/**
 * 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 unitConverter.dimension;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;

/**
 * An object that represents what a unit measures, like length, mass, area, energy, etc.
 * 
 * @author Adrien Hopkins
 * @since 2018-12-11
 * @since v0.1.0
 */
public final class UnitDimension {
	/**
	 * The unit dimension where every exponent is zero
	 * 
	 * @since 2018-12-12
	 * @since v0.1.0
	 */
	public static final UnitDimension EMPTY = new UnitDimension(new HashMap<>());

	/**
	 * Gets an UnitDimension that has 1 of a certain dimension and nothing else
	 * 
	 * @param dimension
	 *            dimension to get
	 * @return unit dimension
	 * @since 2018-12-11
	 * @since v0.1.0
	 */
	public static final UnitDimension getBase(final BaseDimension dimension) {
		final Map<BaseDimension, Integer> map = new HashMap<>();
		map.put(dimension, 1);
		return new UnitDimension(map);
	}

	/**
	 * The base dimensions that make up this dimension.
	 * 
	 * @since 2018-12-11
	 * @since v0.1.0
	 */
	final Map<BaseDimension, Integer> exponents;

	/**
	 * Creates the {@code UnitDimension}.
	 * 
	 * @param exponents
	 *            base dimensions that make up this dimension
	 * @since 2018-12-11
	 * @since v0.1.0
	 */
	private UnitDimension(final Map<BaseDimension, Integer> exponents) {
		this.exponents = new HashMap<>(exponents);
	}

	/**
	 * Divides this dimension by another
	 * 
	 * @param other
	 *            other dimension
	 * @return quotient of two dimensions
	 * @since 2018-12-11
	 * @since v0.1.0
	 */
	public UnitDimension dividedBy(final UnitDimension other) {
		final Map<BaseDimension, Integer> map = new HashMap<>(this.exponents);

		for (final BaseDimension key : other.exponents.keySet()) {
			if (map.containsKey(key)) {
				// add the dimensions
				map.put(key, map.get(key) - other.exponents.get(key));
			} else {
				map.put(key, -other.exponents.get(key));
			}
		}
		return new UnitDimension(map);
	}

	@Override
	public boolean equals(final Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (!(obj instanceof UnitDimension))
			return false;
		final UnitDimension other = (UnitDimension) obj;

		// anything with a value of 0 is equal to a nonexistent value
		for (final BaseDimension b : this.getBaseSet()) {
			if (this.exponents.get(b) != other.exponents.get(b))
				if (!(this.exponents.get(b) == 0 && !other.exponents.containsKey(b)))
					return false;
		}
		for (final BaseDimension b : other.getBaseSet()) {
			if (this.exponents.get(b) != other.exponents.get(b))
				if (!(other.exponents.get(b) == 0 && !this.exponents.containsKey(b)))
					return false;
		}
		return true;
	}

	/**
	 * @return a set of all of the base dimensions with non-zero exponents that make up this dimension.
	 * @since 2018-12-12
	 * @since v0.1.0
	 */
	public final Set<BaseDimension> getBaseSet() {
		final Set<BaseDimension> dimensions = new HashSet<>();

		// add all dimensions with a nonzero exponent - they shouldn't be there in the first place
		for (final BaseDimension dimension : this.exponents.keySet()) {
			if (!this.exponents.get(dimension).equals(0)) {
				dimensions.add(dimension);
			}
		}

		return dimensions;
	}

	/**
	 * Gets the exponent for a specific dimension.
	 * 
	 * @param dimension
	 *            dimension to check
	 * @return exponent for that dimension
	 * @since 2018-12-12
	 * @since v0.1.0
	 */
	public int getExponent(final BaseDimension dimension) {
		return this.exponents.getOrDefault(dimension, 0);
	}

	@Override
	public int hashCode() {
		return Objects.hash(this.exponents);
	}

	/**
	 * @return true if this dimension is a base, i.e. it has one exponent of one and no other nonzero exponents
	 * @since 2019-01-15
	 * @since v0.1.0
	 */
	public boolean isBase() {
		int oneCount = 0;
		boolean twoOrMore = false; // has exponents of 2 or more
		for (final BaseDimension b : this.getBaseSet()) {
			if (this.exponents.get(b) == 1) {
				oneCount++;
			} else if (this.exponents.get(b) != 0) {
				twoOrMore = true;
			}
		}
		return (oneCount == 0 || oneCount == 1) && !twoOrMore;
	}

	/**
	 * Multiplies this dimension by another
	 * 
	 * @param other
	 *            other dimension
	 * @return product of two dimensions
	 * @since 2018-12-11
	 * @since v0.1.0
	 */
	public UnitDimension times(final UnitDimension other) {
		final Map<BaseDimension, Integer> map = new HashMap<>(this.exponents);

		for (final BaseDimension key : other.exponents.keySet()) {
			if (map.containsKey(key)) {
				// add the dimensions
				map.put(key, map.get(key) + other.exponents.get(key));
			} else {
				map.put(key, other.exponents.get(key));
			}
		}
		return new UnitDimension(map);
	}

	/**
	 * Returns this dimension, but to an exponent
	 * 
	 * @param exp
	 *            exponent
	 * @return result of exponientation
	 * @since 2019-01-15
	 * @since v0.1.0
	 */
	public UnitDimension toExponent(final int exp) {
		final Map<BaseDimension, Integer> map = new HashMap<>(this.exponents);
		for (final BaseDimension key : this.exponents.keySet()) {
			map.put(key, this.getExponent(key) * exp);
		}
		return new UnitDimension(map);
	}

	@Override
	public String toString() {
		final List<String> positiveStringComponents = new ArrayList<>();
		final List<String> negativeStringComponents = new ArrayList<>();

		// for each base dimension that makes up this dimension, add it and its exponent
		for (final BaseDimension dimension : this.getBaseSet()) {
			final int exponent = this.exponents.get(dimension);
			if (exponent > 0) {
				positiveStringComponents.add(String.format("%s^%d", dimension.getSymbol(), exponent));
			} else if (exponent < 0) {
				negativeStringComponents.add(String.format("%s^%d", dimension.getSymbol(), -exponent));
			}
		}

		final String positiveString = positiveStringComponents.isEmpty() ? "1"
				: String.join(" ", positiveStringComponents);
		final String negativeString = negativeStringComponents.isEmpty() ? ""
				: " / " + String.join(" ", negativeStringComponents);

		return positiveString + negativeString;
	}
}