From 42914c81df5d742efd98d951a0cc3806a1249c8b Mon Sep 17 00:00:00 2001
From: Billy Keyes <bluekeyes@gmail.com>
Date: Sun, 10 Mar 2019 21:48:59 -0700
Subject: [PATCH] Create parser skeleton and utilities

---
 gitdiff/gitdiff.go | 10 ++++++
 gitdiff/parser.go  | 80 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 gitdiff/gitdiff.go
 create mode 100644 gitdiff/parser.go

diff --git a/gitdiff/gitdiff.go b/gitdiff/gitdiff.go
new file mode 100644
index 0000000..b1c5d4c
--- /dev/null
+++ b/gitdiff/gitdiff.go
@@ -0,0 +1,10 @@
+package gitdiff
+
+// File describes changes to a single file. It can be either a text file or a
+// binary file.
+type File struct {
+	Fragments []*Fragment
+}
+
+// Fragment describes changed lines starting at a specific line in a text file.
+type Fragment struct{}
diff --git a/gitdiff/parser.go b/gitdiff/parser.go
new file mode 100644
index 0000000..7a85fd5
--- /dev/null
+++ b/gitdiff/parser.go
@@ -0,0 +1,80 @@
+package gitdiff
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+)
+
+// Parse parses a patch with changes for one or more files. Any content
+// preceding the first file header is ignored. If an error occurs while
+// parsing, files will contain all files parsed before the error.
+func Parse(r io.Reader) (files []*File, err error) {
+	p := &parser{r: bufio.NewReader(r)}
+
+	var file *File
+	for {
+		file, err = p.ParseNextFileHeader()
+		if err != nil {
+			return
+		}
+		if file == nil {
+			break
+		}
+
+		err = p.ParseFileChanges(file)
+		if err != nil {
+			return
+		}
+
+		files = append(files, file)
+	}
+
+	return files, nil
+}
+
+type parser struct {
+	r        *bufio.Reader
+	lineno   int64
+	nextLine string
+}
+
+// ParseNextFileHeader finds and parses the next file header in the stream. It
+// returns nil if no headers are found before the end of the stream.
+func (p *parser) ParseNextFileHeader() (*File, error) {
+	panic("unimplemented")
+}
+
+// ParseFileChanges parses file changes until the next file header or the end
+// of the stream and attaches them to the given file.
+func (p *parser) ParseFileChanges(f *File) error {
+	panic("unimplemented")
+}
+
+// Line reads and returns the next line.
+func (p *parser) Line() (line string, err error) {
+	if p.nextLine != "" {
+		line = p.nextLine
+		p.nextLine = ""
+	} else {
+		line, err = p.r.ReadString('\n')
+	}
+	p.lineno++
+	return
+}
+
+// PeekLine reads and returns the next line without advancing the parser.
+func (p *parser) PeekLine() (line string, err error) {
+	if p.nextLine != "" {
+		line = p.nextLine
+	} else {
+		line, err = p.r.ReadString('\n')
+	}
+	p.nextLine = line
+	return
+}
+
+// Errorf generates an error and appends the current line information.
+func (p *parser) Errorf(msg string, args ...interface{}) error {
+	return fmt.Errorf("gitdiff: line %d: %s", p.lineno, fmt.Sprintf(msg, args...))
+}