Merge pull request #2513 from jesseduffield/refactor-patch-handling

31 files changed, 931 insertions, 710 deletions

diff --git a/go.mod b/go.mod
index 48401ba65..46ad9d742 100644
--- a/go.mod
+++ b/go.mod
@@ -18,7 +18,7 @@ require (
 	github.com/integrii/flaggy v1.4.0
 	github.com/jesseduffield/generics v0.0.0-20220320043834-727e535cbe68
 	github.com/jesseduffield/go-git/v5 v5.1.2-0.20221018185014-fdd53fef665d
-	github.com/jesseduffield/gocui v0.3.1-0.20230314081453-8d2162479b92
+	github.com/jesseduffield/gocui v0.3.1-0.20230319043340-e793609bfbf5
 	github.com/jesseduffield/kill v0.0.0-20220618033138-bfbe04675d10
 	github.com/jesseduffield/lazycore v0.0.0-20221012050358-03d2e40243c5
 	github.com/jesseduffield/minimal/gitignore v0.3.3-0.20211018110810-9cde264e6b1e
diff --git a/go.sum b/go.sum
index a79a09470..96b177507 100644
--- a/go.sum
+++ b/go.sum
@@ -72,8 +72,8 @@ github.com/jesseduffield/generics v0.0.0-20220320043834-727e535cbe68 h1:EQP2Tv8T
 github.com/jesseduffield/generics v0.0.0-20220320043834-727e535cbe68/go.mod h1:+LLj9/WUPAP8LqCchs7P+7X0R98HiFujVFANdNaxhGk=
 github.com/jesseduffield/go-git/v5 v5.1.2-0.20221018185014-fdd53fef665d h1:bO+OmbreIv91rCe8NmscRwhFSqkDJtzWCPV4Y+SQuXE=
 github.com/jesseduffield/go-git/v5 v5.1.2-0.20221018185014-fdd53fef665d/go.mod h1:nGNEErzf+NRznT+N2SWqmHnDnF9aLgANB1CUNEan09o=
-github.com/jesseduffield/gocui v0.3.1-0.20230314081453-8d2162479b92 h1:GO1Cpn3kdnBuUEzEVuvooD9vxmTd9hbyjwJJ6tvafwI=
-github.com/jesseduffield/gocui v0.3.1-0.20230314081453-8d2162479b92/go.mod h1:znJuCDnF2Ph40YZSlBwdX/4GEofnIoWLGdT4mK5zRAU=
+github.com/jesseduffield/gocui v0.3.1-0.20230319043340-e793609bfbf5 h1:8k7VTfj/RSKwYQ7Cn+iy876CjixBrTyyn+npxT/Wn/Q=
+github.com/jesseduffield/gocui v0.3.1-0.20230319043340-e793609bfbf5/go.mod h1:znJuCDnF2Ph40YZSlBwdX/4GEofnIoWLGdT4mK5zRAU=
 github.com/jesseduffield/kill v0.0.0-20220618033138-bfbe04675d10 h1:jmpr7KpX2+2GRiE91zTgfq49QvgiqB0nbmlwZ8UnOx0=
 github.com/jesseduffield/kill v0.0.0-20220618033138-bfbe04675d10/go.mod h1:aA97kHeNA+sj2Hbki0pvLslmE4CbDyhBeSSTUUnOuVo=
 github.com/jesseduffield/lazycore v0.0.0-20221012050358-03d2e40243c5 h1:CDuQmfOjAtb1Gms6a1p5L2P8RhbLUq5t8aL7PiQd2uY=
diff --git a/pkg/commands/git.go b/pkg/commands/git.go
index 35cead260..caf03db75 100644
--- a/pkg/commands/git.go
+++ b/pkg/commands/git.go
@@ -117,14 +117,14 @@ func NewGitCommandAux(
 	workingTreeCommands := git_commands.NewWorkingTreeCommands(gitCommon, submoduleCommands, fileLoader)
 	rebaseCommands := git_commands.NewRebaseCommands(gitCommon, commitCommands, workingTreeCommands)
 	stashCommands := git_commands.NewStashCommands(gitCommon, fileLoader, workingTreeCommands)
-	// TODO: have patch manager take workingTreeCommands in its entirety
-	patchManager := patch.NewPatchManager(cmn.Log, workingTreeCommands.ApplyPatch,
+	// TODO: have patch builder take workingTreeCommands in its entirety
+	patchBuilder := patch.NewPatchBuilder(cmn.Log, workingTreeCommands.ApplyPatch,
 		func(from string, to string, reverse bool, filename string, plain bool) (string, error) {
-			// TODO: make patch manager take Gui.IgnoreWhitespaceInDiffView into
+			// TODO: make patch builder take Gui.IgnoreWhitespaceInDiffView into
 			// account. For now we just pass false.
 			return workingTreeCommands.ShowFileDiff(from, to, reverse, filename, plain, false)
 		})
-	patchCommands := git_commands.NewPatchCommands(gitCommon, rebaseCommands, commitCommands, statusCommands, stashCommands, patchManager)
+	patchCommands := git_commands.NewPatchCommands(gitCommon, rebaseCommands, commitCommands, statusCommands, stashCommands, patchBuilder)
 	bisectCommands := git_commands.NewBisectCommands(gitCommon)
 
 	branchLoader := git_commands.NewBranchLoader(cmn, branchCommands.GetRawBranches, branchCommands.CurrentBranchInfo, configCommands)
diff --git a/pkg/commands/git_commands/patch.go b/pkg/commands/git_commands/patch.go
index 643091f63..7511d1a5b 100644
--- a/pkg/commands/git_commands/patch.go
+++ b/pkg/commands/git_commands/patch.go
@@ -16,7 +16,7 @@ type PatchCommands struct {
 	status *StatusCommands
 	stash  *StashCommands
 
-	PatchManager *patch.PatchManager
+	PatchBuilder *patch.PatchBuilder
 }
 
 func NewPatchCommands(
@@ -25,7 +25,7 @@ func NewPatchCommands(
 	commit *CommitCommands,
 	status *StatusCommands,
 	stash *StashCommands,
-	patchManager *patch.PatchManager,
+	patchBuilder *patch.PatchBuilder,
 ) *PatchCommands {
 	return &PatchCommands{
 		GitCommon:    gitCommon,
@@ -33,7 +33,7 @@ func NewPatchCommands(
 		commit:       commit,
 		status:       status,
 		stash:        stash,
-		PatchManager: patchManager,
+		PatchBuilder: patchBuilder,
 	}
 }
 
@@ -44,7 +44,7 @@ func (self *PatchCommands) DeletePatchesFromCommit(commits []*models.Commit, com
 	}
 
 	// apply each patch in reverse
-	if err := self.PatchManager.ApplyPatches(true); err != nil {
+	if err := self.PatchBuilder.ApplyPatches(true); err != nil {
 		_ = self.rebase.AbortRebase()
 		return err
 	}
@@ -55,7 +55,7 @@ func (self *PatchCommands) DeletePatchesFromCommit(commits []*models.Commit, com
 	}
 
 	self.rebase.onSuccessfulContinue = func() error {
-		self.PatchManager.Reset()
+		self.PatchBuilder.Reset()
 		return nil
 	}
 
@@ -70,7 +70,7 @@ func (self *PatchCommands) MovePatchToSelectedCommit(commits []*models.Commit, s
 		}
 
 		// apply each patch forward
-		if err := self.PatchManager.ApplyPatches(false); err != nil {
+		if err := self.PatchBuilder.ApplyPatches(false); err != nil {
 			// Don't abort the rebase here; this might cause conflicts, so give
 			// the user a chance to resolve them
 			return err
@@ -82,7 +82,7 @@ func (self *PatchCommands) MovePatchToSelectedCommit(commits []*models.Commit, s
 		}
 
 		self.rebase.onSuccessfulContinue = func() error {
-			self.PatchManager.Reset()
+			self.PatchBuilder.Reset()
 			return nil
 		}
 
@@ -117,7 +117,7 @@ func (self *PatchCommands) MovePatchToSelectedCommit(commits []*models.Commit, s
 	}
 
 	// apply each patch in reverse
-	if err := self.PatchManager.ApplyPatches(true); err != nil {
+	if err := self.PatchBuilder.ApplyPatches(true); err != nil {
 		_ = self.rebase.AbortRebase()
 		return err
 	}
@@ -152,7 +152,7 @@ func (self *PatchCommands) MovePatchToSelectedCommit(commits []*models.Commit, s
 		}
 
 		self.rebase.onSuccessfulContinue = func() error {
-			self.PatchManager.Reset()
+			self.PatchBuilder.Reset()
 			return nil
 		}
 
@@ -173,7 +173,7 @@ func (self *PatchCommands) MovePatchIntoIndex(commits []*models.Commit, commitId
 		return err
 	}
 
-	if err := self.PatchManager.ApplyPatches(true); err != nil {
+	if err := self.PatchBuilder.ApplyPatches(true); err != nil {
 		if self.status.WorkingTreeState() == enums.REBASE_MODE_REBASING {
 			_ = self.rebase.AbortRebase()
 		}
@@ -210,7 +210,7 @@ func (self *PatchCommands) MovePatchIntoIndex(commits []*models.Commit, commitId
 			}
 		}
 
-		self.PatchManager.Reset()
+		self.PatchBuilder.Reset()
 		return nil
 	}
 
@@ -222,7 +222,7 @@ func (self *PatchCommands) PullPatchIntoNewCommit(commits []*models.Commit, comm
 		return err
 	}
 
-	if err := self.PatchManager.ApplyPatches(true); err != nil {
+	if err := self.PatchBuilder.ApplyPatches(true); err != nil {
 		_ = self.rebase.AbortRebase()
 		return err
 	}
@@ -253,7 +253,7 @@ func (self *PatchCommands) PullPatchIntoNewCommit(commits []*models.Commit, comm
 		return errors.New("You are midway through another rebase operation. Please abort to start again")
 	}
 
-	self.PatchManager.Reset()
+	self.PatchBuilder.Reset()
 	return self.rebase.ContinueRebase()
 }
 
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:])
+}
diff --git a/pkg/commands/patch/hunk.go b/pkg/commands/patch/hunk.go
index 605c473c1..6d0177d05 100644
--- a/pkg/commands/patch/hunk.go
+++ b/pkg/commands/patch/hunk.go
@@ -1,130 +1,67 @@
 package patch
 
-import (
-	"fmt"
-	"strings"
-
-	"github.com/jesseduffield/lazygit/pkg/utils"
-	"github.com/samber/lo"
-)
-
-type PatchHunk struct {
-	FirstLineIdx int
-	oldStart     int
-	newStart     int
-	heading      string
-	bodyLines    []string
-}
-
-func (hunk *PatchHunk) LastLineIdx() int {
-	return hunk.FirstLineIdx + len(hunk.bodyLines)
+import "fmt"
+
+// Example hunk:
+// @@ -16,2 +14,3 @@ func (f *CommitFile) Description() string {
+// 	return f.Name
+// -}
+// +
+// +// test
+
+type Hunk struct {
+	// the line number of the first line in the old file ('16' in the above example)
+	oldStart int
+	// the line number of the first line in the new file ('14' in the above example)
+	newStart int
+	// the context at the end of the header line (' func (f *CommitFile) Description() string {' in the above example)
+	headerContext string
+	// the body of the hunk, excluding the header line
+	bodyLines []*PatchLine
 }
 
-func newHunk(lines []string, firstLineIdx int) *PatchHunk {
-	header := lines[0]
-	bodyLines := lines[1:]
-
-	oldStart, newStart, heading := headerInfo(header)
-
-	return &PatchHunk{
-		oldStart:     oldStart,
-		newStart:     newStart,
-		heading:      heading,
-		FirstLineIdx: firstLineIdx,
-		bodyLines:    bodyLines,
-	}
+// Returns the number of lines in the hunk in the original file ('2' in the above example)
+func (self *Hunk) oldLength() int {
+	return nLinesWithKind(self.bodyLines, []PatchLineKind{CONTEXT, DELETION})
 }
 
-func headerInfo(header string) (int, int, string) {
-	match := hunkHeaderRegexp.FindStringSubmatch(header)
-
-	oldStart := utils.MustConvertToInt(match[1])
-	newStart := utils.MustConvertToInt(match[2])
-	heading := match[3]
-
-	return oldStart, newStart, heading
+// Returns the number of lines in the hunk in the new file ('3' in the above example)
+func (self *Hunk) newLength() int {
+	return nLinesWithKind(self.bodyLines, []PatchLineKind{CONTEXT, ADDITION})
 }
 
-func (hunk *PatchHunk) updatedLines(lineIndices []int, reverse bool) []string {
-	skippedNewlineMessageIndex := -1
-	newLines := []string{}
-
-	lineIdx := hunk.FirstLineIdx
-	for _, line := range hunk.bodyLines {
-		lineIdx++ // incrementing at the start to skip the header line
-		if line == "" {
-			break
-		}
-		isLineSelected := lo.Contains(lineIndices, lineIdx)
-
-		firstChar, content := line[:1], line[1:]
-		transformedFirstChar := transformedFirstChar(firstChar, reverse, isLineSelected)
-
-		if isLineSelected || (transformedFirstChar == "\\" && skippedNewlineMessageIndex != lineIdx) || transformedFirstChar == " " {
-			newLines = append(newLines, transformedFirstChar+content)
-			continue
-		}
-
-		if transformedFirstChar == "+" {
-			// we don't want to include the 'newline at end of file' line if it involves an addition we're not including
-			skippedNewlineMessageIndex = lineIdx + 1
-		}
-	}
-
-	return newLines
+// Returns true if the hunk contains any changes (i.e. if it's not just a context hunk).
+// We'll end up with a context hunk if we're transforming a patch and one of the hunks
+// has no selected lines.
+func (self *Hunk) containsChanges() bool {
+	return nLinesWithKind(self.bodyLines, []PatchLineKind{ADDITION, DELETION}) > 0
 }
 
-func transformedFirstChar(firstChar string, reverse bool, isLineSelected bool) string {
-	linesToKeepInPatchContext := "-"
-	if reverse {
-		linesToKeepInPatchContext = "+"
-	}
-	if !isLineSelected && firstChar == linesToKeepInPatchContext {
-		return " "
-	}
-
-	return firstChar
+// Returns the number of lines in the hunk, including the header line
+func (self *Hunk) lineCount() int {
+	return len(self.bodyLines) + 1
 }
 
-func (hunk *PatchHunk) formatHeader(oldStart int, oldLength int, newStart int, newLength int, heading string) string {
-	return fmt.Sprintf("@@ -%d,%d +%d,%d @@%s\n", oldStart, oldLength, newStart, newLength, heading)
+// Returns all lines in the hunk, including the header line
+func (self *Hunk) allLines() []*PatchLine {
+	lines := []*PatchLine{{Content: self.formatHeaderLine(), Kind: HUNK_HEADER}}
+	lines = append(lines, self.bodyLines...)
+	return lines
 }
 
-func (hunk *PatchHunk) formatWithChanges(lineIndices []int, reverse bool, startOffset int) (int, string) {
-	bodyLines := hunk.updatedLines(lineIndices, reverse)
-	startOffset, header, ok := hunk.updatedHeader(bodyLines, startOffset)
-	if !ok {
-		return startOffset, ""
-	}
-	return startOffset, header + strings.Join(bodyLines, "")
+// Returns the header line, including the unified diff header and the context
+func (self *Hunk) formatHeaderLine() string {
+	return fmt.Sprintf("%s%s", self.formatHeaderStart(), self.headerContext)
 }
 
-func (hunk *PatchHunk) updatedHeader(newBodyLines []string, startOffset int) (int, string, bool) {
-	changeCount := nLinesWithPrefix(newBodyLines, []string{"+", "-"})
-	oldLength := nLinesWithPrefix(newBodyLines, []string{" ", "-"})
-	newLength := nLinesWithPrefix(newBodyLines, []string{"+", " "})
-
-	if changeCount == 0 {
-		// if nothing has changed we just return nothing
-		return startOffset, "", false
-	}
-
-	oldStart := hunk.oldStart
-
-	var newStartOffset int
-	// if the hunk went from zero to positive length, we need to increment the starting point by one
-	// if the hunk went from positive to zero length, we need to decrement the starting point by one
-	if oldLength == 0 {
-		newStartOffset = 1
-	} else if newLength == 0 {
-		newStartOffset = -1
-	} else {
-		newStartOffset = 0
+// Returns the first part of the header line i.e. the unified diff part (excluding any context)
+func (self *Hunk) formatHeaderStart() string {
+	newLengthDisplay := ""
+	newLength := self.newLength()
+	// if the new length is 1, it's omitted
+	if newLength != 1 {
+		newLengthDisplay = fmt.Sprintf(",%d", newLength)
 	}
 
-	newStart := oldStart + startOffset + newStartOffset
-
-	newStartOffset = startOffset + newLength - oldLength
-	formattedHeader := hunk.formatHeader(oldStart, oldLength, newStart, newLength, hunk.heading)
-	return newStartOffset, formattedHeader, true
+	return fmt.Sprintf("@@ -%d,%d +%d%s @@", self.oldStart, self.oldLength(), self.newStart, newLengthDisplay)
 }
diff --git a/pkg/commands/patch/parse.go b/pkg/commands/patch/parse.go
new file mode 100644
index 000000000..fee7d2918
--- /dev/null
+++ b/pkg/commands/patch/parse.go
@@ -0,0 +1,85 @@
+package patch
+
+import (
+	"regexp"
+	"strings"
+
+	"github.com/jesseduffield/lazygit/pkg/utils"
+)
+
+var hunkHeaderRegexp = regexp.MustCompile(`(?m)^@@ -(\d+)[^\+]+\+(\d+)[^@]+@@(.*)$`)
+
+func Parse(patchStr string) *Patch {
+	// ignore trailing newline.
+	lines := strings.Split(strings.TrimSuffix(patchStr, "\n"), "\n")
+
+	hunks := []*Hunk{}
+	patchHeader := []string{}
+
+	var currentHunk *Hunk
+	for _, line := range lines {
+		if strings.HasPrefix(line, "@@") {
+			oldStart, newStart, headerContext := headerInfo(line)
+
+			currentHunk = &Hunk{
+				oldStart:      oldStart,
+				newStart:      newStart,
+				headerContext: headerContext,
+				bodyLines:     []*PatchLine{},
+			}
+			hunks = append(hunks, currentHunk)
+		} else if currentHunk != nil {
+			currentHunk.bodyLines = append(currentHunk.bodyLines, newHunkLine(line))
+		} else {
+			patchHeader = append(patchHeader, line)
+		}
+	}
+
+	return &Patch{
+		hunks:  hunks,
+		header: patchHeader,
+	}
+}
+
+func headerInfo(header string) (int, int, string) {
+	match := hunkHeaderRegexp.FindStringSubmatch(header)
+
+	oldStart := utils.MustConvertToInt(match[1])
+	newStart := utils.MustConvertToInt(match[2])
+	headerContext := match[3]
+
+	return oldStart, newStart, headerContext
+}
+
+func newHunkLine(line string) *PatchLine {
+	if line == "" {
+		return &PatchLine{
+			Kind:    CONTEXT,
+			Content: "",
+		}
+	}
+
+	firstChar := line[:1]
+
+	kind := parseFirstChar(firstChar)
+
+	return &PatchLine{
+		Kind:    kind,
+		Content: line,
+	}
+}
+
+func parseFirstChar(firstChar string) PatchLineKind {
+	switch firstChar {
+	case " ":
+		return CONTEXT
+	case "+":
+		return ADDITION
+	case "-":
+		return DELETION
+	case "\\":
+		return NEWLINE_MESSAGE
+	}
+
+	return CONTEXT
+}
diff --git a/pkg/commands/patch/patch.go b/pkg/commands/patch/patch.go
new file mode 100644
index 000000000..5275fb613
--- /dev/null
+++ b/pkg/commands/patch/patch.go
@@ -0,0 +1,151 @@
+package patch
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/utils"
+	"github.com/samber/lo"
+)
+
+type Patch struct {
+	// header of the patch (split on newlines) e.g.
+	// diff --git a/filename b/filename
+	// index dcd3485..1ba5540 100644
+	// --- a/filename
+	// +++ b/filename
+	header []string
+	// hunks of the patch
+	hunks []*Hunk
+}
+
+// Returns a new patch with the specified transformation applied (e.g.
+// only selecting a subset of changes).
+// Leaves the original patch unchanged.
+func (self *Patch) Transform(opts TransformOpts) *Patch {
+	return transform(self, opts)
+}
+
+// Returns the patch as a plain string
+func (self *Patch) FormatPlain() string {
+	return formatPlain(self)
+}
+
+// Returns a range of lines from the patch as a plain string (range is inclusive)
+func (self *Patch) FormatRangePlain(startIdx int, endIdx int) string {
+	return formatRangePlain(self, startIdx, endIdx)
+}
+
+// Returns the patch as a string with ANSI color codes for displaying in a view
+func (self *Patch) FormatView(opts FormatViewOpts) string {
+	return formatView(self, opts)
+}
+
+// Returns the lines of the patch
+func (self *Patch) Lines() []*PatchLine {
+	lines := []*PatchLine{}
+	for _, line := range self.header {
+		lines = append(lines, &PatchLine{Content: line, Kind: PATCH_HEADER})
+	}
+
+	for _, hunk := range self.hunks {
+		lines = append(lines, hunk.allLines()...)
+	}
+
+	return lines
+}
+
+// Returns the patch line index of the first line in the given hunk
+func (self *Patch) HunkStartIdx(hunkIndex int) int {
+	hunkIndex = utils.Clamp(hunkIndex, 0, len(self.hunks)-1)
+
+	result := len(self.header)
+	for i := 0; i < hunkIndex; i++ {
+		result += self.hunks[i].lineCount()
+	}
+	return result
+}
+
+// Returns the patch line index of the last line in the given hunk
+func (self *Patch) HunkEndIdx(hunkIndex int) int {
+	hunkIndex = utils.Clamp(hunkIndex, 0, len(self.hunks)-1)
+
+	return self.HunkStartIdx(hunkIndex) + self.hunks[hunkIndex].lineCount() - 1
+}
+
+func (self *Patch) ContainsChanges() bool {
+	return lo.SomeBy(self.hunks, func(hunk *Hunk) bool {
+		return hunk.containsChanges()
+	})
+}
+
+// Takes a line index in the patch and returns the line number in the new file.
+// If the line is a header line, returns 1.
+// If the line is a hunk header line, returns the first file line number in that hunk.
+// If the line is out of range below, returns the last file line number in the last hunk.
+func (self *Patch) LineNumberOfLine(idx int) int {
+	if idx < len(self.header) || len(self.hunks) == 0 {
+		return 1
+	}
+
+	hunkIdx := self.HunkContainingLine(idx)
+	// cursor out of range, return last file line number
+	if hunkIdx == -1 {
+		lastHunk := self.hunks[len(self.hunks)-1]
+		return lastHunk.newStart + lastHunk.newLength() - 1
+	}
+
+	hunk := self.hunks[hunkIdx]
+	hunkStartIdx := self.HunkStartIdx(hunkIdx)
+	idxInHunk := idx - hunkStartIdx
+
+	if idxInHunk == 0 {
+		return hunk.oldStart
+	}
+
+	lines := hunk.bodyLines[:idxInHunk-1]
+	offset := nLinesWithKind(lines, []PatchLineKind{ADDITION, CONTEXT})
+	return hunk.oldStart + offset
+}
+
+// Returns hunk index containing the line at the given patch line index
+func (self *Patch) HunkContainingLine(idx int) int {
+	for hunkIdx, hunk := range self.hunks {
+		hunkStartIdx := self.HunkStartIdx(hunkIdx)
+		if idx >= hunkStartIdx && idx < hunkStartIdx+hunk.lineCount() {