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/*
 * 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 ([email protected])
 */
package io.jenetics.ext.grammar;

import static java.util.Objects.requireNonNull;

import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.IntUnaryOperator;

import io.jenetics.BitChromosome;
import io.jenetics.BitGene;
import io.jenetics.IntegerGene;
import io.jenetics.internal.util.Bits;
import io.jenetics.internal.util.Requires;
import io.jenetics.util.BaseSeq;

import io.jenetics.ext.grammar.Cfg.Rule;

/**
 * Represents a mapping of a finite set of integers to symbol indexes. If more
 * indexes are needed, the values are read from the beginning again. You have
 * the possibility to create a {@code Codons} object from different chromosome
 * types.
 * {@snippet lang="java":
 * // Create 'classic' codons from a bit-chromosome, where
 * // the genes are split into 8-bit junks and converted
 * // into unsigned int values.
 * final Codons codons = Codons.ofBitGenes(BitChromosome.of(10_000));
 *
 * // Creating a codons object from an integer chromosome.
 * final var ich = IntegerChromosome.of(IntRange.of(0, 256), 1_000);
 * final var codons = Codons.ofIntegerGenes(ich);
 * }
 *
 * @author Franz Wilhelmstötter
 * @since 7.1
 * @version 7.1
 */
public final class Codons implements SymbolIndex {

	private final IntUnaryOperator _values;
	private final int _length;

	private final AtomicInteger _pos = new AtomicInteger(0);

	/**
	 * Create a new {@code Codons} object from a given {@code codons} source and
	 * its {@code length}.
	 *
	 * @param codons the codon source
	 * @param length the length of the codon source
	 * @throws NullPointerException if the {@code codons} source is {@code null}
	 * @throws IllegalArgumentException if the given {@code length} is smaller
	 *         than one
	 */
	public Codons(final IntUnaryOperator codons, final int length) {
		_values = requireNonNull(codons);
		_length = Requires.positive(length);
	}

	@Override
	public int next(final Rule rule, final int bound) {
		final int index = _pos.getAndUpdate(x -> (x + 1)%_length);
		return _values.applyAsInt(index)%bound;
	}

	/**
	 * Creates a new, classical codons object from the given bit-genes.
	 * The genes is split into 8-bit chunks and converted into an unsigned
	 * {@code int[]} array.
	 * {@snippet lang="java":
	 * final Codons codons = Codons.ofBitGenes(BitChromosome.of(10_000));
	 * }
	 *
	 * @param genes the genes used for creating the codon object
	 * @return a new codons object
	 */
	public static Codons ofBitGenes(final BaseSeq genes) {
		if (genes instanceof BitChromosome ch) {
			return ofBytes(ch.toByteArray());
		} else {
			return ofBytes(toByteArray(genes));
		}
	}

	private static Codons ofBytes(final byte[] bytes) {
		final var values = new int[bytes.length];
		for (int i = 0; i < values.length; ++i) {
			values[i] = Byte.toUnsignedInt(bytes[i]);
		}

		return new Codons(i -> values[i], values.length);
	}

	static byte[] toByteArray(final BaseSeq genes) {
		final byte[] bytes = Bits.newArray(genes.length());
		for (int i = 0; i < genes.length(); ++i) {
			if (genes.get(i).booleanValue()) {
				Bits.set(bytes, i);
			}
		}

		return bytes;
	}

	/**
	 * Creates a new codons object from the given int-genes.
	 *
	 * {@snippet lang="java":
	 * final var chromosome = IntegerChromosome.of(IntRange.of(0, 256), 1_000);
	 * final var codons = Codons.ofIntegerGenes(chromosome);
	 * }
	 *
	 * @param genes the genes used for creating the codon object
	 * @return a new codons object
	 */
	public static Codons ofIntegerGenes(final BaseSeq genes) {
		return new Codons(i -> genes.get(i).intValue(), genes.length());
	}

}