1 files changed, 169 insertions, 0 deletions
diff --git a/pkg/commands/patch/format.go b/pkg/commands/patch/format.go
new file mode 100644
index 000000000..d04b6bec1
--- /dev/null
+++ b/pkg/commands/patch/format.go
@@ -0,0 +1,169 @@
+package patch
+
+import (
+	"strings"
+
+	"github.com/jesseduffield/generics/set"
+	"github.com/jesseduffield/lazygit/pkg/gui/style"
+	"github.com/jesseduffield/lazygit/pkg/theme"
+	"github.com/samber/lo"
+)
+
+type patchPresenter struct {
+	patch *Patch
+	// if true, all following fields are ignored
+	plain bool
+
+	isFocused bool
+	// first line index for selected cursor range
+	firstLineIndex int
+	// last line index for selected cursor range
+	lastLineIndex int
+	// line indices for tagged lines (e.g. lines added to a custom patch)
+	incLineIndices *set.Set[int]
+}
+
+// formats the patch as a plain string
+func formatPlain(patch *Patch) string {
+	presenter := &patchPresenter{
+		patch:          patch,
+		plain:          true,
+		incLineIndices: set.New[int](),
+	}
+	return presenter.format()
+}
+
+func formatRangePlain(patch *Patch, startIdx int, endIdx int) string {
+	lines := patch.Lines()[startIdx : endIdx+1]
+	return strings.Join(
+		lo.Map(lines, func(line *PatchLine, _ int) string {
+			return line.Content + "\n"
+		}),
+		"",
+	)
+}
+
+type FormatViewOpts struct {
+	IsFocused bool
+	// first line index for selected cursor range
+	FirstLineIndex int
+	// last line index for selected cursor range
+	LastLineIndex int
+	// line indices for tagged lines (e.g. lines added to a custom patch)
+	IncLineIndices *set.Set[int]
+}
+
+// formats the patch for rendering within a view, meaning it's coloured and
+// highlights selected items
+func formatView(patch *Patch, opts FormatViewOpts) string {
+	includedLineIndices := opts.IncLineIndices
+	if includedLineIndices == nil {
+		includedLineIndices = set.New[int]()
+	}
+	presenter := &patchPresenter{
+		patch:          patch,
+		plain:          false,
+		isFocused:      opts.IsFocused,
+		firstLineIndex: opts.FirstLineIndex,
+		lastLineIndex:  opts.LastLineIndex,
+		incLineIndices: includedLineIndices,
+	}
+	return presenter.format()
+}
+
+func (self *patchPresenter) format() string {
+	// if we have no changes in our patch (i.e. no additions or deletions) then
+	// the patch is effectively empty and we can return an empty string
+	if !self.patch.ContainsChanges() {
+		return ""
+	}
+
+	stringBuilder := &strings.Builder{}
+	lineIdx := 0
+	appendLine := func(line string) {
+		_, _ = stringBuilder.WriteString(line + "\n")
+
+		lineIdx++
+	}
+	appendFormattedLine := func(line string, style style.TextStyle) {
+		formattedLine := self.formatLine(
+			line,
+			style,
+			lineIdx,
+		)
+
+		appendLine(formattedLine)
+	}
+
+	for _, line := range self.patch.header {
+		appendFormattedLine(line, theme.DefaultTextColor.SetBold())
+	}
+
+	for _, hunk := range self.patch.hunks {
+		appendLine(
+			self.formatLine(
+				hunk.formatHeaderStart(),
+				style.FgCyan,
+				lineIdx,
+			) +
+				// we're splitting the line into two parts: the diff header and the context
+				// We explicitly pass 'included' as false here so that we're only tagging the
+				// first half of the line as included if the line is indeed included.
+				self.formatLineAux(
+					hunk.headerContext,
+					theme.DefaultTextColor,
+					lineIdx,
+					false,
+				),
+		)
+
+		for _, line := range hunk.bodyLines {
+			appendFormattedLine(line.Content, self.patchLineStyle(line))
+		}
+	}
+
+	return stringBuilder.String()
+}
+
+func (self *patchPresenter) patchLineStyle(patchLine *PatchLine) style.TextStyle {
+	switch patchLine.Kind {
+	case ADDITION:
+		return style.FgGreen
+	case DELETION:
+		return style.FgRed
+	default:
+		return theme.DefaultTextColor
+	}
+}
+
+func (self *patchPresenter) formatLine(str string, textStyle style.TextStyle, index int) string {
+	included := self.incLineIndices.Includes(index)
+
+	return self.formatLineAux(str, textStyle, index, included)
+}
+
+// 'selected' means you've got it highlighted with your cursor
+// 'included' means the line has been included in the patch (only applicable when
+// building a patch)
+func (self *patchPresenter) formatLineAux(str string, textStyle style.TextStyle, index int, included bool) string {
+	if self.plain {
+		return str
+	}
+
+	selected := self.isFocused && index >= self.firstLineIndex && index <= self.lastLineIndex
+
+	if selected {
+		textStyle = textStyle.MergeStyle(theme.SelectedRangeBgColor)
+	}
+
+	firstCharStyle := textStyle
+	if included {
+		firstCharStyle = firstCharStyle.MergeStyle(style.BgGreen)
+	}
+
+	if len(str) < 2 {
+		return firstCharStyle.Sprint(str)
+	}
+
+	return firstCharStyle.Sprint(str[:1]) + textStyle.Sprint(str[1:])
+}