// Copyright 2016 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// This program ensures source code files have copyright license headers.
// See usage with "addlicence -h".
package main

import (
	"bytes"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"sync"
	"time"
)

const helpText = `Usage: addlicense [flags] pattern [pattern ...]

The program ensures source code files have copyright license headers
by scanning directory patterns recursively.

It modifies all source files in place and avoids adding a license header
to any file that already has one.

The pattern argument can be provided multiple times, and may also refer
to single files.

Flags:
`

var (
	holder  = flag.String("c", "Google Inc.", "copyright holder")
	license = flag.String("l", "apache", "license type: apache, mit")
	year    = flag.Int("y", time.Now().Year(), "year")
)

func main() {
	flag.Usage = func() {
		fmt.Fprintln(os.Stderr, helpText)
		flag.PrintDefaults()
	}
	flag.Parse()
	if flag.NArg() == 0 {
		flag.Usage()
		os.Exit(1)
	}

	data := &copyrightData{
		Year:   *year,
		Holder: *holder,
	}

	// process at most 1000 files in parallel
	ch := make(chan *file, 1000)
	done := make(chan struct{})
	go func() {
		var wg sync.WaitGroup
		for f := range ch {
			wg.Add(1)
			go func(f *file) {
				err := addLicense(f.path, f.mode, *license, data)
				if err != nil {
					log.Printf("%s: %v", f.path, err)
				}
				wg.Done()
			}(f)
		}
		wg.Wait()
		close(done)
	}()

	for _, d := range flag.Args() {
		walk(ch, d)
	}
	close(ch)
	<-done
}

type file struct {
	path string
	mode os.FileMode
}

func walk(ch chan<- *file, start string) {
	filepath.Walk(start, func(path string, fi os.FileInfo, err error) error {
		if err != nil {
			log.Printf("%s error: %v", path, err)
			return nil
		}
		if fi.IsDir() {
			return nil
		}
		ch <- &file{path, fi.Mode()}
		return nil
	})
}

func addLicense(path string, fmode os.FileMode, typ string, data *copyrightData) error {
	var lic []byte
	var err error
	switch filepath.Ext(path) {
	default:
		return nil
	case ".c", ".h":
		lic, err = prefix(typ, data, "/*", " * ", " */")
	case ".js", ".css":
		lic, err = prefix(typ, data, "/**", " * ", " */")
	case ".cc", ".cpp", ".cs", ".go", ".hh", ".hpp", ".java", ".m", ".mm", ".proto", ".rs", ".scala", ".swift", ".dart":
		lic, err = prefix(typ, data, "", "// ", "")
	case ".py", ".sh":
		lic, err = prefix(typ, data, "", "# ", "")
	case ".el", ".lisp":
		lic, err = prefix(typ, data, "", ";; ", "")
	case ".erl":
		lic, err = prefix(typ, data, "", "% ", "")
	case ".hs":
		lic, err = prefix(typ, data, "", "-- ", "")
	case ".html", ".xml":
		lic, err = prefix(typ, data, "<!--", " ", "-->")
	case ".php":
		lic, err = prefix(typ, data, "<?php", "// ", "?>")
	}
	if err != nil || lic == nil {
		return err
	}

	b, err := ioutil.ReadFile(path)
	if err != nil || hasLicense(b) {
		return err
	}

	line := hashBang(b)
	if len(line) > 0 {
		b = b[len(line):]
		if line[len(line)-1] != '\n' {
			line = append(line, '\n')
		}
		lic = append(line, lic...)
	}
	b = append(lic, b...)
	return ioutil.WriteFile(path, b, fmode)
}

func hashBang(b []byte) []byte {
	var line []byte
	for _, c := range b {
		line = append(line, c)
		if c == '\n' {
			break
		}
	}
	if bytes.HasPrefix(line, []byte("#!")) {
		return line
	}
	return nil
}

func hasLicense(b []byte) bool {
	n := 1000
	if len(b) < 1000 {
		n = len(b)
	}
	return bytes.Contains(bytes.ToLower(b[:n]), []byte("copyright"))
}