/**
 * 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.math.RoundingMode;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Optional;

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

/**
 * A possibly uncertain value expressed in a linear unit.
 * 
 * Unless otherwise indicated, all methods in this class throw a
 * {@code NullPointerException} when an argument is null.
 * 
 * @author Adrien Hopkins
 * @since 2020-07-26
 * @since v0.3.0
 */
public final class LinearUnitValue {
	/** The value 1 as a LinearUnitValue. */
	public static final LinearUnitValue ONE = getExact(Metric.ONE, 1);

	/**
	 * Gets an exact {@code LinearUnitValue}
	 * 
	 * @param unit  unit to express with
	 * @param value value to express
	 * @return exact {@code LinearUnitValue} instance
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public static final LinearUnitValue getExact(final LinearUnit unit,
			final double value) {
		return new LinearUnitValue(
				Objects.requireNonNull(unit, "unit must not be null"),
				UncertainDouble.of(value, 0));
	}

	/**
	 * Gets an uncertain {@code LinearUnitValue}
	 * 
	 * @param unit  unit to express with
	 * @param value value to express
	 * @return uncertain {@code LinearUnitValue} instance
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public static final LinearUnitValue of(final LinearUnit unit,
			final UncertainDouble value) {
		return new LinearUnitValue(
				Objects.requireNonNull(unit, "unit must not be null"),
				Objects.requireNonNull(value, "value may not be null"));
	}

	private final LinearUnit unit;

	private final UncertainDouble value;

	/**
	 * @param unit  unit to express as
	 * @param value value to express
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	private LinearUnitValue(final LinearUnit unit, final UncertainDouble value) {
		this.unit = unit;
		this.value = value;
	}

	/**
	 * @return this value as a {@code UnitValue}. All uncertainty information is
	 *         removed from the returned value.
	 * @since 2020-08-04
	 * @since v0.3.0
	 */
	public final UnitValue asUnitValue() {
		return UnitValue.of(this.unit, this.value.value());
	}

	/**
	 * @param other a {@code LinearUnit}
	 * @return true iff this value can be represented with {@code other}.
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public final boolean canConvertTo(final LinearUnit other) {
		return this.unit.canConvertTo(other);
	}

	/**
	 * Returns a LinearUnitValue that represents the same value expressed in a
	 * different unit
	 * 
	 * @param other new unit to express value in
	 * @return value expressed in {@code other}
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public final LinearUnitValue convertTo(final LinearUnit other) {
		return LinearUnitValue.of(other, this.unit.convertTo(other, this.value));
	}

	/**
	 * Convert a LinearUnitValue to a sum of multiple units, where all but the
	 * last have exact integer values.
	 *
	 * @param others units to convert to
	 * @return terms of the sum
	 * @throws IllegalArgumentException if no units are provided or units
	 *                                  provided have incompatible bases
	 * @since 2024-08-15
	 * @since v1.0.0
	 */
	public final List<LinearUnitValue> convertToMultiple(
			final List<LinearUnit> others) {
		if (others.size() < 1)
			throw new IllegalArgumentException("Must have at least one unit");
		for (final LinearUnit unit : others) {
			if (!Objects.equals(this.unit.getBase(), unit.getBase()))
				throw new IllegalArgumentException(
						"All provided units must have the same base as the value.");
		}

		LinearUnitValue remaining = this;
		final List<LinearUnitValue> values = new ArrayList<>(others.size());
		for (final LinearUnit unit : others.subList(0, others.size() - 1)) {
			final LinearUnitValue remainingInUnit = remaining.convertTo(unit);
			final LinearUnitValue value = getExact(unit,
					Math.floor(remainingInUnit.getValueExact() + 1e-12));
			values.add(value);
			remaining = remaining.minus(value);
		}

		final LinearUnitValue lastValue = remaining
				.convertTo(others.get(others.size() - 1));
		values.add(lastValue);
		return values;
	}

	/**
	 * Divides this value by a scalar
	 * 
	 * @param divisor value to divide by
	 * @return multiplied value
	 * @since 2020-07-28
	 * @since v0.3.0
	 */
	public LinearUnitValue dividedBy(final double divisor) {
		return LinearUnitValue.of(this.unit, this.value.dividedByExact(divisor));
	}

	/**
	 * Divides this value by another value
	 * 
	 * @param divisor value to multiply by
	 * @return quotient
	 * @since 2020-07-28
	 * @since v0.3.0
	 */
	public LinearUnitValue dividedBy(final LinearUnitValue divisor) {
		return LinearUnitValue.of(this.unit.dividedBy(divisor.unit),
				this.value.dividedBy(divisor.value));
	}

	/**
	 * Returns true if this and obj represent the same value, regardless of
	 * whether or not they are expressed in the same unit. So (1000 m).equals(1
	 * km) returns true.
	 * 
	 * @since 2020-07-26
	 * @since v0.3.0
	 * @see #equals(Object, boolean)
	 */
	@Override
	public boolean equals(final Object obj) {
		if (!(obj instanceof LinearUnitValue))
			return false;
		final LinearUnitValue other = (LinearUnitValue) obj;
		return Objects.equals(this.unit.getBase(), other.unit.getBase())
				&& this.unit.convertToBase(this.value)
						.equals(other.unit.convertToBase(other.value));
	}

	/**
	 * Returns true if this and obj represent the same value, regardless of
	 * whether or not they are expressed in the same unit. So (1000 m).equals(1
	 * km) returns true.
	 * 
	 * @param obj           object to test equality with
	 * @param avoidFPErrors if true, this method will attempt to avoid
	 *                      floating-point errors, at the cost of not always
	 *                      being transitive.
	 * @return true iff this and obj are equal
	 * 
	 * @since 2020-07-28
	 * @since v0.3.0
	 */
	public boolean equals(final Object obj, final boolean avoidFPErrors) {
		if (!avoidFPErrors)
			return this.equals(obj);
		if (!(obj instanceof LinearUnitValue))
			return false;
		final LinearUnitValue other = (LinearUnitValue) obj;
		return Objects.equals(this.unit.getBase(), other.unit.getBase())
				&& DecimalComparison.equals(this.unit.convertToBase(this.value),
						other.unit.convertToBase(other.value));
	}

	/**
	 * @param other another {@code LinearUnitValue}
	 * @return true iff this and other are within each other's uncertainty range
	 * 
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public boolean equivalent(final LinearUnitValue other) {
		if (other == null
				|| !Objects.equals(this.unit.getBase(), other.unit.getBase()))
			return false;
		final LinearUnit base = LinearUnit.valueOf(this.unit.getBase(), 1);
		final LinearUnitValue thisBase = this.convertTo(base);
		final LinearUnitValue otherBase = other.convertTo(base);

		return thisBase.value.equivalent(otherBase.value);
	}

	/**
	 * @return the unit
	 * @since 2020-09-29
	 * @since v0.3.0
	 */
	public final LinearUnit getUnit() {
		return this.unit;
	}

	/**
	 * @return the value
	 * @since 2020-09-29
	 * @since v0.3.0
	 */
	public final UncertainDouble getValue() {
		return this.value;
	}

	/**
	 * @return the exact value
	 * @since 2020-09-07
	 * @since v0.3.0
	 */
	public final double getValueExact() {
		return this.value.value();
	}

	@Override
	public int hashCode() {
		return Objects.hash(this.unit.getBase(),
				this.unit.convertToBase(this.getValue()));
	}

	/**
	 * Returns the difference of this value and another, expressed in this
	 * value's unit
	 * 
	 * @param subtrahend value to subtract
	 * @return difference of values
	 * @throws IllegalArgumentException if {@code subtrahend} has a unit that is
	 *                                  not compatible for addition
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public LinearUnitValue minus(final LinearUnitValue subtrahend) {
		Objects.requireNonNull(subtrahend, "subtrahend may not be null");

		if (!this.canConvertTo(subtrahend.unit))
			throw new IllegalArgumentException(String.format(
					"Incompatible units for subtraction \"%s\" and \"%s\".",
					this.unit, subtrahend.unit));

		final LinearUnitValue otherConverted = subtrahend.convertTo(this.unit);
		return LinearUnitValue.of(this.unit,
				this.value.minus(otherConverted.value));
	}

	/**
	 * Returns the sum of this value and another, expressed in this value's unit
	 * 
	 * @param addend value to add
	 * @return sum of values
	 * @throws IllegalArgumentException if {@code addend} has a unit that is not
	 *                                  compatible for addition
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public LinearUnitValue plus(final LinearUnitValue addend) {
		Objects.requireNonNull(addend, "addend may not be null");

		if (!this.canConvertTo(addend.unit))
			throw new IllegalArgumentException(String.format(
					"Incompatible units for addition \"%s\" and \"%s\".", this.unit,
					addend.unit));

		final LinearUnitValue otherConverted = addend.convertTo(this.unit);
		return LinearUnitValue.of(this.unit,
				this.value.plus(otherConverted.value));
	}

	/**
	 * Multiplies this value by a scalar
	 * 
	 * @param multiplier value to multiply by
	 * @return multiplied value
	 * @since 2020-07-28
	 * @since v0.3.0
	 */
	public LinearUnitValue times(final double multiplier) {
		return LinearUnitValue.of(this.unit, this.value.timesExact(multiplier));
	}

	/**
	 * Multiplies this value by another value
	 * 
	 * @param multiplier value to multiply by
	 * @return product
	 * @since 2020-07-28
	 * @since v0.3.0
	 */
	public LinearUnitValue times(final LinearUnitValue multiplier) {
		return LinearUnitValue.of(this.unit.times(multiplier.unit),
				this.value.times(multiplier.value));
	}

	/**
	 * Raises a value to an exponent
	 * 
	 * @param exponent exponent to raise to
	 * @return result of exponentiation
	 * @since 2020-07-28
	 * @since v0.3.0
	 */
	public LinearUnitValue toExponent(final int exponent) {
		return LinearUnitValue.of(this.unit.toExponent(exponent),
				this.value.toExponentExact(exponent));
	}

	/**
	 * Raises this value to an exponent, rounding all dimensions to integers.
	 * 
	 * @param exponent exponent to raise this value to
	 * @return result of exponentation
	 *
	 * @since 2024-08-22
	 * @since v1.0.0
	 * @see ObjectProduct#toExponentRounded
	 */
	public LinearUnitValue toExponentRounded(final double exponent) {
		return LinearUnitValue.of(this.unit.toExponentRounded(exponent),
				this.value.toExponentExact(exponent));
	}

	@Override
	public String toString() {
		return this.toString(!this.value.isExact(), RoundingMode.HALF_EVEN);
	}

	/**
	 * Returns a string representing the object. <br>
	 * If the attached unit has a name or symbol, the string looks like "12 km".
	 * Otherwise, it looks like "13 unnamed unit (= 2 m/s)".
	 * <p>
	 * If showUncertainty is true, strings like "35 � 8" are shown instead of
	 * single numbers.
	 * <p>
	 * Non-exact values are rounded intelligently based on their uncertainty.
	 * 
	 * @param showUncertainty whether to show the value's uncertainty
	 * @param roundingMode how to round numbers in this string
	 * @return string representing this value
	 * 
	 * @since 2020-07-26
	 * @since v0.3.0
	 */
	public String toString(final boolean showUncertainty,
			RoundingMode roundingMode) {
		final Optional<String> primaryName = this.unit.getPrimaryName();
		final Optional<String> symbol = this.unit.getSymbol();
		final String chosenName = symbol.orElse(primaryName.orElse(null));

		final UncertainDouble baseValue = this.unit.convertToBase(this.value);

		// get rounded strings
		// if showUncertainty is true, add brackets around the string
		final String valueString = (showUncertainty ? "(" : "")
				+ this.value.toString(showUncertainty, roundingMode)
				+ (showUncertainty ? ")" : "");
		final String baseValueString = (showUncertainty ? "(" : "")
				+ baseValue.toString(showUncertainty, roundingMode)
				+ (showUncertainty ? ")" : "");

		// create string
		if (chosenName == null)
			return String.format("%s unnamed unit (= %s %s)", valueString,
					baseValueString, this.unit.getBase()
							.toString(unit -> unit.getSymbol().orElseThrow()));
		else
			return String.format("%s %s", valueString, chosenName);
	}
}