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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 2012 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;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.Ordering;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.List;

/**
 * Replaces user-visible messages with appropriate calls to
 * chrome.i18n.getMessage. The first argument to getMessage is the id of the
 * message, as a string. If the message contains placeholders, the second
 * argument is an array of the values being used for the placeholders, sorted
 * by placeholder name.
 */
@GwtIncompatible("JsMessage")
class ReplaceMessagesForChrome extends JsMessageVisitor {

  ReplaceMessagesForChrome(AbstractCompiler compiler,
      JsMessage.IdGenerator idGenerator,
      boolean checkDuplicatedMessages, JsMessage.Style style) {

    super(compiler, checkDuplicatedMessages, style, idGenerator);
  }

  private static Node getChromeI18nGetMessageNode(String messageId) {
    Node chromeI18n = IR.getprop(IR.name("chrome"), IR.string("i18n"));
    Node getMessage =  IR.getprop(chromeI18n, IR.string("getMessage"));
    return IR.call(getMessage, IR.string(messageId));
  }

  @Override
  protected void processJsMessage(
      JsMessage message, JsMessageDefinition definition) {
    try {
      Node msgNode = definition.getMessageNode();
      Node newValue = getNewValueNode(msgNode, message);
      newValue.useSourceInfoIfMissingFromForTree(msgNode);

      msgNode.replaceWith(newValue);
      compiler.reportChangeToEnclosingScope(newValue);
    } catch (MalformedException e) {
      compiler.report(JSError.make(e.getNode(),
          MESSAGE_TREE_MALFORMED, e.getMessage()));
    }
  }

  private Node getNewValueNode(Node origNode, JsMessage message)
      throws MalformedException {
    Node newValueNode = getChromeI18nGetMessageNode(message.getId());

    boolean isHtml = isHtml(origNode);
    if (!message.placeholders().isEmpty() || isHtml) {
      Node placeholderValues = origNode.getChildAtIndex(2);
      checkNode(placeholderValues, Token.OBJECTLIT);

      // Output the placeholders, sorted alphabetically by placeholder name,
      // regardless of what order they appear in the original message.
      List placeholderNames = Ordering.natural().sortedCopy(message.placeholders());

      Node placeholderValueArray = IR.arraylit();
      for (String name : placeholderNames) {
        Node value = getPlaceholderValue(placeholderValues, name);
        if (value == null) {
          throw new MalformedException(
              "No value was provided for placeholder " + name,
              origNode);
        }
        placeholderValueArray.addChildToBack(value);
      }
      if (isHtml) {
        Node args = IR.arraylit(IR.string(message.getId()), placeholderValueArray);
        Node options = IR.arraylit(IR.objectlit(IR.stringKey("escapeLt", IR.trueNode())));
        Node regexp = IR.regexp(IR.string("Chrome\\/(\\d+)"));
        Node userAgent = NodeUtil.newQName(compiler, "navigator.userAgent");
        Node version =
            IR.getelem(
                IR.or(IR.call(IR.getprop(regexp, "exec"), userAgent), IR.arraylit()), IR.number(1));
        Node condition = IR.ge(version, IR.number(79));
        args = IR.call(IR.getprop(args, "concat"), IR.hook(condition, options, IR.arraylit()));
        newValueNode =
            IR.call(
                NodeUtil.newQName(compiler, "chrome.i18n.getMessage.apply"), IR.nullNode(), args);
      } else {
        newValueNode.addChildToBack(placeholderValueArray);
      }
    }

    newValueNode.useSourceInfoIfMissingFromForTree(origNode);
    return newValueNode;
  }

  private boolean isHtml(Node node) throws MalformedException {
    if (node.getChildCount() > 3) {
      Node options = node.getChildAtIndex(3);
      checkNode(options, Token.OBJECTLIT);
      for (Node opt = options.getFirstChild(); opt != null; opt = opt.getNext()) {
        checkNode(opt, Token.STRING_KEY);
        if (opt.getString().equals("html")) {
          return opt.getFirstChild().isTrue();
        }
      }
    }
    return false;
  }

  private static Node getPlaceholderValue(
      Node placeholderValues, String placeholderName) {
    for (Node key : placeholderValues.children()) {
      if (key.getString().equals(placeholderName)) {
        return key.getFirstChild().cloneTree();
      }
    }
    return null;
  }
}