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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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/*
 * Copyright 2014 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.refactoring;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.base.Ascii;
import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import java.util.LinkedHashSet;

/**
 * Implements {@see go/js-style#file-goog-require} for selecting import aliases.
 *
 * This imeplementation is a heuristic for selecting a likely good alias. In addition to
 * conforming to the style guide, the ideal heurisitc is simple engough to explain in a few bullets,
 * in priority order:
 *
 * 

 *   Alias never collides with a name already in use in the same file
 *   
Alias is not blacklisted
 *   
Alias is always only composed of segments of the full namespace
 * 
 */
final class RequireNameShortener {

  private static final ImmutableSet BLACKLISTED_ALIASES = createBlacklistedAliases();

  private static ImmutableSet createBlacklistedAliases() {
    ImmutableSet seeds =
        ImmutableSet.of(
            "", //
            "array",
            "event",
            "map",
            "math",
            "object",
            "promise",
            "set",
            "string",
            "thenable");

    ImmutableSet.Builder builder = ImmutableSet.builder();
    for (String seed : seeds) {
      builder.add(upperCaseFirstChar(seed));
      builder.add(Ascii.toLowerCase(seed));
    }
    return builder.build();
  }

  private static final Splitter DOT_SPLITTER = Splitter.on('.');

  private final LinkedHashSet namesInUse = new LinkedHashSet<>(BLACKLISTED_ALIASES);

  static String shorten(String namespace, Node script) {
    checkArgument(script.isScript() || script.isModuleBody());

    RequireNameShortener shortener = new RequireNameShortener();
    shortener.recordNamesInUse(script, false);
    return shortener.shortenInternal(namespace);
  }

  private RequireNameShortener() {}

  private String shortenInternal(String namespace) {
    ImmutableList parts = ImmutableList.copyOf(DOT_SPLITTER.split(namespace)).reverse();
    String lastPart = parts.get(0);
    boolean shouldUpperCaseFirstChar = Ascii.isUpperCase(lastPart.charAt(0));

    String result = "";

    for (String part : parts) {
      if (this.isValidAlias(result)) {
        return result;
      }

      if (shouldUpperCaseFirstChar) {
        part = upperCaseFirstChar(part);
      }
      result = part + upperCaseFirstChar(result);
    }

    final String allParts = result;

    for (int i = 0; !this.isValidAlias(result); i++) {
      result = allParts + i;
    }

    return result;
  }

  private boolean isValidAlias(String alias) {
    return !this.namesInUse.contains(alias);
  }

  private void recordNamesInUse(Node n, boolean isJsdoc) {
    if (isJsdoc) {
      if (n.isString()) {
        this.namesInUse.add(DOT_SPLITTER.split(n.getString()).iterator().next());
      }
    } else {
      if (n.isName()) {
        this.namesInUse.add(n.getString());
      }
    }

    JSDocInfo jsdoc = n.getJSDocInfo();
    if (jsdoc != null) {
      for (Node expr : jsdoc.getTypeNodes()) {
        this.recordNamesInUse(expr, true);
      }
    }

    for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
      this.recordNamesInUse(c, isJsdoc);
    }
  }

  private static String upperCaseFirstChar(String w) {
    if (w.isEmpty() || Ascii.isUpperCase(w.charAt(0))) {
      return w;
    }

    return Ascii.toUpperCase(w.charAt(0)) + w.substring(1);
  }
}