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A combination of the Try monad and the Either monad, to help tame complex business flows.
There is a newer version: 10.3.0
/*
 * Copyright 2016 Liam Williams .
 *
 * This file is part of business-flows.
 *
 * 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 io.github.theangrydev.businessflows;

/**
 * A {@link SadPath} is a {@link BusinessFlow} that is biased towards the result being {@link Sad}.
 *
 * {@inheritDoc}
 */
public class SadPath extends BusinessFlow {

    SadPath(BusinessCase businessCase) {
        super(BusinessCase::sadOptional, businessCase);
    }

    /**
     * @param sad The sad object to initiate the flow with
     * @param  The type of happy object the resulting {@link SadPath} may represent
     * @param  The type of sad object the resulting {@link SadPath} may represent
     * @return A {@link SadPath} that is sad on the inside
     */
    public static  SadPath sadPath(Sad sad) {
        return new SadPath<>(new SadCase<>(sad));
    }

    /**
     * @param happy The happy object to initiate the flow with
     * @param  The type of happy object the resulting {@link SadPath} may represent
     * @param  The type of sad object the resulting {@link SadPath} may represent
     * @return A {@link SadPath} that is happy on the inside
     */
    public static  SadPath happyPath(Happy happy) {
        return new SadPath<>(new HappyCase<>(happy));
    }

    /**
     * @param technicalFailure The technical failure object to initiate the flow with
     * @param  The type of happy object the resulting {@link SadPath} may represent
     * @param  The type of sad object the resulting {@link SadPath} may represent
     * @return A {@link SadPath} that is a technical failure on the inside
     */
    public static  SadPath technicalFailure(Exception technicalFailure) {
        return new SadPath<>(new TechnicalFailureCase<>(technicalFailure));
    }

    /**
     * If the underlying business case is sad, then apply the given action, otherwise do nothing to the underlying case.
     *
     * @param action The action to apply to an existing sad case
     * @param  The type of sad object that will be present after the action is applied to an existing sad object
     * @return The result of applying the action to the existing sad path, if applicable
     */
    public  SadPath then(Mapping> action) {
        return join(SadPath::happyPath, action, SadPath::technicalFailure);
    }

    /**
     * If the underlying business case is sad, then apply the given mapping, otherwise do nothing to the underlying case.
     *
     * @param mapping The action to apply to an existing sad case
     * @param  The type of sad object that will be present after the mapping is applied to an existing sad object
     * @return The result of applying the mapping to the existing sad path, if applicable
     */
    public  SadPath map(Mapping mapping) {
        return then(mapping.andThen(SadPath::sadPath));
    }

    /**
     * If the underlying business case is sad, recover to a happy path using the given recovery mapping.
     *
     * @param recovery The recovery to apply to an existing sad case
     * @return The result of applying the recovery to the existing sad path, if applicable
     */
    public HappyPath recover(Mapping recovery) {
        return this.then(sad -> happyPath(recovery.map(sad))).ifHappy();
    }

    /**
     * If the underlying business case is sad, recover to a happy path using the {@link Attempt}.
     *
     * @param recovery The recovery to apply to an existing sad case
     * @return The result of applying {@link Attempt}, if applicable
     */
    public HappyPath recover(Attempt recovery) {
        return recover(sad -> recovery.attempt());
    }

    /**
     * Take a look at the sad case (if there really is one).
     *
     * @param peek What to do if the underlying business case is sad
     * @return The same {@link SadPath}
     */
    public SadPath peek(Peek peek) {
        return then(sad -> {
            peek.peek(sad);
            return this;
        });
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public SadPath ifSad() {
        return this;
    }
}