empty.
     //
     // An insertion/deletion can still occur when the replacement destination is not
     // collapsed, or the replacement source is not empty.
     //
     // On native platforms when composing text, the entire composing region is
     // replaced on input, rather than reporting character by character
     // insertion/deletion. In these cases we can detect if there was an
     // insertion/deletion by checking if the text inside the original composing
     // region was modified by the replacement. If the text is the same then we have
     // an insertion/deletion. If the text is different then we can say we have
     // a replacement.
     //
     // For example say we are currently composing the word: 'world'.
     // Our current state is 'worl|' with the cursor at the end of 'l'. If we
     // input the character 'd', the platform will tell us 'worl' was replaced
     // with 'world' at range (0,4). Here we can check if the text found in the
     // composing region (0,4) has been modified. We see that it hasn't because
     // 'worl' == 'worl', so this means that the text in
     // 'world'{replacementDestinationEnd, replacementDestinationStart + replacementSourceEnd}
     // can be considered an insertion. In this case we inserted 'd'.
     //
     // Similarly for a a deletion, say we are currently composing the word: 'worl'.
     // Our current state is 'world|' with the cursor at the end of 'd'. If we
     // press backspace to delete the character 'd', the platform will tell us 'world'
     // was replaced with 'worl' at range (0,5). Here we can check if the text found
     // in the new composing region, is the same as the replacement text. We can do this
     // by using oldText{replacementDestinationStart, replacementDestinationStart + replacementSourceEnd}
     // which in this case is 'worl'. We then compare 'worl' with 'worl' and
     // verify that they are the same. This means that the text in
     // 'world'{replacementDestinationEnd, replacementDestinationStart + replacementSourceEnd} was deleted.
     // In this case the character 'd' was deleted.
     //
     // A replacement delta occurs when the original composing region has been
     // modified.
     //
     // A non text update delta occurs when the selection and/or composing region
     // has been changed by the platform, and there have been no changes to the
     // text value.
     final String oldText = encoded['oldText'] as String;
     final int replacementDestinationStart = encoded['deltaStart'] as int;
     final int replacementDestinationEnd = encoded['deltaEnd'] as int;
     final String replacementSource = encoded['deltaText'] as String;
     const int replacementSourceStart = 0;
     final int replacementSourceEnd = replacementSource.length;

     // This delta is explicitly a non text update.
     final bool isNonTextUpdate = replacementDestinationStart == -1 && replacementDestinationStart == replacementDestinationEnd;
     final TextRange newComposing = TextRange(
       start: encoded['composingBase'] as int? ?? -1,
       end: encoded['composingExtent'] as int? ?? -1,
     );
     final TextSelection newSelection = TextSelection(
       baseOffset: encoded['selectionBase'] as int? ?? -1,
       extentOffset: encoded['selectionExtent'] as int? ?? -1,
       affinity: _toTextAffinity(encoded['selectionAffinity'] as String?) ??
           TextAffinity.downstream,
       isDirectional: encoded['selectionIsDirectional'] as bool? ?? false,
     );

     if (isNonTextUpdate) {
       return TextEditingDeltaNonTextUpdate(
         oldText: oldText,
         selection: newSelection,
         composing: newComposing,
       );
     }

     final String newText = _replace(oldText, replacementSource, replacementDestinationStart, replacementDestinationEnd);
     final bool isEqual = oldText == newText;

     final bool isDeletionGreaterThanOne = (replacementDestinationEnd - replacementDestinationStart) - (replacementSourceEnd - replacementSourceStart) > 1;
     final bool isDeletingByReplacingWithEmpty = replacementSource.isEmpty && replacementSourceStart == 0 && replacementSourceStart == replacementSourceEnd;

     final bool isReplacedByShorter = isDeletionGreaterThanOne && (replacementSourceEnd - replacementSourceStart < replacementDestinationEnd - replacementDestinationStart);
     final bool isReplacedByLonger = replacementSourceEnd - replacementSourceStart > replacementDestinationEnd - replacementDestinationStart;
     final bool isReplacedBySame = replacementSourceEnd - replacementSourceStart == replacementDestinationEnd - replacementDestinationStart;

     final bool isInsertingInsideComposingRegion = replacementDestinationStart + replacementSourceEnd > replacementDestinationEnd;
     final bool isDeletingInsideComposingRegion =
         !isReplacedByShorter && !isDeletingByReplacingWithEmpty && replacementDestinationStart + replacementSourceEnd < replacementDestinationEnd;

     String newComposingText;
     String originalComposingText;

     if (isDeletingByReplacingWithEmpty || isDeletingInsideComposingRegion || isReplacedByShorter) {
       newComposingText = replacementSource.substring(replacementSourceStart, replacementSourceEnd);
       originalComposingText = oldText.substring(replacementDestinationStart, replacementDestinationStart + replacementSourceEnd);
     } else {
       newComposingText = replacementSource.substring(replacementSourceStart, replacementSourceStart + (replacementDestinationEnd - replacementDestinationStart));
       originalComposingText = oldText.substring(replacementDestinationStart, replacementDestinationEnd);
     }

     final bool isOriginalComposingRegionTextChanged = !(originalComposingText == newComposingText);
     final bool isReplaced = isOriginalComposingRegionTextChanged ||
         (isReplacedByLonger || isReplacedByShorter || isReplacedBySame);

     if (isEqual) {
       return TextEditingDeltaNonTextUpdate(
         oldText: oldText,
         selection: newSelection,
         composing: newComposing,
       );
     } else if ((isDeletingByReplacingWithEmpty || isDeletingInsideComposingRegion) &&
         !isOriginalComposingRegionTextChanged) {  // Deletion.
       int actualStart = replacementDestinationStart;

       if (!isDeletionGreaterThanOne) {
         actualStart = replacementDestinationEnd - 1;
       }

       return TextEditingDeltaDeletion(
         oldText: oldText,
         deletedRange: TextRange(
           start: actualStart,
           end: replacementDestinationEnd,
         ),
         selection: newSelection,
         composing: newComposing,
       );
     } else if ((replacementDestinationStart == replacementDestinationEnd || isInsertingInsideComposingRegion) &&
         !isOriginalComposingRegionTextChanged) {  // Insertion.
       return TextEditingDeltaInsertion(
         oldText: oldText,
         textInserted: replacementSource.substring(replacementDestinationEnd - replacementDestinationStart, (replacementDestinationEnd - replacementDestinationStart) + (replacementSource.length - (replacementDestinationEnd - replacementDestinationStart))),
         insertionOffset: replacementDestinationEnd,
         selection: newSelection,
         composing: newComposing,
       );
     } else if (isReplaced) {  // Replacement.
       return TextEditingDeltaReplacement(
         oldText: oldText,
         replacementText: replacementSource,
         replacedRange: TextRange(
           start: replacementDestinationStart,
           end: replacementDestinationEnd,
         ),
         selection: newSelection,
         composing: newComposing,
       );
     }
     assert(false);
     return TextEditingDeltaNonTextUpdate(
       oldText: oldText,
       selection: newSelection,
       composing: newComposing,
     );
   }

   /// The old text state before the delta has occurred.
   final String oldText;

   /// The range of text that is currently selected after the delta has been
   /// applied.
   final TextSelection selection;

   /// The range of text that is still being composed after the delta has been
   /// applied.
   final TextRange composing;

   /// This method will take the given [TextEditingValue] and return a new
   /// [TextEditingValue] with that instance of [TextEditingDelta] applied to it.
   TextEditingValue apply(TextEditingValue value);
 }

 /// A structure representing an insertion of a single/or contigous sequence of
 /// characters at some offset of an editing state.
 @immutable
 class TextEditingDeltaInsertion extends TextEditingDelta {
   /// Creates an insertion delta for a given change to the editing state.
   ///
   /// {@macro flutter.services.TextEditingDelta}
   ///
   /// {@template flutter.services.TextEditingDelta.optIn}
   /// See also:
   ///
   ///  * [TextInputConfiguration], to opt-in your [DeltaTextInputClient] to receive
   ///    [TextEditingDelta]'s you must set [TextInputConfiguration.enableDeltaModel]
   ///    to true.
   /// {@endtemplate}
   const TextEditingDeltaInsertion({
     required super.oldText,
     required this.textInserted,
     required this.insertionOffset,
     required super.selection,
     required super.composing,
   });

   /// The text that is being inserted into [oldText].
   final String textInserted;

   /// The offset in the [oldText] where the insertion begins.
   final int insertionOffset;

   @override
   TextEditingValue apply(TextEditingValue value) {
     // To stay inline with the plain text model we should follow a last write wins
     // policy and apply the delta to the oldText. This is due to the asyncronous
     // nature of the connection between the framework and platform text input plugins.
     String newText = oldText;
     newText = _replace(newText, textInserted, insertionOffset, insertionOffset);
     return value.copyWith(text: newText, selection: selection, composing: composing);
   }
 }

 /// A structure representing the deletion of a single/or contiguous sequence of
 /// characters in an editing state.
 @immutable
 class TextEditingDeltaDeletion extends TextEditingDelta {
   /// Creates a deletion delta for a given change to the editing state.
   ///
   /// {@macro flutter.services.TextEditingDelta}
   ///
   /// {@macro flutter.services.TextEditingDelta.optIn}
   const TextEditingDeltaDeletion({
     required super.oldText,
     required this.deletedRange,
     required super.selection,
     required super.composing,
   });

   /// The range in [oldText] that is being deleted.
   final TextRange deletedRange;

   /// The text from [oldText] that is being deleted.
   String get textDeleted => oldText.substring(deletedRange.start, deletedRange.end);

   @override
   TextEditingValue apply(TextEditingValue value) {
     // To stay inline with the plain text model we should follow a last write wins
     // policy and apply the delta to the oldText. This is due to the asyncronous
     // nature of the connection between the framework and platform text input plugins.
     String newText = oldText;
     newText = _replace(newText, '', deletedRange.start, deletedRange.end);
     return value.copyWith(text: newText, selection: selection, composing: composing);
   }
 }

 /// A structure representing a replacement of a range of characters with a
 /// new sequence of text.
 @immutable
 class TextEditingDeltaReplacement extends TextEditingDelta {
   /// Creates a replacement delta for a given change to the editing state.
   ///
   /// The range that is being replaced can either grow or shrink based on the
   /// given replacement text.
   ///
   /// A replacement can occur in cases such as auto-correct, suggestions, and
   /// when a selection is replaced by a single character.
   ///
   /// {@macro flutter.services.TextEditingDelta}
   ///
   /// {@macro flutter.services.TextEditingDelta.optIn}
   const TextEditingDeltaReplacement({
     required super.oldText,
     required this.replacementText,
     required this.replacedRange,
     required super.selection,
     required super.composing,
   });

   /// The new text that is replacing [replacedRange] in [oldText].
   final String replacementText;

   /// The range in [oldText] that is being replaced.
   final TextRange replacedRange;

   /// The original text that is being replaced in [oldText].
   String get textReplaced => oldText.substring(replacedRange.start, replacedRange.end);

   @override
   TextEditingValue apply(TextEditingValue value) {
     // To stay inline with the plain text model we should follow a last write wins
     // policy and apply the delta to the oldText. This is due to the asyncronous
     // nature of the connection between the framework and platform text input plugins.
     String newText = oldText;
     newText = _replace(newText, replacementText, replacedRange.start, replacedRange.end);
     return value.copyWith(text: newText, selection: selection, composing: composing);
   }
 }

 /// A structure representing changes to the selection and/or composing regions
 /// of an editing state and no changes to the text value.
 @immutable
 class TextEditingDeltaNonTextUpdate extends TextEditingDelta {
   /// Creates a delta representing no updates to the text value of the current
   /// editing state. This delta includes updates to the selection and/or composing
   /// regions.
   ///
   /// A situation where this delta would be created is when dragging the selection
   /// handles. There are no changes to the text, but there are updates to the selection
   /// and potentially the composing region as well.
   ///
   /// {@macro flutter.services.TextEditingDelta}
   ///
   /// {@macro flutter.services.TextEditingDelta.optIn}
   const TextEditingDeltaNonTextUpdate({
     required super.oldText,
     required super.selection,
     required super.composing,
   });

   @override
   TextEditingValue apply(TextEditingValue value) {
     // To stay inline with the plain text model we should follow a last write wins
     // policy and apply the delta to the oldText. This is due to the asyncronous
     // nature of the connection between the framework and platform text input plugins.
     return TextEditingValue(text: oldText, selection: selection, composing: composing);
   }
 }
	// Copyright 2014 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'dart:ui' show TextRange;

	import 'package:flutter/foundation.dart';

	import 'text_editing.dart';
	import 'text_input.dart' show TextEditingValue;

	export 'dart:ui' show TextRange;

	export 'text_editing.dart' show TextSelection;
	export 'text_input.dart' show TextEditingValue;

	TextAffinity? _toTextAffinity(String? affinity) {
	switch (affinity) {
	case 'TextAffinity.downstream':
	return TextAffinity.downstream;
	case 'TextAffinity.upstream':
	return TextAffinity.upstream;
	}
	return null;
	}

	/// Replaces a range of text in the original string with the text given in the
	/// replacement string.
	String _replace(String originalText, String replacementText, int start, int end) {
	final String textStart = originalText.substring(0, start);
	final String textEnd = originalText.substring(end, originalText.length);
	final String newText = textStart + replacementText + textEnd;
	return newText;
	}

	/// A structure representing a granular change that has occurred to the editing
	/// state as a result of text editing.
	///
	/// See also:
	///
	/// * [TextEditingDeltaInsertion], a delta representing an insertion.
	/// * [TextEditingDeltaDeletion], a delta representing a deletion.
	/// * [TextEditingDeltaReplacement], a delta representing a replacement.
	/// * [TextEditingDeltaNonTextUpdate], a delta representing an update to the
	/// selection and/or composing region.
	/// * [TextInputConfiguration], to opt-in your [DeltaTextInputClient] to receive
	/// [TextEditingDelta]'s you must set [TextInputConfiguration.enableDeltaModel]
	/// to true.
	abstract class TextEditingDelta {
	/// Creates a delta for a given change to the editing state.
	///
	/// {@template flutter.services.TextEditingDelta}
	/// The [oldText], [selection], and [composing] arguments must not be null.
	/// {@endtemplate}
	const TextEditingDelta({
	required this.oldText,
	required this.selection,
	required this.composing,
	}) : assert(oldText != null),
	assert(selection != null),
	assert(composing != null);

	/// Creates an instance of this class from a JSON object by inferring the
	/// type of delta based on values sent from the engine.
	factory TextEditingDelta.fromJSON(Map<String, dynamic> encoded) {
	// An insertion delta is one where replacement destination is collapsed.
	//
	// A deletion delta is one where the replacement source is empty.
	//
	// An insertion/deletion can still occur when the replacement destination is not
	// collapsed, or the replacement source is not empty.
	//
	// On native platforms when composing text, the entire composing region is
	// replaced on input, rather than reporting character by character
	// insertion/deletion. In these cases we can detect if there was an
	// insertion/deletion by checking if the text inside the original composing
	// region was modified by the replacement. If the text is the same then we have
	// an insertion/deletion. If the text is different then we can say we have
	// a replacement.
	//
	// For example say we are currently composing the word: 'world'.
	// Our current state is 'worl\|' with the cursor at the end of 'l'. If we
	// input the character 'd', the platform will tell us 'worl' was replaced
	// with 'world' at range (0,4). Here we can check if the text found in the
	// composing region (0,4) has been modified. We see that it hasn't because
	// 'worl' == 'worl', so this means that the text in
	// 'world'{replacementDestinationEnd, replacementDestinationStart + replacementSourceEnd}
	// can be considered an insertion. In this case we inserted 'd'.
	//
	// Similarly for a a deletion, say we are currently composing the word: 'worl'.
	// Our current state is 'world\|' with the cursor at the end of 'd'. If we
	// press backspace to delete the character 'd', the platform will tell us 'world'
	// was replaced with 'worl' at range (0,5). Here we can check if the text found
	// in the new composing region, is the same as the replacement text. We can do this
	// by using oldText{replacementDestinationStart, replacementDestinationStart + replacementSourceEnd}
	// which in this case is 'worl'. We then compare 'worl' with 'worl' and
	// verify that they are the same. This means that the text in
	// 'world'{replacementDestinationEnd, replacementDestinationStart + replacementSourceEnd} was deleted.
	// In this case the character 'd' was deleted.
	//
	// A replacement delta occurs when the original composing region has been
	// modified.
	//
	// A non text update delta occurs when the selection and/or composing region
	// has been changed by the platform, and there have been no changes to the
	// text value.
	final String oldText = encoded['oldText'] as String;
	final int replacementDestinationStart = encoded['deltaStart'] as int;
	final int replacementDestinationEnd = encoded['deltaEnd'] as int;
	final String replacementSource = encoded['deltaText'] as String;
	const int replacementSourceStart = 0;
	final int replacementSourceEnd = replacementSource.length;

	// This delta is explicitly a non text update.
	final bool isNonTextUpdate = replacementDestinationStart == -1 && replacementDestinationStart == replacementDestinationEnd;
	final TextRange newComposing = TextRange(
	start: encoded['composingBase'] as int? ?? -1,
	end: encoded['composingExtent'] as int? ?? -1,
	);
	final TextSelection newSelection = TextSelection(
	baseOffset: encoded['selectionBase'] as int? ?? -1,
	extentOffset: encoded['selectionExtent'] as int? ?? -1,
	affinity: _toTextAffinity(encoded['selectionAffinity'] as String?) ??
	TextAffinity.downstream,
	isDirectional: encoded['selectionIsDirectional'] as bool? ?? false,
	);

	if (isNonTextUpdate) {
	return TextEditingDeltaNonTextUpdate(
	oldText: oldText,
	selection: newSelection,
	composing: newComposing,
	);
	}

	final String newText = _replace(oldText, replacementSource, replacementDestinationStart, replacementDestinationEnd);
	final bool isEqual = oldText == newText;

	final bool isDeletionGreaterThanOne = (replacementDestinationEnd - replacementDestinationStart) - (replacementSourceEnd - replacementSourceStart) > 1;
	final bool isDeletingByReplacingWithEmpty = replacementSource.isEmpty && replacementSourceStart == 0 && replacementSourceStart == replacementSourceEnd;

	final bool isReplacedByShorter = isDeletionGreaterThanOne && (replacementSourceEnd - replacementSourceStart < replacementDestinationEnd - replacementDestinationStart);
	final bool isReplacedByLonger = replacementSourceEnd - replacementSourceStart > replacementDestinationEnd - replacementDestinationStart;
	final bool isReplacedBySame = replacementSourceEnd - replacementSourceStart == replacementDestinationEnd - replacementDestinationStart;

	final bool isInsertingInsideComposingRegion = replacementDestinationStart + replacementSourceEnd > replacementDestinationEnd;
	final bool isDeletingInsideComposingRegion =
	!isReplacedByShorter && !isDeletingByReplacingWithEmpty && replacementDestinationStart + replacementSourceEnd < replacementDestinationEnd;

	String newComposingText;
	String originalComposingText;

	if (isDeletingByReplacingWithEmpty \|\| isDeletingInsideComposingRegion \|\| isReplacedByShorter) {
	newComposingText = replacementSource.substring(replacementSourceStart, replacementSourceEnd);
	originalComposingText = oldText.substring(replacementDestinationStart, replacementDestinationStart + replacementSourceEnd);
	} else {
	newComposingText = replacementSource.substring(replacementSourceStart, replacementSourceStart + (replacementDestinationEnd - replacementDestinationStart));
	originalComposingText = oldText.substring(replacementDestinationStart, replacementDestinationEnd);
	}

	final bool isOriginalComposingRegionTextChanged = !(originalComposingText == newComposingText);
	final bool isReplaced = isOriginalComposingRegionTextChanged \|\|
	(isReplacedByLonger \|\| isReplacedByShorter \|\| isReplacedBySame);

	if (isEqual) {
	return TextEditingDeltaNonTextUpdate(
	oldText: oldText,
	selection: newSelection,
	composing: newComposing,
	);
	} else if ((isDeletingByReplacingWithEmpty \|\| isDeletingInsideComposingRegion) &&
	!isOriginalComposingRegionTextChanged) { // Deletion.
	int actualStart = replacementDestinationStart;

	if (!isDeletionGreaterThanOne) {
	actualStart = replacementDestinationEnd - 1;
	}

	return TextEditingDeltaDeletion(
	oldText: oldText,
	deletedRange: TextRange(
	start: actualStart,
	end: replacementDestinationEnd,
	),
	selection: newSelection,
	composing: newComposing,
	);
	} else if ((replacementDestinationStart == replacementDestinationEnd \|\| isInsertingInsideComposingRegion) &&
	!isOriginalComposingRegionTextChanged) { // Insertion.
	return TextEditingDeltaInsertion(
	oldText: oldText,
	textInserted: replacementSource.substring(replacementDestinationEnd - replacementDestinationStart, (replacementDestinationEnd - replacementDestinationStart) + (replacementSource.length - (replacementDestinationEnd - replacementDestinationStart))),
	insertionOffset: replacementDestinationEnd,
	selection: newSelection,
	composing: newComposing,
	);
	} else if (isReplaced) { // Replacement.
	return TextEditingDeltaReplacement(
	oldText: oldText,
	replacementText: replacementSource,
	replacedRange: TextRange(
	start: replacementDestinationStart,
	end: replacementDestinationEnd,
	),
	selection: newSelection,
	composing: newComposing,
	);
	}
	assert(false);
	return TextEditingDeltaNonTextUpdate(
	oldText: oldText,
	selection: newSelection,
	composing: newComposing,
	);
	}

	/// The old text state before the delta has occurred.
	final String oldText;

	/// The range of text that is currently selected after the delta has been
	/// applied.
	final TextSelection selection;

	/// The range of text that is still being composed after the delta has been
	/// applied.
	final TextRange composing;

	/// This method will take the given [TextEditingValue] and return a new
	/// [TextEditingValue] with that instance of [TextEditingDelta] applied to it.
	TextEditingValue apply(TextEditingValue value);
	}

	/// A structure representing an insertion of a single/or contigous sequence of
	/// characters at some offset of an editing state.
	@immutable
	class TextEditingDeltaInsertion extends TextEditingDelta {
	/// Creates an insertion delta for a given change to the editing state.
	///
	/// {@macro flutter.services.TextEditingDelta}
	///
	/// {@template flutter.services.TextEditingDelta.optIn}
	/// See also:
	///
	/// * [TextInputConfiguration], to opt-in your [DeltaTextInputClient] to receive
	/// [TextEditingDelta]'s you must set [TextInputConfiguration.enableDeltaModel]
	/// to true.
	/// {@endtemplate}
	const TextEditingDeltaInsertion({
	required super.oldText,
	required this.textInserted,
	required this.insertionOffset,
	required super.selection,
	required super.composing,
	});

	/// The text that is being inserted into [oldText].
	final String textInserted;

	/// The offset in the [oldText] where the insertion begins.
	final int insertionOffset;

	@override
	TextEditingValue apply(TextEditingValue value) {
	// To stay inline with the plain text model we should follow a last write wins
	// policy and apply the delta to the oldText. This is due to the asyncronous
	// nature of the connection between the framework and platform text input plugins.
	String newText = oldText;
	newText = _replace(newText, textInserted, insertionOffset, insertionOffset);
	return value.copyWith(text: newText, selection: selection, composing: composing);
	}
	}

	/// A structure representing the deletion of a single/or contiguous sequence of
	/// characters in an editing state.
	@immutable
	class TextEditingDeltaDeletion extends TextEditingDelta {
	/// Creates a deletion delta for a given change to the editing state.
	///
	/// {@macro flutter.services.TextEditingDelta}
	///
	/// {@macro flutter.services.TextEditingDelta.optIn}
	const TextEditingDeltaDeletion({
	required super.oldText,
	required this.deletedRange,
	required super.selection,
	required super.composing,
	});

	/// The range in [oldText] that is being deleted.
	final TextRange deletedRange;

	/// The text from [oldText] that is being deleted.
	String get textDeleted => oldText.substring(deletedRange.start, deletedRange.end);

	@override
	TextEditingValue apply(TextEditingValue value) {
	// To stay inline with the plain text model we should follow a last write wins
	// policy and apply the delta to the oldText. This is due to the asyncronous
	// nature of the connection between the framework and platform text input plugins.
	String newText = oldText;
	newText = _replace(newText, '', deletedRange.start, deletedRange.end);
	return value.copyWith(text: newText, selection: selection, composing: composing);
	}
	}

	/// A structure representing a replacement of a range of characters with a
	/// new sequence of text.
	@immutable
	class TextEditingDeltaReplacement extends TextEditingDelta {
	/// Creates a replacement delta for a given change to the editing state.
	///
	/// The range that is being replaced can either grow or shrink based on the
	/// given replacement text.
	///
	/// A replacement can occur in cases such as auto-correct, suggestions, and
	/// when a selection is replaced by a single character.
	///
	/// {@macro flutter.services.TextEditingDelta}
	///
	/// {@macro flutter.services.TextEditingDelta.optIn}
	const TextEditingDeltaReplacement({
	required super.oldText,
	required this.replacementText,
	required this.replacedRange,
	required super.selection,
	required super.composing,
	});

	/// The new text that is replacing [replacedRange] in [oldText].
	final String replacementText;

	/// The range in [oldText] that is being replaced.
	final TextRange replacedRange;

	/// The original text that is being replaced in [oldText].
	String get textReplaced => oldText.substring(replacedRange.start, replacedRange.end);

	@override
	TextEditingValue apply(TextEditingValue value) {
	// To stay inline with the plain text model we should follow a last write wins
	// policy and apply the delta to the oldText. This is due to the asyncronous
	// nature of the connection between the framework and platform text input plugins.
	String newText = oldText;
	newText = _replace(newText, replacementText, replacedRange.start, replacedRange.end);
	return value.copyWith(text: newText, selection: selection, composing: composing);
	}
	}

	/// A structure representing changes to the selection and/or composing regions
	/// of an editing state and no changes to the text value.
	@immutable
	class TextEditingDeltaNonTextUpdate extends TextEditingDelta {
	/// Creates a delta representing no updates to the text value of the current
	/// editing state. This delta includes updates to the selection and/or composing
	/// regions.
	///
	/// A situation where this delta would be created is when dragging the selection
	/// handles. There are no changes to the text, but there are updates to the selection
	/// and potentially the composing region as well.
	///
	/// {@macro flutter.services.TextEditingDelta}
	///
	/// {@macro flutter.services.TextEditingDelta.optIn}
	const TextEditingDeltaNonTextUpdate({
	required super.oldText,
	required super.selection,
	required super.composing,
	});

	@override
	TextEditingValue apply(TextEditingValue value) {
	// To stay inline with the plain text model we should follow a last write wins
	// policy and apply the delta to the oldText. This is due to the asyncronous
	// nature of the connection between the framework and platform text input plugins.
	return TextEditingValue(text: oldText, selection: selection, composing: composing);
	}
	}