/**
 * Copyright (C) 2020 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.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.function.DoubleFunction;
import java.util.function.ToDoubleFunction;

import org.unitConverter.math.ObjectProduct;

/**
 * An object that can convert a value between multiple forms (instances of the
 * object); like a unit but the "converted value" can be any type.
 *
 * @since 2020-09-07
 */
public abstract class Unitlike<V> implements Nameable {
	/**
	 * Returns a unitlike form from its base and the functions it uses to convert
	 * to and from its base.
	 * 
	 * @param base          unitlike form's base
	 * @param converterFrom function that accepts a value expressed in the
	 *                      unitlike form's base and returns that value expressed
	 *                      in this unitlike form.
	 * @param converterTo   function that accepts a value expressed in the
	 *                      unitlike form and returns that value expressed in the
	 *                      unit's base.
	 * @return a unitlike form that uses the provided functions to convert.
	 * @since 2020-09-07
	 * @throws NullPointerException if any argument is null
	 */
	public static final <W> Unitlike<W> fromConversionFunctions(
			final ObjectProduct<BaseUnit> base,
			final DoubleFunction<W> converterFrom,
			final ToDoubleFunction<W> converterTo) {
		return new FunctionalUnitlike<>(base, NameSymbol.EMPTY, converterFrom,
				converterTo);
	}
	
	/**
	 * Returns a unitlike form from its base and the functions it uses to convert
	 * to and from its base.
	 * 
	 * @param base          unitlike form's base
	 * @param converterFrom function that accepts a value expressed in the
	 *                      unitlike form's base and returns that value expressed
	 *                      in this unitlike form.
	 * @param converterTo   function that accepts a value expressed in the
	 *                      unitlike form and returns that value expressed in the
	 *                      unit's base.
	 * @param ns            names and symbol of unit
	 * @return a unitlike form that uses the provided functions to convert.
	 * @since 2020-09-07
	 * @throws NullPointerException if any argument is null
	 */
	public static final <W> Unitlike<W> fromConversionFunctions(
			final ObjectProduct<BaseUnit> base,
			final DoubleFunction<W> converterFrom,
			final ToDoubleFunction<W> converterTo, final NameSymbol ns) {
		return new FunctionalUnitlike<>(base, ns, converterFrom, converterTo);
	}
	
	/**
	 * The combination of units that this unit is based on.
	 * 
	 * @since 2019-10-16
	 */
	private final ObjectProduct<BaseUnit> unitBase;
	
	/**
	 * This unit's name(s) and symbol
	 * 
	 * @since 2020-09-07
	 */
	private final NameSymbol nameSymbol;
	
	/**
	 * Cache storing the result of getDimension()
	 *
	 * @since 2019-10-16
	 */
	private transient ObjectProduct<BaseDimension> dimension = null;
	
	/**
	 * @param unitBase
	 * @since 2020-09-07
	 */
	Unitlike(ObjectProduct<BaseUnit> unitBase, NameSymbol ns) {
		this.unitBase = Objects.requireNonNull(unitBase,
				"unitBase may not be null");
		this.nameSymbol = Objects.requireNonNull(ns, "ns may not be null");
	}
	
	/**
	 * Checks if a value expressed in this unitlike form can be converted to a
	 * value expressed in {@code other}
	 * 
	 * @param other unit or unitlike form to test with
	 * @return true if they are compatible
	 * @since 2019-01-13
	 * @since v0.1.0
	 * @throws NullPointerException if other is null
	 */
	public final boolean canConvertTo(final Unit other) {
		Objects.requireNonNull(other, "other must not be null.");
		return Objects.equals(this.getBase(), other.getBase());
	}
	
	/**
	 * Checks if a value expressed in this unitlike form can be converted to a
	 * value expressed in {@code other}
	 * 
	 * @param other unit or unitlike form to test with
	 * @return true if they are compatible
	 * @since 2019-01-13
	 * @since v0.1.0
	 * @throws NullPointerException if other is null
	 */
	public final <W> boolean canConvertTo(final Unitlike<W> other) {
		Objects.requireNonNull(other, "other must not be null.");
		return Objects.equals(this.getBase(), other.getBase());
	}
	
	protected abstract V convertFromBase(double value);
	
	/**
	 * Converts a value expressed in this unitlike form to a value expressed in
	 * {@code other}.
	 * 
	 * @implSpec If conversion is possible, this implementation returns
	 *           {@code other.convertFromBase(this.convertToBase(value))}.
	 *           Therefore, overriding either of those methods will change the
	 *           output of this method.
	 * 
	 * @param other unit to convert to
	 * @param value value to convert
	 * @return converted value
	 * @since 2019-05-22
	 * @throws IllegalArgumentException if {@code other} is incompatible for
	 *                                  conversion with this unitlike form (as
	 *                                  tested by {@link Unit#canConvertTo}).
	 * @throws NullPointerException     if other is null
	 */
	public final double convertTo(final Unit other, final V value) {
		Objects.requireNonNull(other, "other must not be null.");
		if (this.canConvertTo(other))
			return other.convertFromBase(this.convertToBase(value));
		else
			throw new IllegalArgumentException(
					String.format("Cannot convert from %s to %s.", this, other));
	}
	
	/**
	 * Converts a value expressed in this unitlike form to a value expressed in
	 * {@code other}.
	 * 
	 * @implSpec If conversion is possible, this implementation returns
	 *           {@code other.convertFromBase(this.convertToBase(value))}.
	 *           Therefore, overriding either of those methods will change the
	 *           output of this method.
	 * 				
	 * @param other unitlike form to convert to
	 * @param value value to convert
	 * @param <W>   type of value to convert to
	 * @return converted value
	 * @since 2020-09-07
	 * @throws IllegalArgumentException if {@code other} is incompatible for
	 *                                  conversion with this unitlike form (as
	 *                                  tested by {@link Unit#canConvertTo}).
	 * @throws NullPointerException     if other is null
	 */
	public final <W> W convertTo(final Unitlike<W> other, final V value) {
		Objects.requireNonNull(other, "other must not be null.");
		if (this.canConvertTo(other))
			return other.convertFromBase(this.convertToBase(value));
		else
			throw new IllegalArgumentException(
					String.format("Cannot convert from %s to %s.", this, other));
	}
	
	protected abstract double convertToBase(V value);
	
	/**
	 * @return combination of units that this unit is based on
	 * @since 2018-12-22
	 * @since v0.1.0
	 */
	public final ObjectProduct<BaseUnit> getBase() {
		return this.unitBase;
	}
	
	/**
	 * @return dimension measured by this unit
	 * @since 2018-12-22
	 * @since v0.1.0
	 */
	public final ObjectProduct<BaseDimension> getDimension() {
		if (this.dimension == null) {
			final Map<BaseUnit, Integer> mapping = this.unitBase.exponentMap();
			final Map<BaseDimension, Integer> dimensionMap = new HashMap<>();
			
			for (final BaseUnit key : mapping.keySet()) {
				dimensionMap.put(key.getBaseDimension(), mapping.get(key));
			}
			
			this.dimension = ObjectProduct.fromExponentMapping(dimensionMap);
		}
		return this.dimension;
	}
	
	/**
	 * @return the nameSymbol
	 * @since 2020-09-07
	 */
	@Override
	public final NameSymbol getNameSymbol() {
		return this.nameSymbol;
	}
	
	@Override
	public String toString() {
		return this.getPrimaryName().orElse("Unnamed unitlike form")
				+ (this.getSymbol().isPresent()
						? String.format(" (%s)", this.getSymbol().get())
						: "")
				+ ", derived from "
				+ this.getBase().toString(u -> u.getSymbol().get())
				+ (this.getOtherNames().isEmpty() ? ""
						: ", also called " + String.join(", ", this.getOtherNames()));
	}
	
	/**
	 * @param ns name(s) and symbol to use
	 * @return a copy of this unitlike form with provided name(s) and symbol
	 * @since 2020-09-07
	 * @throws NullPointerException if ns is null
	 */
	public Unitlike<V> withName(final NameSymbol ns) {
		return fromConversionFunctions(this.getBase(), this::convertFromBase,
				this::convertToBase,
				Objects.requireNonNull(ns, "ns must not be null."));
	}
}