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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;

import com.mysema.commons.lang.CloseableIterator;
import com.querydsl.core.FetchableQuery;
import com.querydsl.core.Tuple;
import com.querydsl.core.types.Expression;
import com.querydsl.core.types.FactoryExpression;
import com.querydsl.core.types.FactoryExpressionUtils;
import com.querydsl.core.types.Projections;
import com.querydsl.core.util.TupleUtils;
import java.util.NoSuchElementException;
import java.util.Objects;

/**
 * Provides aggregated results as an iterator
 *
 * @author tiwe
 * @param 
 * @param 
 */
public class GroupByIterate extends AbstractGroupByTransformer> {

  GroupByIterate(Expression key, Expression... expressions) {
    super(key, expressions);
  }

  @Override
  public CloseableIterator transform(FetchableQuery query) {
    // create groups
    FactoryExpression expr = FactoryExpressionUtils.wrap(Projections.tuple(expressions));
    boolean hasGroups = false;
    for (Expression e : expr.getArgs()) {
      hasGroups |= e instanceof GroupExpression;
    }
    if (hasGroups) {
      expr = withoutGroupExpressions(expr);
    }
    final CloseableIterator iter = query.select(expr).iterate();

    return new CloseableIterator() {

      private GroupImpl group;

      private K groupId;

      @Override
      public boolean hasNext() {
        return group != null || iter.hasNext();
      }

      @Override
      public V next() {
        if (!iter.hasNext()) {
          if (group != null) {
            Group current = group;
            group = null;
            return transform(current);
          } else {
            throw new NoSuchElementException();
          }
        }

        while (iter.hasNext()) {
          // workaround from https://github.com/querydsl/querydsl/issues/3264
          Tuple tuple = TupleUtils.toTuple(iter.next(), expressions);

          @SuppressWarnings("unchecked") // This type is mandated by the key type
          K[] row = (K[]) tuple.toArray();
          // end of workaround
          if (group == null) {
            group = new GroupImpl(groupExpressions, maps);
            groupId = row[0];
            group.add(row);
          } else if (Objects.equals(groupId, row[0])) {
            group.add(row);
          } else {
            Group current = group;
            group = new GroupImpl(groupExpressions, maps);
            groupId = row[0];
            group.add(row);
            return transform(current);
          }
        }
        Group current = group;
        group = null;
        return transform(current);
      }

      @Override
      public void remove() {
        throw new UnsupportedOperationException();
      }

      @Override
      public void close() {
        iter.close();
      }
    };
  }

  @SuppressWarnings("unchecked")
  protected V transform(Group group) {
    return (V) group;
  }
}