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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;

import com.google.common.collect.HashMultiset;
import com.google.common.collect.Multiset;
import java.io.Serializable;

/**
 * Generates unique String Ids when requested via a compiler instance.
 *
 * This supplier provides Ids that are deterministic and unique across all input files given to
 * the compiler. The generated ID format is: uniqueId = "fileHashCode$counterForThisFile"
 */
public final class UniqueIdSupplier implements Serializable {
  private final Multiset counter;

  UniqueIdSupplier() {
    counter = HashMultiset.create();
  }

  /**
   * Creates and returns a unique Id across all compiler input source files.
   *
   * @param input The compiler input for which the unique Id is requested.
   * @return unique ID as String
   */
  public String getUniqueId(CompilerInput input) {
    String filePath = input.getSourceFile().getName();
    int fileHashCode = filePath.hashCode();
    int id = counter.add(fileHashCode, 1);
    String fileHashString = (fileHashCode < 0) ? ("m" + -fileHashCode) : ("" + fileHashCode);
    return fileHashString + "$" + id;
  }
}