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package com.annimon.stream.operator;

import com.landawn.abacus.util.function.BiFunction;
import com.annimon.stream.iterator.LsaIterator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Queue;

public class ObjMerge extends LsaIterator {

    public enum MergeResult {
        TAKE_FIRST, TAKE_SECOND;
    }

    private final Iterator iterator1;
    private final Iterator iterator2;
    private final BiFunction selector;
    private final Queue buffer1;
    private final Queue buffer2;

    public ObjMerge(Iterator iterator1, Iterator iterator2,
                    BiFunction selector) {
        this.iterator1 = iterator1;
        this.iterator2 = iterator2;
        this.selector = selector;
        buffer1 = new LinkedList();
        buffer2 = new LinkedList();
    }

    @Override
    public boolean hasNext() {
        return !buffer1.isEmpty() || !buffer2.isEmpty()
                || iterator1.hasNext() || iterator2.hasNext();
    }

    @Override
    public T nextIteration() {
        if (!buffer1.isEmpty()) {
            final T v1 = buffer1.poll();
            if (iterator2.hasNext()) {
                return select(v1, iterator2.next());
            }
            return v1;
        }
        if (!buffer2.isEmpty()) {
            final T v2 = buffer2.poll();
            if (iterator1.hasNext()) {
                return select(iterator1.next(), v2);
            }
            return v2;
        }

        if (!iterator1.hasNext()) {
            return iterator2.next();
        }
        if (!iterator2.hasNext()) {
            return iterator1.next();
        }

        return select(iterator1.next(), iterator2.next());
    }

    private T select(T v1, T v2) {
        final MergeResult result = selector.apply(v1, v2);
        switch (result) {
            case TAKE_FIRST:
                buffer2.add(v2);
                return v1;

            case TAKE_SECOND:
            default:
                buffer1.add(v1);
                return v2;
        }
    }
}