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/*
 * Copyright (c) 2010-2017, KolibriFX AS. Licensed under the Apache License, version 2.0.
 */

package com.kolibrifx.plovercrest.server.streams.folds;

import java.util.Collection;
import com.kolibrifx.plovercrest.server.internal.folds.FoldCallback;
import com.kolibrifx.plovercrest.server.internal.folds.PeekableInputStream;

/**
 * @see com.kolibrifx.plovercrest.server.folds.FoldCombinators#live()
 */
public class LiveCombinatorStrategy implements CombinatorStrategy {
    @Override
    public  boolean tryConsumeNext(final Collection> feeds,
                                      final FoldCallback cb) {
        if (feeds.isEmpty()) {
            return false;
        }
        PeekableInputStream best = null;
        for (final PeekableInputStream feed : feeds) {
            if (!feed.hasNext()) {
                // Missing data from one table. For this strategy, we continue searching.
                // This ensures that (live) updates trigger events immediately, but can cause
                // out-of-order timestamps.
                continue;
            }
            if (best == null || feed.nextTimestamp() < best.nextTimestamp()) {
                best = feed;
            }
        }
        if (best == null) {
            cb.onEnd();
            return false;
        }
        assert best.hasNext();
        best.consumeNext(cb);
        return true;
    }
}