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/*
 * Copyright (c) 2021-2022. caoccao.com Sam Cao
 *
 * 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 com.caoccao.javet.interfaces;

import java.util.Objects;

/**
 * Represents a function that accepts one argument and produces a result.
 * 
 * It is a polyfill to the built-in Supplier for Android compatibility.
 *
 * @param  the type of the input to the function
 * @param  the type of the result of the function
 * @see java.util.function.Function
 * @since 1.0.3
 */
@FunctionalInterface
public interface IJavaFunction {

    /**
     * Returns a function that always returns its input argument.
     *
     * @param  the type of the input and output objects to the function
     * @return a function that always returns its input argument
     * @since 1.0.3
     */
    static  IJavaFunction identity() {
        return t -> t;
    }

    /**
     * Returns a composed function that first applies this function to
     * its input, and then applies the {@code after} function to the result.
     * If evaluation of either function throws an exception, it is relayed to
     * the caller of the composed function.
     *
     * @param    the type of output of the {@code after} function, and of the
     *              composed function
     * @param after the function to apply after this function is applied
     * @return a composed function that first applies this function and then
     * applies the {@code after} function
     * @throws NullPointerException if after is null
     * @see #compose(IJavaFunction)
     * @since 1.0.3
     */
    default  IJavaFunction andThen(IJavaFunction after) {
        Objects.requireNonNull(after);
        return (T t) -> after.apply(apply(t));
    }

    /**
     * Applies this function to the given argument.
     *
     * @param t the function argument
     * @return the function result
     * @since 1.0.3
     */
    R apply(T t);

    /**
     * Returns a composed function that first applies the {@code before}
     * function to its input, and then applies this function to the result.
     * If evaluation of either function throws an exception, it is relayed to
     * the caller of the composed function.
     *
     * @param     the type of input to the {@code before} function, and to the
     *               composed function
     * @param before the function to apply before this function is applied
     * @return a composed function that first applies the {@code before}
     * function and then applies this function
     * @throws NullPointerException if before is null
     * @see #andThen(IJavaFunction)
     * @since 1.0.3
     */
    default  IJavaFunction compose(IJavaFunction before) {
        Objects.requireNonNull(before);
        return (V v) -> apply(before.apply(v));
    }
}