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/*
 * Copyright (C) Posten Norge AS
 *
 * 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 no.digipost.function;

import no.digipost.DiggExceptions;

import java.util.Optional;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;

/**
 * Represents a function that accepts one argument and produces a result,
 * and it may throw an exception.
 *
 * @param  the type of the input to the function
 * @param  the type of the result of the function
 * @param  the exception type which may be thrown when applying the function
 */
@FunctionalInterface
public interface ThrowingFunction {

    /**
     * Unification of {@link ThrowingFunction} and {@link java.util.function.Function}.
     * This type is applicable as a return type from methods producing functions,
     * and never as an input parameter type. This enables such returned functions to be used
     * both where a {@code ThrowingFunction} is expected, as well as the JDK's {@code Function} type.
     *
     * @param  the type of the input to the function
     * @param  the type of the result of the function
     * @param  unchecked exception type
     *
     * @see ThrowingFunction#identity()
     */
    @FunctionalInterface
    interface OfUncheckedException extends ThrowingFunction, Function {
    }


    /**
     * 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
     */
    static  ThrowingFunction.OfUncheckedException identity() {
        return t -> t;
    }


    R apply(T t) throws X;


    default Function asUnchecked() {
        return ifExceptionThrow(e -> DiggExceptions.asUnchecked(e));
    }

    default Function ifExceptionThrow(Function exceptionMapper) {
        return ifExceptionThrow((t, e) -> exceptionMapper.apply(e));
    }

    default Function ifExceptionThrow(BiFunction exceptionMapper) {
        return ifException((t, e) -> { throw exceptionMapper.apply(t, e); }).andThen(o -> o.orElse(null));
    }

    default Function> ifException(Consumer exceptionHandler) {
        return ifException((t, e) -> exceptionHandler.accept(e));
    }

    default Function> ifException(BiConsumer exceptionHandler) {
        return t -> {
            return Optional.ofNullable(ifExceptionApply((failingT, e) -> {
                exceptionHandler.accept(failingT, e);
                return null;
            }).apply(t));
        };
    }

    default Function ifExceptionApply(Function exceptionMapper) {
        return ifExceptionApply((t, e) -> exceptionMapper.apply(e));
    }

    default Function ifExceptionApply(BiFunction exceptionMapper) {
        return t -> {
            try {
                return apply(t);
            } catch (Exception e) {
                return exceptionMapper.apply(t, e);
            } catch (Error err) {
                throw err;
            } catch (Throwable thr) {
                throw DiggExceptions.asUnchecked(thr);
            }
        };
    }

    default  ThrowingFunction andThen(ThrowingFunction after) {
        return t -> after.apply(apply(t));
    }

    default  ThrowingFunction compose(ThrowingFunction before) {
        return t -> apply(before.apply(t));
    }

}