format/diff: unified diff encoder and public API

- Added Patch interface
- Added a Unified Diff encoder from Patches
- Added Change method to generate Patches
- Added Changes method to generate Patches
- Added Tree method to generate Patches
- Added Commit method to generate Patches

1 files changed, 355 insertions, 0 deletions

diff --git a/plumbing/format/diff/unified_encoder.go b/plumbing/format/diff/unified_encoder.go
new file mode 100644
index 0000000..a4ff7ab
--- /dev/null
+++ b/plumbing/format/diff/unified_encoder.go
@@ -0,0 +1,355 @@
+package diff
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+const (
+	diffInit = "diff --git a/%s b/%s\n"
+
+	chunkStart  = "@@ -"
+	chunkMiddle = " +"
+	chunkEnd    = " @@%s\n"
+	chunkCount  = "%d,%d"
+
+	noFilePath = "/dev/null"
+	aDir       = "a/"
+	bDir       = "b/"
+
+	fPath  = "--- %s\n"
+	tPath  = "+++ %s\n"
+	binary = "Binary files %s and %s differ\n"
+
+	addLine    = "+%s\n"
+	deleteLine = "-%s\n"
+	equalLine  = " %s\n"
+
+	oldMode         = "old mode %o\n"
+	newMode         = "new mode %o\n"
+	deletedFileMode = "deleted file mode %o\n"
+	newFileMode     = "new file mode %o\n"
+
+	renameFrom     = "from"
+	renameTo       = "to"
+	renameFileMode = "rename %s %s\n"
+
+	indexAndMode = "index %s..%s %o\n"
+	indexNoMode  = "index %s..%s\n"
+
+	DefaultContextLines = 3
+)
+
+var ErrBothFilesEmpty = errors.New("both files are empty")
+
+// UnifiedEncoder encodes an unified diff into the provided Writer.
+// There are some unsupported features:
+//     - Similarity index for renames
+//     - Sort hash representation
+type UnifiedEncoder struct {
+	io.Writer
+
+	// ctxLines is the count of unchanged lines that will appear
+	// surrounding a change.
+	ctxLines int
+
+	buf bytes.Buffer
+}
+
+func NewUnifiedEncoder(w io.Writer, ctxLines int) *UnifiedEncoder {
+	return &UnifiedEncoder{ctxLines: ctxLines, Writer: w}
+}
+
+func (e *UnifiedEncoder) Encode(patch Patch) error {
+	e.printMessage(patch.Message())
+
+	if err := e.encodeFilePatch(patch.FilePatches()); err != nil {
+		return err
+	}
+
+	_, err := e.buf.WriteTo(e)
+
+	return err
+}
+
+func (e *UnifiedEncoder) encodeFilePatch(filePatches []FilePatch) error {
+	for _, p := range filePatches {
+		f, t := p.Files()
+		if err := e.header(f, t, p.IsBinary()); err != nil {
+			return err
+		}
+
+		g := newHunksGenerator(p.Chunks(), e.ctxLines)
+		for _, c := range g.Generate() {
+			c.WriteTo(&e.buf)
+		}
+	}
+
+	return nil
+}
+
+func (e *UnifiedEncoder) printMessage(message string) {
+	isEmpty := message == ""
+	hasSuffix := strings.HasSuffix(message, "\n")
+	if !isEmpty && !hasSuffix {
+		message = message + "\n"
+	}
+
+	e.buf.WriteString(message)
+}
+
+func (e *UnifiedEncoder) header(from, to File, isBinary bool) error {
+	switch {
+	case from == nil && to == nil:
+		return ErrBothFilesEmpty
+	case from != nil && to != nil:
+		hashEquals := from.Hash() == to.Hash()
+
+		fmt.Fprintf(&e.buf, diffInit, from.Path(), to.Path())
+
+		if from.Mode() != to.Mode() {
+			fmt.Fprintf(&e.buf, oldMode+newMode, from.Mode(), to.Mode())
+		}
+
+		if from.Path() != to.Path() {
+			fmt.Fprintf(&e.buf,
+				renameFileMode+renameFileMode,
+				renameFrom, from.Path(), renameTo, to.Path())
+		}
+
+		if from.Mode() != to.Mode() && !hashEquals {
+			fmt.Fprintf(&e.buf, indexNoMode, from.Hash(), to.Hash())
+		} else if !hashEquals {
+			fmt.Fprintf(&e.buf, indexAndMode, from.Hash(), to.Hash(), from.Mode())
+		}
+
+		if !hashEquals {
+			e.pathLines(isBinary, aDir+from.Path(), bDir+to.Path())
+		}
+	case from == nil:
+		fmt.Fprintf(&e.buf, diffInit, to.Path(), to.Path())
+		fmt.Fprintf(&e.buf, newFileMode, to.Mode())
+		fmt.Fprintf(&e.buf, indexNoMode, plumbing.ZeroHash, to.Hash())
+		e.pathLines(isBinary, noFilePath, bDir+to.Path())
+	case to == nil:
+		fmt.Fprintf(&e.buf, diffInit, from.Path(), from.Path())
+		fmt.Fprintf(&e.buf, deletedFileMode, from.Mode())
+		fmt.Fprintf(&e.buf, indexNoMode, from.Hash(), plumbing.ZeroHash)
+		e.pathLines(isBinary, aDir+from.Path(), noFilePath)
+	}
+
+	return nil
+}
+
+func (e *UnifiedEncoder) pathLines(isBinary bool, fromPath, toPath string) {
+	format := fPath + tPath
+	if isBinary {
+		format = binary
+	}
+
+	fmt.Fprintf(&e.buf, format, fromPath, toPath)
+}
+
+type hunksGenerator struct {
+	fromLine, toLine            int
+	ctxLines                    int
+	chunks                      []Chunk
+	current                     *hunk
+	hunks                       []*hunk
+	beforeContext, afterContext []string
+}
+
+func newHunksGenerator(chunks []Chunk, ctxLines int) *hunksGenerator {
+	return &hunksGenerator{
+		chunks:   chunks,
+		ctxLines: ctxLines,
+	}
+}
+
+func (c *hunksGenerator) Generate() []*hunk {
+	for i, chunk := range c.chunks {
+		ls := splitLines(chunk.Content())
+		lsLen := len(ls)
+
+		switch chunk.Type() {
+		case Equal:
+			c.fromLine += lsLen
+			c.toLine += lsLen
+			c.processEqualsLines(ls, i)
+		case Delete:
+			if lsLen != 0 {
+				c.fromLine++
+			}
+
+			c.processHunk(i, chunk.Type())
+			c.fromLine += lsLen - 1
+			c.current.AddOp(chunk.Type(), ls...)
+		case Add:
+			if lsLen != 0 {
+				c.toLine++
+			}
+			c.processHunk(i, chunk.Type())
+			c.toLine += lsLen - 1
+			c.current.AddOp(chunk.Type(), ls...)
+		}
+
+		if i == len(c.chunks)-1 && c.current != nil {
+			c.hunks = append(c.hunks, c.current)
+		}
+	}
+
+	return c.hunks
+}
+
+func (c *hunksGenerator) processHunk(i int, op Operation) {
+	if c.current != nil {
+		return
+	}
+
+	var ctxPrefix string
+	linesBefore := len(c.beforeContext)
+	if linesBefore > c.ctxLines {
+		ctxPrefix = " " + c.beforeContext[linesBefore-c.ctxLines-1]
+		c.beforeContext = c.beforeContext[linesBefore-c.ctxLines:]
+		linesBefore = c.ctxLines
+	}
+
+	c.current = &hunk{ctxPrefix: ctxPrefix}
+	c.current.AddOp(Equal, c.beforeContext...)
+
+	switch op {
+	case Delete:
+		c.current.fromLine, c.current.toLine =
+			c.addLineNumbers(c.fromLine, c.toLine, linesBefore, i, Add)
+	case Add:
+		c.current.toLine, c.current.fromLine =
+			c.addLineNumbers(c.toLine, c.fromLine, linesBefore, i, Delete)
+	}
+
+	c.beforeContext = nil
+}
+
+// addLineNumbers obtains the line numbers in a new chunk
+func (c *hunksGenerator) addLineNumbers(la, lb int, linesBefore int, i int, op Operation) (cla, clb int) {
+	cla = la - linesBefore
+	// we need to search for a reference for the next diff
+	switch {
+	case linesBefore != 0 && c.ctxLines != 0:
+		clb = lb - c.ctxLines + 1
+	case c.ctxLines == 0:
+		clb = lb - c.ctxLines
+	case i != len(c.chunks)-1:
+		next := c.chunks[i+1]
+		if next.Type() == op || next.Type() == Equal {
+			// this diff will be into this chunk
+			clb = lb + 1
+		}
+	}
+
+	return
+}
+
+func (c *hunksGenerator) processEqualsLines(ls []string, i int) {
+	if c.current == nil {
+		c.beforeContext = append(c.beforeContext, ls...)
+		return
+	}
+
+	c.afterContext = append(c.afterContext, ls...)
+	if len(c.afterContext) <= c.ctxLines*2 && i != len(c.chunks)-1 {
+		c.current.AddOp(Equal, c.afterContext...)
+		c.afterContext = nil
+	} else {
+		c.current.AddOp(Equal, c.afterContext[:c.ctxLines]...)
+		c.hunks = append(c.hunks, c.current)
+
+		c.current = nil
+		c.beforeContext = c.afterContext[c.ctxLines:]
+		c.afterContext = nil
+	}
+}
+
+func splitLines(s string) []string {
+	out := strings.Split(s, "\n")
+	if out[len(out)-1] == "" {
+		out = out[:len(out)-1]
+	}
+
+	return out
+}
+
+type hunk struct {
+	fromLine int
+	toLine   int
+
+	fromCount int
+	toCount   int
+
+	ctxPrefix string
+	ops       []*op
+}
+
+func (c *hunk) WriteTo(buf *bytes.Buffer) {
+	buf.WriteString(chunkStart)
+
+	if c.fromCount == 1 {
+		fmt.Fprintf(buf, "%d", c.fromLine)
+	} else {
+		fmt.Fprintf(buf, chunkCount, c.fromLine, c.fromCount)
+	}
+
+	buf.WriteString(chunkMiddle)
+
+	if c.toCount == 1 {
+		fmt.Fprintf(buf, "%d", c.toLine)
+	} else {
+		fmt.Fprintf(buf, chunkCount, c.toLine, c.toCount)
+	}
+
+	fmt.Fprintf(buf, chunkEnd, c.ctxPrefix)
+
+	for _, d := range c.ops {
+		buf.WriteString(d.String())
+	}
+}
+
+func (c *hunk) AddOp(t Operation, s ...string) {
+	ls := len(s)
+	switch t {
+	case Add:
+		c.toCount += ls
+	case Delete:
+		c.fromCount += ls
+	case Equal:
+		c.toCount += ls
+		c.fromCount += ls
+	}
+
+	for _, l := range s {
+		c.ops = append(c.ops, &op{l, t})
+	}
+}
+
+type op struct {
+	text string
+	t    Operation
+}
+
+func (o *op) String() string {
+	var prefix string
+	switch o.t {
+	case Add:
+		prefix = addLine
+	case Delete:
+		prefix = deleteLine
+	case Equal:
+		prefix = equalLine
+	}
+
+	return fmt.Sprintf(prefix, o.text)
+}