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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 2017 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.deps;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.javascript.jscomp.ErrorHandler;
import com.google.javascript.jscomp.deps.ModuleLoader.PathEscaper;
import java.util.Map;
import org.jspecify.nullness.Nullable;

/** Base class for algorithms that resolve JavaScript module references to input files. */
public abstract class ModuleResolver {
  /** The set of all known input module URIs (including trailing .js), after normalization. */
  protected final ImmutableSet modulePaths;

  /** Root URIs to match module roots against. */
  protected final ImmutableList moduleRootPaths;

  protected ErrorHandler errorHandler;
  private final PathEscaper pathEscaper;

  public ModuleResolver(
      ImmutableSet modulePaths,
      ImmutableList moduleRootPaths,
      ErrorHandler errorHandler,
      PathEscaper pathEscaper) {
    this.modulePaths = modulePaths;
    this.moduleRootPaths = moduleRootPaths;
    this.errorHandler = errorHandler;
    this.pathEscaper = pathEscaper;
  }

  Map getPackageJsonMainEntries() {
    return ImmutableMap.of();
  }

  public abstract @Nullable String resolveJsModule(
      String scriptAddress, String moduleAddress, String sourcename, int lineno, int colno);

  public String resolveModuleAsPath(String scriptAddress, String moduleAddress) {
    if (!moduleAddress.endsWith(".js")) {
      moduleAddress += ".js";
    }
    String path = pathEscaper.escape(moduleAddress);
    if (ModuleLoader.isRelativeIdentifier(moduleAddress)) {
      String ourPath = scriptAddress;
      int lastIndex = ourPath.lastIndexOf(ModuleLoader.MODULE_SLASH);
      path =
          ModuleNames.canonicalizePath(
              ourPath.substring(0, lastIndex + ModuleLoader.MODULE_SLASH.length()) + path);
    }
    return ModuleLoader.normalize(path, moduleRootPaths);
  }

  /**
   * Locates the module with the given name, but returns null if there is no JS file in the expected
   * location.
   */
  protected @Nullable String locate(String scriptAddress, String name) {
    String canonicalizedPath = canonicalizePath(scriptAddress, name);

    String normalizedPath = canonicalizedPath;
    if (ModuleLoader.isAmbiguousIdentifier(canonicalizedPath)) {
      normalizedPath = ModuleLoader.MODULE_SLASH + canonicalizedPath;
    }

    // First check to see if the module is known with it's provided path
    if (modulePaths.contains(normalizedPath)) {
      return canonicalizedPath;
    }

    // Check for the module beneath each of the module roots
    for (String rootPath : moduleRootPaths) {
      String modulePath = rootPath + normalizedPath;

      // Since there might be code that relying on whether the path has a leading slash or not,
      // honor the state it was provided in. In an ideal world this would always be normalized
      // to contain a leading slash.
      if (modulePaths.contains(modulePath)) {
        return canonicalizedPath;
      }
    }

    return null;
  }

  /**
   * Normalizes a module path reference. Includes escaping special characters and converting
   * relative paths to absolute references.
   */
  protected String canonicalizePath(String scriptAddress, String moduleAddress) {
    String path = pathEscaper.escape(moduleAddress);
    if (ModuleLoader.isRelativeIdentifier(moduleAddress)) {
      String ourPath = scriptAddress;
      int lastIndex = ourPath.lastIndexOf(ModuleLoader.MODULE_SLASH);
      path =
          ModuleNames.canonicalizePath(
              ourPath.substring(0, lastIndex + ModuleLoader.MODULE_SLASH.length()) + path);
    }
    return path;
  }

  public void setErrorHandler(ErrorHandler errorHandler) {
    this.errorHandler = errorHandler;
  }
}