feat: Implement git-style diff viewer in pkg/x/diff

go.mod

@@ -23,6 +23,7 @@ require (
 	gioui.org/x v0.9.0 // indirect
 	git.wow.st/gmp/jni v0.0.0-20210610011705-34026c7e22d0 // indirect
 	github.com/godbus/dbus/v5 v5.0.6 // indirect
+	github.com/sergi/go-diff v1.4.0 // indirect
 	github.com/zodimo/go-lazy v0.1.1 // indirect
 	golang.org/x/mod v0.32.0 // indirect
 	golang.org/x/sys v0.41.0 // indirect

go.sum

@@ -11,12 +11,22 @@ git.sr.ht/~schnwalter/gio-mw v0.0.0-20250713180710-9d8d98474447 h1:HYmUhTNys/xHf
 git.sr.ht/~schnwalter/gio-mw v0.0.0-20250713180710-9d8d98474447/go.mod h1:2delIHRFXOUBnmXbltTSUCnnbpzWawIGwQGxqw2K7p0=
 git.wow.st/gmp/jni v0.0.0-20210610011705-34026c7e22d0 h1:bGG/g4ypjrCJoSvFrP5hafr9PPB5aw8SjcOWWila7ZI=
 git.wow.st/gmp/jni v0.0.0-20210610011705-34026c7e22d0/go.mod h1:+axXBRUTIDlCeE73IKeD/os7LoEnTKdkp8/gQOFjqyo=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-text/typesetting-utils v0.0.0-20250618110550-c820a94c77b8 h1:4KCscI9qYWMGTuz6BpJtbUSRzcBrUSSE0ENMJbNSrFs=
 github.com/go-text/typesetting-utils v0.0.0-20250618110550-c820a94c77b8/go.mod h1:3/62I4La/HBRX9TcTpBj4eipLiwzf+vhI+7whTc9V7o=
 github.com/godbus/dbus/v5 v5.0.6 h1:mkgN1ofwASrYnJ5W6U/BxG15eXXXjirgZc7CLqkcaro=
 github.com/godbus/dbus/v5 v5.0.6/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sergi/go-diff v1.4.0 h1:n/SP9D5ad1fORl+llWyN+D6qoUETXNZARKjyY2/KVCw=
+github.com/sergi/go-diff v1.4.0/go.mod h1:A0bzQcvG0E7Rwjx0REVgAGH58e96+X0MeOfepqsbeW4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 github.com/zodimo/go-lazy v0.1.1 h1:lYsYK6eH1rbQ6VkVqPJntjiGIIoFe0Vsu4wH50j3uWE=
 github.com/zodimo/go-lazy v0.1.1/go.mod h1:+GKplxvAWyHv/XirM6KZwdHDvXBQDGGjCRpbUGlrZyg=
 github.com/zodimo/go-maybe v0.1.6 h1:Htq0qrJn/1OcMsKkoMSnjRBwEXyqWNLVuHAY/abSzu4=
@@ -43,3 +53,7 @@ golang.org/x/text v0.33.0 h1:B3njUFyqtHDUI5jMn1YIr5B0IE2U0qck04r6d4KPAxE=
 golang.org/x/text v0.33.0/go.mod h1:LuMebE6+rBincTi9+xWTY8TztLzKHc/9C1uBCG27+q8=
 golang.org/x/tools v0.41.0 h1:a9b8iMweWG+S0OBnlU36rzLp20z1Rp10w+IY2czHTQc=
 golang.org/x/tools v0.41.0/go.mod h1:XSY6eDqxVNiYgezAVqqCeihT4j1U2CCsqvH3WhQpnlg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=

pkg/x/diff/diff.go

@@ -0,0 +1,151 @@
+package diff
+
+import (
+	"strings"
+
+	"github.com/sergi/go-diff/diffmatchpatch"
+
+	"github.com/zodimo/go-compose/compose/foundation/layout/column"
+	"github.com/zodimo/go-compose/compose/foundation/layout/row"
+	fText "github.com/zodimo/go-compose/compose/foundation/text"
+	iconbutton "github.com/zodimo/go-compose/compose/material3/iconbutton"
+	m3Text "github.com/zodimo/go-compose/compose/material3/text"
+	"github.com/zodimo/go-compose/compose/ui/graphics"
+	"github.com/zodimo/go-compose/modifiers/background"
+	"github.com/zodimo/go-compose/modifiers/weight"
+	"github.com/zodimo/go-compose/pkg/api"
+	"github.com/zodimo/go-compose/compose/ui"
+	"golang.org/x/exp/shiny/materialdesign/icons"
+)
+
+type ChangeType int
+
+const (
+	ChangeEqual ChangeType = iota
+	ChangeDiff
+)
+
+type DiffSection struct {
+	Type     ChangeType
+	Original string
+	Modified string
+}
+
+func CalculateDiff(original, modified string) []DiffSection {
+	dmp := diffmatchpatch.New()
+	a, b, c := dmp.DiffLinesToChars(original, modified)
+	diffs := dmp.DiffMain(a, b, false)
+	diffs = dmp.DiffCharsToLines(diffs, c)
+
+	var sections []DiffSection
+	for i := 0; i < len(diffs); {
+		if diffs[i].Type == diffmatchpatch.DiffEqual {
+			sections = append(sections, DiffSection{
+				Type:     ChangeEqual,
+				Original: diffs[i].Text,
+				Modified: diffs[i].Text,
+			})
+			i++
+		} else {
+			// Combine adjacent deletes and inserts into a single section
+			var orig, mod strings.Builder
+			for i < len(diffs) && diffs[i].Type != diffmatchpatch.DiffEqual {
+				if diffs[i].Type == diffmatchpatch.DiffDelete {
+					orig.WriteString(diffs[i].Text)
+				} else if diffs[i].Type == diffmatchpatch.DiffInsert {
+					mod.WriteString(diffs[i].Text)
+				}
+				i++
+			}
+			sections = append(sections, DiffSection{
+				Type:     ChangeDiff,
+				Original: orig.String(),
+				Modified: mod.String(),
+			})
+		}
+	}
+	return sections
+}
+
+// DiffViewer renders the diff between original and modified strings
+func DiffViewer(original, modified string, onApplyLeftToRight, onApplyRightToLeft func(sectionIndex int, section DiffSection)) api.Composable {
+	sections := CalculateDiff(original, modified)
+
+	return func(c api.Composer) api.Composer {
+		c.StartBlock("DiffViewer")
+		defer c.EndBlock()
+
+		column.Column(
+			c.Sequence(
+				c.Range(len(sections), func(i int) api.Composable {
+					return row.Row(
+						c.Sequence(
+							// Left Side
+							row.Row(
+								c.Sequence(renderSection(i, sections[i], true, onApplyLeftToRight)),
+								row.WithModifier(weight.Weight(1)),
+							),
+							// Right Side
+							row.Row(
+								c.Sequence(renderSection(i, sections[i], false, onApplyRightToLeft)),
+								row.WithModifier(weight.Weight(1)),
+							),
+						),
+					)
+				}),
+			),
+		)(c)
+
+		return c
+	}
+}
+
+func renderSection(index int, section DiffSection, isLeft bool, onApply func(int, DiffSection)) api.Composable {
+	return func(c api.Composer) api.Composer {
+		c.StartBlock("DiffSection")
+		defer c.EndBlock()
+
+		return column.Column(
+			c.Sequence(func(c api.Composer) api.Composer {
+				textStr := section.Original
+				if !isLeft {
+					textStr = section.Modified
+				}
+
+				if textStr == "" && section.Type == ChangeDiff {
+					// Placeholder for deleted/empty blocks
+					m3Text.Text("---", fText.WithModifier(
+						background.Background(graphics.Color(0xFFC8C8C8)),
+					))(c)
+					return c
+				}
+
+				lines := strings.Split(strings.TrimSuffix(textStr, "\n"), "\n")
+				var mod ui.Modifier = ui.EmptyModifier
+
+				if section.Type == ChangeDiff {
+					if isLeft {
+						mod = background.Background(graphics.Color(0xFFFFC8C8)) // Faint red
+					} else {
+						mod = background.Background(graphics.Color(0xFFC8FFC8)) // Faint green
+					}
+				}
+
+				c.Range(len(lines), func(j int) api.Composable {
+					return m3Text.Text(lines[j], fText.WithModifier(mod))
+				})(c)
+
+				// Inline button for changes
+				if section.Type == ChangeDiff {
+					if isLeft {
+						iconbutton.Standard(func() { onApply(index, section) }, icons.HardwareKeyboardArrowRight, "Apply Left to Right")(c)
+					} else {
+						iconbutton.Standard(func() { onApply(index, section) }, icons.HardwareKeyboardArrowLeft, "Apply Right to Left")(c)
+					}
+				}
+
+				return c
+			}),
+		)(c)
+	}
+}

pkg/x/diff/diff_test.go

@@ -0,0 +1,60 @@
+package diff
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestCalculateDiff(t *testing.T) {
+	tests := []struct {
+		name     string
+		original string
+		modified string
+		want     []DiffSection
+	}{
+		{
+			name:     "identical strings",
+			original: "line1\nline2\n",
+			modified: "line1\nline2\n",
+			want: []DiffSection{
+				{Type: ChangeEqual, Original: "line1\nline2\n", Modified: "line1\nline2\n"},
+			},
+		},
+		{
+			name:     "one line changed",
+			original: "line1\nline2\nline3\n",
+			modified: "line1\nline2 modified\nline3\n",
+			want: []DiffSection{
+				{Type: ChangeEqual, Original: "line1\n", Modified: "line1\n"},
+				{Type: ChangeDiff, Original: "line2\n", Modified: "line2 modified\n"},
+				{Type: ChangeEqual, Original: "line3\n", Modified: "line3\n"},
+			},
+		},
+		{
+			name:     "line added",
+			original: "line1\n",
+			modified: "line1\nline2\n",
+			want: []DiffSection{
+				{Type: ChangeEqual, Original: "line1\n", Modified: "line1\n"},
+				{Type: ChangeDiff, Original: "", Modified: "line2\n"},
+			},
+		},
+		{
+			name:     "line removed",
+			original: "line1\nline2\n",
+			modified: "line1\n",
+			want: []DiffSection{
+				{Type: ChangeEqual, Original: "line1\n", Modified: "line1\n"},
+				{Type: ChangeDiff, Original: "line2\n", Modified: ""},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := CalculateDiff(tt.original, tt.modified); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("CalculateDiff() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

run_tests.sh

@@ -0,0 +1,2 @@
+#!/bin/bash
+go test ./...