code: /*
   * Copyright (C) 2011 Google Inc.
   *
   * 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 tools.com.google.gson.internal.bind;
  
  import tools.com.google.gson.Gson;
  import tools.com.google.gson.JsonElement;
  import tools.com.google.gson.JsonPrimitive;
  import tools.com.google.gson.JsonSyntaxException;
  import tools.com.google.gson.TypeAdapter;
  import tools.com.google.gson.TypeAdapterFactory;
  import tools.com.google.gson.internal.$Gson$Types;
  import tools.com.google.gson.internal.ConstructorConstructor;
  import tools.com.google.gson.internal.JsonReaderInternalAccess;
  import tools.com.google.gson.internal.ObjectConstructor;
  import tools.com.google.gson.internal.Streams;
  import tools.com.google.gson.reflect.TypeToken;
  import tools.com.google.gson.stream.JsonReader;
  import tools.com.google.gson.stream.JsonToken;
  import tools.com.google.gson.stream.JsonWriter;
  import java.io.IOException;
  import java.lang.reflect.Type;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Map;
  
  /**
   * Adapts maps to either JSON objects or JSON arrays.
   *
   * <h3>Maps as JSON objects</h3>
   * For primitive keys or when complex map key serialization is not enabled, this
   * converts Java {@link Map Maps} to JSON Objects. This requires that map keys
   * can be serialized as strings; this is insufficient for some key types. For
   * example, consider a map whose keys are points on a grid. The default JSON
   * form encodes reasonably: <pre>   {@code
   *   Map<Point, String> original = new LinkedHashMap<Point, String>();
   *   original.put(new Point(5, 6), "a");
   *   original.put(new Point(8, 8), "b");
   *   System.out.println(gson.toJson(original, type));
   * }</pre>
   * The above code prints this JSON object:<pre>   {@code
   *   {
   *     "(5,6)": "a",
   *     "(8,8)": "b"
   *   }
   * }</pre>
   * But GSON is unable to deserialize this value because the JSON string name is
   * just the {@link Object#toString() toString()} of the map key. Attempting to
   * convert the above JSON to an object fails with a parse exception:
   * <pre>com.google.gson.JsonParseException: Expecting object found: "(5,6)"
   *   at com.google.gson.JsonObjectDeserializationVisitor.visitFieldUsingCustomHandler
   *   at com.google.gson.ObjectNavigator.navigateClassFields
   *   ...</pre>
   *
   * <h3>Maps as JSON arrays</h3>
   * An alternative approach taken by this type adapter when it is required and
   * complex map key serialization is enabled is to encode maps as arrays of map
   * entries. Each map entry is a two element array containing a key and a value.
   * This approach is more flexible because any type can be used as the map's key;
   * not just strings. But it's also less portable because the receiver of such
   * JSON must be aware of the map entry convention.
   *
   * <p>Register this adapter when you are creating your GSON instance.
   * <pre>   {@code
   *   Gson gson = new GsonBuilder()
   *     .registerTypeAdapter(Map.class, new MapAsArrayTypeAdapter())
   *     .create();
   * }</pre>
   * This will change the structure of the JSON emitted by the code above. Now we
   * get an array. In this case the arrays elements are map entries:
   * <pre>   {@code
   *   [
   *     [
   *       {
   *         "x": 5,
   *         "y": 6
   *       },
   *       "a",
   *     ],
   *     [
   *       {
   *         "x": 8,
   *         "y": 8
   *       },
   *       "b"
   *     ]
   *   ]
   * }</pre>
   * This format will serialize and deserialize just fine as long as this adapter
   * is registered.
   */
  public final class MapTypeAdapterFactory implements TypeAdapterFactory {
    private final ConstructorConstructor constructorConstructor;
    final boolean complexMapKeySerialization;
  
    public MapTypeAdapterFactory(ConstructorConstructor constructorConstructor,
        boolean complexMapKeySerialization) {
      this.constructorConstructor = constructorConstructor;
      this.complexMapKeySerialization = complexMapKeySerialization;
    }
  
    @Override public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
      Type type = typeToken.getType();
  
      Class<? super T> rawType = typeToken.getRawType();
      if (!Map.class.isAssignableFrom(rawType)) {
        return null;
      }
  
      Class<?> rawTypeOfSrc = $Gson$Types.getRawType(type);
      Type[] keyAndValueTypes = $Gson$Types.getMapKeyAndValueTypes(type, rawTypeOfSrc);
      TypeAdapter<?> keyAdapter = getKeyAdapter(gson, keyAndValueTypes[0]);
      TypeAdapter<?> valueAdapter = gson.getAdapter(TypeToken.get(keyAndValueTypes[1]));
      ObjectConstructor<T> constructor = constructorConstructor.get(typeToken);
  
      @SuppressWarnings({"unchecked", "rawtypes"})
      // we don't define a type parameter for the key or value types
      TypeAdapter<T> result = new Adapter(gson, keyAndValueTypes[0], keyAdapter,
          keyAndValueTypes[1], valueAdapter, constructor);
      return result;
    }
  
    /**
     * Returns a type adapter that writes the value as a string.
     */
    private TypeAdapter<?> getKeyAdapter(Gson context, Type keyType) {
      return (keyType == boolean.class || keyType == Boolean.class)
          ? TypeAdapters.BOOLEAN_AS_STRING
          : context.getAdapter(TypeToken.get(keyType));
    }
  
    private final class Adapter<K, V> extends TypeAdapter<Map<K, V>> {
      private final TypeAdapter<K> keyTypeAdapter;
      private final TypeAdapter<V> valueTypeAdapter;
      private final ObjectConstructor<? extends Map<K, V>> constructor;
  
      public Adapter(Gson context, Type keyType, TypeAdapter<K> keyTypeAdapter,
          Type valueType, TypeAdapter<V> valueTypeAdapter,
          ObjectConstructor<? extends Map<K, V>> constructor) {
        this.keyTypeAdapter =
          new TypeAdapterRuntimeTypeWrapper<K>(context, keyTypeAdapter, keyType);
        this.valueTypeAdapter =
          new TypeAdapterRuntimeTypeWrapper<V>(context, valueTypeAdapter, valueType);
        this.constructor = constructor;
      }
  
      @Override public Map<K, V> read(JsonReader in) throws IOException {
        JsonToken peek = in.peek();
        if (peek == JsonToken.NULL) {
          in.nextNull();
          return null;
        }
  
        Map<K, V> map = constructor.construct();
  
        if (peek == JsonToken.BEGIN_ARRAY) {
          in.beginArray();
          while (in.hasNext()) {
            in.beginArray(); // entry array
            K key = keyTypeAdapter.read(in);
            V value = valueTypeAdapter.read(in);
            V replaced = map.put(key, value);
            if (replaced != null) {
              throw new JsonSyntaxException("duplicate key: " + key);
            }
            in.endArray();
          }
          in.endArray();
        } else {
          in.beginObject();
          while (in.hasNext()) {
            JsonReaderInternalAccess.INSTANCE.promoteNameToValue(in);
            K key = keyTypeAdapter.read(in);
            V value = valueTypeAdapter.read(in);
            V replaced = map.put(key, value);
            if (replaced != null) {
              throw new JsonSyntaxException("duplicate key: " + key);
            }
          }
          in.endObject();
        }
        return map;
      }
  
      @Override public void write(JsonWriter out, Map<K, V> map) throws IOException {
        if (map == null) {
          out.nullValue();
          return;
        }
  
        if (!complexMapKeySerialization) {
          out.beginObject();
          for (Map.Entry<K, V> entry : map.entrySet()) {
            out.name(String.valueOf(entry.getKey()));
            valueTypeAdapter.write(out, entry.getValue());
          }
          out.endObject();
          return;
        }
  
        boolean hasComplexKeys = false;
        List<JsonElement> keys = new ArrayList<JsonElement>(map.size());
  
        List<V> values = new ArrayList<V>(map.size());
        for (Map.Entry<K, V> entry : map.entrySet()) {
          JsonElement keyElement = keyTypeAdapter.toJsonTree(entry.getKey());
          keys.add(keyElement);
          values.add(entry.getValue());
          hasComplexKeys |= keyElement.isJsonArray() || keyElement.isJsonObject();
        }
  
        if (hasComplexKeys) {
          out.beginArray();
          for (int i = 0, size = keys.size(); i < size; i++) {
            out.beginArray(); // entry array
            Streams.write(keys.get(i), out);
            valueTypeAdapter.write(out, values.get(i));
            out.endArray();
          }
          out.endArray();
        } else {
          out.beginObject();
          for (int i = 0, size = keys.size(); i < size; i++) {
            JsonElement keyElement = keys.get(i);
            out.name(keyToString(keyElement));
            valueTypeAdapter.write(out, values.get(i));
          }
          out.endObject();
        }
      }
  
      private String keyToString(JsonElement keyElement) {
        if (keyElement.isJsonPrimitive()) {
          JsonPrimitive primitive = keyElement.getAsJsonPrimitive();
          if (primitive.isNumber()) {
            return String.valueOf(primitive.getAsNumber());
          } else if (primitive.isBoolean()) {
            return Boolean.toString(primitive.getAsBoolean());
          } else if (primitive.isString()) {
            return primitive.getAsString();
          } else {
            throw new AssertionError();
          }
        } else if (keyElement.isJsonNull()) {
          return "null";
        } else {
          throw new AssertionError();
        }
      }
    }
  }
  