/**
 * Copyright (C) 2018 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 unitConverter.unit;

import java.util.HashSet;
import java.util.Objects;
import java.util.Set;

import unitConverter.dimension.StandardDimensions;
import unitConverter.dimension.UnitDimension;

/**
 * The SI, which holds all SI units
 * 
 * @author Adrien Hopkins
 * @since 2018-12-23
 */
public enum SI implements UnitSystem {
	SI;

	/**
	 * This system's base units.
	 * 
	 * @since 2019-01-25
	 */
	private static final Set<BaseUnit> baseUnits = new HashSet<>();

	// base units
	public static final BaseUnit METRE = SI.getBaseUnit(StandardDimensions.LENGTH);
	public static final BaseUnit KILOGRAM = SI.getBaseUnit(StandardDimensions.MASS);
	public static final BaseUnit SECOND = SI.getBaseUnit(StandardDimensions.TIME);
	public static final BaseUnit AMPERE = SI.getBaseUnit(StandardDimensions.ELECTRIC_CURRENT);
	public static final BaseUnit KELVIN = SI.getBaseUnit(StandardDimensions.TEMPERATURE);
	public static final BaseUnit MOLE = SI.getBaseUnit(StandardDimensions.QUANTITY);
	public static final BaseUnit CANDELA = SI.getBaseUnit(StandardDimensions.LUMINOUS_INTENSITY);

	@Override
	public BaseUnit getBaseUnit(final UnitDimension dimension) {
		// try to find an existing unit before creating a new one

		Objects.requireNonNull(dimension, "dimension must not be null.");
		for (final BaseUnit unit : baseUnits) {
			// it will be equal since the conditions for equality are dimension and system,
			// and system is always SI.
			if (unit.getDimension().equals(dimension))
				return unit;
		}
		// could not find an existing base unit
		final BaseUnit unit = new BaseUnit(dimension, this);
		baseUnits.add(unit);
		return unit;
	}

	@Override
	public String getName() {
		return "SI";
	}
}