PairContext.java

// =================================================================================================
// Copyright 2011 Twitter, Inc.
// -------------------------------------------------------------------------------------------------
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this work except in compliance with the License.
// You may obtain a copy of the License in the LICENSE file, or 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.twitter.common.thrift.text;

import java.util.Iterator;
import java.util.Map;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonPrimitive;

/**
 * A map parsing context that tracks if we are parsing a key, which
 * is on the left hand side of the ":" operator, or a value.
 * Json mandates that keys are strings
 * e.g.
 * {
 *   "1" : 1,
 *   "2" : 2,
 * }
 * Note the required quotes on the lhs.
 * We maintain an iterator over all of our child name/value pairs, and
 * a pointer to the current one being parsed.
 *
 * @author Alex Roetter
 */
class PairContext extends BaseContext {

  private boolean lhs;
  private final Iterator<Map.Entry<String, JsonElement>> children;
  private Map.Entry<String, JsonElement> currentChild;

  /**
   * Create an iterator over this object's children
   */
  protected PairContext(JsonObject json) {
    children = (null != json) ? json.entrySet().iterator() : null;
  }

  @Override
  protected void write() {
    lhs = !lhs;
  }

  @Override
  protected void read() {
    lhs = !lhs;
    // every other time, do a read, since the read gets the name & value
    // at once.
    if (isLhs()) {
      if (!children.hasNext()) {
        throw new RuntimeException(
            "Called PairContext.read() too many times!");
      }
      currentChild = children.next();
    }
  }

  @Override
  protected JsonElement getCurrentChild() {
    if (lhs) {
      return new JsonPrimitive(currentChild.getKey());
    }
    return currentChild.getValue();
  }

  @Override
  protected boolean hasMoreChildren() {
    return children.hasNext();
  }

  protected boolean isLhs() {
    return lhs;
  }
}