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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2015 Saxonica Limited.
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package net.sf.saxon.expr.flwor;

import net.sf.saxon.expr.Atomizer;
import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.expr.sort.GenericAtomicComparer;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.om.SequenceTool;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.AtomicValue;
import net.sf.saxon.value.EmptySequence;
import net.sf.saxon.value.SequenceExtent;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;

/**
 * Represents the tuple stream delivered by an "group by" clause. This groups the tuple stream supplied
 * as its input, and outputs a new set of tuples one per group of the input tuples. No groups are output
 * until all the groups have been read.
 */
public class GroupByClausePull extends TuplePull {

    private TuplePull base;
    private GroupByClause groupByClause;
    /*@Nullable*/ Iterator> groupIterator;
    private XPathContext context;
    private GenericAtomicComparer[] comparers;


    public GroupByClausePull(TuplePull base, GroupByClause groupBy, XPathContext context) {
        this.base = base;
        this.groupByClause = groupBy;
        this.context = context;
        comparers = new GenericAtomicComparer[groupBy.comparers.length];
        for (int i = 0; i < comparers.length; i++) {
            comparers[i] = groupBy.comparers[i].provideContext(context);
        }
    }

    /**
     * Move on to the next tuple. Before returning, this method must set all the variables corresponding
     * to the "returned" tuple in the local stack frame associated with the context object
     *
     * @param context the dynamic evaluation context
     * @return true if another tuple has been generated; false if the tuple stream is exhausted. If the
     *         method returns false, the values of the local variables corresponding to this tuple stream
     *         are undefined.
     */
    @Override
    public boolean nextTuple(XPathContext context) throws XPathException {
        if (groupIterator == null) {

            // First do the grouping

            TupleExpression groupingTupleExpr = groupByClause.getGroupingTupleExpression();
            TupleExpression retainedTupleExpr = groupByClause.getRetainedTupleExpression();
            HashMap> map = new HashMap>();
            while (base.nextTuple(context)) {
                GroupByClause.ObjectToBeGrouped otbg = new GroupByClause.ObjectToBeGrouped();
                Sequence[] groupingValues = groupingTupleExpr.evaluateItem(context).getMembers();
                for (int i = 0; i < groupingValues.length; i++) {
                    Sequence v = groupingValues[i];
                    if (!(v instanceof EmptySequence || v instanceof AtomicValue)) {
                        v = SequenceExtent.makeSequenceExtent(Atomizer.getAtomizingIterator(v.iterate(), false));
                        if (SequenceTool.getLength(v) > 1) {
                            throw new XPathException("Grouping key value cannot be a sequence of more than one item", "XPTY0004");
                        }
                        groupingValues[i] = v;
                    }
                }
                otbg.groupingValues = new Tuple(groupingValues);
                otbg.retainedValues = retainedTupleExpr.evaluateItem(context);
                Object key = groupByClause.getComparisonKey(otbg.groupingValues, comparers);
                List group = map.get(key);
                if (group != null) {
                    group.add(otbg);
                    map.put(key, group);
                } else {
                    List list = new ArrayList();
                    list.add(otbg);
                    map.put(key, list);
                }
            }
            // get an iterator over the groups

            groupIterator = map.values().iterator();

        }

        if (groupIterator.hasNext()) {
            List group = groupIterator.next();
            groupByClause.processGroup(group, context);
            return true;
        } else {
            return false;
        }

    }


    /**
     * Close the tuple stream, indicating that although not all tuples have been read,
     * no further tuples are required and resources can be released
     */

    @Override
    public void close() {
        base.close();
        groupIterator = null;
    }

}

// Copyright (c) 2011 Saxonica Limited. All rights reserved.