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A monad result wraps a T if success and Status if failure.
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/*
 * Copyright (c) 2016 Network New Technologies Inc.
 *
 * 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.networknt.monad;

import com.networknt.status.Status;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;

public interface Result {

    boolean isSuccess();

    default boolean isFailure() {
        return !isSuccess();
    }

    Status getError();

    T getResult();

    /*
        Use this method when you want to apply a function on the insides of the Result
        without unwrapping it. Mapper won't be invoked if the Result is Failure
     */
    default  Result map(Function mapper) {
        return isSuccess() ?
                Success.of(mapper.apply(getResult())) :
                (Failure) this;
    }

    /*
        Use this method when you your mapping function is returning a Result (which will make
        the return type the Result> using just 'map').
     */
    default  Result flatMap(Function> mapper) {
        return isSuccess() ?
                mapper.apply(getResult()) :
                (Failure) this;
    }

    /*
        Use this method if you want to reduce your Result to some type R. For example at the
        end of the flow, you could convert it to two different client responses depending on
        the insides.
     */
    default  R fold(Function successFunction, Function, ? extends R> failureFunction) {
        return isSuccess() ?
                successFunction.apply(getResult()) :
                failureFunction.apply((Failure) this);
    }

    /*
        Use this method when you have two instances of Result and you want to invoke a function on
        their insides without unwrapping them separately. If both of them are Failures then only
        the first (this) Failure will be returned.
     */
    default  Result lift(Result other, BiFunction function) {
        return flatMap(first -> other.map(second -> function.apply(first, second)));
    }

    default Result ifSuccess(Consumer successConsumer) {
        if (isSuccess()) {
            successConsumer.accept(this.getResult());
        }
        return this;
    }

    default Result ifFailure(Consumer> failureConsumer) {
        if (isFailure()) {
            failureConsumer.accept((Failure) this);
        }
        return this;
    }
}