/*
 * Java Genetic Algorithm Library (jenetics-8.1.0).
 * 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.prog;

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

import java.io.Serial;
import java.util.function.Function;

import io.jenetics.Gene;
import io.jenetics.util.ISeq;
import io.jenetics.util.RandomRegistry;

import io.jenetics.ext.AbstractTreeGene;
import io.jenetics.ext.util.TreeNode;

import io.jenetics.prog.op.Op;
import io.jenetics.prog.op.Program;

/**
 * This gene represents a program, build upon an AST of {@link Op} functions.
 * Because of the tight coupling with the {@link ProgramChromosome}, a
 * {@code ProgramGene} can't be created directly. This reduces the possible
 * <em>error space</em>. Since the {@code ProgramGene} also is a {@code Tree},
 * it can be easily used as a result.
 *
 * {@snippet lang="java":
 * final ProgramGene<Double> program = engine.stream()
 *     .limit(300)
 *     .collect(EvolutionResult.toBestGenotype())
 *     .getGene();
 *
 * final double result = program.eval(3.4);
 * }
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 5.2
 * @since 3.9
 */
public final class ProgramGene<A>
        extends AbstractTreeGene<Op<A>, ProgramGene<A>>
        implements Gene<Op<A>, ProgramGene<A>>, Function<A[], A>
{

        @Serial
        private static final long serialVersionUID = 1L;

        private final ISeq<? extends Op<A>> _operations;
        private final ISeq<? extends Op<A>> _terminals;

        ProgramGene(
                final Op<A> op,
                final int childOffset,
                final ISeq<? extends Op<A>> operations,
                final ISeq<? extends Op<A>> terminals
        ) {
                super(requireNonNull(get(op)), childOffset, op.arity());
                _operations = requireNonNull(operations);
                _terminals = requireNonNull(terminals);
        }

        private static <A> Op<A> get(final Op<A> op) {
                final Op<A> instance = op.get();
                if (instance != op && instance.arity() != op.arity()) {
                        throw new IllegalArgumentException(format(
                                "Original op and created op have different arity: %d != %d,",
                                instance.arity(), op.arity()
                        ));
                }
                return instance;
        }

        /**
         * Evaluates this program gene (recursively) with the given variable values.
         *
         * @see ProgramGene#eval(Object[])
         * @see ProgramChromosome#eval(Object[])
         *
         * @param args the input variables
         * @return the evaluated value
         * @throws NullPointerException if the given variable array is {@code null}
         */
        @Override
        public A apply(final A[] args) {
                checkTreeState();
                return Program.eval(this, args);
        }

        /**
         * Convenient method, which lets you apply the program function without
         * explicitly create a wrapper array.
         *
         * @see ProgramGene#apply(Object[])
         * @see ProgramChromosome#eval(Object[])
         *
         * @param args the function arguments
         * @return the evaluated value
         * @throws NullPointerException if the given variable array is {@code null}
         */
        @SafeVarargs
        public final A eval(final A... args) {
                return apply(args);
        }

        /**
         * Return the allowed operations.
         *
         * @return the allowed operations
         */
        public ISeq<Op<A>> operations() {
                return ISeq.upcast(_operations);
        }

        /**
         * Return the allowed terminal operations.
         *
         * @return the allowed terminal operations
         */
        public ISeq<Op<A>> terminals() {
                return ISeq.upcast(_terminals);
        }

        /**
         * Creates a new {@link TreeNode} from this program gene.
         *
         * @since 5.0
         *
         * @return a new tree node value build from this program gene
         */
        public TreeNode<Op<A>> toTreeNode() {
                return TreeNode.ofTree(this);
        }

        @Override
        public ProgramGene<A> newInstance() {
                final var random = RandomRegistry.random();

                Op<A> operation = value();
                if (isLeaf()) {
                        operation = _terminals.get(random.nextInt(_terminals.length()));
                } else {
                        final ISeq<Op<A>> operations = _operations.stream()
                                .filter(op -> op.arity() == value().arity())
                                .collect(ISeq.toISeq());

                        if (operations.length() > 1) {
                                operation = operations.get(random.nextInt(operations.length()));
                        }
                }

                return newInstance(operation);
        }

        /**
         * Create a new program gene with the given operation.
         *
         * @param op the operation of the new program gene
         * @return a new program gene with the given operation
         * @throws NullPointerException if the given {@code op} is {@code null}
         * @throws IllegalArgumentException if the arity of the given operation is
         *         different from the arity of the current operation. This restriction
         *         ensures that only valid program genes are created by this method.
         */
        @Override
        public ProgramGene<A> newInstance(final Op<A> op) {
                if (value().arity() != op.arity()) {
                        throw new IllegalArgumentException(format(
                                "New operation must have same arity: %s[%d] != %s[%d]",
                                value().name(), value().arity(), op.name(), op.arity()
                        ));
                }
                return new ProgramGene<>(op, childOffset(), _operations, _terminals);
        }

        /**
         * Return a new program gene with the given operation and the <em>local</em>
         * tree structure.
         *
         * @param op the new operation
         * @param childOffset the offset of the first node child within the
         *        chromosome
         * @param childCount the number of children of the new tree gene
         * @return a new tree gene with the given parameters
         * @throws IllegalArgumentException  if the {@code childCount} is smaller
         *         than zero
         * @throws IllegalArgumentException if the operation arity is different from
         *         the {@code childCount}.
         * @throws NullPointerException if the given {@code op} is {@code null}
         */
        @Override
        public ProgramGene<A> newInstance(
                final Op<A> op,
                final int childOffset,
                final int childCount
        ) {
                if (op.arity() != childCount) {
                        throw new IllegalArgumentException(format(
                                "Operation arity and child count are different: %d, != %d",
                                op.arity(), childCount
                        ));
                }

                return new ProgramGene<>(op, childOffset, _operations, _terminals);
        }

}