Copyright (c) 2016-present, RxJava Contributors.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
the License for the specific language governing permissions and limitations under the License.
/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex.internal.util;

import java.util.*;

import io.reactivex.functions.BiFunction;

A BiFunction that merges two Lists into a new list.
Type parameters:
<T> – the value type/**
 * A BiFunction that merges two Lists into a new list.
 * @param <T> the value type
 */
public final class MergerBiFunction<T> implements BiFunction<List<T>, List<T>, List<T>> {

    final Comparator<? super T> comparator;

    public MergerBiFunction(Comparator<? super T> comparator) {
        this.comparator = comparator;
    }

    @Override
    public List<T> apply(List<T> a, List<T> b) throws Exception {
        int n = a.size() + b.size();
        if (n == 0) {
            return new ArrayList<T>();
        }
        List<T> both = new ArrayList<T>(n);

        Iterator<T> at = a.iterator();
        Iterator<T> bt = b.iterator();

        T s1 = at.hasNext() ? at.next() : null;
        T s2 = bt.hasNext() ? bt.next() : null;

        while (s1 != null && s2 != null) {
            if (comparator.compare(s1, s2) < 0) { // s1 comes before s2
                both.add(s1);
                s1 = at.hasNext() ? at.next() : null;
            } else {
                both.add(s2);
                s2 = bt.hasNext() ? bt.next() : null;
            }
        }

        if (s1 != null) {
            both.add(s1);
            while (at.hasNext()) {
                both.add(at.next());
            }
        } else {
            both.add(s2);
            while (bt.hasNext()) {
                both.add(bt.next());
            }
        }

        return both;
    }
}