/**
 * Copyright (C) 2022, 2024, 2025 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.Objects;
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 v0.4.0
 * @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.
	 *
	 * @since v0.4.0
	 */
	public static final PrefixSearchRule NO_PREFIXES = getUniversalRule(
			Set.of());

	/**
	 * A rule that gives every unit a common set of prefixes.
	 *
	 * @since v0.4.0
	 */
	public static final PrefixSearchRule COMMON_PREFIXES = getCoherentOnlyRule(
			Set.of(Metric.MILLI, Metric.KILO));

	/**
	 * A rule that gives every unit all metric prefixes.
	 *
	 * @since v0.4.0
	 */
	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 v0.4.0
	 * @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 v0.4.0
	 * @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> prefixableUnitRule;

	/**
	 * @param prefixes           prefixes to add to units
	 * @param prefixableUnitRule function that determines which units get
	 *                           prefixes
	 * @since v0.4.0
	 * @since 2022-07-06
	 */
	public PrefixSearchRule(Set<UnitPrefix> prefixes,
			Predicate<LinearUnit> prefixableUnitRule) {
		this.prefixes = Collections.unmodifiableSet(new HashSet<>(prefixes));
		this.prefixableUnitRule = prefixableUnitRule;
	}

	@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.prefixableUnitRule.test(originalUnit)) {
			for (final UnitPrefix prefix : this.prefixes) {
				outputUnits.put(prefix.getName() + originalName,
						originalUnit.withPrefix(prefix));
			}
		}
		return Collections.unmodifiableMap(outputUnits);
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (!(obj instanceof PrefixSearchRule))
			return false;
		final PrefixSearchRule other = (PrefixSearchRule) obj;
		return Objects.equals(this.prefixableUnitRule, other.prefixableUnitRule)
				&& Objects.equals(this.prefixes, other.prefixes);
	}

	/**
	 * @return rule that determines which units get prefixes
	 * @since v0.4.0
	 * @since 2022-07-09
	 */
	public Predicate<LinearUnit> getPrefixableUnitRule() {
		return this.prefixableUnitRule;
	}

	/**
	 * @return the prefixes that are applied by this rule
	 * @since v0.4.0
	 * @since 2022-07-06
	 */
	public Set<UnitPrefix> getPrefixes() {
		return this.prefixes;
	}

	@Override
	public int hashCode() {
		return Objects.hash(this.prefixableUnitRule, this.prefixes);
	}

	@Override
	public String toString() {
		return "Apply the following prefixes: " + this.prefixes;
	}
}