/*
 * Java Genetic Algorithm Library (jenetics-7.2.0).
 * Copyright (c) 2007-2023 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.internal.util;

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

import java.io.Externalizable;
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.Objects;
import java.util.function.Supplier;

/**
 * Class for lazy value initialization.
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @since 3.0
 * @version 5.0
 */
public final class Lazy<T> implements Supplier<T>, Serializable {

        @Serial
        private static final long serialVersionUID = 2L;

        private final transient Supplier<T> _supplier;

        private T _value;
        private transient volatile boolean _evaluated;

        private Lazy(
                final T value,
                final boolean evaluated,
                final Supplier<T> supplier
        ) {
                _value = value;
                _evaluated = evaluated;
                _supplier = supplier;
        }

        private Lazy(final Supplier<T> supplier) {
                this(null, false, requireNonNull(supplier));
        }

        @Override
        public T get() {
                return _evaluated ? _value : evaluate();
        }

        /**
         * Return the evaluation state of the {@code Lazy} variable.
         *
         * @return {@code true} is the {@code Lazy} variable has been evaluated,
         *         {@code false} otherwise
         */
        public boolean isEvaluated() {
                return _supplier == null || _evaluated || _evaluated();
        }

        private synchronized boolean _evaluated() {
                return _evaluated;
        }

        private synchronized T evaluate() {
                if (!_evaluated) {
                        _value = _supplier.get();
                        _evaluated = true;
                }

                return _value;
        }

    @Override
    public int hashCode() {
        return Objects.hashCode(get());
    }

    @Override
    public boolean equals(final Object obj) {
                return obj == this ||
                        obj instanceof Lazy<?> other &&
                        Objects.equals(other.get(), get());
    }

    @Override
    public String toString() {
                return format("Lazy[%s]", isEvaluated() ? get() : "?");
    }

        /**
         * Create a new lazy value initialization.
         *
         * @param supplier the lazy value supplier
         * @param <T> the value type
         * @return a new lazy value initialization
         * @throws java.lang.NullPointerException if the given supplier is
         *         {@code null}
         */
        public static <T> Lazy<T> of(final Supplier<T> supplier) {
                return new Lazy<>(supplier);
        }

        /**
         * Create a new {@code Lazy} object with the given {@code value}. This
         * method allows creating a <em>lazy</em> object with the given
         * {@code value}.
         *
         * @since 3.7
         *
         * @param value the value this {@code Lazy} object is initialized with
         * @param <T> the value type
         * @return return a new lazy value with the given value
         */
        public static <T> Lazy<T> ofValue(final T value) {
                return new Lazy<>(value, true, null);
        }


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

        static final class SerialProxy implements Externalizable  {

                @Serial
                private static final long serialVersionUID = 1L;

                private Lazy<?> _object;

                public SerialProxy() {
                }

                SerialProxy(final Lazy<?> object) {
                        _object = object;
                }

                @Serial
                private Object readResolve() {
                        return _object;
                }

                @Override
                public void writeExternal(final ObjectOutput out) throws IOException {
                        out.writeObject(_object.get());
                }

                @Override
                public void readExternal(ObjectInput in)
                        throws IOException, ClassNotFoundException
                {
                        _object = Lazy.ofValue(in.readObject());
                }
        }

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

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

}