opencode/internal/diff/diff.go

package diff

import (
	"bytes"
	"fmt"
	"io"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/alecthomas/chroma/v2"
	"github.com/alecthomas/chroma/v2/formatters"
	"github.com/alecthomas/chroma/v2/lexers"
	"github.com/alecthomas/chroma/v2/styles"
	"github.com/charmbracelet/lipgloss"
	"github.com/charmbracelet/x/ansi"
	"github.com/sergi/go-diff/diffmatchpatch"
)

// LineType represents the kind of line in a diff.
type LineType int

const (
	// LineContext represents a line that exists in both the old and new file.
	LineContext LineType = iota
	// LineAdded represents a line added in the new file.
	LineAdded
	// LineRemoved represents a line removed from the old file.
	LineRemoved
)

// DiffLine represents a single line in a diff, either from the old file,
// the new file, or a context line.
type DiffLine struct {
	OldLineNo int      // Line number in the old file (0 for added lines)
	NewLineNo int      // Line number in the new file (0 for removed lines)
	Kind      LineType // Type of line (added, removed, context)
	Content   string   // Content of the line
}

// Hunk represents a section of changes in a diff.
type Hunk struct {
	Header string
	Lines  []DiffLine
}

// DiffResult contains the parsed result of a diff.
type DiffResult struct {
	OldFile string
	NewFile string
	Hunks   []Hunk
}

// HunkDelta represents the change statistics for a hunk.
type HunkDelta struct {
	StartLine1 int
	LineCount1 int
	StartLine2 int
	LineCount2 int
}

// linePair represents a pair of lines to be displayed side by side.
type linePair struct {
	left  *DiffLine
	right *DiffLine
}

// -------------------------------------------------------------------------
// Style Configuration with Option Pattern
// -------------------------------------------------------------------------

// StyleConfig defines styling for diff rendering.
type StyleConfig struct {
	RemovedLineBg       lipgloss.Color
	AddedLineBg         lipgloss.Color
	ContextLineBg       lipgloss.Color
	HunkLineBg          lipgloss.Color
	HunkLineFg          lipgloss.Color
	RemovedFg           lipgloss.Color
	AddedFg             lipgloss.Color
	LineNumberFg        lipgloss.Color
	HighlightStyle      string
	RemovedHighlightBg  lipgloss.Color
	AddedHighlightBg    lipgloss.Color
	RemovedLineNumberBg lipgloss.Color
	AddedLineNamerBg    lipgloss.Color
	RemovedHighlightFg  lipgloss.Color
	AddedHighlightFg    lipgloss.Color
}

// StyleOption defines a function that modifies a StyleConfig.
type StyleOption func(*StyleConfig)

// NewStyleConfig creates a StyleConfig with default values and applies any provided options.
func NewStyleConfig(opts ...StyleOption) StyleConfig {
	// Set default values
	config := StyleConfig{
		RemovedLineBg:       lipgloss.Color("#3A3030"),
		AddedLineBg:         lipgloss.Color("#303A30"),
		ContextLineBg:       lipgloss.Color("#212121"),
		HunkLineBg:          lipgloss.Color("#2A2822"),
		HunkLineFg:          lipgloss.Color("#D4AF37"),
		RemovedFg:           lipgloss.Color("#7C4444"),
		AddedFg:             lipgloss.Color("#478247"),
		LineNumberFg:        lipgloss.Color("#888888"),
		HighlightStyle:      "dracula",
		RemovedHighlightBg:  lipgloss.Color("#612726"),
		AddedHighlightBg:    lipgloss.Color("#256125"),
		RemovedLineNumberBg: lipgloss.Color("#332929"),
		AddedLineNamerBg:    lipgloss.Color("#293229"),
		RemovedHighlightFg:  lipgloss.Color("#FADADD"),
		AddedHighlightFg:    lipgloss.Color("#DAFADA"),
	}

	// Apply all provided options
	for _, opt := range opts {
		opt(&config)
	}

	return config
}

// WithRemovedLineBg sets the background color for removed lines.
func WithRemovedLineBg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.RemovedLineBg = color
	}
}

// WithAddedLineBg sets the background color for added lines.
func WithAddedLineBg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.AddedLineBg = color
	}
}

// WithContextLineBg sets the background color for context lines.
func WithContextLineBg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.ContextLineBg = color
	}
}

// WithRemovedFg sets the foreground color for removed line markers.
func WithRemovedFg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.RemovedFg = color
	}
}

// WithAddedFg sets the foreground color for added line markers.
func WithAddedFg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.AddedFg = color
	}
}

// WithLineNumberFg sets the foreground color for line numbers.
func WithLineNumberFg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.LineNumberFg = color
	}
}

// WithHighlightStyle sets the syntax highlighting style.
func WithHighlightStyle(style string) StyleOption {
	return func(s *StyleConfig) {
		s.HighlightStyle = style
	}
}

// WithRemovedHighlightColors sets the colors for highlighted parts in removed text.
func WithRemovedHighlightColors(bg, fg lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.RemovedHighlightBg = bg
		s.RemovedHighlightFg = fg
	}
}

// WithAddedHighlightColors sets the colors for highlighted parts in added text.
func WithAddedHighlightColors(bg, fg lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.AddedHighlightBg = bg
		s.AddedHighlightFg = fg
	}
}

// WithRemovedLineNumberBg sets the background color for removed line numbers.
func WithRemovedLineNumberBg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.RemovedLineNumberBg = color
	}
}

// WithAddedLineNumberBg sets the background color for added line numbers.
func WithAddedLineNumberBg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.AddedLineNamerBg = color
	}
}

func WithHunkLineBg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.HunkLineBg = color
	}
}

func WithHunkLineFg(color lipgloss.Color) StyleOption {
	return func(s *StyleConfig) {
		s.HunkLineFg = color
	}
}

// -------------------------------------------------------------------------
// Parse Options with Option Pattern
// -------------------------------------------------------------------------

// ParseConfig configures the behavior of diff parsing.
type ParseConfig struct {
	ContextSize int // Number of context lines to include
}

// ParseOption defines a function that modifies a ParseConfig.
type ParseOption func(*ParseConfig)

// NewParseConfig creates a ParseConfig with default values and applies any provided options.
func NewParseConfig(opts ...ParseOption) ParseConfig {
	// Set default values
	config := ParseConfig{
		ContextSize: 3,
	}

	// Apply all provided options
	for _, opt := range opts {
		opt(&config)
	}

	return config
}

// WithContextSize sets the number of context lines to include.
func WithContextSize(size int) ParseOption {
	return func(p *ParseConfig) {
		if size >= 0 {
			p.ContextSize = size
		}
	}
}

// -------------------------------------------------------------------------
// Side-by-Side Options with Option Pattern
// -------------------------------------------------------------------------

// SideBySideConfig configures the rendering of side-by-side diffs.
type SideBySideConfig struct {
	TotalWidth int
	Style      StyleConfig
}

// SideBySideOption defines a function that modifies a SideBySideConfig.
type SideBySideOption func(*SideBySideConfig)

// NewSideBySideConfig creates a SideBySideConfig with default values and applies any provided options.
func NewSideBySideConfig(opts ...SideBySideOption) SideBySideConfig {
	// Set default values
	config := SideBySideConfig{
		TotalWidth: 160, // Default width for side-by-side view
		Style:      NewStyleConfig(),
	}

	// Apply all provided options
	for _, opt := range opts {
		opt(&config)
	}

	return config
}

// WithTotalWidth sets the total width for side-by-side view.
func WithTotalWidth(width int) SideBySideOption {
	return func(s *SideBySideConfig) {
		if width > 0 {
			s.TotalWidth = width
		}
	}
}

// WithStyle sets the styling configuration.
func WithStyle(style StyleConfig) SideBySideOption {
	return func(s *SideBySideConfig) {
		s.Style = style
	}
}

// WithStyleOptions applies the specified style options.
func WithStyleOptions(opts ...StyleOption) SideBySideOption {
	return func(s *SideBySideConfig) {
		s.Style = NewStyleConfig(opts...)
	}
}

// -------------------------------------------------------------------------
// Diff Parsing and Generation
// -------------------------------------------------------------------------

// ParseUnifiedDiff parses a unified diff format string into structured data.
func ParseUnifiedDiff(diff string) (DiffResult, error) {
	var result DiffResult
	var currentHunk *Hunk

	hunkHeaderRe := regexp.MustCompile(`^@@ -(\d+),?(\d*) \+(\d+),?(\d*) @@`)
	lines := strings.Split(diff, "\n")

	var oldLine, newLine int
	inFileHeader := true

	for _, line := range lines {
		// Parse the file headers
		if inFileHeader {
			if strings.HasPrefix(line, "--- a/") {
				result.OldFile = strings.TrimPrefix(line, "--- a/")
				continue
			}
			if strings.HasPrefix(line, "+++ b/") {
				result.NewFile = strings.TrimPrefix(line, "+++ b/")
				inFileHeader = false
				continue
			}
		}

		// Parse hunk headers
		if matches := hunkHeaderRe.FindStringSubmatch(line); matches != nil {
			if currentHunk != nil {
				result.Hunks = append(result.Hunks, *currentHunk)
			}
			currentHunk = &Hunk{
				Header: line,
				Lines:  []DiffLine{},
			}

			oldStart, _ := strconv.Atoi(matches[1])
			newStart, _ := strconv.Atoi(matches[3])
			oldLine = oldStart
			newLine = newStart

			continue
		}

		if currentHunk == nil {
			continue
		}

		if len(line) > 0 {
			// Process the line based on its prefix
			switch line[0] {
			case '+':
				currentHunk.Lines = append(currentHunk.Lines, DiffLine{
					OldLineNo: 0,
					NewLineNo: newLine,
					Kind:      LineAdded,
					Content:   line[1:], // skip '+'
				})
				newLine++
			case '-':
				currentHunk.Lines = append(currentHunk.Lines, DiffLine{
					OldLineNo: oldLine,
					NewLineNo: 0,
					Kind:      LineRemoved,
					Content:   line[1:], // skip '-'
				})
				oldLine++
			default:
				currentHunk.Lines = append(currentHunk.Lines, DiffLine{
					OldLineNo: oldLine,
					NewLineNo: newLine,
					Kind:      LineContext,
					Content:   line,
				})
				oldLine++
				newLine++
			}
		} else {
			// Handle empty lines
			currentHunk.Lines = append(currentHunk.Lines, DiffLine{
				OldLineNo: oldLine,
				NewLineNo: newLine,
				Kind:      LineContext,
				Content:   "",
			})
			oldLine++
			newLine++
		}
	}

	// Add the last hunk if there is one
	if currentHunk != nil {
		result.Hunks = append(result.Hunks, *currentHunk)
	}

	return result, nil
}

// HighlightIntralineChanges updates the content of lines in a hunk to show
// character-level differences within lines.
func HighlightIntralineChanges(h *Hunk, style StyleConfig) {
	var updated []DiffLine
	dmp := diffmatchpatch.New()

	for i := 0; i < len(h.Lines); i++ {
		// Look for removed line followed by added line, which might have similar content
		if i+1 < len(h.Lines) &&
			h.Lines[i].Kind == LineRemoved &&
			h.Lines[i+1].Kind == LineAdded {

			oldLine := h.Lines[i]
			newLine := h.Lines[i+1]

			// Find character-level differences
			patches := dmp.DiffMain(oldLine.Content, newLine.Content, false)
			patches = dmp.DiffCleanupEfficiency(patches)
			patches = dmp.DiffCleanupSemantic(patches)

			// Apply highlighting to the differences
			oldLine.Content = colorizeSegments(patches, true, style)
			newLine.Content = colorizeSegments(patches, false, style)

			updated = append(updated, oldLine, newLine)
			i++ // Skip the next line as we've already processed it
		} else {
			updated = append(updated, h.Lines[i])
		}
	}

	h.Lines = updated
}

// colorizeSegments applies styles to the character-level diff segments.
func colorizeSegments(diffs []diffmatchpatch.Diff, isOld bool, style StyleConfig) string {
	var buf strings.Builder

	removeBg := lipgloss.NewStyle().
		Background(style.RemovedHighlightBg).
		Foreground(style.RemovedHighlightFg)

	addBg := lipgloss.NewStyle().
		Background(style.AddedHighlightBg).
		Foreground(style.AddedHighlightFg)

	removedLineStyle := lipgloss.NewStyle().Background(style.RemovedLineBg)
	addedLineStyle := lipgloss.NewStyle().Background(style.AddedLineBg)

	afterBg := false

	for _, d := range diffs {
		switch d.Type {
		case diffmatchpatch.DiffEqual:
			// Handle text that's the same in both versions
			if afterBg {
				if isOld {
					buf.WriteString(removedLineStyle.Render(d.Text))
				} else {
					buf.WriteString(addedLineStyle.Render(d.Text))
				}
			} else {
				buf.WriteString(d.Text)
			}
		case diffmatchpatch.DiffDelete:
			// Handle deleted text (only show in old version)
			if isOld {
				buf.WriteString(removeBg.Render(d.Text))
				afterBg = true
			}
		case diffmatchpatch.DiffInsert:
			// Handle inserted text (only show in new version)
			if !isOld {
				buf.WriteString(addBg.Render(d.Text))
				afterBg = true
			}
		}
	}

	return buf.String()
}

// pairLines converts a flat list of diff lines to pairs for side-by-side display.
func pairLines(lines []DiffLine) []linePair {
	var pairs []linePair
	i := 0

	for i < len(lines) {
		switch lines[i].Kind {
		case LineRemoved:
			// Check if the next line is an addition, if so pair them
			if i+1 < len(lines) && lines[i+1].Kind == LineAdded {
				pairs = append(pairs, linePair{left: &lines[i], right: &lines[i+1]})
				i += 2
			} else {
				pairs = append(pairs, linePair{left: &lines[i], right: nil})
				i++
			}
		case LineAdded:
			pairs = append(pairs, linePair{left: nil, right: &lines[i]})
			i++
		case LineContext:
			pairs = append(pairs, linePair{left: &lines[i], right: &lines[i]})
			i++
		}
	}

	return pairs
}

// -------------------------------------------------------------------------
// Syntax Highlighting
// -------------------------------------------------------------------------

// SyntaxHighlight applies syntax highlighting to a string based on the file extension.
func SyntaxHighlight(w io.Writer, source, fileName, formatter string, bg lipgloss.TerminalColor) error {
	// Determine the language lexer to use
	l := lexers.Match(fileName)
	if l == nil {
		l = lexers.Analyse(source)
	}
	if l == nil {
		l = lexers.Fallback
	}
	l = chroma.Coalesce(l)

	// Get the formatter
	f := formatters.Get(formatter)
	if f == nil {
		f = formatters.Fallback
	}

	// Get the style
	s := styles.Get("dracula")
	if s == nil {
		s = styles.Fallback
	}

	// Modify the style to use the provided background
	s, err := s.Builder().Transform(
		func(t chroma.StyleEntry) chroma.StyleEntry {
			r, g, b, _ := bg.RGBA()
			ru8 := uint8(r >> 8)
			gu8 := uint8(g >> 8)
			bu8 := uint8(b >> 8)
			t.Background = chroma.NewColour(ru8, gu8, bu8)
			return t
		},
	).Build()
	if err != nil {
		s = styles.Fallback
	}

	// Tokenize and format
	it, err := l.Tokenise(nil, source)
	if err != nil {
		return err
	}

	return f.Format(w, s, it)
}

// highlightLine applies syntax highlighting to a single line.
func highlightLine(fileName string, line string, bg lipgloss.TerminalColor) string {
	var buf bytes.Buffer
	err := SyntaxHighlight(&buf, line, fileName, "terminal16m", bg)
	if err != nil {
		return line
	}
	return buf.String()
}

// createStyles generates the lipgloss styles needed for rendering diffs.
func createStyles(config StyleConfig) (removedLineStyle, addedLineStyle, contextLineStyle, lineNumberStyle lipgloss.Style) {
	removedLineStyle = lipgloss.NewStyle().Background(config.RemovedLineBg)
	addedLineStyle = lipgloss.NewStyle().Background(config.AddedLineBg)
	contextLineStyle = lipgloss.NewStyle().Background(config.ContextLineBg)
	lineNumberStyle = lipgloss.NewStyle().Foreground(config.LineNumberFg)

	return
}

// renderLeftColumn formats the left side of a side-by-side diff.
func renderLeftColumn(fileName string, dl *DiffLine, colWidth int, styles StyleConfig) string {
	if dl == nil {
		contextLineStyle := lipgloss.NewStyle().Background(styles.ContextLineBg)
		return contextLineStyle.Width(colWidth).Render("")
	}

	removedLineStyle, _, contextLineStyle, lineNumberStyle := createStyles(styles)

	var marker string
	var bgStyle lipgloss.Style

	switch dl.Kind {
	case LineRemoved:
		marker = removedLineStyle.Foreground(styles.RemovedFg).Render("-")
		bgStyle = removedLineStyle
		lineNumberStyle = lineNumberStyle.Foreground(styles.RemovedFg).Background(styles.RemovedLineNumberBg)
	case LineAdded:
		marker = "?"
		bgStyle = contextLineStyle
	case LineContext:
		marker = contextLineStyle.Render(" ")
		bgStyle = contextLineStyle
	}

	lineNum := ""
	if dl.OldLineNo > 0 {
		lineNum = fmt.Sprintf("%6d", dl.OldLineNo)
	}

	prefix := lineNumberStyle.Render(lineNum + " " + marker)
	content := highlightLine(fileName, dl.Content, bgStyle.GetBackground())

	if dl.Kind == LineRemoved {
		content = bgStyle.Render(" ") + content
	}

	lineText := prefix + content
	return bgStyle.MaxHeight(1).Width(colWidth).Render(ansi.Truncate(lineText, colWidth, "..."))
}

// renderRightColumn formats the right side of a side-by-side diff.
func renderRightColumn(fileName string, dl *DiffLine, colWidth int, styles StyleConfig) string {
	if dl == nil {
		contextLineStyle := lipgloss.NewStyle().Background(styles.ContextLineBg)
		return contextLineStyle.Width(colWidth).Render("")
	}

	_, addedLineStyle, contextLineStyle, lineNumberStyle := createStyles(styles)

	var marker string
	var bgStyle lipgloss.Style

	switch dl.Kind {
	case LineAdded:
		marker = addedLineStyle.Foreground(styles.AddedFg).Render("+")
		bgStyle = addedLineStyle
		lineNumberStyle = lineNumberStyle.Foreground(styles.AddedFg).Background(styles.AddedLineNamerBg)
	case LineRemoved:
		marker = "?"
		bgStyle = contextLineStyle
	case LineContext:
		marker = contextLineStyle.Render(" ")
		bgStyle = contextLineStyle
	}

	lineNum := ""
	if dl.NewLineNo > 0 {
		lineNum = fmt.Sprintf("%6d", dl.NewLineNo)
	}

	prefix := lineNumberStyle.Render(lineNum + " " + marker)
	content := highlightLine(fileName, dl.Content, bgStyle.GetBackground())

	if dl.Kind == LineAdded {
		content = bgStyle.Render(" ") + content
	}

	lineText := prefix + content
	return bgStyle.MaxHeight(1).Width(colWidth).Render(ansi.Truncate(lineText, colWidth, "..."))
}

// -------------------------------------------------------------------------
// Public API Methods
// -------------------------------------------------------------------------

// RenderSideBySideHunk formats a hunk for side-by-side display.
func RenderSideBySideHunk(fileName string, h Hunk, opts ...SideBySideOption) string {
	// Apply options to create the configuration
	config := NewSideBySideConfig(opts...)

	// Make a copy of the hunk so we don't modify the original
	hunkCopy := Hunk{Lines: make([]DiffLine, len(h.Lines))}
	copy(hunkCopy.Lines, h.Lines)

	// Highlight changes within lines
	HighlightIntralineChanges(&hunkCopy, config.Style)

	// Pair lines for side-by-side display
	pairs := pairLines(hunkCopy.Lines)

	// Calculate column width
	colWidth := config.TotalWidth / 2

	var sb strings.Builder
	for _, p := range pairs {
		leftStr := renderLeftColumn(fileName, p.left, colWidth, config.Style)
		rightStr := renderRightColumn(fileName, p.right, colWidth, config.Style)
		sb.WriteString(leftStr + rightStr + "\n")
	}

	return sb.String()
}

// FormatDiff creates a side-by-side formatted view of a diff.
func FormatDiff(diffText string, opts ...SideBySideOption) (string, error) {
	diffResult, err := ParseUnifiedDiff(diffText)
	if err != nil {
		return "", err
	}

	var sb strings.Builder

	config := NewSideBySideConfig(opts...)
	for i, h := range diffResult.Hunks {
		if i > 0 {
			sb.WriteString(lipgloss.NewStyle().Background(config.Style.HunkLineBg).Foreground(config.Style.HunkLineFg).Width(config.TotalWidth).Render(h.Header) + "\n")
		}
		sb.WriteString(RenderSideBySideHunk(diffResult.OldFile, h, opts...))
	}

	return sb.String(), nil
}

// GenerateDiff creates a unified diff from two file contents.
func GenerateDiff(beforeContent, afterContent, beforeFilename, afterFilename string, opts ...ParseOption) (string, int, int) {
	config := NewParseConfig(opts...)

	var output strings.Builder

	// Ensure we handle newlines correctly
	beforeHasNewline := len(beforeContent) > 0 && beforeContent[len(beforeContent)-1] == '\n'
	afterHasNewline := len(afterContent) > 0 && afterContent[len(afterContent)-1] == '\n'

	// Split into lines
	beforeLines := strings.Split(beforeContent, "\n")
	afterLines := strings.Split(afterContent, "\n")

	// Remove empty trailing element from the split if the content ended with a newline
	if beforeHasNewline && len(beforeLines) > 0 {
		beforeLines = beforeLines[:len(beforeLines)-1]
	}
	if afterHasNewline && len(afterLines) > 0 {
		afterLines = afterLines[:len(afterLines)-1]
	}

	dmp := diffmatchpatch.New()
	dmp.DiffTimeout = 5 * time.Second

	// Convert lines to characters for efficient diffing
	lineArray1, lineArray2, lineArrays := dmp.DiffLinesToChars(beforeContent, afterContent)
	diffs := dmp.DiffMain(lineArray1, lineArray2, false)
	diffs = dmp.DiffCharsToLines(diffs, lineArrays)

	// Default filenames if not provided
	if beforeFilename == "" {
		beforeFilename = "a"
	}
	if afterFilename == "" {
		afterFilename = "b"
	}

	// Write diff header
	output.WriteString(fmt.Sprintf("diff --git a/%s b/%s\n", beforeFilename, afterFilename))
	output.WriteString(fmt.Sprintf("--- a/%s\n", beforeFilename))
	output.WriteString(fmt.Sprintf("+++ b/%s\n", afterFilename))

	line1 := 0 // Line numbers start from 0 internally
	line2 := 0
	additions := 0
	deletions := 0

	var hunks []string
	var currentHunk strings.Builder
	var hunkStartLine1, hunkStartLine2 int
	var hunkLines1, hunkLines2 int
	inHunk := false

	contextSize := config.ContextSize

	// startHunk begins recording a new hunk
	startHunk := func(startLine1, startLine2 int) {
		inHunk = true
		hunkStartLine1 = startLine1
		hunkStartLine2 = startLine2
		hunkLines1 = 0
		hunkLines2 = 0
		currentHunk.Reset()
	}

	// writeHunk adds the current hunk to the hunks slice
	writeHunk := func() {
		if inHunk {
			hunkHeader := fmt.Sprintf("@@ -%d,%d +%d,%d @@\n",
				hunkStartLine1+1, hunkLines1,
				hunkStartLine2+1, hunkLines2)
			hunks = append(hunks, hunkHeader+currentHunk.String())
			inHunk = false
		}
	}

	// Process diffs to create hunks
	pendingContext := make([]string, 0, contextSize*2)
	var contextLines1, contextLines2 int

	// Helper function to add context lines to the hunk
	addContextToHunk := func(lines []string, count int) {
		for i := 0; i < count; i++ {
			if i < len(lines) {
				currentHunk.WriteString(" " + lines[i] + "\n")
				hunkLines1++
				hunkLines2++
			}
		}
	}

	// Process diffs
	for _, diff := range diffs {
		lines := strings.Split(diff.Text, "\n")

		// Remove empty trailing line that comes from splitting a string that ends with \n
		if len(lines) > 0 && lines[len(lines)-1] == "" && diff.Text[len(diff.Text)-1] == '\n' {
			lines = lines[:len(lines)-1]
		}

		switch diff.Type {
		case diffmatchpatch.DiffEqual:
			// If we have enough equal lines to serve as context, add them to pending
			pendingContext = append(pendingContext, lines...)

			// If pending context grows too large, trim it
			if len(pendingContext) > contextSize*2 {
				pendingContext = pendingContext[len(pendingContext)-contextSize*2:]
			}

			// If we're in a hunk, add the necessary context
			if inHunk {
				// Only add the first contextSize lines as trailing context
				numContextLines := min(contextSize, len(lines))
				addContextToHunk(lines[:numContextLines], numContextLines)

				// If we've added enough trailing context, close the hunk
				if numContextLines >= contextSize {
					writeHunk()
				}
			}

			line1 += len(lines)
			line2 += len(lines)
			contextLines1 += len(lines)
			contextLines2 += len(lines)

		case diffmatchpatch.DiffDelete, diffmatchpatch.DiffInsert:
			// Start a new hunk if needed
			if !inHunk {
				// Determine how many context lines we can add before
				contextBefore := min(contextSize, len(pendingContext))
				ctxStartIdx := len(pendingContext) - contextBefore

				// Calculate the correct start lines
				startLine1 := line1 - contextLines1 + ctxStartIdx
				startLine2 := line2 - contextLines2 + ctxStartIdx

				startHunk(startLine1, startLine2)

				// Add the context lines before
				addContextToHunk(pendingContext[ctxStartIdx:], contextBefore)
			}

			// Reset context tracking when we see a diff
			pendingContext = pendingContext[:0]
			contextLines1 = 0
			contextLines2 = 0

			// Add the changes
			if diff.Type == diffmatchpatch.DiffDelete {
				for _, line := range lines {
					currentHunk.WriteString("-" + line + "\n")
					hunkLines1++
					deletions++
				}
				line1 += len(lines)
			} else { // DiffInsert
				for _, line := range lines {
					currentHunk.WriteString("+" + line + "\n")
					hunkLines2++
					additions++
				}
				line2 += len(lines)
			}
		}
	}

	// Write the final hunk if there's one pending
	if inHunk {
		writeHunk()
	}

	// Merge hunks that are close to each other (within 2*contextSize lines)
	var mergedHunks []string
	if len(hunks) > 0 {
		mergedHunks = append(mergedHunks, hunks[0])

		for i := 1; i < len(hunks); i++ {
			prevHunk := mergedHunks[len(mergedHunks)-1]
			currHunk := hunks[i]

			// Extract line numbers to check proximity
			var prevStart, prevLen, currStart, currLen int
			fmt.Sscanf(prevHunk, "@@ -%d,%d", &prevStart, &prevLen)
			fmt.Sscanf(currHunk, "@@ -%d,%d", &currStart, &currLen)

			prevEnd := prevStart + prevLen - 1

			// If hunks are close, merge them
			if currStart-prevEnd <= contextSize*2 {
				// Create a merged hunk - this is a simplification, real git has more complex merging logic
				merged := mergeHunks(prevHunk, currHunk)
				mergedHunks[len(mergedHunks)-1] = merged
			} else {
				mergedHunks = append(mergedHunks, currHunk)
			}
		}
	}

	// Write all hunks to output
	for _, hunk := range mergedHunks {
		output.WriteString(hunk)
	}

	// Handle "No newline at end of file" notifications
	if !beforeHasNewline && len(beforeLines) > 0 {
		// Find the last deletion in the diff and add the notification after it
		lastPos := strings.LastIndex(output.String(), "\n-")
		if lastPos != -1 {
			// Insert the notification after the line
			str := output.String()
			output.Reset()
			output.WriteString(str[:lastPos+1])
			output.WriteString("\\ No newline at end of file\n")
			output.WriteString(str[lastPos+1:])
		}
	}

	if !afterHasNewline && len(afterLines) > 0 {
		// Find the last insertion in the diff and add the notification after it
		lastPos := strings.LastIndex(output.String(), "\n+")
		if lastPos != -1 {
			// Insert the notification after the line
			str := output.String()
			output.Reset()
			output.WriteString(str[:lastPos+1])
			output.WriteString("\\ No newline at end of file\n")
			output.WriteString(str[lastPos+1:])
		}
	}

	// Return the diff without the summary line
	return output.String(), additions, deletions
}

// Helper function to merge two hunks
func mergeHunks(hunk1, hunk2 string) string {
	// This is a simplified implementation
	// A full implementation would need to properly recalculate the hunk header
	// and remove redundant context lines

	// Extract header info from both hunks
	var start1, len1, start2, len2 int
	var startB1, lenB1, startB2, lenB2 int

	fmt.Sscanf(hunk1, "@@ -%d,%d +%d,%d @@", &start1, &len1, &startB1, &lenB1)
	fmt.Sscanf(hunk2, "@@ -%d,%d +%d,%d @@", &start2, &len2, &startB2, &lenB2)

	// Split the hunks to get content
	parts1 := strings.SplitN(hunk1, "\n", 2)
	parts2 := strings.SplitN(hunk2, "\n", 2)

	content1 := ""
	content2 := ""

	if len(parts1) > 1 {
		content1 = parts1[1]
	}
	if len(parts2) > 1 {
		content2 = parts2[1]
	}

	// Calculate the new header
	newEnd := max(start1+len1-1, start2+len2-1)
	newEndB := max(startB1+lenB1-1, startB2+lenB2-1)

	newLen := newEnd - start1 + 1
	newLenB := newEndB - startB1 + 1

	newHeader := fmt.Sprintf("@@ -%d,%d +%d,%d @@", start1, newLen, startB1, newLenB)

	// Combine the content, potentially with some overlap handling
	return newHeader + "\n" + content1 + content2
}