/* 
 * esodata - data structures and other things, of varying utility
 * Copyright 2022, Ben Culkin
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
package bjc.optics;

import static bjc.optics.Lenses.immutable;

import java.util.function.*;

import bjc.typeclasses.BiContainer;

/**
 * A type-invariant var Laarhoven lens.
 * 
 * @author bjcul
 *
 * @param <Whole> The item this lens can focus on
 * @param <Part>  The field this lens focuses on
 */
public interface Lens<Whole, Part>
		extends LensX<Whole, Whole, Part, Part>, BiContainer<Whole, Part, Lens<Whole, Part>> {
	/**
	 * Modify a given whole using an operation
	 * 
	 * @param source The whole to modify.
	 * @param mod    The operation to use for modifying a part
	 * 
	 * @return A modified whole
	 */
	default Whole modify(Whole source, UnaryOperator<Part> mod) {
		return set(source, mod.apply(get(source)));
	}

	/**
	 * Create a function which sets the part of a given whole.
	 * 
	 * @param part The part to set
	 * 
	 * @return A function that sets the given part on a whole.
	 */
	default Function<Whole, Whole> setting(Part part) {
		return (whole) -> set(whole, part);
	}

	/**
	 * Lift a function that modifies parts to one that modifies wholes.
	 * 
	 * @param f The function which operates on parts
	 * 
	 * @return A corresponding function which applies the given modification to a
	 *         part.
	 */
	default Function<Whole, Whole> lift(UnaryOperator<Part> f) {
		// modify will be more efficient for some lenses
		return (whole) -> modify(whole, f);
	}

	/**
	 * Compose two type-variant lenses together.
	 * 
	 * @param <V1>  The first type the second lens focuses on
	 * @param <V2>  The second type the second lens focuses on.
	 * 
	 * @param other The second lens to use.
	 * 
	 * @return A lens composed from this one and the given one.
	 */
	default <V1> Lens<Whole, V1> compose(Lens<Part, V1> other) {
		LensX<Whole, Whole, V1, V1> lensX = immutable((whole) -> other.get(get(whole)),
				(whole, part) -> update(whole, (val2) -> other.set(val2, part)));
		// Note: if lensX is inlined, then the setter function for the lens has to be
		// externalized, otherwise type-inference goes BOOM and everything fails.
		// Should ask on stack overflow why that is
		return (Lens<Whole, V1>) lensX;
	}
}