Avalonia/src/Avalonia.Controls/SelectableTextBlock.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using Avalonia.Controls.Documents;
using Avalonia.Controls.Utils;
using Avalonia.Input;
using Avalonia.Input.Platform;
using Avalonia.Interactivity;
using Avalonia.Media;
using Avalonia.Media.TextFormatting;
using Avalonia.Platform;
using Avalonia.Utilities;

namespace Avalonia.Controls
{
    /// <summary>
    /// A control that displays a block of formatted text.
    /// </summary>
    public class SelectableTextBlock : TextBlock, IInlineHost
    {
        public static readonly StyledProperty<int> SelectionStartProperty =
            TextBox.SelectionStartProperty.AddOwner<SelectableTextBlock>();

        public static readonly StyledProperty<int> SelectionEndProperty =
            TextBox.SelectionEndProperty.AddOwner<SelectableTextBlock>();

        public static readonly DirectProperty<SelectableTextBlock, string> SelectedTextProperty =
            AvaloniaProperty.RegisterDirect<SelectableTextBlock, string>(
                nameof(SelectedText),
                o => o.SelectedText);

        public static readonly StyledProperty<IBrush?> SelectionBrushProperty =
            TextBox.SelectionBrushProperty.AddOwner<SelectableTextBlock>();

        public static readonly StyledProperty<IBrush?> SelectionForegroundBrushProperty =
            TextBox.SelectionForegroundBrushProperty.AddOwner<SelectableTextBlock>();

        public static readonly DirectProperty<SelectableTextBlock, bool> CanCopyProperty =
            TextBox.CanCopyProperty.AddOwner<SelectableTextBlock>(o => o.CanCopy);

        public static readonly RoutedEvent<RoutedEventArgs> CopyingToClipboardEvent =
            RoutedEvent.Register<SelectableTextBlock, RoutedEventArgs>(
                nameof(CopyingToClipboard), RoutingStrategies.Bubble);

        private bool _canCopy;
        private int _wordSelectionStart = -1;

        static SelectableTextBlock()
        {
            FocusableProperty.OverrideDefaultValue(typeof(SelectableTextBlock), true);
            AffectsRender<SelectableTextBlock>(SelectionStartProperty, SelectionEndProperty, SelectionBrushProperty);
        }

        public event EventHandler<RoutedEventArgs>? CopyingToClipboard
        {
            add => AddHandler(CopyingToClipboardEvent, value);
            remove => RemoveHandler(CopyingToClipboardEvent, value);
        }

        /// <summary>
        /// Gets or sets the brush that highlights selected text.
        /// </summary>
        public IBrush? SelectionBrush
        {
            get => GetValue(SelectionBrushProperty);
            set => SetValue(SelectionBrushProperty, value);
        }

        /// <summary>
        /// Gets or sets a brush that is used for the foreground of selected text
        /// </summary>
        public IBrush? SelectionForegroundBrush
        {
            get => GetValue(SelectionForegroundBrushProperty);
            set => SetValue(SelectionForegroundBrushProperty, value);
        }

        /// <summary>
        /// Gets or sets a character index for the beginning of the current selection.
        /// </summary>
        public int SelectionStart
        {
            get => GetValue(SelectionStartProperty);
            set => SetValue(SelectionStartProperty, value);
        }

        /// <summary>
        /// Gets or sets a character index for the end of the current selection.
        /// </summary>
        public int SelectionEnd
        {
            get => GetValue(SelectionEndProperty);
            set => SetValue(SelectionEndProperty, value);
        }

        /// <summary>
        /// Gets the content of the current selection.
        /// </summary>
        public string SelectedText
        {
            get => GetSelection();
        }

        /// <summary>
        /// Property for determining if the Copy command can be executed.
        /// </summary>
        public bool CanCopy
        {
            get => _canCopy;
            private set => SetAndRaise(CanCopyProperty, ref _canCopy, value);
        }

        /// <summary>
        /// Copies the current selection to the Clipboard.
        /// </summary>
        public async void Copy()
        {
            if (!_canCopy)
            {
                return;
            }

            var text = GetSelection();

            if (string.IsNullOrEmpty(text))
            {
                return;
            }

            var eventArgs = new RoutedEventArgs(CopyingToClipboardEvent);

            RaiseEvent(eventArgs);

            if (!eventArgs.Handled)
            {
                var clipboard = TopLevel.GetTopLevel(this)?.Clipboard;

                if (clipboard != null)
                    await clipboard.SetTextAsync(text);
            }
        }

        /// <summary>
        /// Select all text in the TextBox
        /// </summary>
        public void SelectAll()
        {
            var text = HasComplexContent ? Inlines?.Text : Text;

            SetCurrentValue(SelectionStartProperty, 0);
            SetCurrentValue(SelectionEndProperty, text?.Length ?? 0);
        }

        /// <summary>
        /// Clears the current selection
        /// </summary>
        public void ClearSelection()
        {
            SetCurrentValue(SelectionEndProperty, SelectionStart);
        }

        protected override void OnGotFocus(FocusChangedEventArgs e)
        {
            base.OnGotFocus(e);

            UpdateCommandStates();
        }

        protected override void OnLostFocus(FocusChangedEventArgs e)
        {
            base.OnLostFocus(e);

            if ((ContextFlyout == null || !ContextFlyout.IsOpen) &&
               (ContextMenu == null || !ContextMenu.IsOpen))
            {
                ClearSelection();
            }

            UpdateCommandStates();
        }

        protected override TextLayout CreateTextLayout(string? text)
        {
            var typeface = new Typeface(FontFamily, FontStyle, FontWeight, FontStretch);
            var effectiveFontSize = TextScaling.GetScaledFontSize(this, FontSize);
            var fontScaleFactor = effectiveFontSize / FontSize;

            var defaultProperties = new GenericTextRunProperties(
                typeface,
                effectiveFontSize,
                TextDecorations,
                Foreground,
                fontFeatures: FontFeatures);

            var paragraphProperties = new GenericTextParagraphProperties(FlowDirection, TextAlignment, true, false,
                defaultProperties, TextWrapping, LineHeight * fontScaleFactor, 0, LetterSpacing * fontScaleFactor)
            {
                LineSpacing = LineSpacing * fontScaleFactor,
            };

            List<ValueSpan<TextRunProperties>>? textStyleOverrides = null;
            var selectionStart = SelectionStart;
            var selectionEnd = SelectionEnd;
            var start = Math.Min(selectionStart, selectionEnd);
            var length = Math.Max(selectionStart, selectionEnd) - start;

            if (length > 0 && SelectionForegroundBrush != null)
            {
                if (_textRuns != null)
                {
                    // Apply selection foreground color without changing the original text formatting.
                    // The built-in SelectableTextBlock selection logic recreates TextRunProperties,
                    // which overwrites run-specific Typeface/FontFeatures/FontSize and breaks bold/italic.
                    // Here we reuse each run's existing properties and only override the foreground brush.

                    var accumulatedLength = 0;
                    foreach (var textRun in _textRuns)
                    {
                        var runLength = textRun.Text.Length;
                        if (accumulatedLength + runLength <= start ||
                            accumulatedLength >= start + length)
                        {
                            accumulatedLength += runLength;
                            continue;
                        }

                        var overlapStart = Math.Max(start, accumulatedLength);
                        var overlapEnd = Math.Min(start + length, accumulatedLength + runLength);
                        var overlapLength = overlapEnd - overlapStart;

                        textStyleOverrides ??= [];

                        textStyleOverrides.Add(
                            new ValueSpan<TextRunProperties>(
                                overlapStart,
                                overlapLength,
                                new GenericTextRunProperties(
                                    textRun.Properties?.Typeface ?? typeface,
                                    effectiveFontSize,
                                    foregroundBrush: SelectionForegroundBrush,
                                    fontFeatures: textRun.Properties?.FontFeatures ?? FontFeatures)));

                        accumulatedLength += runLength;
                    }
                }
                else
                {
                    textStyleOverrides =
                    [
                        new ValueSpan<TextRunProperties>(start, length,
                            new GenericTextRunProperties(
                                typeface,
                                effectiveFontSize,
                                foregroundBrush: SelectionForegroundBrush,
                                fontFeatures: FontFeatures))
                    ];
                }
            }

            ITextSource textSource;

            if (_textRuns != null)
            {
                textSource = new InlinesTextSource(_textRuns, textStyleOverrides);
            }
            else
            {
                textSource = new FormattedTextSource(text ?? "", defaultProperties, textStyleOverrides);
            }

            var maxSize = GetMaxSizeFromConstraint();

            return new TextLayout(
                textSource,
                paragraphProperties,
                TextTrimming,
                maxSize.Width,
                maxSize.Height,
                MaxLines);
        }

        protected override void RenderTextLayout(DrawingContext context, Point origin)
        {
            var selectionStart = SelectionStart;
            var selectionEnd = SelectionEnd;
            var selectionBrush = SelectionBrush;

            if (selectionStart != selectionEnd && selectionBrush != null)
            {
                var start = Math.Min(selectionStart, selectionEnd);
                var length = Math.Max(selectionStart, selectionEnd) - start;

                var rects = TextLayout.HitTestTextRange(start, length);

                using (context.PushTransform(Matrix.CreateTranslation(origin)))
                {
                    foreach (var rect in rects)
                    {
                        context.FillRectangle(selectionBrush, PixelRect.FromRect(rect, 1).ToRect(1));
                    }
                }
            }

            base.RenderTextLayout(context, origin);
        }

        protected override void OnKeyDown(KeyEventArgs e)
        {
            base.OnKeyDown(e);

            var handled = false;
            var modifiers = e.KeyModifiers;
            var keymap = Application.Current!.PlatformSettings!.HotkeyConfiguration;

            bool Match(List<KeyGesture> gestures) => gestures.Any(g => g.Matches(e));

            if (Match(keymap.Copy))
            {
                Copy();
                handled = true;
            }
            else if (Match(keymap.SelectAll))
            {
                SelectAll();
                handled = true;
            }

            e.Handled = handled;
        }

        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
        {
            base.OnPropertyChanged(change);

            if (change.Property == SelectionStartProperty || 
                change.Property == SelectionEndProperty)
            {
                RaisePropertyChanged(SelectedTextProperty, "", "");
                UpdateCommandStates();
                InvalidateTextLayout();
            }

            if(change.Property == SelectionForegroundBrushProperty)
            {
                InvalidateTextLayout();
            }
        }

        protected override void OnPointerPressed(PointerPressedEventArgs e)
        {
            base.OnPointerPressed(e);

            var text = HasComplexContent ? Inlines?.Text : Text;
            var clickInfo = e.GetCurrentPoint(this);

            if (text != null && clickInfo.Properties.IsLeftButtonPressed)
            {
                var padding = Padding;

                var point = e.GetPosition(this) - new Point(padding.Left, padding.Top);

                var clickToSelect = e.KeyModifiers.HasFlag(KeyModifiers.Shift);

                var oldIndex = SelectionStart;

                var hit = TextLayout.HitTestPoint(point);
                var index = hit.TextPosition;

                switch (e.ClickCount)
                {
                    case 1:
                        if (clickToSelect)
                        {
                            if (_wordSelectionStart >= 0)
                            {
                                var previousWord = StringUtils.PreviousWord(text, index);

                                if (index > _wordSelectionStart)
                                {
                                    SetCurrentValue(SelectionEndProperty, StringUtils.NextWord(text, index));
                                }

                                if (index < _wordSelectionStart || previousWord == _wordSelectionStart)
                                {
                                    SetCurrentValue(SelectionStartProperty, previousWord);
                                }
                            }
                            else
                            {
                                SetCurrentValue(SelectionStartProperty, Math.Min(oldIndex, index));
                                SetCurrentValue(SelectionEndProperty, Math.Max(oldIndex, index));
                            }
                        }
                        else
                        {
                            SetCurrentValue(SelectionStartProperty, index);
                            SetCurrentValue(SelectionEndProperty, index);
                            _wordSelectionStart = -1;
                        }

                        break;
                    case 2:
                        if (!StringUtils.IsStartOfWord(text, index))
                        {
                            SetCurrentValue(SelectionStartProperty, StringUtils.PreviousWord(text, index));
                        }

                        _wordSelectionStart = SelectionStart;

                        if (!StringUtils.IsEndOfWord(text, index))
                        {
                            SetCurrentValue(SelectionEndProperty, StringUtils.NextWord(text, index));
                        }

                        break;
                    case 3:
                        _wordSelectionStart = -1;

                        SelectAll();
                        break;
                }
            }

            e.Pointer.Capture(this);
            e.Handled = true;
        }

        protected override void OnPointerMoved(PointerEventArgs e)
        {
            base.OnPointerMoved(e);

            // selection should not change during pointer move if the user right clicks
            if (e.Pointer.Captured == this && e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
            {
                var text = HasComplexContent ? Inlines?.Text : Text;
                var padding = Padding;

                var point = e.GetPosition(this) - new Point(padding.Left, padding.Top);

                point = new Point(
                    MathUtilities.Clamp(point.X, 0, Math.Max(TextLayout.WidthIncludingTrailingWhitespace, 0)),
                    MathUtilities.Clamp(point.Y, 0, Math.Max(TextLayout.Height, 0)));

                var hit = TextLayout.HitTestPoint(point);
                var textPosition = hit.TextPosition;

                if (text != null && _wordSelectionStart >= 0)
                {
                    var distance = textPosition - _wordSelectionStart;

                    if (distance <= 0)
                    {
                        SetCurrentValue(SelectionStartProperty, StringUtils.PreviousWord(text, textPosition));
                    }

                    if (distance >= 0)
                    {
                        if (SelectionStart != _wordSelectionStart)
                        {
                            SetCurrentValue(SelectionStartProperty, _wordSelectionStart);
                        }

                        SetCurrentValue(SelectionEndProperty, StringUtils.NextWord(text, textPosition));
                    }
                }
                else
                {
                    SetCurrentValue(SelectionEndProperty, textPosition);
                }

            }
        }

        protected override void OnPointerReleased(PointerReleasedEventArgs e)
        {
            base.OnPointerReleased(e);

            if (e.Pointer.Captured != this)
            {
                return;
            }

            if (e.InitialPressMouseButton == MouseButton.Right)
            {
                var padding = Padding;

                var point = e.GetPosition(this) - new Point(padding.Left, padding.Top);

                var hit = TextLayout.HitTestPoint(point);

                var caretIndex = hit.TextPosition;

                // see if mouse clicked inside current selection
                // if it did not, we change the selection to where the user clicked
                var firstSelection = Math.Min(SelectionStart, SelectionEnd);
                var lastSelection = Math.Max(SelectionStart, SelectionEnd);
                var didClickInSelection = SelectionStart != SelectionEnd &&
                                          caretIndex >= firstSelection && caretIndex <= lastSelection;
                if (!didClickInSelection)
                {
                    SetCurrentValue(SelectionStartProperty, caretIndex);
                    SetCurrentValue(SelectionEndProperty, caretIndex);
                }
            }

            e.Pointer.Capture(null);
        }

        private void UpdateCommandStates()
        {
            var text = GetSelection();

            CanCopy = !string.IsNullOrEmpty(text);
        }

        private string GetSelection()
        {
            var text = HasComplexContent ? Inlines?.Text : Text;

            var textLength = text?.Length ?? 0;

            if (textLength == 0)
            {
                return "";
            }

            var selectionStart = SelectionStart;
            var selectionEnd = SelectionEnd;
            var start = Math.Min(selectionStart, selectionEnd);
            var end = Math.Max(selectionStart, selectionEnd);

            if (start == end || textLength < end)
            {
                return "";
            }

            var length = Math.Max(0, end - start);

            var selectedText = text!.Substring(start, length);

            return selectedText;
        }
    }
}