// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import (
	"bytes"
	"flag"
	"fmt"
	"go/scanner"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"

	"golang.org/x/tools/imports"
)

var (
	// main operation modes
	list   = flag.Bool("l", false, "list files whose formatting differs from goimport's")
	write  = flag.Bool("w", false, "write result to (source) file instead of stdout")
	doDiff = flag.Bool("d", false, "display diffs instead of rewriting files")
	srcdir = flag.String("srcdir", "", "choose imports as if source code is from `dir`")

	options = &imports.Options{
		TabWidth:  8,
		TabIndent: true,
		Comments:  true,
		Fragment:  true,
	}
	exitCode = 0
)

func init() {
	flag.BoolVar(&options.AllErrors, "e", false, "report all errors (not just the first 10 on different lines)")
}

func report(err error) {
	scanner.PrintError(os.Stderr, err)
	exitCode = 2
}

func usage() {
	fmt.Fprintf(os.Stderr, "usage: goimports [flags] [path ...]\n")
	flag.PrintDefaults()
	os.Exit(2)
}

func isGoFile(f os.FileInfo) bool {
	// ignore non-Go files
	name := f.Name()
	return !f.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go")
}

func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error {
	opt := options
	if stdin {
		nopt := *options
		nopt.Fragment = true
		opt = &nopt
	}

	if in == nil {
		f, err := os.Open(filename)
		if err != nil {
			return err
		}
		defer f.Close()
		in = f
	}

	src, err := ioutil.ReadAll(in)
	if err != nil {
		return err
	}

	target := filename
	if *srcdir != "" {
		// Pretend that file is from *srcdir in order to decide
		// visible imports correctly.
		target = filepath.Join(*srcdir, filepath.Base(filename))
	}

	res, err := imports.Process(target, src, opt)
	if err != nil {
		return err
	}

	if !bytes.Equal(src, res) {
		// formatting has changed
		if *list {
			fmt.Fprintln(out, filename)
		}
		if *write {
			err = ioutil.WriteFile(filename, res, 0)
			if err != nil {
				return err
			}
		}
		if *doDiff {
			data, err := diff(src, res)
			if err != nil {
				return fmt.Errorf("computing diff: %s", err)
			}
			fmt.Printf("diff %s gofmt/%s\n", filename, filename)
			out.Write(data)
		}
	}

	if !*list && !*write && !*doDiff {
		_, err = out.Write(res)
	}

	return err
}

func visitFile(path string, f os.FileInfo, err error) error {
	if err == nil && isGoFile(f) {
		err = processFile(path, nil, os.Stdout, false)
	}
	if err != nil {
		report(err)
	}
	return nil
}

func walkDir(path string) {
	filepath.Walk(path, visitFile)
}

func main() {
	runtime.GOMAXPROCS(runtime.NumCPU())

	// call gofmtMain in a separate function
	// so that it can use defer and have them
	// run before the exit.
	gofmtMain()
	os.Exit(exitCode)
}

// parseFlags parses command line flags and returns the paths to process.
// It's a var so that custom implementations can replace it in other files.
var parseFlags = func() []string {
	flag.Parse()
	return flag.Args()
}

func gofmtMain() {
	flag.Usage = usage
	paths := parseFlags()

	if options.TabWidth < 0 {
		fmt.Fprintf(os.Stderr, "negative tabwidth %d\n", options.TabWidth)
		exitCode = 2
		return
	}

	if len(paths) == 0 {
		if err := processFile("<standard input>", os.Stdin, os.Stdout, true); err != nil {
			report(err)
		}
		return
	}

	for _, path := range paths {
		switch dir, err := os.Stat(path); {
		case err != nil:
			report(err)
		case dir.IsDir():
			walkDir(path)
		default:
			if err := processFile(path, nil, os.Stdout, false); err != nil {
				report(err)
			}
		}
	}
}

func diff(b1, b2 []byte) (data []byte, err error) {
	f1, err := ioutil.TempFile("", "gofmt")
	if err != nil {
		return
	}
	defer os.Remove(f1.Name())
	defer f1.Close()

	f2, err := ioutil.TempFile("", "gofmt")
	if err != nil {
		return
	}
	defer os.Remove(f2.Name())
	defer f2.Close()

	f1.Write(b1)
	f2.Write(b2)

	data, err = exec.Command("diff", "-u", f1.Name(), f2.Name()).CombinedOutput()
	if len(data) > 0 {
		// diff exits with a non-zero status when the files don't match.
		// Ignore that failure as long as we get output.
		err = nil
	}
	return
}