/* 
 * 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.data;

import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;

import bjc.funcdata.ListEx;
import bjc.funcdata.bst.TreeLinearizationMethod;

/**
 * A node in a homogeneous tree with a unlimited amount of children.
 *
 * @author ben
 *
 * @param <ContainedType> The type of data contained in the tree nodes.
 *
 */
public interface Tree<ContainedType> {
	/**
	 * Append a child to this node.
	 *
	 * @param child The child to append to this node.
	 */
	void addChild(Tree<ContainedType> child);

	/**
	 * Append a child to this node.
	 *
	 * @param child The child to append to this node.
	 */
	void addChild(ContainedType child);

	/**
	 * Prepend a child to this node.
	 *
	 * @param child The child to prepend to this node.
	 */
	void prependChild(Tree<ContainedType> child);

	/**
	 * Collapse a tree into a single version.
	 *
	 * @param <NewType>         The intermediate type being folded.
	 *
	 * @param <ReturnedType>    The type that is the end result.
	 *
	 * @param leafTransform     The function to use to convert leaf values.
	 *
	 * @param nodeCollapser     The function to use to convert internal nodes and
	 *                          their children.
	 *
	 * @param resultTransformer The function to use to convert a state to the
	 *                          returned version.
	 *
	 * @return The final transformed state.
	 */
	<NewType, ReturnedType> ReturnedType collapse(Function<ContainedType, NewType> leafTransform,
			BiFunction<ContainedType, ListEx<NewType>, NewType> nodeCollapser,
			Function<NewType, ReturnedType> resultTransformer);

	/**
	 * Execute a given action for each of this tree's children.
	 *
	 * @param action The action to execute for each child.
	 */
	void doForChildren(Consumer<Tree<ContainedType>> action);

	/**
	 * Expand the nodes of a tree into trees, and then merge the contents of those
	 * trees into a single tree.
	 *
	 * @param mapper The function to use to map values into trees.
	 *
	 * @return A tree, with some nodes expanded into trees.
	 */
	default Tree<ContainedType> flatMapTree(final Function<ContainedType, Tree<ContainedType>> mapper) {
		return topDownTransform(dat -> TopDownTransformResult.PUSHDOWN, node -> {
			if (node.getChildrenCount() > 0) {
				final Tree<ContainedType> parent = node.transformHead(mapper);

				node.doForChildren(parent::addChild);

				return parent;
			}

			return node.transformHead(mapper);
		});
	}

	/**
	 * Get the specified child of this tree.
	 *
	 * @param childNo The number of the child to get.
	 *
	 * @return The specified child of this tree.
	 */
	default Tree<ContainedType> getChild(final int childNo) {
		return transformChild(childNo, child -> child);
	}

	/**
	 * Get a count of the number of direct children this node has.
	 *
	 * @return The number of direct children this node has.
	 */
	int getChildrenCount();

	/**
	 * Get a count of the number of direct children this node has.
	 *
	 * @return The number of direct children this node has.
	 */
	default int size() {
		return getChildrenCount();
	}

	/**
	 * Get the data stored in this node.
	 *
	 * @return The data stored in this node.
	 */
	default ContainedType getHead() {
		return transformHead(head -> head);
	}

	/**
	 * Rebuild the tree with the same structure, but different nodes.
	 *
	 * @param <MappedType>        The type of the new tree.
	 *
	 * @param leafTransformer     The function to use to transform leaf tokens.
	 *
	 * @param internalTransformer The function to use to transform internal tokens.
	 *
	 * @return The tree, with the nodes changed.
	 */
	<MappedType> Tree<MappedType> rebuildTree(Function<ContainedType, MappedType> leafTransformer,
			Function<ContainedType, MappedType> internalTransformer);

	/**
	 * Transform some of the nodes in this tree.
	 *
	 * @param nodePicker  The predicate to use to pick nodes to transform.
	 *
	 * @param transformer The function to use to transform picked nodes.
	 */
	void selectiveTransform(Predicate<ContainedType> nodePicker, UnaryOperator<ContainedType> transformer);

	/**
	 * Do a top-down transform of the tree.
	 *
	 * @param transformPicker The function to use to pick how to progress.
	 *
	 * @param transformer     The function used to transform picked subtrees.
	 *
	 * @return The tree with the transform applied to picked subtrees.
	 */
	Tree<ContainedType> topDownTransform(Function<ContainedType, TopDownTransformResult> transformPicker,
			UnaryOperator<Tree<ContainedType>> transformer);

	/**
	 * Transform one of this nodes children.
	 *
	 * @param <TransformedType> The type of the transformed value.
	 *
	 * @param childNo           The number of the child to transform.
	 *
	 * @param transformer       The function to use to transform the value.
	 *
	 * @return The transformed value.
	 *
	 * @throws IllegalArgumentException if the childNo is out of bounds (0 &lt;=
	 *                                  childNo &lt;= childCount()).
	 */
	<TransformedType> TransformedType transformChild(int childNo,
			Function<Tree<ContainedType>, TransformedType> transformer);

	/**
	 * Transform the value that is the head of this node.
	 *
	 * @param <TransformedType> The type of the transformed value.
	 *
	 * @param transformer       The function to use to transform the value.
	 *
	 * @return The transformed value.
	 */
	<TransformedType> TransformedType transformHead(Function<ContainedType, TransformedType> transformer);

	/**
	 * Transform the tree into a tree with a different type of token.
	 *
	 * @param <MappedType> The type of the new tree.
	 *
	 * @param transformer  The function to use to transform tokens.
	 *
	 * @return A tree with the token types transformed.
	 */
	default <MappedType> Tree<MappedType> transformTree(final Function<ContainedType, MappedType> transformer) {
		return rebuildTree(transformer, transformer);
	}

	// TODO: Add method which traverses tree, but randomizes order children are
	// visited in
	
	// TODO: Add method which allows parallel traversal of children.
	/**
	 * Perform an action on each part of the tree.
	 *
	 * @param linearizationMethod The way to traverse the tree.
	 *
	 * @param action              The action to perform on each tree node.
	 */
	void traverse(TreeLinearizationMethod linearizationMethod, Consumer<ContainedType> action);

	/**
	 * Find the farthest to right child that satisfies the given predicate.
	 *
	 * @param childPred The predicate to satisfy.
	 *
	 * @return The index of the right-most child that satisfies the predicate, or -1
	 *         if one doesn't exist.
	 */
	int revFind(Predicate<Tree<ContainedType>> childPred);

	/**
	 * Check if this tree contains any nodes that satisfy the predicate.
	 *
	 * @param pred The predicate to look for.
	 *
	 * @return Whether or not any items satisfied the predicate.
	 */
	default boolean containsMatching(Predicate<ContainedType> pred) {
		Toggle<Boolean> tog = new OneWayToggle<>(false, true);

		traverse(TreeLinearizationMethod.POSTORDER, val -> {
			if (pred.test(val))
				tog.get();
		});

		return tog.get();
	}

	/**
	 * Set the head of the tree.
	 *
	 * @param dat The value to set as the head of the tree.
	 */
	void setHead(ContainedType dat);
}