/**
 * 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.unit;

import java.util.Objects;

import org.unitConverter.math.DecimalComparison;
import org.unitConverter.math.ObjectProduct;

/**
 * A unit that can be expressed as a product of its base and a number. For example, kilometres, inches and pounds.
 * 
 * @author Adrien Hopkins
 * @since 2019-10-16
 */
public final class LinearUnit extends Unit {
	/**
	 * Gets a {@code LinearUnit} from a unit and a value. For example, converts '59 °F' to a linear unit with the value
	 * of '288.15 K'
	 * 
	 * @param unit
	 *            unit to convert
	 * @param value
	 *            value to convert
	 * @return value expressed as a {@code LinearUnit}
	 * @since 2019-10-16
	 */
	public static LinearUnit fromUnitValue(final Unit unit, final double value) {
		return new LinearUnit(unit.getBase(), unit.convertToBase(value));
	}

	/**
	 * Gets a {@code LinearUnit} from a unit base and a conversion factor. In other words, gets the product of
	 * {@code unitBase} and {@code conversionFactor}, expressed as a {@code LinearUnit}.
	 * 
	 * @param unitBase
	 *            unit base to multiply by
	 * @param conversionFactor
	 *            number to multiply base by
	 * @return product of base and conversion factor
	 * @since 2019-10-16
	 */
	public static LinearUnit valueOf(final ObjectProduct<BaseUnit> unitBase, final double conversionFactor) {
		return new LinearUnit(unitBase, conversionFactor);
	}

	/**
	 * The value of this unit as represented in its base form. Mathematically,
	 * 
	 * <pre>
	 * this = conversionFactor * getBase()
	 * </pre>
	 * 
	 * @since 2019-10-16
	 */
	private final double conversionFactor;

	/**
	 * Creates the {@code LinearUnit}.
	 * 
	 * @param unitBase
	 *            base of linear unit
	 * @param conversionFactor
	 *            conversion factor between base and unit
	 * @since 2019-10-16
	 */
	private LinearUnit(final ObjectProduct<BaseUnit> unitBase, final double conversionFactor) {
		super(unitBase);
		this.conversionFactor = conversionFactor;
	}

	@Override
	protected double convertFromBase(final double value) {
		return value / this.getConversionFactor();
	}

	@Override
	protected double convertToBase(final double value) {
		return value * this.getConversionFactor();
	}

	/**
	 * Divides this unit by a scalar.
	 * 
	 * @param divisor
	 *            scalar to divide by
	 * @return quotient
	 * @since 2018-12-23
	 * @since v0.1.0
	 */
	public LinearUnit dividedBy(final double divisor) {
		return valueOf(this.getBase(), this.getConversionFactor() / divisor);
	}

	/**
	 * Returns the quotient of this unit and another.
	 * 
	 * @param divisor
	 *            unit to divide by
	 * @return quotient of two units
	 * @throws NullPointerException
	 *             if {@code divisor} is null
	 * @since 2018-12-22
	 * @since v0.1.0
	 */
	public LinearUnit dividedBy(final LinearUnit divisor) {
		Objects.requireNonNull(divisor, "other must not be null");

		// divide the units
		final ObjectProduct<BaseUnit> base = this.getBase().dividedBy(divisor.getBase());
		return valueOf(base, this.getConversionFactor() / divisor.getConversionFactor());
	}

	@Override
	public boolean equals(final Object obj) {
		if (!(obj instanceof LinearUnit))
			return false;
		final LinearUnit other = (LinearUnit) obj;
		return Objects.equals(this.getBase(), other.getBase())
				&& DecimalComparison.equals(this.getConversionFactor(), other.getConversionFactor());
	}

	/**
	 * @return conversion factor
	 * @since 2019-10-16
	 */
	public double getConversionFactor() {
		return this.conversionFactor;
	}

	@Override
	public int hashCode() {
		return 31 * this.getBase().hashCode() + DecimalComparison.hash(this.getConversionFactor());
	}

	/**
	 * @return whether this unit is equivalent to a {@code BaseUnit} (i.e. there is a {@code BaseUnit b} where
	 *         {@code b.asLinearUnit().equals(this)} returns {@code true}.)
	 * @since 2019-10-16
	 */
	public boolean isBase() {
		return this.isCoherent() && this.getBase().isSingleObject();
	}

	/**
	 * @return whether this unit is coherent (i.e. has conversion factor 1)
	 * @since 2019-10-16
	 */
	public boolean isCoherent() {
		return this.getConversionFactor() == 1;
	}

	/**
	 * Returns the difference of this unit and another.
	 * <p>
	 * Two units can be subtracted if they have the same base. Note that {@link #canConvertTo} can be used to determine
	 * this. If {@code subtrahend} does not meet this condition, an {@code IllegalArgumentException} will be thrown.
	 * </p>
	 * 
	 * @param subtrahend
	 *            unit to subtract
	 * @return difference of units
	 * @throws IllegalArgumentException
	 *             if {@code subtrahend} is not compatible for subtraction as described above
	 * @throws NullPointerException
	 *             if {@code subtrahend} is null
	 * @since 2019-03-17
	 * @since v0.2.0
	 */
	public LinearUnit minus(final LinearUnit subtrahendend) {
		Objects.requireNonNull(subtrahendend, "addend must not be null.");

		// reject subtrahends that cannot be added to this unit
		if (!this.getBase().equals(subtrahendend.getBase()))
			throw new IllegalArgumentException(
					String.format("Incompatible units for subtraction \"%s\" and \"%s\".", this, subtrahendend));

		// add the units
		return valueOf(this.getBase(), this.getConversionFactor() - subtrahendend.getConversionFactor());
	}

	/**
	 * Returns the sum of this unit and another.
	 * <p>
	 * Two units can be added if they have the same base. Note that {@link #canConvertTo} can be used to determine this.
	 * If {@code addend} does not meet this condition, an {@code IllegalArgumentException} will be thrown.
	 * </p>
	 * 
	 * @param addend
	 *            unit to add
	 * @return sum of units
	 * @throws IllegalArgumentException
	 *             if {@code addend} is not compatible for addition as described above
	 * @throws NullPointerException
	 *             if {@code addend} is null
	 * @since 2019-03-17
	 * @since v0.2.0
	 */
	public LinearUnit plus(final LinearUnit addend) {
		Objects.requireNonNull(addend, "addend must not be null.");

		// reject addends that cannot be added to this unit
		if (!this.getBase().equals(addend.getBase()))
			throw new IllegalArgumentException(
					String.format("Incompatible units for addition \"%s\" and \"%s\".", this, addend));

		// add the units
		return valueOf(this.getBase(), this.getConversionFactor() + addend.getConversionFactor());
	}

	/**
	 * Multiplies this unit by a scalar.
	 * 
	 * @param multiplier
	 *            scalar to multiply by
	 * @return product
	 * @since 2018-12-23
	 * @since v0.1.0
	 */
	public LinearUnit times(final double multiplier) {
		return valueOf(this.getBase(), this.getConversionFactor() * multiplier);
	}

	/**
	 * Returns the product of this unit and another.
	 * 
	 * @param multiplier
	 *            unit to multiply by
	 * @return product of two units
	 * @throws NullPointerException
	 *             if {@code multiplier} is null
	 * @since 2018-12-22
	 * @since v0.1.0
	 */
	public LinearUnit times(final LinearUnit multiplier) {
		Objects.requireNonNull(multiplier, "other must not be null");

		// multiply the units
		final ObjectProduct<BaseUnit> base = this.getBase().times(multiplier.getBase());
		return valueOf(base, this.getConversionFactor() * multiplier.getConversionFactor());
	}

	/**
	 * Returns this unit but to an exponent.
	 * 
	 * @param exponent
	 *            exponent to exponentiate unit to
	 * @return exponentiated unit
	 * @since 2019-01-15
	 * @since v0.1.0
	 */
	public LinearUnit toExponent(final int exponent) {
		return valueOf(this.getBase().toExponent(exponent), Math.pow(this.conversionFactor, exponent));
	}

	// returns a definition of the unit
	@Override
	public String toString() {
		return Double.toString(this.conversionFactor) + " * " + this.getBase().toString(BaseUnit::getSymbol);
	}

	/**
	 * Returns the result of applying {@code prefix} to this unit.
	 * 
	 * @param prefix
	 *            prefix to apply
	 * @return unit with prefix
	 * @since 2019-03-18
	 * @since v0.2.0
	 */
	public LinearUnit withPrefix(final UnitPrefix prefix) {
		return this.times(prefix.getMultiplier());
	}
}