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core module for querydsl

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/*
 * Copyright 2015, The Querydsl Team (http://www.querydsl.com/team)
 *
 * 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.querydsl.core.group;

/**
 * {@code MixinGroupExpression} provides nesting support for {@link GroupExpression} instances
 *
 * @param 
 * @param 
 * @param 
 */
public class MixinGroupExpression extends AbstractGroupExpression {

  private static final long serialVersionUID = -5419707469727395643L;

  private class GroupCollectorImpl implements GroupCollector {

    private final GroupCollector mixinGroupCollector;

    private GroupCollector groupCollector;

    GroupCollectorImpl() {
      mixinGroupCollector = mixin.createGroupCollector();
    }

    @Override
    public void add(E input) {
      if (groupCollector == null) {
        groupCollector = groupExpression.createGroupCollector();
      }
      groupCollector.add(input);
    }

    @Override
    public R get() {
      if (groupCollector != null) {
        F output = groupCollector.get();
        mixinGroupCollector.add(output);
        groupCollector = null;
      }
      return mixinGroupCollector.get();
    }
  }

  private final GroupExpression mixin;

  private final GroupExpression groupExpression;

  @SuppressWarnings({"unchecked", "rawtypes"})
  public MixinGroupExpression(GroupExpression groupExpression, GroupExpression mixin) {
    super((Class) mixin.getType(), groupExpression.getExpression());
    this.mixin = mixin;
    this.groupExpression = groupExpression;
  }

  @Override
  public GroupCollector createGroupCollector() {
    return new GroupCollectorImpl();
  }
}