/**
 * Copyright (C) 2019, 2021, 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 sevenUnits.unit;

import java.util.Objects;

import sevenUnits.utils.DecimalComparison;
import sevenUnits.utils.NameSymbol;
import sevenUnits.utils.ObjectProduct;
import sevenUnits.utils.UncertainDouble;

/**
 * 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
 * @since v0.3.0
 */
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
	 * @since v0.3.0
	 * @throws NullPointerException if unit is null
	 */
	public static LinearUnit fromUnitValue(final Unit unit, final double value) {
		return new LinearUnit(
				Objects.requireNonNull(unit, "unit must not be null.").getBase(),
				unit.convertToBase(value), NameSymbol.EMPTY);
	}

	/**
	 * 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
	 * @param ns    name(s) and symbol of unit
	 * @return value expressed as a {@code LinearUnit}
	 * @since 2019-10-21
	 * @since v0.3.0
	 * @throws NullPointerException if unit or ns is null
	 */
	public static LinearUnit fromUnitValue(final Unit unit, final double value,
			final NameSymbol ns) {
		return new LinearUnit(
				Objects.requireNonNull(unit, "unit must not be null.").getBase(),
				unit.convertToBase(value), ns);
	}

	/**
	 * @param unit unit to get base version of
	 * @return the base unit associated with {@code unit}, as a
	 *         {@code LinearUnit}.
	 * @since 2020-10-02
	 * @since v0.3.0
	 */
	public static LinearUnit getBase(final Unit unit) {
		return new LinearUnit(unit.getBase(), 1, NameSymbol.EMPTY);
	}

	/**
	 * 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
	 * @since v0.3.0
	 * @throws NullPointerException if unitBase is null
	 */
	public static LinearUnit valueOf(final ObjectProduct<BaseUnit> unitBase,
			final double conversionFactor) {
		return new LinearUnit(unitBase, conversionFactor, NameSymbol.EMPTY);
	}

	/**
	 * 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
	 * @param ns               name(s) and symbol of unit
	 * @return product of base and conversion factor
	 * @since 2019-10-21
	 * @since v0.3.0
	 * @throws NullPointerException if unitBase is null
	 */
	public static LinearUnit valueOf(final ObjectProduct<BaseUnit> unitBase,
			final double conversionFactor, final NameSymbol ns) {
		return new LinearUnit(unitBase, conversionFactor, ns);
	}

	/**
	 * The value of this unit as represented in its base form. Mathematically,
	 *
	 * <pre>
	 * this = conversionFactor * getBase()
	 * </pre>
	 *
	 * @since 2019-10-16
	 * @since v0.3.0
	 */
	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
	 * @since v0.3.0
	 */
	private LinearUnit(final ObjectProduct<BaseUnit> unitBase,
			final double conversionFactor, final NameSymbol ns) {
		super(unitBase, ns);
		this.conversionFactor = conversionFactor;
	}

	/**
	 * {@inheritDoc}
	 *
	 * Converts by dividing by {@code conversionFactor}
	 */
	@Override
	protected double convertFromBase(final double value) {
		return value / this.getConversionFactor();
	}

	/**
	 * Converts an {@code UncertainDouble} value expressed in this unit to an
	 * {@code UncertainValue} value expressed in {@code other}.
	 *
	 * @param other unit to convert to
	 * @param value value to convert
	 * @return converted value
	 * @since 2019-09-07
	 * @since v0.3.0
	 * @throws IllegalArgumentException if {@code other} is incompatible for
	 *                                  conversion with this unit (as tested by
	 *                                  {@link Unit#canConvertTo}).
	 * @throws NullPointerException     if value or other is null
	 */
	public UncertainDouble convertTo(LinearUnit other, UncertainDouble value) {
		Objects.requireNonNull(other, "other must not be null.");
		Objects.requireNonNull(value, "value may not be null.");
		if (this.canConvertTo(other))
			return value.timesExact(
					this.getConversionFactor() / other.getConversionFactor());
		throw new IllegalArgumentException(
				String.format("Cannot convert from %s to %s.", this, other));

	}

	/**
	 * {@inheritDoc}
	 *
	 * Converts by multiplying by {@code conversionFactor}
	 */
	@Override
	protected double convertToBase(final double value) {
		return value * this.getConversionFactor();
	}

	/**
	 * Converts an {@code UncertainDouble} to the base unit.
	 *
	 * @since 2020-09-07
	 * @since v0.3.0
	 */
	UncertainDouble convertToBase(final UncertainDouble value) {
		return value.timesExact(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 var base = this.getBase().dividedBy(divisor.getBase());
		return valueOf(base,
				this.getConversionFactor() / divisor.getConversionFactor());
	}

	/**
	 * {@inheritDoc}
	 *
	 * Uses the base and conversion factor of units to test for equality.
	 */
	@Override
	public boolean equals(final Object obj) {
		if (!(obj instanceof LinearUnit))
			return false;
		final var other = (LinearUnit) obj;
		return Objects.equals(this.getBase(), other.getBase())
				&& Double.compare(this.getConversionFactor(),
						other.getConversionFactor()) == 0;
	}

	/**
	 * @param other unit to test equality with
	 * @return true iff this unit and other are equal, ignoring small differences
	 *         caused by floating-point error.
	 *
	 * @apiNote This method is not transitive, so it cannot be used as an equals
	 *          method.
	 */
	public boolean equalsApproximately(final LinearUnit other) {
		return Objects.equals(this.getBase(), other.getBase())
				&& DecimalComparison.equals(this.getConversionFactor(),
						other.getConversionFactor());
	}

	/**
	 * @return conversion factor
	 * @since 2019-10-16
	 * @since v0.3.0
	 */
	public double getConversionFactor() {
		return this.conversionFactor;
	}

	/**
	 * {@inheritDoc}
	 *
	 * Uses the base and conversion factor to compute a hash code.
	 */
	@Override
	public int hashCode() {
		return 31 * this.getBase().hashCode()
				+ Double.hashCode(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
	 * @since v0.3.0
	 */
	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
	 * @since v0.3.0
	 */
	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 subtrahend) {
		Objects.requireNonNull(subtrahend, "addend must not be null.");

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

		// subtract the units
		return valueOf(this.getBase(),
				this.getConversionFactor() - subtrahend.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 var base = this.getBase().times(multiplier.getBase());
		return valueOf(base,
				this.getConversionFactor() * multiplier.getConversionFactor());
	}

	@Override
	public String toDefinitionString() {
		return Double.toString(this.conversionFactor)
				+ (this.getBase().equals(ObjectProduct.empty()) ? ""
						: " " + this.getBase().toString(BaseUnit::getShortName));
	}

	/**
	 * 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 this unit to an exponent, rounding the resulting dimensions to the
	 * nearest integer.
	 *
	 * @param exponent exponent to raise unit to
	 * @return result of rounded exponentation
	 * @since 2024-08-22
	 * @since v1.0.0
	 * @see ObjectProduct#toExponentRounded
	 */
	public LinearUnit toExponentRounded(final double exponent) {
		return valueOf(this.getBase().toExponentRounded(exponent),
				Math.pow(this.conversionFactor, exponent));
	}

	@Override
	public LinearUnit withName(final NameSymbol ns) {
		return valueOf(this.getBase(), this.getConversionFactor(), ns);
	}

	/**
	 * Returns the result of applying {@code prefix} to this unit.
	 * <p>
	 * If this unit and the provided prefix have a primary name, the returned
	 * unit will have a primary name (prefix's name + unit's name). <br>
	 * If this unit and the provided prefix have a symbol, the returned unit will
	 * have a symbol. <br>
	 * This method ignores alternate names of both this unit and the provided
	 * prefix.
	 *
	 * @param prefix prefix to apply
	 * @return unit with prefix
	 * @since 2019-03-18
	 * @since v0.2.0
	 * @throws NullPointerException if prefix is null
	 */
	public LinearUnit withPrefix(final UnitPrefix prefix) {
		final var unit = this.times(prefix.getMultiplier());

		// create new name and symbol, if possible
		final String name;
		if (this.getPrimaryName().isPresent()
				&& prefix.getPrimaryName().isPresent()) {
			name = prefix.getPrimaryName().get() + this.getPrimaryName().get();
		} else {
			name = null;
		}

		final String symbol;
		if (this.getSymbol().isPresent() && prefix.getSymbol().isPresent()) {
			symbol = prefix.getSymbol().get() + this.getSymbol().get();
		} else {
			symbol = null;
		}

		return unit.withName(NameSymbol.ofNullable(name, symbol));
	}
}