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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.debugging.sourcemap;

import com.google.common.collect.ImmutableList;
import elemental2.core.JSONType;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import jsinterop.annotations.JsPackage;
import jsinterop.annotations.JsProperty;
import jsinterop.annotations.JsType;
import jsinterop.base.Js;
import jsinterop.base.JsPropertyMap;

/**
 * ClientSide implementation of the source map parser using jsinterop.
 *
 * Note: This is invoked through super sourcing of SourceMapObjectParser.
 */
public class SourceMapObjectParserJs {

  @JsProperty(namespace = JsPackage.GLOBAL)
  private static native JSONType getJSON();

  @JsType(
      isNative = true,
      namespace = JsPackage.GLOBAL,
      name = "com_google_debugging_sourcemap_SourceMapObjectParserJs$JsonMap")
  private abstract static class JsonMap implements JsPropertyMap {
    int version;
    String file;
    String mappings;
    String sourceRoot;
    Section[] sections;
    String[] sources;
    String[] names;
  }

  @JsType(
      isNative = true,
      namespace = JsPackage.GLOBAL,
      name = "com_google_debugging_sourcemap_SourceMapObjectParserJs$Section")
  private abstract static class Section {
    Offset offset;
    String url;
    String map;
  }

  @JsType(
      isNative = true,
      namespace = JsPackage.GLOBAL,
      name = "com_google_debugging_sourcemap_SourceMapObjectParserJs$Offset")
  private abstract static class Offset {
    int line;
    int column;
  }

  public static SourceMapObject parse(String contents) throws SourceMapParseException {
    JsonMap sourceMap = Js.uncheckedCast(getJSON().parse(contents));
    SourceMapObject.Builder builder = SourceMapObject.builder();

    builder.setVersion(sourceMap.version);
    builder.setFile(sourceMap.file);
    // Line count is no longer part of the source map spec. -1 is the magic "not provided" value
    builder.setLineCount(-1);
    builder.setMappings(sourceMap.mappings);
    builder.setSourceRoot(sourceMap.sourceRoot);

    if (sourceMap.sections != null) {
      ImmutableList.Builder listBuilder = ImmutableList.builder();
      for (Section section : sourceMap.sections) {
        listBuilder.add(buildSection(section));
      }
      builder.setSections(listBuilder.build());
    } else {
      builder.setSections(null);
    }

    builder.setSources(sourceMap.sources);
    builder.setNames(sourceMap.names);

    Map extensions = new LinkedHashMap<>();
    sourceMap.forEach(
        (key) -> {
          if (key.startsWith("x_")) {
            extensions.put(key, sourceMap.get(key));
          }
        });
    builder.setExtensions(Collections.unmodifiableMap(extensions));
    return builder.build();
  }

  private static SourceMapSection buildSection(Section section) throws SourceMapParseException {
    int line = section.offset.line;
    int column = section.offset.column;

    if (section.map != null && section.url != null) {
      throw new SourceMapParseException(
          "Invalid map format: section may not have both 'map' and 'url'");
    } else if (section.url != null) {
      return SourceMapSection.forURL(section.url, line, column);
    } else if (section.map != null) {
      return SourceMapSection.forMap(String.valueOf(section.map), line, column);
    }

    throw new SourceMapParseException(
        "Invalid map format: section must have either 'map' or 'url'");
  }
}