server.js

const express = require("express"); // Import Express
const mongoose = require("mongoose"); // Import Mongoose library to connect and work with MongoDB
const nano = require("nano")("http://admin:Qd45jKbY89Z@localhost:5984"); // Import Nano library to connect and work with CouchDB
const cors = require("cors"); // Imported to allow cross-origin requests, in case frontend is added
const path = require("path");  // Imported for working with file paths, in case frontend is added

// Import datamodel (MongoDB) and validation (CouchDB)
const Patient = require("./mongodb_model/Patient");
const validatePatientData = require("./couchdb_validation/validatePatientData");

const app = express(); // Create a new Express application
const PORT = 3000; // Define the port the server will run on

// Connection to databases
const mongodb_URL = "mongodb://localhost:27017/Examensarbete_MongoDB_databas"; // MongoDB URL
const couchdb_DB_NAME = "examensarbete_couchdb_databas"; // CouchDB database name

// Global error handling for uncaught exceptions in the rest of the scripts (in case any error handling is missing)
process.on('uncaughtException', (error) => {
    console.error('Uncaught exception:', error);
});

// Global error handling for failed promises in the rest of the scripts (if any async/await errors are not caught)
process.on('unhandledRejection', (reason, promise) => {
    console.error('Unhandled rejection at:', promise, 'reason:', reason);
});

// Import route files for operations POST/GET/PUT
const mongoPatientRoutes = require("./routes/mongoPatientRoutes");
const couchPatientRoutes = require("./routes/couchPatientRoutes");

// Middleware
app.use(express.json({ limit: '50mb' })); // Middleware function to transform incoming JSON to JavaScript objects (node.js only understand JavaScript objects). Limit: allows 50 megabyte big JSON body (instead of 100 kilobyte request size, that is deafult for Express)
app.use(cors()); // Allows requests from other addresses, e.g if a web page tries to reach the server (allows cross-origin HTTP requests). Not used since I don´t use a frontend, but server is ready
app.use(express.static(path.join(__dirname))); // Server is prepared to serve frontend files (HTML, CSS, JS) if a frontend is added. Not used since I don´t use a frontend, but server is ready

// Simple test route 
app.get("/", (request, response) => {
    response.send("Server is up and running!");
});

// Use route files
app.use("/mongo/patient", mongoPatientRoutes);
app.use("/couch/patient", couchPatientRoutes);

// Connect to MongoDB
async function connectMongoDB() {
    try {
        await mongoose.connect(mongodb_URL);// Try connecting
        console.log("Connected to MongoDB");
    } catch (error) {
        console.error("Could not connect to MongoDB:", error);
        process.exit(1); // Stops the server if connection fails
    }
}

// Connect to CouchDB
async function connectCouchDB() {
    try {
        const dbList = await nano.db.list(); // Fetches list of databases
        if (!dbList.includes(couchdb_DB_NAME)) {
            throw new Error(`CouchDB database '${couchdb_DB_NAME}' does not exist.`);
        }
        console.log("Connected to CouchDB");
    } catch (error) {
        console.error("Could not connect to CouchDB:", error);
        process.exit(1); // Stops the server if connection fails
    }
}

// Start the server after both databases are connected
async function startServer() {
    await connectMongoDB(); // Connect to MongoDB
    await connectCouchDB(); // Connect to CouchDB

    //Server starts listening for HTTP-requests on port 3000 and announces that it´s ready in console
    app.listen(PORT, () => {
        console.log(`Server running on http://localhost:${PORT}`);
    });
}

// Start the process
startServer();