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

    HappyPath(BusinessCase businessCase) {
        super(BusinessCase::happyOptional, businessCase);
    }

    /**
     * @param happyPathAttempt The {@link Attempt} to execute
     * @param  The type of happy object this {@link HappyPath} may represent
     * @param  The type of sad object this {@link HappyPath} may represent
     * @return A {@link HappyPath} that is happy or sad or a technical failure on the inside
     */
    public static  HappyPath happyPathAttempt(Attempt> happyPathAttempt) {
        try {
            return happyPathAttempt.attempt();
        } catch (Exception technicalFailure) {
            return technicalFailure(technicalFailure);
        }
    }

    /**
     * @param attempt The {@link Attempt} to execute
     * @param  The type of happy object this {@link HappyPath} may represent
     * @param  The type of sad object this {@link HappyPath} may represent
     * @return A {@link HappyPath} that is either happy on the inside or a technical failure
     */
    public static  HappyPath happyAttempt(Attempt attempt) {
        try {
            return happyPath(attempt.attempt());
        } catch (Exception technicalFailure) {
            return technicalFailure(technicalFailure);
        }
    }

    /**
     * @param attempt The {@link Attempt} to execute
     * @param failureMapping What to do if there is a technical failure during the {@link Attempt}
     * @param  The type of happy object the resulting {@link HappyPath} may represent
     * @param  The type of sad object the resulting {@link HappyPath} may represent
     * @return A {@link HappyPath} that is either happy on the inside, sad on the inside or a technical failure
     */
    public static  HappyPath happyAttempt(Attempt attempt, Mapping failureMapping) {
        try {
            return happyPath(attempt.attempt());
        } catch (Exception technicalFailure) {
            try {
                return sadPath(failureMapping.map(technicalFailure));
            } catch (Exception technicalFailureDuringFailureMapping) {
                return technicalFailure(technicalFailureDuringFailureMapping);
            }
        }
    }

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

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

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

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

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

    /**
     * @param actionThatMightFail The {@link ActionThatMightFail} to apply if the underlying business case is happy
     * @return The same {@link HappyPath} if the action did not fail; if the action failure then a {@link HappyPath} that is now sad inside
     */
    public HappyPath attempt(ActionThatMightFail actionThatMightFail) {
        return then(actionThatMightFail::attemptHappyPath);
    }

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

    /**
     * {@inheritDoc}
     */
    @Override
    public HappyPath ifHappy() {
        return this;
    }
}