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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * 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 com.google.javascript.jscomp.resources;

import com.google.common.collect.ImmutableMap;

/**
 * Parses a Java properties file in a a way that can be transpiled into JS.
 *
 * The format is probably not fully parsed by this code, but is suitable for simple use-cases
 * inside Closure.
 */
final class PropertiesParser {

  @SuppressWarnings("StringSplitter") // Can't use Splitter.onPattern in J2CL.
  static ImmutableMap parse(String source) {
    ImmutableMap.Builder builder = ImmutableMap.builder();

    String[] lines = source.split("\r?\n");
    for (int i = 0; i < lines.length; ++i) {
      String line = lines[i];
      if (line.isEmpty() || line.startsWith("#") || line.startsWith("!")) {
        continue; // skip if empty or starts with # or !
      }

      int delimeterIndex = findDelimiter(line);
      if (delimeterIndex == -1) {
        continue;
      }

      String data = "";
      // Remove whitespace on both sides of key.
      String key = line.substring(0, delimeterIndex).trim();
      // Remove whitespace only on left side of data value. Trailing white space is data.
      line = trimLeft(line.substring(delimeterIndex + 1));
      while (true) {
        if (line.endsWith("\\")) {
          data += line.substring(0, line.length() - 1);
          if (i + 1 == lines.length) {
            break;
          }
          line = trimLeft(lines[++i]);
        } else {
          data += line;
          break;
        }
      }

      builder.put(key, data);
    }

    return builder.buildOrThrow();
  }

  private static String trimLeft(String str) {
    for (int i = 0; i < str.length(); i++) {
      if (str.charAt(i) != ' ') {
        return str.substring(i);
      }
    }
    return str;
  }

  private static int findDelimiter(String line) {
    for (int i = 0; i < line.length(); i++) {
      switch (line.charAt(i)) {
        case ':':
        case '=':
          return i;
        default:
          break;
      }
    }

    // If no : or =, delimiter is first whitespace.
    return line.indexOf(' ');
  }

  private PropertiesParser() {}
}