Implemented change-block navigation

Modified behavior of the Prev/Next Change buttons in DiffView toolbar.
Well-defined change-blocks are pre-calculated and can be navigated between.
Current change-block is highlighted in the Diff panel(s).

src/Commands/Diff.cs

@@ -51,6 +51,9 @@ namespace SourceGit.Commands
                     _result.TextDiff.MaxLineNumber = Math.Max(_newLine, _oldLine);
             }
 
+            if (_result.TextDiff != null)
+                _result.TextDiff.ProcessChangeBlocks();
+
             return _result;
         }
 

src/Models/DiffResult.cs

@@ -2,6 +2,8 @@
 using System.Text;
 using System.Text.RegularExpressions;
 
+using CommunityToolkit.Mvvm.ComponentModel;
+
 using Avalonia;
 using Avalonia.Media.Imaging;
 
@@ -59,16 +61,70 @@ namespace SourceGit.Models
         }
     }
 
-    public partial class TextDiff
+    public class TextDiffChangeBlock
+    {
+        public TextDiffChangeBlock(int startLine, int endLine)
+        {
+            StartLine = startLine;
+            EndLine = endLine;
+        }
+
+        public int StartLine { get; set; } = 0;
+        public int EndLine { get; set; } = 0;
+
+        public bool IsInRange(int line)
+        {
+            return line >= StartLine && line <= EndLine;
+        }
+    }
+
+    public partial class TextDiff : ObservableObject
     {
         public string File { get; set; } = string.Empty;
         public List<TextDiffLine> Lines { get; set; } = new List<TextDiffLine>();
         public Vector ScrollOffset { get; set; } = Vector.Zero;
         public int MaxLineNumber = 0;
 
+        public int CurrentChangeBlockIdx
+        {
+            get => _currentChangeBlockIdx;
+            set => SetProperty(ref _currentChangeBlockIdx, value);
+        }
+
         public string Repo { get; set; } = null;
         public DiffOption Option { get; set; } = null;
 
+        public List<TextDiffChangeBlock> ChangeBlocks { get; set; } = [];
+
+        public void ProcessChangeBlocks()
+        {
+            ChangeBlocks.Clear();
+            int lineIdx = 0, blockStartIdx = 0;
+            bool isNewBlock = true;
+            foreach (var line in Lines)
+            {
+                lineIdx++;
+                if (line.Type == Models.TextDiffLineType.Added ||
+                    line.Type == Models.TextDiffLineType.Deleted ||
+                    line.Type == Models.TextDiffLineType.None) // Empty
+                {
+                    if (isNewBlock)
+                    {
+                        isNewBlock = false;
+                        blockStartIdx = lineIdx;
+                    }
+                }
+                else
+                {
+                    if (!isNewBlock)
+                    {
+                        ChangeBlocks.Add(new TextDiffChangeBlock(blockStartIdx, lineIdx - 1));
+                        isNewBlock = true;
+                    }
+                }
+            }
+        }
+
         public TextDiffSelection MakeSelection(int startLine, int endLine, bool isCombined, bool isOldSide)
         {
             var rs = new TextDiffSelection();
@@ -626,6 +682,8 @@ namespace SourceGit.Models
             return true;
         }
 
+        private int _currentChangeBlockIdx = -1; // NOTE: Use -1 as "not set".
+
         [GeneratedRegex(@"^@@ \-(\d+),?\d* \+(\d+),?\d* @@")]
         private static partial Regex REG_INDICATOR();
     }

src/ViewModels/DiffContext.cs

@@ -75,12 +75,22 @@ namespace SourceGit.ViewModels
 
         public void PrevChange()
         {
-            // To be implemented...
+            if (_content is Models.TextDiff textDiff)
+            {
+                if (textDiff.CurrentChangeBlockIdx > 0)
+                    textDiff.CurrentChangeBlockIdx--;
+                else if (textDiff.CurrentChangeBlockIdx == -1 && textDiff.ChangeBlocks.Count > 0)
+                    textDiff.CurrentChangeBlockIdx = 0; // Jump to first change block
+            }
         }
 
         public void NextChange()
         {
-            // To be implemented...
+            if (_content is Models.TextDiff textDiff)
+            {
+                if (textDiff.CurrentChangeBlockIdx < textDiff.ChangeBlocks.Count - 1)
+                    textDiff.CurrentChangeBlockIdx++;
+            }
         }
 
         public void ToggleFullTextDiff()

src/ViewModels/TwoSideTextDiff.cs

@@ -45,10 +45,43 @@ namespace SourceGit.ViewModels
 
             FillEmptyLines();
 
+            ProcessChangeBlocks();
+
             if (previous != null && previous.File == File)
                 _syncScrollOffset = previous._syncScrollOffset;
         }
 
+        public List<Models.TextDiffChangeBlock> ChangeBlocks { get; set; } = [];
+
+        public void ProcessChangeBlocks()
+        {
+            ChangeBlocks.Clear();
+            int lineIdx = 0, blockStartIdx = 0;
+            bool isNewBlock = true;
+            foreach (var line in Old) // NOTE: Same block size in both Old and New lines.
+            {
+                lineIdx++;
+                if (line.Type == Models.TextDiffLineType.Added ||
+                    line.Type == Models.TextDiffLineType.Deleted ||
+                    line.Type == Models.TextDiffLineType.None) // Empty
+                {
+                    if (isNewBlock)
+                    {
+                        isNewBlock = false;
+                        blockStartIdx = lineIdx;
+                    }
+                }
+                else
+                {
+                    if (!isNewBlock)
+                    {
+                        ChangeBlocks.Add(new Models.TextDiffChangeBlock(blockStartIdx, lineIdx - 1));
+                        isNewBlock = true;
+                    }
+                }
+            }
+        }
+
         public void ConvertsToCombinedRange(Models.TextDiff combined, ref int startLine, ref int endLine, bool isOldSide)
         {
             endLine = Math.Min(endLine, combined.Lines.Count - 1);

src/Views/DiffView.axaml

@@ -241,7 +241,8 @@
           <DataTemplate DataType="m:TextDiff">
             <v:TextDiffView 
               UseSideBySideDiff="{Binding Source={x:Static vm:Preference.Instance}, Path=UseSideBySideDiff, Mode=OneWay}"
-              UseFullTextDiff="{Binding Source={x:Static vm:Preference.Instance}, Path=UseFullTextDiff, Mode=OneWay}"/>
+              UseFullTextDiff="{Binding Source={x:Static vm:Preference.Instance}, Path=UseFullTextDiff, Mode=OneWay}"
+              CurrentChangeBlockIdx="{Binding CurrentChangeBlockIdx, Mode=OneWay}"/>
           </DataTemplate>
 
           <!-- Empty or only EOL changes -->

src/Views/TextDiffView.axaml

@@ -30,6 +30,7 @@
                                          UseSyntaxHighlighting="{Binding Source={x:Static vm:Preference.Instance}, Path=UseSyntaxHighlighting}"
                                          WordWrap="{Binding Source={x:Static vm:Preference.Instance}, Path=EnableDiffViewWordWrap}"
                                          ShowHiddenSymbols="{Binding Source={x:Static vm:Preference.Instance}, Path=ShowHiddenSymbolsInDiffView}"
+                                         CurrentChangeBlockIdx="{Binding #ThisControl.CurrentChangeBlockIdx}"
                                          EnableChunkSelection="{Binding #ThisControl.EnableChunkSelection}"
                                          SelectedChunk="{Binding #ThisControl.SelectedChunk, Mode=TwoWay}"/>
             
@@ -61,6 +62,7 @@
                                            UseSyntaxHighlighting="{Binding Source={x:Static vm:Preference.Instance}, Path=UseSyntaxHighlighting}"
                                            WordWrap="False"
                                            ShowHiddenSymbols="{Binding Source={x:Static vm:Preference.Instance}, Path=ShowHiddenSymbolsInDiffView}"
+                                           CurrentChangeBlockIdx="{Binding #ThisControl.CurrentChangeBlockIdx}"
                                            EnableChunkSelection="{Binding #ThisControl.EnableChunkSelection}"
                                            SelectedChunk="{Binding #ThisControl.SelectedChunk, Mode=TwoWay}"/>
 
@@ -82,6 +84,7 @@
                                            UseSyntaxHighlighting="{Binding Source={x:Static vm:Preference.Instance}, Path=UseSyntaxHighlighting}"
                                            WordWrap="False"
                                            ShowHiddenSymbols="{Binding Source={x:Static vm:Preference.Instance}, Path=ShowHiddenSymbolsInDiffView}"
+                                           CurrentChangeBlockIdx="{Binding #ThisControl.CurrentChangeBlockIdx}"
                                            EnableChunkSelection="{Binding #ThisControl.EnableChunkSelection}"
                                            SelectedChunk="{Binding #ThisControl.SelectedChunk, Mode=TwoWay}"/>
             

src/Views/TextDiffView.axaml.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
+using System.Linq;
 using System.Text;
 
 using Avalonia;
@@ -254,6 +255,10 @@ namespace SourceGit.Views
                 if (_presenter.Document == null || !textView.VisualLinesValid)
                     return;
 
+                var changeBlock = _presenter.GetCurrentChangeBlock();
+                Brush changeBlockBG = new SolidColorBrush(Colors.Gray, 0.25);
+                Pen changeBlockFG = new Pen(Brushes.Gray, 1);
+
                 var lines = _presenter.GetLines();
                 var width = textView.Bounds.Width;
                 foreach (var line in textView.VisualLines)
@@ -266,12 +271,14 @@ namespace SourceGit.Views
                         break;
 
                     var info = lines[index - 1];
-                    var bg = GetBrushByLineType(info.Type);
-                    if (bg == null)
-                        continue;
 
                     var startY = line.GetTextLineVisualYPosition(line.TextLines[0], VisualYPosition.LineTop) - textView.VerticalOffset;
                     var endY = line.GetTextLineVisualYPosition(line.TextLines[^1], VisualYPosition.LineBottom) - textView.VerticalOffset;
+
+                    var bg = GetBrushByLineType(info.Type);
+                    if (bg != null)
+                    {
+                        if (bg != null)
                             drawingContext.DrawRectangle(bg, null, new Rect(0, startY, width, endY - startY));
 
                         if (info.Highlights.Count > 0)
@@ -312,6 +319,16 @@ namespace SourceGit.Views
                             }
                         }
                     }
+
+                    if (changeBlock != null && changeBlock.IsInRange(index))
+                    {
+                        drawingContext.DrawRectangle(changeBlockBG, null, new Rect(0, startY, width, endY - startY));
+                        if (index == changeBlock.StartLine)
+                            drawingContext.DrawLine(changeBlockFG, new Point(0, startY), new Point(width, startY));
+                        if (index == changeBlock.EndLine)
+                            drawingContext.DrawLine(changeBlockFG, new Point(0, endY), new Point(width, endY));
+                    }
+                }
             }
 
             private IBrush GetBrushByLineType(Models.TextDiffLineType type)
@@ -486,6 +503,15 @@ namespace SourceGit.Views
             set => SetValue(DisplayRangeProperty, value);
         }
 
+        public static readonly StyledProperty<int> CurrentChangeBlockIdxProperty =
+            AvaloniaProperty.Register<ThemedTextDiffPresenter, int>(nameof(CurrentChangeBlockIdx));
+
+        public int CurrentChangeBlockIdx
+        {
+            get => GetValue(CurrentChangeBlockIdxProperty);
+            set => SetValue(CurrentChangeBlockIdxProperty, value);
+        }
+
         protected override Type StyleKeyOverride => typeof(TextEditor);
 
         public ThemedTextDiffPresenter(TextArea area, TextDocument doc) : base(area, doc)
@@ -590,6 +616,27 @@ namespace SourceGit.Views
             }
         }
 
+        public Models.TextDiffChangeBlock GetCurrentChangeBlock()
+        {
+            return GetChangeBlock(CurrentChangeBlockIdx);
+        }
+
+        public virtual Models.TextDiffChangeBlock GetChangeBlock(int changeBlockIdx)
+        {
+            return null;
+        }
+
+        public void JumpToChangeBlock(int changeBlockIdx)
+        {
+            var changeBlock = GetChangeBlock(changeBlockIdx);
+            if (changeBlock != null)
+            {
+                TextArea.Caret.Line = changeBlock.StartLine;
+                //TextArea.Caret.BringCaretToView(); // NOTE: Brings caret line (barely) into view.
+                ScrollToLine(changeBlock.StartLine); // NOTE: Brings specified line into center of view.
+            }
+        }
+
         public override void Render(DrawingContext context)
         {
             base.Render(context);
@@ -1017,6 +1064,16 @@ namespace SourceGit.Views
             }
         }
 
+        public override Models.TextDiffChangeBlock GetChangeBlock(int changeBlockIdx)
+        {
+            if (DataContext is Models.TextDiff diff)
+            {
+                if (changeBlockIdx >= 0 && changeBlockIdx < diff.ChangeBlocks.Count)
+                    return diff.ChangeBlocks[changeBlockIdx];
+            }
+            return null;
+        }
+
         protected override void OnLoaded(RoutedEventArgs e)
         {
             base.OnLoaded(e);
@@ -1233,6 +1290,16 @@ namespace SourceGit.Views
             }
         }
 
+        public override Models.TextDiffChangeBlock GetChangeBlock(int changeBlockIdx)
+        {
+            if (DataContext is ViewModels.TwoSideTextDiff diff)
+            {
+                if (changeBlockIdx >= 0 && changeBlockIdx < diff.ChangeBlocks.Count)
+                    return diff.ChangeBlocks[changeBlockIdx];
+            }
+            return null;
+        }
+
         protected override void OnLoaded(RoutedEventArgs e)
         {
             base.OnLoaded(e);
@@ -1479,6 +1546,15 @@ namespace SourceGit.Views
             set => SetValue(EnableChunkSelectionProperty, value);
         }
 
+        public static readonly StyledProperty<int> CurrentChangeBlockIdxProperty =
+            AvaloniaProperty.Register<TextDiffView, int>(nameof(CurrentChangeBlockIdx));
+
+        public int CurrentChangeBlockIdx
+        {
+            get => GetValue(CurrentChangeBlockIdxProperty);
+            set => SetValue(CurrentChangeBlockIdxProperty, value);
+        }
+
         static TextDiffView()
         {
             UseSideBySideDiffProperty.Changed.AddClassHandler<TextDiffView>((v, _) =>
@@ -1505,6 +1581,17 @@ namespace SourceGit.Views
                 v.Popup.Margin = new Thickness(0, top, right, 0);
                 v.Popup.IsVisible = true;
             });
+
+            CurrentChangeBlockIdxProperty.Changed.AddClassHandler<TextDiffView>((v, e) =>
+            {
+                if (v.Editor.Presenter != null)
+                {
+                    foreach (var p in v.Editor.Presenter.GetVisualDescendants().OfType<ThemedTextDiffPresenter>())
+                    {
+                        p.JumpToChangeBlock((int)e.NewValue);
+                    }
+                }
+            });
         }
 
         public TextDiffView()
@@ -1552,6 +1639,8 @@ namespace SourceGit.Views
 
             IsUnstagedChange = diff.Option.IsUnstaged;
             EnableChunkSelection = diff.Option.WorkingCopyChange != null;
+
+            diff.CurrentChangeBlockIdx = -1; // Unset current change block.
         }
 
         private void OnStageChunk(object _1, RoutedEventArgs _2)