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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;
import java.util.Collection;
import java.util.Map;

/**
 * GWT-compatible helper for dealing with Java .properties files. The format is probably not fully
 * parsed by this code, but is suitable for simple use-cases inside Closure.
 */
public class GwtProperties {
  private final Map contents;

  private GwtProperties(Map contents) {
    this.contents = contents;
  }

  /**
   * @param key Property key to retrieve.
   * @return The string value of this key.
   */
  public String getProperty(String key) {
    return contents.get(key);
  }

  /** @return The collection of property names. */
  public Collection propertyNames() {
    return contents.keySet();
  }

  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) {
    if (line.contains(":") || line.contains("=")) {
      if (line.indexOf(':') == -1) {
        return line.indexOf('=');
      }
      if (line.indexOf('=') == -1) {
        return line.indexOf(':');
      }
      // Both delimeters exist!
      return Math.min(line.indexOf('='), line.indexOf(':'));
    }
    // If no : or =, delimiter is first whitespace.
    return line.indexOf(' ');
  }
  /**
   * Constructs a new {@link GwtProperties} from the given source string.
   *
   * @param source To load from.
   * @return The {@link GwtProperties} object from the source.
   */
  public static GwtProperties load(String source) {
    String[] lines = source.split("\r?\n");
    ImmutableMap.Builder builder = ImmutableMap.builder();

    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 !
      }

      String data = "";

      int delimeterIndex = findDelimiter(line);
      if (delimeterIndex == -1) {
        continue;
      }
      // 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 new GwtProperties(builder.build());
    }

  }