/*
 * Java Genetic Algorithm Library (jenetics-9.1.0).
 * Copyright (c) 2007-2026 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;

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

import java.io.Serial;
import java.io.Serializable;
import java.util.Objects;
import java.util.Optional;

import io.jenetics.util.BaseSeq;
import io.jenetics.util.ISeq;

/**
 * Abstract implementation of the {@link TreeGene} interface..
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 6.0
 * @since 3.9
 */
public abstract class AbstractTreeGene<A, G extends AbstractTreeGene<A, G>>
        implements TreeGene<A, G>, Serializable
{

        @Serial
        private static final long serialVersionUID = 1L;

        /**
         * The allele of the tree-gene.
         */
        private final A _allele;
        private final int _childOffset;
        private final int _childCount;

        private BaseSeq<G> _genes;

        /**
         * Creates a new tree-gene from the given data.
         *
         * @param allele the actual value (allele) of the tree-gene
         * @param childOffset the offset index of the child in the containing
         *        chromosome. If this node has no child, the value should be set
         *        to zero.
         * @param childCount the number of children of this gene
         * @throws IllegalArgumentException if the {@code childCount} is smaller
         *         than zero
         */
        protected AbstractTreeGene(
                final A allele,
                final int childOffset,
                final int childCount
        ) {
                if (childCount < 0) {
                        throw new IllegalArgumentException(format(
                                "Child count smaller than zero: %s", childCount
                        ));
                }

                _allele = allele;
                _childOffset = childOffset;
                _childCount = childCount;
        }

        /**
         * Return the whole flattened tree values in breadth-first order. This method
         * will always return the same {@code ISeq} instance.
         *
         * @return the whole flattened tree values
         */
        @Override
        public ISeq<G> flattenedNodes() {
                return ISeq.of(_genes);
        }

        @Override
        public G root() {
                return _genes.get(0);
        }

        @Override
        public boolean isRoot() {
                return root() == this;
        }

        @Override
        public int size() {
                return isRoot() ? _genes.length() : TreeGene.super.size();
        }

        protected void checkTreeState() {
                if (_genes == null) {
                        throw new IllegalStateException(
                                "Gene is not attached to a chromosome."
                        );
                }
        }

        /**
         * This method is used by the {@code AbstractTreeChromosome} to attach
         * itself to this gene.
         *
         * @param genes the genes of the attached chromosome
         */
        protected void bind(final BaseSeq<G> genes) {
                _genes = requireNonNull(genes);
        }

        @Override
        public int childOffset() {
                return _childOffset;
        }

        @Override
        public A allele() {
                return _allele;
        }

        /**
         * Return the <em>parent</em> node of this tree node.
         *
         * @return the parent node, or {@code Optional.empty()} if this node is the
         *         root of the tree
         * @throws IllegalStateException if this gene is not part of a chromosome
         */
        @Override
        public Optional<G> parent() {
                checkTreeState();

                return _genes.stream()
                        .filter(g -> g.childStream().anyMatch(this::identical))
                        .findFirst();
        }

        /**
         * Return the child gene with the given index.
         *
         * @param index the child index
         * @return the child node with the given index
         * @throws IndexOutOfBoundsException  if the {@code index} is out of
         *         bounds ({@code [0, childCount())})
         * @throws IllegalStateException if this gene is not part of a chromosome
         */
        @Override
        public G childAt(final int index) {
                checkTreeState();
                if (index < 0 || index >= childCount()) {
                        throw new IndexOutOfBoundsException(format(
                                "Child index out of bounds: %s", index
                        ));
                }

                assert _genes != null;
                return _genes.get(_childOffset + index);
        }

        @Override
        public int childCount() {
                return _childCount;
        }

        @Override
        public boolean isValid() {
                return _genes != null;
        }

        @Override
        public int hashCode() {
                return Objects.hash(_allele, _childCount, _childCount);
        }

        @Override
        public boolean equals(final Object obj) {
                return obj instanceof AbstractTreeGene<?, ?> other &&
                        Objects.equals(other._allele, _allele) &&
                        other._childOffset == _childOffset &&
                        other._childCount == _childCount;
        }

        @Override
        public String toString() {
                return Objects.toString(_allele);
        }

}