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package com.ulisesbocchio.jasyptspringboot.util;

import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;

/**
 * Singleton initializer class that uses an internal supplier to supply the singleton instance. The supplier
 * originally checks whether the instanceSupplier
 * has been initialized or not, but after initialization the instance supplier is changed to avoid extra logic
 * execution.
 *
 * @author Sergio.U.Bocchio
 * @version $Id: $Id
 */
public final class Singleton implements Supplier {

    private boolean initialized = false;
    private volatile Supplier instanceSupplier;

    /**
     * from.
     *
     * @param original a {@link java.util.function.Supplier} object
     * @param  a R class
     * @return a {@link com.ulisesbocchio.jasyptspringboot.util.Singleton} object
     */
    public static  Singleton from(final Supplier original) {
        return new Singleton<>(original);
    }

    /**
     * from.
     *
     * @param original a {@link java.util.function.Function} object
     * @param arg0 a T object
     * @param  a T class
     * @param  a R class
     * @return a {@link com.ulisesbocchio.jasyptspringboot.util.Singleton} object
     */
    public static  Singleton from(final Function original, T arg0) {
        return fromLazy(original, () -> arg0);
    }

    /**
     * from.
     *
     * @param original a {@link java.util.function.BiFunction} object
     * @param arg0 a T object
     * @param arg1 a U object
     * @param  a T class
     * @param  a U class
     * @param  a R class
     * @return a {@link com.ulisesbocchio.jasyptspringboot.util.Singleton} object
     */
    public static  Singleton from(final BiFunction original, T arg0, U arg1) {
        return fromLazy(original, () -> arg0, () -> arg1);
    }

    /**
     * fromLazy.
     *
     * @param original a {@link java.util.function.Function} object
     * @param arg0Supplier a {@link java.util.function.Supplier} object
     * @param  a T class
     * @param  a R class
     * @return a {@link com.ulisesbocchio.jasyptspringboot.util.Singleton} object
     */
    public static  Singleton fromLazy(final Function original, Supplier arg0Supplier) {
        return from(() -> original.apply(arg0Supplier.get()));
    }

    /**
     * fromLazy.
     *
     * @param original a {@link java.util.function.BiFunction} object
     * @param arg0Supplier a {@link java.util.function.Supplier} object
     * @param arg1Supplier a {@link java.util.function.Supplier} object
     * @param  a T class
     * @param  a U class
     * @param  a R class
     * @return a {@link com.ulisesbocchio.jasyptspringboot.util.Singleton} object
     */
    public static  Singleton fromLazy(final BiFunction original, Supplier arg0Supplier, Supplier arg1Supplier) {
        return from(() -> original.apply(arg0Supplier.get(), arg1Supplier.get()));
    }

    /**
     * Constructor for Singleton.
     *
     * @param original a {@link java.util.function.Supplier} object
     */
    public Singleton(final Supplier original) {
        instanceSupplier = () -> {
            synchronized (original) {
                if (!initialized) {
                    final R singletonInstance = original.get();
                    instanceSupplier = () -> singletonInstance;
                    initialized = true;
                }
                return instanceSupplier.get();
            }
        };
    }

    /** {@inheritDoc} */
    @Override
    public R get() {
        return instanceSupplier.get();
    }
}