/*
 * Java Genetic Algorithm Library (jenetics-8.3.0).
 * Copyright (c) 2007-2025 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.util.Objects.requireNonNull;
import static io.jenetics.internal.util.SerialIO.readIntArray;
import static io.jenetics.internal.util.SerialIO.readObjectArray;
import static io.jenetics.internal.util.SerialIO.writeIntArray;
import static io.jenetics.internal.util.SerialIO.writeObjectArray;

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.lang.reflect.Array;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Optional;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import io.jenetics.util.ISeq;

/**
 * Default implementation of the {@link FlatTree} interface. Beside the
 * flattened and dense layout it is also an <em>immutable</em> implementation of
 * the {@link Tree} interface. It can only be created from an existing tree.
 * {@snippet lang="java":
 * final Tree<String, ?> immutable = FlatTreeNode.ofTree(TreeNode.parse(null)); // @replace substring='null' replacement="..."
 * }
 *
 * @implNote
 * This class is immutable and thread-safe.
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 7.1
 * @since 3.9
 */
public final class FlatTreeNode<V>
        implements
                FlatTree<V, FlatTreeNode<V>>,
                Serializable
{

        /**
         * The flattened tree nodes.
         */
        private record Nodes(Object[] values, int[] childOffsets, int[] childCounts) {
                Nodes(final int size) {
                        this(new Object[size], new int[size], new int[size]);
                }
        }

        @Serial
        private static final long serialVersionUID = 3L;

        private static final int NULL_INDEX = -1;

        private final Nodes _nodes;
        private final int _index;

        private FlatTreeNode(final Nodes nodes, final int index) {
                _nodes = requireNonNull(nodes);
                _index = index;
        }

        private FlatTreeNode(final Nodes nodes) {
                this(nodes, 0);
        }

        /**
         * Returns the root of the tree that contains this node. The root is the
         * ancestor with no parent. This implementation has a runtime complexity
         * of O(1).
         *
         * @return the root of the tree that contains this node
         */
        @Override
        public FlatTreeNode<V> root() {
                return nodeAt(0);
        }

        @Override
        public boolean isRoot() {
                return _index == 0;
        }

        private FlatTreeNode<V> nodeAt(final int index) {
                return new FlatTreeNode<>(_nodes, index);
        }

        @SuppressWarnings("unchecked")
        @Override
        public V value() {
                return (V)_nodes.values[_index];
        }

        @Override
        public Optional<FlatTreeNode<V>> parent() {
                int index = NULL_INDEX;
                for (int i = _index; --i >= 0 && index == NULL_INDEX;) {
                        if (isParent(i)) {
                                index = i;
                        }
                }

                return index != NULL_INDEX
                        ? Optional.of(nodeAt(index))
                        : Optional.empty();
        }

        private boolean isParent(final int index) {
                return _nodes.childCounts[index] > 0 &&
                        _nodes.childOffsets[index] <= _index &&
                        _nodes.childOffsets[index] + _nodes.childCounts[index] > _index;
        }

        @Override
        public FlatTreeNode<V> childAt(final int index) {
                if (index < 0 || index >= childCount()) {
                        throw new IndexOutOfBoundsException(Integer.toString(index));
                }

                return nodeAt(childOffset() + index);
        }

        @Override
        public int childCount() {
                return _nodes.childCounts[_index];
        }

        /**
         * Return the index of the first child node in the underlying node array.
         * {@code -1} is returned if {@code this} node is a leaf.
         *
         * @return Return the index of the first child node in the underlying node
         *         array, or {@code -1} if {@code this} node is a leaf
         */
        @Override
        public int childOffset() {
                return _nodes.childOffsets[_index];
        }

        @Override
        public ISeq<FlatTreeNode<V>> flattenedNodes() {
                return stream().collect(ISeq.toISeq());
        }

        @Override
        public Iterator<FlatTreeNode<V>> breadthFirstIterator() {
                return isRoot()
                        ? new IntFunctionIterator<>(this::nodeAt, _nodes.values.length)
                        : FlatTree.super.breadthFirstIterator();
        }

        @Override
        public Stream<FlatTreeNode<V>> breadthFirstStream() {
                return isRoot()
                        ? IntStream.range(0, _nodes.values.length).mapToObj(this::nodeAt)
                        : FlatTree.super.breadthFirstStream();
        }

        /**
         * Return a sequence of all <em>mapped</em> nodes of the whole underlying
         * tree. This is a convenient method for
         * {@snippet lang="java":
         * final ISeq<B> seq = stream()
         *     .map(mapper)
         *     .collect(ISeq.toISeq());
         * }
         *
         * @param mapper the mapper function
         * @param <B> the mapped type
         * @return a sequence of all <em>mapped</em> nodes
         */
        public <B> ISeq<B>
        map(final Function<? super FlatTreeNode<V>, ? extends B> mapper) {
                return stream()
                        .map(mapper)
                        .collect(ISeq.toISeq());
        }

        @Override
        public boolean identical(final Tree<?, ?> other) {
                return other instanceof FlatTreeNode<?> node &&
                        node._index == _index &&
                        node._nodes == _nodes;
        }

        @Override
        public <U> U reduce(
                final U[] neutral,
                final BiFunction<? super V, ? super U[], ? extends U> reducer
        ) {
                requireNonNull(neutral);
                requireNonNull(reducer);

                @SuppressWarnings("unchecked")
                final class Reducing {
                        private U reduce(final int index) {
                                return _nodes.childCounts[index] == 0
                                        ? reducer.apply((V)_nodes.values[index], neutral)
                                        : reducer.apply((V)_nodes.values[index], children(index));
                        }
                        private U[] children(final int index) {
                                final U[] values = (U[])Array.newInstance(
                                        neutral.getClass().getComponentType(),
                                        _nodes.childCounts[index]
                                );
                                for (int i = 0; i < _nodes.childCounts[index]; ++i) {
                                        values[i] = reduce(_nodes.childOffsets[index] + i);
                                }
                                return values;
                        }
                }

                return isEmpty() ? null : new Reducing().reduce(_index);
        }

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

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

        private boolean equals(final FlatTreeNode<?> tree) {
                return tree._index == _index &&
                        Arrays.equals(tree._nodes.values, _nodes.values) &&
                        Arrays.equals(tree._nodes.childCounts, _nodes.childCounts) &&
                        Arrays.equals(tree._nodes.childOffsets, _nodes.childOffsets);
        }

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

        @Override
        public int size() {
                return isRoot()
                        ? _nodes.values.length
                        : countChildren(_index) + 1;
        }

        private int countChildren(final int index) {
                int count = _nodes.childCounts[index];
                for (int i = 0; i < _nodes.childCounts[index]; ++i) {
                        count += countChildren(_nodes.childOffsets[index] + i);
                }
                return count;
        }

        /* *************************************************************************
         *  Static factories
         * ************************************************************************/

        /**
         * Create a new, immutable {@code FlatTreeNode} from the given {@code tree}.
         *
         * @param tree the source tree
         * @param <V> the tree value types
         * @return a {@code FlatTreeNode} from the given {@code tree}
         * @throws NullPointerException if the given {@code tree} is {@code null}
         */
        public static <V> FlatTreeNode<V> ofTree(final Tree<? extends V, ?> tree) {
                requireNonNull(tree);

                if (tree instanceof FlatTreeNode<?> ft && ft.isRoot()) {
                        @SuppressWarnings("unchecked")
                        final var result = (FlatTreeNode<V>)ft;
                        return result;
                }

                final int size = tree.size();
                assert size >= 1;

                final var nodes = new Nodes(size);

                int childOffset = 1;
                int index = 0;

                for (var node : tree) {
                        nodes.values[index] = node.value();
                        nodes.childCounts[index] = node.childCount();
                        nodes.childOffsets[index] = node.isLeaf() ? NULL_INDEX : childOffset;

                        childOffset += node.childCount();
                        ++index;
                }
                assert index == size;

                return new FlatTreeNode<>(nodes);
        }

        /**
         * 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>
         *
         * @see Tree#toParenthesesString(Function)
         * @see Tree#toParenthesesString()
         * @see TreeNode#parse(String)
         *
         * @since 5.0
         *
         * @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 FlatTreeNode<String> parse(final String tree) {
                return ofTree(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 = FlatTreeNode.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, Function)
         *
         * @since 5.0
         *
         * @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> FlatTreeNode<B> parse(
                final String tree,
                final Function<? super String, ? extends B> mapper
        ) {
                return ofTree(ParenthesesTreeParser.parse(tree, mapper));
        }


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

        @Serial
        private Object writeReplace() {
                return new SerialProxy(SerialProxy.FLAT_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 {
                final FlatTreeNode<V> node = isRoot()
                        ? this
                        : FlatTreeNode.ofTree(this);

                writeObjectArray(node._nodes.values, out);
                writeIntArray(node._nodes.childOffsets, out);
                writeIntArray(node._nodes.childCounts, out);
        }

        @SuppressWarnings("rawtypes")
        static FlatTreeNode read(final ObjectInput in)
                throws IOException, ClassNotFoundException
        {
                return new FlatTreeNode(new Nodes(
                        readObjectArray(in),
                        readIntArray(in),
                        readIntArray(in)
                ));
        }

}