/**
 * 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 org.unitConverter.unit;

import java.util.Objects;

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

/**
 * A unit that is the base for its dimension. It does not have to be for a base dimension, so units like the Newton and
 * Joule are still base units.
 * <p>
 * {@code BaseUnit} does not have any public constructors or static factories. There are two ways to obtain
 * {@code BaseUnit} instances.
 * <ol>
 * <li>The class {@link SI} in this package has constants for all of the SI base units. You can use these constants and
 * multiply or divide them to get other units. For example:
 * 
 * <pre>
 * BaseUnit JOULE = SI.KILOGRAM.times(SI.METRE.toExponent(2)).dividedBy(SI.SECOND.toExponent(2));
 * </pre>
 * 
 * </li>
 * <li>You can also query a unit system for a base unit using a unit dimension. The previously mentioned {@link SI}
 * class can do this for SI and SI-derived units (including imperial and USC), but if you want to use another system,
 * this is the way to do it. {@link StandardDimensions} contains common unit dimensions that you can use for this. Here
 * is an example:
 * 
 * <pre>
 * BaseUnit JOULE = SI.SI.getBaseUnit(StandardDimensions.ENERGY);
 * </pre>
 * 
 * </li>
 * </ol>
 * 
 * @author Adrien Hopkins
 * @since 2018-12-23
 * @since v0.1.0
 */
public final class BaseUnit extends LinearUnit {
	/**
	 * Is this unit a full base (i.e. m, s, ... but not N, J, ...)
	 * 
	 * @since 2019-01-15
	 * @since v0.1.0
	 */
	private final boolean isFullBase;

	/**
	 * Creates the {@code BaseUnit}.
	 * 
	 * @param dimension
	 *            dimension measured by unit
	 * @param system
	 *            system that unit is a part of
	 * @param name
	 *            name of unit
	 * @param symbol
	 *            symbol of unit
	 * @since 2018-12-23
	 * @since v0.1.0
	 */
	BaseUnit(final UnitDimension dimension, final UnitSystem system) {
		super(dimension, system, 1);
		this.isFullBase = dimension.isBase();
	}

	/**
	 * Returns the quotient of this unit and another.
	 * <p>
	 * Two units can be divided if they are part of the same unit system. If {@code divisor} does not meet this
	 * condition, an {@code IllegalArgumentException} should be thrown.
	 * </p>
	 * 
	 * @param divisor
	 *            unit to divide by
	 * @return quotient of two units
	 * @throws IllegalArgumentException
	 *             if {@code divisor} is not compatible for division as described above
	 * @throws NullPointerException
	 *             if {@code divisor} is null
	 * @since 2018-12-22
	 * @since v0.1.0
	 */
	public BaseUnit dividedBy(final BaseUnit divisor) {
		Objects.requireNonNull(divisor, "other must not be null.");

		// check that these units can be multiplied
		if (!this.getSystem().equals(divisor.getSystem()))
			throw new IllegalArgumentException(
					String.format("Incompatible units for division \"%s\" and \"%s\".", this, divisor));

		return new BaseUnit(this.getDimension().dividedBy(divisor.getDimension()), this.getSystem());
	}

	/**
	 * @return true if the unit is a "full base" unit like the metre or second.
	 * @since 2019-04-10
	 * @since v0.2.0
	 */
	public final boolean isFullBase() {
		return this.isFullBase;
	}

	/**
	 * Returns the product of this unit and another.
	 * <p>
	 * Two units can be multiplied if they are part of the same unit system. If {@code multiplier} does not meet this
	 * condition, an {@code IllegalArgumentException} should be thrown.
	 * </p>
	 * 
	 * @param multiplier
	 *            unit to multiply by
	 * @return product of two units
	 * @throws IllegalArgumentException
	 *             if {@code multiplier} is not compatible for multiplication as described above
	 * @throws NullPointerException
	 *             if {@code multiplier} is null
	 * @since 2018-12-22
	 * @since v0.1.0
	 */
	public BaseUnit times(final BaseUnit multiplier) {
		Objects.requireNonNull(multiplier, "other must not be null");

		// check that these units can be multiplied
		if (!this.getSystem().equals(multiplier.getSystem()))
			throw new IllegalArgumentException(
					String.format("Incompatible units for multiplication \"%s\" and \"%s\".", this, multiplier));

		// multiply the units
		return new BaseUnit(this.getDimension().times(multiplier.getDimension()), this.getSystem());
	}

	/**
	 * Returns this unit, but to an exponent.
	 * 
	 * @param exponent
	 *            exponent
	 * @return result of exponentiation
	 * @since 2019-01-15
	 * @since v0.1.0
	 */
	@Override
	public BaseUnit toExponent(final int exponent) {
		return this.getSystem().getBaseUnit(this.getDimension().toExponent(exponent));
	}

	@Override
	public String toString() {
		return String.format("%s base unit of%s dimension %s", this.getSystem(), this.isFullBase ? " base" : "",
				this.getDimension());
	}
}