// Copyright 2020 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.

// +build ignore

// This file generates exceptions.gen.go.
// It builds a map from the files in the subdirectory "exception-files".
// Run by a "go:generate" comment in licenses.go.

package main

import (
	"bytes"
	"crypto/sha256"
	"errors"
	"fmt"
	"go/format"
	"io/ioutil"
	"log"
	"path/filepath"
	"strings"
)

const outfile = "exceptions.gen.go"

type fileData struct {
	key    [sha256.Size]byte
	source string
	types  []string
}

func main() {
	files, err := filepath.Glob(filepath.Join("exception-files", "*"))
	if err != nil {
		log.Fatal(err)
	}
	if len(files) == 0 {
		log.Fatal("no files")
	}

	out := new(bytes.Buffer)

	fmt.Fprint(out, `
// Copyright 2020 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.

// Code generated by gen_data.go; DO NOT EDIT.

package licenses

import (
	"bytes"
	"crypto/sha256"
)

// exceptionFileTypesMap maps SHAs of normalized licenses (see the exceptionKey function)
// to a list of types for each license.
var exceptionFileTypesMap = map[[sha256.Size]byte][]string{
`)

	for _, file := range files {
		base := filepath.Base(file)
		if base == "README" {
			continue
		}
		// Ignore common editor backup files.
		if strings.HasSuffix(base, "~") || strings.HasSuffix(base, ".swp") {
			continue
		}
		data, err := readFile(file)
		if err != nil {
			log.Fatalf("%s: %v", file, err)
		}
		fmt.Fprintf(out, "\n// file %s\n", base)
		fmt.Fprintf(out, "// from %s\n", data.source)
		fmt.Fprintf(out, "\t%#v: %#v,\n", data.key, data.types)
	}
	fmt.Fprintf(out, "}\n")
	fmt.Fprintln(out, exceptionKeyText)

	src, err := format.Source(out.Bytes())
	if err != nil {
		fmt.Println(string(out.Bytes()))
		log.Fatalf("format.Source: %v", err)
	}
	if err := ioutil.WriteFile(outfile, src, 0640); err != nil {
		log.Fatal(err)
	}
	fmt.Printf("wrote %s\n", outfile)
}

func readFile(file string) (_ *fileData, err error) {
	data, err := ioutil.ReadFile(file)
	if err != nil {
		return nil, err
	}
	parts := bytes.SplitN(data, []byte("\n\n"), 2)
	if len(parts) != 2 {
		return nil, errors.New("missing blank line separating header")
	}
	header, err := parseHeader(parts[0])
	if err != nil {
		return nil, err
	}
	source := header["source"]
	types := header["types"]
	if source == "" || types == "" {
		log.Fatal("%s: missing header: source=%q, types=%q", file, source, types)
	}
	return &fileData{
		key:    exceptionKey(parts[1]),
		source: source,
		types:  strings.Fields(types),
	}, nil
}

func parseHeader(h []byte) (map[string]string, error) {
	m := map[string]string{}
	lines := strings.Split(string(h), "\n")
	for _, l := range lines {
		kv := strings.SplitN(l, ":", 2)
		if len(kv) != 2 {
			return nil, fmt.Errorf("malformed header line %q", l)
		}
		m[strings.TrimSpace(kv[0])] = strings.TrimSpace(kv[1])
	}
	return m, nil
}

// exceptionKey computes the key for the exceptionFileTypesMap.
// Keep in sync with exceptionKeyText, below.
func exceptionKey(data []byte) [sha256.Size]byte {
	norm := bytes.Join(bytes.Fields(bytes.ToLower(data)), []byte{' '})
	return sha256.Sum256(norm)
}

const exceptionKeyText = `
// exceptionKey computes the key for the exceptionFileTypesMap.
func exceptionKey(data []byte) [sha256.Size]byte {
	norm := bytes.Join(bytes.Fields(bytes.ToLower(data)), []byte{' '})
	return sha256.Sum256(norm)
}
`