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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.sequence;

import org.d2ab.collection.ChainedList;
import org.d2ab.collection.FilteredList;
import org.d2ab.collection.MappedList;
import org.d2ab.collection.ReverseList;

import java.util.*;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;

import static java.util.Collections.emptyList;
import static java.util.Collections.singletonList;

/**
 * A {@link Sequence} backed by a {@link List}. Implements certain operations on {@link Sequence} in a more performant
 * way due to the {@link List} backing. This class should normally not be used directly as e.g.
 * {@link Sequence#from(Iterable)} and other methods return this class directly where appropriate.
 */
public class ListSequence implements Sequence {
	private List list;

	public static  Sequence empty() {
		return from(emptyList());
	}

	public static  Sequence of(T item) {
		return from(singletonList(item));
	}

	@SuppressWarnings("unchecked")
	public static  Sequence of(T... items) {
		return from(Arrays.asList(items));
	}

	public static  Sequence from(List list) {
		return new ListSequence<>(list);
	}

	public static  Sequence concat(List... lists) {
		return from(ChainedList.from(lists));
	}

	public static  Sequence concat(List> lists) {
		return from(ChainedList.from(lists));
	}

	private ListSequence(List list) {
		this.list = list;
	}

	@Override
	public Iterator iterator() {
		return list.iterator();
	}

	@Override
	public List toList() {
		return new ArrayList<>(list);
	}

	@Override
	public List asList() {
		return list;
	}

	@Override
	public > U collectInto(U collection) {
		collection.addAll(list);
		return collection;
	}

	@Override
	public void clear() {
		list.clear();
	}

	@Override
	public long size() {
		return list.size();
	}

	@Override
	public Stream stream() {
		return list.stream();
	}

	@Override
	public boolean isEmpty() {
		return list.isEmpty();
	}

	@Override
	public boolean contains(T item) {
		return list.contains(item);
	}

	@Override
	public Optional at(long index) {
		if (index >= list.size())
			return Optional.empty();

		return Optional.of(list.get((int) index));
	}

	@Override
	public Optional last() {
		if (list.size() < 1)
			return Optional.empty();

		return Optional.of(list.get(list.size() - 1));
	}

	@Override
	public Sequence reverse() {
		return from(ReverseList.from(list));
	}

	@Override
	public Sequence filter(Predicate predicate) {
		return from(FilteredList.from(list, predicate));
	}

	@Override
	public  Sequence map(Function mapper) {
		return from(MappedList.from(list, mapper));
	}

	@SuppressWarnings("unchecked")
	@Override
	public Sequence append(Iterable iterable) {
		if (iterable instanceof List)
			return from(ChainedList.from(list, (List) iterable));
		
		return Sequence.concat(this, iterable);
	}

	@SuppressWarnings("unchecked")
	@Override
	public Sequence append(T... items) {
		return append(Arrays.asList(items));
	}
}