// Copyright 2019 The Fuchsia 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 gotidy

import (
	"fmt"
	"go/scanner"
	"go/token"
	"strings"
)

var (
	copyrightTemplate = strings.TrimSpace(`
// Copyright %d The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.`)
)

// AddCopyrightHeader inserts the Fuchsia copyright header into a file if no copyright
// header is present.
type AddCopyrightHeader struct {
	Year int
}

func (t *AddCopyrightHeader) Tidy(input []byte) ([]byte, error) {
	var s scanner.Scanner
	fset := token.NewFileSet()
	file := fset.AddFile("", fset.Base(), len(input)) // register file
	s.Init(file, input, nil /* no error handler */, scanner.ScanComments)

	for {
		pos, tok, literal := s.Scan()
		// We scanned the entire file without finding the header.
		if tok == token.EOF {
			return t.addCopyrightHeader(input)
		}

		// We moved past the start of the file. It's missing the header.
		if tok == token.COMMENT && pos > 1 {
			return t.addCopyrightHeader(input)
		}

		if tok == token.COMMENT {
			// The file starts with a comment and it has the header
			if strings.HasPrefix(strings.ToLower(literal), "// copyright") {
				return input, nil
			}
			return t.addCopyrightHeader(input)
		}
	}
}

func (t *AddCopyrightHeader) addCopyrightHeader(input []byte) ([]byte, error) {
	header := fmt.Sprintf(copyrightTemplate, t.Year)
	return []byte(header + "\n\n" + string(input)), nil
}