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A lightweight alternative to Java 8 sequential Stream
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/*
 * Copyright 2016 Daniel Skogquist Åborg
 *
 * 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 org.d2ab.collection;

import org.d2ab.iterator.ChainedListIterator;
import org.d2ab.iterator.ChainingIterator;

import java.util.*;

import static org.d2ab.collection.SizedIterable.SizeType.*;

/**
 * A {@link List} of multiple {@link List}s strung together in a chain.
 */
public class ChainedList extends AbstractList implements SizedIterable {
	private final List> lists;
	private final SizeType sizeType;

	@SafeVarargs
	public static  List concat(List... lists) {
		return concat(Lists.of(lists));
	}

	public static  List concat(List> lists) {
		return new ChainedList<>(lists);
	}

	private ChainedList(List> lists) {
		this.lists = lists;
		this.sizeType = Iterables.sizeType(lists);
	}

	@Override
	public Iterator iterator() {
		return new ChainingIterator<>(lists);
	}

	@Override
	public ListIterator listIterator(int index) {
		return new ChainedListIterator<>(lists, index);
	}

	@Override
	public T get(int index) {
		for (List list : lists) {
			if (list.size() > index)
				return list.get(index);
			index -= list.size();
		}
		throw new IndexOutOfBoundsException();
	}

	@Override
	public T set(int index, T element) {
		for (List list : lists) {
			if (list.size() > index)
				return list.set(index, element);
			index -= list.size();
		}
		throw new IndexOutOfBoundsException();
	}

	@Override
	public void add(int index, T element) {
		if (index == 0 && lists.isEmpty())
			lists.add(new ArrayList<>());

		for (List list : lists) {
			if (index <= list.size()) {
				list.add(index, element);
				return;
			}
			index -= list.size();
		}

		throw new IndexOutOfBoundsException();
	}

	@Override
	public T remove(int index) {
		for (List list : lists) {
			if (list.size() > index)
				return list.remove(index);
			index -= list.size();
		}

		throw new IndexOutOfBoundsException();
	}

	@Override
	public boolean addAll(int index, Collection c) {
		if (index == 0 && lists.isEmpty())
			lists.add(new ArrayList<>());

		for (List list : lists) {
			if (index <= list.size())
				return list.addAll(index, c);
			index -= list.size();
		}

		throw new IndexOutOfBoundsException();
	}

	@Override
	public int size() {
		if (sizeType == INFINITE)
			throw new UnsupportedOperationException();

		int size = 0;
		for (List list : lists)
			size += list.size();
		return size;
	}

	@Override
	public SizeType sizeType() {
		if (sizeType == INFINITE)
			throw new UnsupportedOperationException();

		SizeType sizeType = this.sizeType != FIXED ? AVAILABLE : FIXED;

		for (List list : lists)
			sizeType = sizeType.concat(Iterables.sizeType(list));

		return sizeType;
	}

	@Override
	public void clear() {
		if (sizeType == INFINITE)
			throw new UnsupportedOperationException();

		for (List l : lists)
			l.clear();
	}

	@Override
	public boolean isEmpty() {
		if (sizeType == INFINITE)
			throw new UnsupportedOperationException();

		for (List list : lists)
			if (!list.isEmpty())
				return false;

		return true;
	}

	@Override
	public Spliterator spliterator() {
		if (sizeType == INFINITE || sizeType() == INFINITE)
			return Spliterators.spliteratorUnknownSize(iterator(), 0);

		return Spliterators.spliterator(this, 0);
	}
}