/**
 * Copyright (C) 2019 Adrien Hopkins
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
package org.unitConverter.math;

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;

/**
 * A "wrapper" for an existing map that treats a zero value as equivalent to null.
 * 
 * @author Adrien Hopkins
 * @since 2019-10-16
 * @param <T>
 *            type of key
 */
public final class ZeroIsNullMap<T> extends AbstractMap<T, Integer> {
	/**
	 * Create a ZeroIsNullMap. This method always creates a new map.
	 * 
	 * @param <T>
	 *            type of key
	 * @param map
	 *            map to input
	 * @return map that treats zero as null
	 * @throws NullPointerException
	 *             if map is null
	 * @since 2019-10-16
	 */
	public static <T> Map<T, Integer> create(final Map<T, Integer> map) {
		return new ZeroIsNullMap<>(Objects.requireNonNull(map, "map must not be null."));
	}

	private final Map<T, Integer> map;

	/**
	 * Creates the {@code ObjectProductMap}.
	 * 
	 * @param map
	 * @since 2019-10-16
	 */
	private ZeroIsNullMap(final Map<T, Integer> map) {
		this.map = map;
	}

	@Override
	public void clear() {
		this.map.clear();
	}

	@Override
	public boolean containsKey(final Object key) {
		return this.map.containsKey(key) && this.map.get(key) != 0;
	}

	@Override
	public boolean containsValue(final Object value) {
		return this.values().contains(value);
	}

	@Override
	public Set<Entry<T, Integer>> entrySet() {
		final Set<Entry<T, Integer>> entrySet = new HashSet<>(this.map.entrySet());
		entrySet.removeIf(e -> e.getValue() == 0);
		return entrySet;
	}

	@Override
	public Integer get(final Object key) {
		final Integer i = this.map.get(key);
		if (Objects.equals(i, 0))
			return null;
		else
			return i;
	}

	@Override
	public Set<T> keySet() {
		final Set<T> keySet = new HashSet<>(this.map.keySet());
		keySet.removeIf(k -> this.map.get(k) == 0);
		return keySet;
	}

	@Override
	public Integer put(final T key, final Integer value) {
		if (value != 0)
			return this.map.put(key, value);
		else
			return null;
	}

	@Override
	public void putAll(final Map<? extends T, ? extends Integer> m) {
		for (final T key : m.keySet()) {
			this.put(key, m.get(key));
		}
	}

	@Override
	public Integer remove(final Object key) {
		return this.map.remove(key);
	}

	@Override
	public Collection<Integer> values() {
		final List<Integer> values = new ArrayList<>(this.map.values());
		values.removeIf(i -> i == 0);
		return values;
	}
}