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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 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.XPathContext;
import net.sf.saxon.expr.sort.*;
import net.sf.saxon.trans.NoDynamicContextException;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.AtomicValue;

import java.util.ArrayList;

/**
 * Represents the tuple stream delivered by an "order by" clause. This sorts the tuple stream supplied
 * as its input, and outputs the same tuples but in sorted order.
 */
public class OrderByClausePull extends TuplePull implements Sortable {

    private TuplePull base;
    private OrderByClause orderByClause;
    private TupleExpression tupleExpr;
    private int currentPosition = -1;
    protected AtomicComparer[] comparers;
    private ArrayList tupleArray = new ArrayList(100);

    public OrderByClausePull(TuplePull base, TupleExpression tupleExpr, OrderByClause orderBy, XPathContext context) {
        this.base = base;
        this.tupleExpr = tupleExpr;
        this.orderByClause = orderBy;

        AtomicComparer[] suppliedComparers = orderBy.getAtomicComparers();
        comparers = new AtomicComparer[suppliedComparers.length];
        for (int n=0; n< comparers.length; n++) {
            this.comparers[n] = suppliedComparers[n].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 (currentPosition < 0) {
            currentPosition = 0;
            int position = 0;

            while (base.nextTuple(context)) {
                Tuple tuple = tupleExpr.evaluateItem(context);
                SortKeyDefinition[] sortKeyDefinitions = orderByClause.getSortKeyDefinitions();
                ItemToBeSorted itbs = new ItemToBeSorted(sortKeyDefinitions.length);
                itbs.value = tuple;
                for (int i=0; i0 if obj[a]>obj[b]
     */
    public int compare(int a, int b) {
        try {
            for (int i=0; i< comparers.length; i++) {
                int comp = comparers[i].compareAtomicValues(
                        (AtomicValue)tupleArray.get(a).sortKeyValues[i], (AtomicValue)tupleArray.get(b).sortKeyValues[i]);
                if (comp != 0) {
                    // we have found a difference, so we can return
                    return comp;
                }
            }
        } catch (NoDynamicContextException e) {
            throw new AssertionError("Sorting without dynamic context: " + e.getMessage());
        }

        // all sort keys equal: return the items in their original order

        return tupleArray.get(a).originalPosition - tupleArray.get(b).originalPosition;
    }

    /**
     * Swap two objects within this Sortable, identified by their position.
     */
    public void swap(int a, int b) {
        ItemToBeSorted temp = tupleArray.get(a);
        tupleArray.set(a, tupleArray.get(b));
        tupleArray.set(b, temp);
    }

    /**
     * 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();
    }
}