/**
 * Copyright (C) 2022 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 sevenUnitsGUI;

import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.function.Function;
import java.util.function.Predicate;

import sevenUnits.unit.LinearUnit;
import sevenUnits.unit.Metric;
import sevenUnits.unit.UnitPrefix;

/**
 * A search rule that applies a certain set of prefixes to a unit. It always
 * includes the original unit in the output map.
 *
 * @since 2022-07-06
 */
public final class PrefixSearchRule implements
		Function<Map.Entry<String, LinearUnit>, Map<String, LinearUnit>> {
	/**
	 * A rule that does not add any prefixed versions of units.
	 */
	public static final PrefixSearchRule NO_PREFIXES = getUniversalRule(
			Set.of());
	
	/**
	 * A rule that gives every unit a common set of prefixes.
	 */
	public static final PrefixSearchRule COMMON_PREFIXES = getCoherentOnlyRule(
			Set.of(Metric.MILLI, Metric.KILO));
	
	/**
	 * A rule that gives every unit all metric prefixes.
	 */
	public static final PrefixSearchRule ALL_METRIC_PREFIXES = getCoherentOnlyRule(
			Metric.ALL_PREFIXES);
	
	/**
	 * Gets a rule that applies the provided prefixes to coherent units only (as
	 * defined by {@link LinearUnit#isCoherent}), except the kilogram
	 * (specifically, units named "kilogram").
	 *
	 * @param prefixes prefixes to apply
	 * @return prefix rule
	 * @since 2022-07-06
	 */
	public static final PrefixSearchRule getCoherentOnlyRule(
			Set<UnitPrefix> prefixes) {
		return new PrefixSearchRule(prefixes,
				u -> u.isCoherent() && !u.getName().equals("kilogram"));
	}
	
	/**
	 * Gets a rule that applies the provided prefixes to all units.
	 *
	 * @param prefixes prefixes to apply
	 * @return prefix rule
	 * @since 2022-07-06
	 */
	public static final PrefixSearchRule getUniversalRule(
			Set<UnitPrefix> prefixes) {
		return new PrefixSearchRule(prefixes, u -> true);
	}
	
	/**
	 * The set of prefixes that will be applied to the unit.
	 */
	private final Set<UnitPrefix> prefixes;
	
	/**
	 * Determines which units are given prefixes.
	 */
	private final Predicate<LinearUnit> allowUnit;
	
	/**
	 * @param prefixes
	 * @param metricOnly
	 * @since 2022-07-06
	 */
	public PrefixSearchRule(Set<UnitPrefix> prefixes,
			Predicate<LinearUnit> allowUnit) {
		this.prefixes = Collections.unmodifiableSet(new HashSet<>(prefixes));
		this.allowUnit = allowUnit;
	}
	
	@Override
	public Map<String, LinearUnit> apply(Entry<String, LinearUnit> t) {
		final Map<String, LinearUnit> outputUnits = new HashMap<>();
		final String originalName = t.getKey();
		final LinearUnit originalUnit = t.getValue();
		outputUnits.put(originalName, originalUnit);
		if (this.allowUnit.test(originalUnit)) {
			for (final UnitPrefix prefix : this.prefixes) {
				outputUnits.put(prefix.getName() + originalName,
						originalUnit.withPrefix(prefix));
			}
		}
		return outputUnits;
	}
	
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (!(obj instanceof PrefixSearchRule))
			return false;
		final PrefixSearchRule other = (PrefixSearchRule) obj;
		if (this.allowUnit == null) {
			if (other.allowUnit != null)
				return false;
		} else if (!this.allowUnit.equals(other.allowUnit))
			return false;
		if (this.prefixes == null) {
			if (other.prefixes != null)
				return false;
		} else if (!this.prefixes.equals(other.prefixes))
			return false;
		return true;
	}
	
	/**
	 * @return the allowUnit
	 * @since 2022-07-06
	 */
	public Predicate<LinearUnit> getAllowUnit() {
		return this.allowUnit;
	}
	
	/**
	 * @return the prefixes that are applied by this rule
	 * @since 2022-07-06
	 */
	public Set<UnitPrefix> getPrefixes() {
		return this.prefixes;
	}
	
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result
				+ (this.allowUnit == null ? 0 : this.allowUnit.hashCode());
		result = prime * result
				+ (this.prefixes == null ? 0 : this.prefixes.hashCode());
		return result;
	}
	
	@Override
	public String toString() {
		return "Apply the following prefixes: " + this.prefixes;
	}
}