Sample workflow using vavr

Workflow.java

package dev.rockyj;

import io.vavr.API;
import io.vavr.control.Either;

import static io.vavr.API.*;

enum PossibleWorkflowStates {
    INIT,
    IN_PROGRESS,
    PD_ACCEPT,
    PD_REJECT,
    MM1_SUCCESS,
    UPDATE_STATUS_SUCCESS,
    UPDATE_STATUS_FAILED,
    NOTIFICATION_SUCCESS,
    NOTIFICATION_FAILED
}

enum ErrorStates {
    PD_ERROR,
    MM1_FAIL,
}

@FunctionalInterface
interface StateModifier {
    Either<ErrorStates, WorkflowState> execute(WorkflowState state);
}

@FunctionalInterface
interface ErrorHandler {
    void execute(ErrorStates errorState);
}

record WorkflowState(PossibleWorkflowStates currentState){} // can be class as well

public class Workflow {
    public static void main(String[] args) {
        StateModifier insertRecordInDB = (WorkflowState state) -> {
            // do work here
            System.out.println("insert record in DB...");
            var newState = new WorkflowState(PossibleWorkflowStates.IN_PROGRESS);
            return Either.right(newState);
        };

        StateModifier callPDE = (WorkflowState state) -> {
            // do work here
            System.out.println("make PDE call...");
            var newState = new WorkflowState(PossibleWorkflowStates.PD_ACCEPT);
            return Either.right(newState);
            // return Either.left(ErrorStates.PD_ERROR);
        };

        StateModifier moveMoney1 = (WorkflowState state) -> {
            // do work here
            System.out.println("make MM1 call...");
            var newState = new WorkflowState(PossibleWorkflowStates.MM1_SUCCESS);
            return Either.right(newState);
            // return Either.left(ErrorStates.MM1_FAIL);
        };

        ErrorHandler handleFailure = (ErrorStates errorState) -> {
            System.out.println(errorState);
            System.out.println("handling failure ...");
        };

        // start
        System.out.println("here we go...");

        var initialState = new WorkflowState(PossibleWorkflowStates.INIT);

        var finalState = insertRecordInDB
                .execute(initialState)
                .flatMap(state -> callPDE.execute(state))
                .flatMap(state -> moveMoney1.execute(state));

        // handle error states
        if(finalState.isLeft()) {
            API.Match(finalState.getLeft()).of(
                    Case($(ErrorStates.PD_ERROR), (errorState) -> run(() -> handleFailure.execute(errorState))),
                    Case($(ErrorStates.MM1_FAIL), (errorState) -> run(() -> handleFailure.execute(errorState)))
            );
        }
    }
}