// Copyright 2021 Google Inc. All rights reserved.
//
// 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.

package response

import (
	"io"
	"io/ioutil"
	"unicode"
)

const noQuote = '\x00'

// ReadRspFile reads a file in Ninja's response file format and returns its contents.
func ReadRspFile(r io.Reader) ([]string, error) {
	var files []string
	var file []byte

	buf, err := ioutil.ReadAll(r)
	if err != nil {
		return nil, err
	}

	isEscaping := false
	quotingStart := byte(noQuote)
	for _, c := range buf {
		switch {
		case isEscaping:
			if quotingStart == '"' {
				if !(c == '"' || c == '\\') {
					// '\"' or '\\' will be escaped under double quoting.
					file = append(file, '\\')
				}
			}
			file = append(file, c)
			isEscaping = false
		case c == '\\' && quotingStart != '\'':
			isEscaping = true
		case quotingStart == noQuote && (c == '\'' || c == '"'):
			quotingStart = c
		case quotingStart != noQuote && c == quotingStart:
			quotingStart = noQuote
		case quotingStart == noQuote && unicode.IsSpace(rune(c)):
			// Current character is a space outside quotes
			if len(file) != 0 {
				files = append(files, string(file))
			}
			file = file[:0]
		default:
			file = append(file, c)
		}
	}

	if len(file) != 0 {
		files = append(files, string(file))
	}

	return files, nil
}