/*
 * Java Genetic Algorithm Library (jenetics-8.0.0).
 * Copyright (c) 2007-2024 Franz Wilhelmstötter
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Author:
 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
 */
package io.jenetics.ext.util;

import static java.lang.String.format;
import static java.util.Objects.requireNonNull;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.Serial;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Optional;
import java.util.function.Function;
import java.util.stream.Stream;

import io.jenetics.util.Copyable;

/**
 * A general purpose node in a tree data-structure. The {@code TreeNode} is a
 * mutable implementation of the {@link Tree} interface.
 *
 * @param <T> the value type of the tree node
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 5.2
 * @since 3.9
 */
public final class TreeNode<T>
        implements
                Tree<T, TreeNode<T>>,
                Iterable<TreeNode<T>>,
                Copyable<TreeNode<T>>,
                Serializable
{
        @Serial
        private static final long serialVersionUID = 2L;

        private T _value;
        private TreeNode<T> _parent;
        private List<TreeNode<T>> _children;

        /**
         * Create a new tree node with no parent and children, but with the given
         * user {@code value}.
         *
         * @param value the user value of the new tree node
         */
        private TreeNode(final T value) {
                _value = value;
        }


        /* *************************************************************************
         * Basic operations
         **************************************************************************/

        /**
         * Sets the user object for this node.
         *
         * @param value the node {@code value}
         */
        public void value(final T value) {
                _value = value;
        }

        /**
         * Return the node value
         *
         * @return the node value
         */
        @Override
        public T value() {
                return _value;
        }

        /**
         * Returns this node's parent if available.
         *
         * @return the tree-node, or an empty value if this node has no parent
         */
        @Override
        public Optional<TreeNode<T>> parent() {
                return Optional.ofNullable(_parent);
        }

        /**
         * Sets this node's parent, but does not change the parent's child array.
         * This method is called from {@code insert()} and {@code remove()} to
         * reassign a child's parent, and it should not be messaged from anywhere
         * else.
         *
         * @param parent this node's new parent
         */
        void parent(final TreeNode<T> parent) {
                _parent = parent;
        }

        /**
         * Returns the child at the specified index in this node's child array.
         *
         * @param index   an index into this node's child array
         * @return the tree-node in this node's child array at the specified index
         * @throws ArrayIndexOutOfBoundsException  if the {@code index} is out of
         *         bounds
         */
        @Override
        public TreeNode<T> childAt(final int index) {
                if (_children == null) {
                        throw new ArrayIndexOutOfBoundsException(format(
                                "Child index is out of bounds: %s", index
                        ));
                }

                return _children.get(index);
        }

        @Override
        public int childCount() {
                return _children != null ? _children.size() : 0;
        }

        @Override
        public Iterator<TreeNode<T>> childIterator() {
                return _children != null
                        ? _children.iterator()
                        : Collections.emptyIterator();
        }

        @Override
        public Stream<TreeNode<T>> childStream() {
                return _children != null
                        ? _children.stream()
                        : Stream.empty();
        }

        /**
         * Removes the {@code child} from its present parent (if it has one), sets
         * the child's parent to this node, and then adds the child to this node's
         * child array at index {@code index}. The new {@code child} must not be
         * {@code null} and must not be an ancestor of {@code this} node.
         *
         * @param index the index in the child array where this node is to be
         *        inserted
         * @param child the sub-node to be inserted
         * @return {@code this} tree-node, for method chaining
         * @throws ArrayIndexOutOfBoundsException if {@code index} is out of bounds
         * @throws IllegalArgumentException if {@code child} is an ancestor of
         *         {@code this} node
         * @throws NullPointerException if the given {@code child} is {@code null}
         */
        public TreeNode<T> insert(final int index, final TreeNode<T> child) {
                requireNonNull(child);
                if (isAncestor(child)) {
                        throw new IllegalArgumentException("The new child is an ancestor.");
                }

                if (child._parent != null) {
                        child._parent.remove(child);
                }

                child.parent(this);
                createChildrenIfMissing();
                _children.add(index, child);

                return this;
        }

        // Only entry point for checking and creating a non-existing children list.
        private void createChildrenIfMissing() {
                if (_children == null) {
                        _children = new ArrayList<>(2);
                }
        }

        /**
         * Replaces the child at the give index with the given {@code child}
         *
         * @param index the index of the child which will be replaced
         * @param child the new child
         * @return {@code this} tree-node, for method chaining
         * @throws ArrayIndexOutOfBoundsException  if the {@code index} is out of
         *         bounds
         * @throws IllegalArgumentException if {@code child} is an ancestor of
         *         {@code this} node
         * @throws NullPointerException if the given {@code child} is {@code null}
         */
        public TreeNode<T> replace(final int index, final TreeNode<T> child) {
                requireNonNull(child);
                if (_children == null) {
                        throw new ArrayIndexOutOfBoundsException(format(
                                "Child index is out of bounds: %s", index
                        ));
                }
                if (isAncestor(child)) {
                        throw new IllegalArgumentException("The new child is an ancestor.");
                }

                final TreeNode<T> oldChild = _children.set(index, child);
                assert oldChild != null;
                assert oldChild._parent == this;

                oldChild.parent(null);
                child.parent(this);

                return this;
        }

        /**
         * Removes the child at the specified index from this node's children and
         * sets that node's parent to {@code null}.
         *
         * @param index the index in this node's child array of the child to remove
         * @return {@code this} tree-node, for method chaining
         * @throws ArrayIndexOutOfBoundsException  if the {@code index} is out of
         *         bounds
         */
        public TreeNode<T> remove(final int index) {
                if (_children == null) {
                        throw new ArrayIndexOutOfBoundsException(format(
                                "Child index is out of bounds: %s", index
                        ));
                }

                final TreeNode<T> child = _children.remove(index);
                assert child._parent == this;
                child.parent(null);

                if (_children.isEmpty()) {
                        _children = null;
                }

                return this;
        }

        /**
         * Removes the child at the given {@code path}. If no child exists on the
         * given path, nothing is removed.
         *
         * @since 4.4
         *
         * @param path the path of the child to replace
         * @return {@code true} if a child at the given {@code path} existed and
         *         has been removed
         * @throws NullPointerException if one of the given arguments is {@code null}
         */
        public boolean removeAtPath(final Path path) {
                final Optional<TreeNode<T>> parent = childAtPath(path)
                        .flatMap(Tree::parent);

                parent.ifPresent(p -> p.remove(path.get(path.length() - 1)));
                return parent.isPresent();
        }

        /**
         * Replaces the child at the given {@code path} with the given new
         * {@code child}. If no child exists on the given path, nothing is replaced.
         *
         * @since 4.4
         *
         * @param path the path of the child to replace
         * @param child the new child
         * @return {@code true} if a child at the given {@code path} existed and
         *         has been replaced
         * @throws NullPointerException if one of the given arguments is {@code null}
         */
        public boolean replaceAtPath(final Path path, final TreeNode<T> child) {
                requireNonNull(path);
                requireNonNull(child);

                final Optional<TreeNode<T>> old = childAtPath(path);
                final Optional<TreeNode<T>> parent = old.flatMap(TreeNode::parent);

                parent.ifPresentOrElse(
                        p -> p.replace(path.get(path.length() - 1), child),
                        () -> {
                                removeAllChildren();
                                value(child.value());

                                // Need to create a copy of the children, before attaching it.
                                final List<TreeNode<T>> nodes = child._children != null
                                        ? List.copyOf(child._children)
                                        : List.of();

                                nodes.forEach(this::attach);
                        }
                );

                return old.isPresent();
        }

        /* *************************************************************************
         * Derived operations
         **************************************************************************/

        /**
         * Detaches the subtree rooted at {@code this} node from the tree, giving
         * {@code this} node a {@code null} parent. Does nothing if {@code this}
         * node is the root of its tree.
         *
         * @return {@code this}
         */
        public TreeNode<T> detach() {
                if (_parent != null) {
                        _parent.remove(this);
                }

                return this;
        }

        /**
         * Remove the {@code child} from {@code this} node's child array, giving it
         * a {@code null} parent.
         *
         * @param child the child of this node to remove
         * @throws NullPointerException if the given {@code child} is {@code null}
         * @throws IllegalArgumentException if the given {@code child} is not a
         *         child of this node
         */
        public void remove(final Tree<?, ?> child) {
                requireNonNull(child);

                if (!isChild(child)) {
                        throw new IllegalArgumentException("The given child is not a child.");
                }
                remove(indexOf(child));
        }

        /**
         * Removes all children fo {@code this} node and setting their parents to
         * {@code null}. If {@code this} node has no children, this method does
         * nothing.
         */
        public void removeAllChildren() {
                if (_children != null) {
                        for (TreeNode<T> child : _children) {
                                child.parent(null);
                        }

                        _children = null;
                }
        }

        /**
         * Remove the given {@code child} from its parent and makes it a child of
         * this node by adding it to the end of this node's child array.
         *
         * @param child the new child added to this node
         * @return {@code this} tree-node, for method chaining
         * @throws NullPointerException if the given {@code child} is {@code null}
         */
        public TreeNode<T> attach(final TreeNode<T> child) {
                requireNonNull(child);

                if (child._parent == this) {
                        insert(childCount() - 1, child);
                } else {
                        insert(childCount(), child);
                }

                return this;
        }

        /**
         * Attaches the given {@code children} to {@code this} node.
         *
         * @param children the children to attach to {@code this} node
         * @return {@code this} tree-node, for method chaining
         * @throws NullPointerException if the given {@code children} array is
         *         {@code null}
         */
        @SafeVarargs
        public final TreeNode<T> attach(final T... children) {
                for (T child : children) {
                        attach(TreeNode.of(child));
                }

                return this;
        }

        /**
         * Attaches the given {@code child} to {@code this} node.
         *
         * @param child the child to attach to {@code this} node
         * @return {@code this} tree-node, for method chaining
         */
        public TreeNode<T> attach(final T child) {
                return attach(TreeNode.of(child));
        }

        @Override
        public TreeNode<T> copy() {
                return ofTree(this);
        }

        /**
         * Returns a new {@code TreeNode} consisting of all nodes of {@code this}
         * tree, but with a different value type, created by applying the given
         * function to the node values of {@code this} tree.
         *
         * @param mapper the node value mapper
         * @param <B> the new node type
         * @return a new tree consisting of all nodes of {@code this} tree
         * @throws NullPointerException if the given {@code mapper} function is
         *         {@code null}
         */
        public <B> TreeNode<B> map(final Function<? super T, ? extends B> mapper) {
                final TreeNode<B> target = TreeNode.of(mapper.apply(value()));
                copy(this, target, mapper);
                return target;
        }


        @Override
        public int hashCode() {
                return Tree.hashCode(this);
        }

        @Override
        public boolean equals(final Object obj) {
                return obj instanceof Tree<?, ?> other && Tree.equals(this, other);
        }

        @Override
        public String toString() {
                return toParenthesesString();
        }



        /* *************************************************************************
         * Static factory methods.
         **************************************************************************/

        /**
         * Return a new {@code TreeNode} with a {@code null} tree value.
         *
         * @param <T> the tree-node type
         * @return a new tree-node
         */
        public static <T> TreeNode<T> of() {
                return TreeNode.of(null);
        }

        /**
         * Return a new {@code TreeNode} with the given node {@code value}.
         *
         * @param value the node value
         * @param <T> the tree-node type
         * @return a new tree-node
         */
        public static <T> TreeNode<T> of(final T value) {
                return new TreeNode<>(value);
        }

        /**
         * Return a new {@code TreeNode} from the given source {@code tree}. The
         * whole tree is copied.
         *
         * @param tree the source tree the new tree-node is created from
         * @param mapper the tree value mapper function
         * @param <T> the current tree value type
         * @param <B> the mapped tree value type
         * @return a new {@code TreeNode} from the given source {@code tree}
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <T, B> TreeNode<B> ofTree(
                final Tree<? extends T, ?> tree,
                final Function<? super T, ? extends B> mapper
        ) {
                final TreeNode<B> target = of(mapper.apply(tree.value()));
                copy(tree, target, mapper);
                return target;
        }

        private static <T, B> void copy(
                final Tree<? extends T, ?> source,
                final TreeNode<B> target,
                final Function<? super T, ? extends B> mapper
        ) {
                for (int i = 0; i < source.childCount(); ++i) {
                        final var child = source.childAt(i);
                        final TreeNode<B> targetChild = of(mapper.apply(child.value()));
                        target.attach(targetChild);
                        copy(child, targetChild, mapper);
                }
        }

        /**
         * Return a new {@code TreeNode} from the given source {@code tree}. The
         * whole tree is copied.
         *
         * @param tree the source tree the new tree-node is created from
         * @param <T> the current tree value type
         * @return a new {@code TreeNode} from the given source {@code tree}
         * @throws NullPointerException if the source {@code tree} is {@code null}
         */
        public static <T> TreeNode<T> ofTree(final Tree<? extends T, ?> tree) {
                return ofTree(tree, Function.identity());
        }

        /**
         * Parses a (parentheses) tree string, created with
         * {@link Tree#toParenthesesString()}. The tree string might look like this:
         * <pre>
         *  mul(div(cos(1.0),cos(π)),sin(mul(1.0,z)))
         * </pre>
         *
         * The parse method doesn't strip the space between the parentheses and
         * the commas. If you want to remove this <em>formatting</em> space,
         * you should do the parsing with an addition <em>mapper</em> function.
         * {@snippet lang="java":
         * final TreeNode<String> tree = TreeNode.parse(
         *     "mul(  div(cos( 1.0) , cos(π )), sin(mul(1.0, z) ) )",
         *     String::trim
         * );
         * }
         * The code above will trim all tree nodes during the parsing process.
         *
         * @see Tree#toParenthesesString(Function)
         * @see Tree#toParenthesesString()
         * @see TreeNode#parse(String, Function)
         *
         * @since 4.3
         *
         * @param tree the parentheses tree string
         * @return the parsed tree
         * @throws NullPointerException if the given {@code tree} string is
         *         {@code null}
         * @throws IllegalArgumentException if the given tree string could not be
         *         parsed
         */
        public static TreeNode<String> parse(final String tree) {
                return ParenthesesTreeParser.parse(tree, Function.identity());
        }

        /**
         * Parses a (parentheses) tree string, created with
         * {@link Tree#toParenthesesString()}. The tree string might look like this
         * <pre>
         *  0(1(4,5),2(6),3(7(10,11),8,9))
         * </pre>
         * and can be parsed to an integer tree with the following code:
         * {@snippet lang="java":
         * final Tree<Integer, ?> tree = TreeNode.parse(
         *     "0(1(4,5),2(6),3(7(10,11),8,9))",
         *     Integer::parseInt
         * );
         * }
         *
         * @see Tree#toParenthesesString(Function)
         * @see Tree#toParenthesesString()
         * @see TreeNode#parse(String)
         *
         * @since 4.3
         *
         * @param <B> the tree node value type
         * @param tree the parentheses tree string
         * @param mapper the mapper which converts the serialized string value to
         *        the desired type
         * @return the parsed tree object
         * @throws NullPointerException if one of the arguments is {@code null}
         * @throws IllegalArgumentException if the given parentheses tree string
         *         doesn't represent a valid tree
         */
        public static <B> TreeNode<B> parse(
                final String tree,
                final Function<? super String, ? extends B> mapper
        ) {
                return ParenthesesTreeParser.parse(tree, mapper);
        }


        /* *************************************************************************
         *  Java object serialization
         * ************************************************************************/

        @Serial
        private Object writeReplace() {
                return new SerialProxy(SerialProxy.TREE_NODE, this);
        }

        @Serial
        private void readObject(final ObjectInputStream stream)
                throws InvalidObjectException
        {
                throw new InvalidObjectException("Serialization proxy required.");
        }


        void write(final ObjectOutput out) throws IOException {
                FlatTreeNode.ofTree(this).write(out);
        }

        @SuppressWarnings("unchecked")
        static Object read(final ObjectInput in)
                throws IOException, ClassNotFoundException
        {
                return TreeNode.ofTree(FlatTreeNode.read(in));
        }

}