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.JsonArray;
  import tools.com.google.gson.JsonElement;
  import tools.com.google.gson.JsonNull;
  import tools.com.google.gson.JsonObject;
  import tools.com.google.gson.JsonPrimitive;
  import tools.com.google.gson.stream.JsonWriter;
  import java.io.IOException;
  import java.io.Writer;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * This writer creates a JsonElement.
   */
  public final class JsonTreeWriter extends JsonWriter {
    private static final Writer UNWRITABLE_WRITER = new Writer() {
      @Override public void write(char[] buffer, int offset, int counter) {
        throw new AssertionError();
      }
      @Override public void flush() throws IOException {
        throw new AssertionError();
      }
      @Override public void close() throws IOException {
        throw new AssertionError();
      }
    };
    /** Added to the top of the stack when this writer is closed to cause following ops to fail. */
    private static final JsonPrimitive SENTINEL_CLOSED = new JsonPrimitive("closed");
  
    /** The JsonElements and JsonArrays under modification, outermost to innermost. */
    private final List<JsonElement> stack = new ArrayList<JsonElement>();
  
    /** The name for the next JSON object value. If non-null, the top of the stack is a JsonObject. */
    private String pendingName;
  
    /** the JSON element constructed by this writer. */
    private JsonElement product = JsonNull.INSTANCE; // TODO: is this really what we want?;
  
    public JsonTreeWriter() {
      super(UNWRITABLE_WRITER);
    }
  
    /**
     * Returns the top level object produced by this writer.
     */
    public JsonElement get() {
      if (!stack.isEmpty()) {
        throw new IllegalStateException("Expected one JSON element but was " + stack);
      }
      return product;
    }
  
    private JsonElement peek() {
      return stack.get(stack.size() - 1);
    }
  
    private void put(JsonElement value) {
      if (pendingName != null) {
        if (!value.isJsonNull() || getSerializeNulls()) {
          JsonObject object = (JsonObject) peek();
          object.add(pendingName, value);
        }
        pendingName = null;
      } else if (stack.isEmpty()) {
        product = value;
      } else {
        JsonElement element = peek();
        if (element instanceof JsonArray) {
          ((JsonArray) element).add(value);
        } else {
          throw new IllegalStateException();
        }
      }
    }
  
    @Override public JsonWriter beginArray() throws IOException {
      JsonArray array = new JsonArray();
      put(array);
      stack.add(array);
      return this;
    }
  
    @Override public JsonWriter endArray() throws IOException {
      if (stack.isEmpty() || pendingName != null) {
        throw new IllegalStateException();
      }
      JsonElement element = peek();
      if (element instanceof JsonArray) {
        stack.remove(stack.size() - 1);
        return this;
      }
      throw new IllegalStateException();
    }
  
    @Override public JsonWriter beginObject() throws IOException {
      JsonObject object = new JsonObject();
      put(object);
      stack.add(object);
      return this;
    }
  
    @Override public JsonWriter endObject() throws IOException {
      if (stack.isEmpty() || pendingName != null) {
        throw new IllegalStateException();
      }
      JsonElement element = peek();
      if (element instanceof JsonObject) {
        stack.remove(stack.size() - 1);
        return this;
      }
      throw new IllegalStateException();
    }
  
    @Override public JsonWriter name(String name) throws IOException {
      if (stack.isEmpty() || pendingName != null) {
        throw new IllegalStateException();
      }
      JsonElement element = peek();
      if (element instanceof JsonObject) {
        pendingName = name;
        return this;
      }
      throw new IllegalStateException();
    }
  
    @Override public JsonWriter value(String value) throws IOException {
      if (value == null) {
        return nullValue();
      }
      put(new JsonPrimitive(value));
      return this;
    }
  
    @Override public JsonWriter nullValue() throws IOException {
      put(JsonNull.INSTANCE);
      return this;
    }
  
    @Override public JsonWriter value(boolean value) throws IOException {
      put(new JsonPrimitive(value));
      return this;
    }
  
    @Override public JsonWriter value(Boolean value) throws IOException {
      if (value == null) {
        return nullValue();
      }
      put(new JsonPrimitive(value));
      return this;
    }
  
    @Override public JsonWriter value(double value) throws IOException {
      if (!isLenient() && (Double.isNaN(value) || Double.isInfinite(value))) {
        throw new IllegalArgumentException("JSON forbids NaN and infinities: " + value);
      }
      put(new JsonPrimitive(value));
      return this;
    }
  
    @Override public JsonWriter value(long value) throws IOException {
      put(new JsonPrimitive(value));
      return this;
    }
  
    @Override public JsonWriter value(Number value) throws IOException {
      if (value == null) {
        return nullValue();
      }
  
      if (!isLenient()) {
        double d = value.doubleValue();
        if (Double.isNaN(d) || Double.isInfinite(d)) {
          throw new IllegalArgumentException("JSON forbids NaN and infinities: " + value);
        }
      }
  
      put(new JsonPrimitive(value));
      return this;
    }
  
    @Override public void flush() throws IOException {
    }
  
    @Override public void close() throws IOException {
      if (!stack.isEmpty()) {
        throw new IOException("Incomplete document");
      }
      stack.add(SENTINEL_CLOSED);
    }
  }
  