// Command pkg-diff-example implements a subset of the diff command using

// github.com/pkg/diff.

package main

import (

"flag"

"fmt"

"io/ioutil"

"log"

"os"

"github.com/pkg/diff"

"github.com/pkg/diff/write"

)

var color = flag.Bool("color", false, "colorize the output")

// check logs a fatal error and exits if err is not nil.

func check(err error) {

if err != nil {

log.Fatal(err)

}

}

func usage() {

fmt.Fprintf(os.Stderr, "pkg-diff-example [flags] file1 file2\n")

flag.PrintDefaults()

os.Exit(2)

}

func main() {

log.SetPrefix("pkg-diff-example: ")

log.SetFlags(0)

flag.Usage = usage

flag.Parse()

var aName, bName string

var a, b interface{}

switch flag.NArg() {

case 2:

// A human has invoked us.

aName, bName = flag.Arg(0), flag.Arg(1)

case 7, 9:

// We are a git external diff tool.

// We have been passed the following arguments:

// path old-file old-hex old-mode new-file new-hex new-mode [new-path similarity-metrics]

aName = "a/" + flag.Arg(0)

if flag.NArg() == 7 {

bName = "b/" + flag.Arg(0)

} else {

bName = "b/" + flag.Arg(7)

}

var err error

a, err = ioutil.ReadFile(flag.Arg(1))

check(err)

b, err = ioutil.ReadFile(flag.Arg(4))

check(err)

default:

flag.Usage()

}

var opts []write.Option

if *color {

opts = append(opts, write.TerminalColor())

}

err := diff.Text(aName, bName, a, b, os.Stdout, opts...)

check(err)

}