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/*
 * Copyright 2020 the original author or authors.
 *
 * 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.
 */

package org.gradle.internal.serialization;

import org.gradle.internal.Try;

import java.util.concurrent.Callable;

/**
 * Represents a computation that must execute only once and
 * whose result must be cached even (or specially) at serialization time.
 *
 * @param  the resulting type
 */
public abstract class Cached {

    public static  Cached of(Callable computation) {
        return new Deferred<>(computation);
    }

    public abstract T get();

    private static class Deferred extends Cached implements java.io.Serializable {

        private Callable computation;
        private Try result;

        public Deferred(Callable computation) {
            this.computation = computation;
        }

        @Override
        public T get() {
            return result().get();
        }

        private Try result() {
            if (result == null) {
                result = Try.ofFailable(computation);
                computation = null;
            }
            return result;
        }

        private Object writeReplace() {
            return new Fixed<>(result());
        }
    }

    private static class Fixed extends Cached {

        private final Try result;

        public Fixed(Try result) {
            this.result = result;
        }

        @Override
        public T get() {
            return result.get();
        }
    }
}