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/*
 * Copyright 2020, 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 java.util.Collection;
import java.util.Objects;
import java.util.function.Supplier;

/**
 * Provides aggregated results as a collection
 *
 * @param  Key type
 * @param  Value type
 * @param  Concrete collection type
 * @author Jan-Willem Gmelig Meyling
 */
public class GroupByGenericCollection> extends AbstractGroupByTransformer {

    private final Supplier resultFactory;

    GroupByGenericCollection(Supplier resultFactory, Expression key, Expression... expressions) {
        super(key, expressions);
        this.resultFactory = resultFactory;
    }

    @Override
    public RES 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();

        RES list = resultFactory.get();
        GroupImpl group = null;
        K groupId = null;
        while (iter.hasNext()) {
            @SuppressWarnings("unchecked") //This type is mandated by the key type
                    K[] row = (K[]) iter.next().toArray();
            if (group == null) {
                group = new GroupImpl(groupExpressions, maps);
                groupId = row[0];
            } else if (!Objects.equals(groupId, row[0])) {
                list.add(transform(group));
                group = new GroupImpl(groupExpressions, maps);
                groupId = row[0];
            }
            group.add(row);
        }
        if (group != null) {
            list.add(transform(group));
        }
        iter.close();
        return list;
    }

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