tasks/saga/source.js

// File: tasks/saga/source.js
// Express.js payment saga source bundle.

const TRANSITIONS = {
    "Idle:Reserve": "Reserved",
    "Reserved:Authorize": "Authorized",
    "Authorized:Capture": "Captured",
    "Captured:Settle": "Settled",
    "Reserved:CompensateReserve": "Compensated",
    "Authorized:CompensateAuthorize": "Compensating",
    "Compensating:CompensateReserve": "Compensated",
    "Captured:CompensateCapture": "Compensating",
};

function transition(state, event) {
    if (event === "Fail") {
        return "Failed";
    }
    return TRANSITIONS[`${state}:${event}`] ?? state;
}

function runSaga(events) {
    return events.reduce(transition, "Idle");
}

function isCharged(state) {
    return state === "Captured" || state === "Settled";
}

const HAPPY_PATH = ["Reserve", "Authorize", "Capture", "Settle"];

const express = require("express");
const app = express();
app.use(express.json());

const sagaStore = {};

app.post("/saga/start", (request, response) => {
    const sagaId = `saga_${Date.now()}`;
    sagaStore[sagaId] = { state: "Idle", history: [] };
    response.json({ sagaId, state: "Idle" });
});

app.post("/saga/:sagaId/event", (request, response) => {
    const { sagaId } = request.params;
    const { event } = request.body;
    if (!sagaStore[sagaId]) {
        return response.status(404).json({ error: "Not found" });
    }
    const saga = sagaStore[sagaId];
    const nextState = transition(saga.state, event);
    saga.history.push({ from: saga.state, event, to: nextState });
    saga.state = nextState;
    response.json({ sagaId, state: nextState, charged: isCharged(nextState) });
});

app.get("/saga/:sagaId", (request, response) => {
    const saga = sagaStore[request.params.sagaId];
    if (!saga) {
        return response.status(404).json({ error: "Not found" });
    }
    response.json({ state: saga.state, history: saga.history });
});