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QuestDB is High Performance Time Series Database

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 * Copyright (C) 2014-2016 Appsicle
 *
 * This program is free software: you can redistribute it and/or  modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
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package com.questdb.iter;

import java.util.Comparator;
import java.util.Iterator;
import java.util.List;

public class MergingPeekingIterator extends MergingIterator implements PeekingIterator {

    public static > PeekingIterator mergePeek(List iterators, Comparator comparator) {
        return mergePeek(iterators, comparator, 0);
    }

    public MergingPeekingIterator $new(Iterator a, Iterator b, Comparator comparator) {
        this.a = a;
        this.b = b;
        this.comparator = comparator;
        this.nextA = null;
        this.nextB = null;
        return this;
    }

    @Override
    public boolean isEmpty() {
        return ((PeekingIterator) a).isEmpty() || ((PeekingIterator) b).isEmpty();
    }

    @Override
    public T peekFirst() {
        T va = ((PeekingIterator) a).peekFirst();
        T vb = ((PeekingIterator) b).peekFirst();
        return comparator.compare(va, vb) < 0 ? va : vb;
    }

    @Override
    public T peekLast() {
        T va = ((PeekingIterator) a).peekLast();
        T vb = ((PeekingIterator) b).peekLast();
        return comparator.compare(va, vb) > 0 ? va : vb;
    }

    private static > PeekingIterator mergePeek(List iterators, Comparator comparator, int index) {
        if (iterators == null || iterators.isEmpty()) {
            throw new IllegalArgumentException();
        }

        if (iterators.size() - index == 1) {
            return iterators.get(index);
        }

        return new MergingPeekingIterator().$new(iterators.get(index), mergePeek(iterators, comparator, index + 1), comparator);
    }
}