const next = require("next");
const { createServer } = require("http");
const appInsights = require("applicationinsights");

const initAppInsights = (instrumentationKey) => {
    if (!instrumentationKey) {
        console.log("App Insights not configured.");
        return false;
    }

    appInsights
        .setup(instrumentationKey)
        .setAutoCollectConsole(true, true)
        .setSendLiveMetrics(true)
        .start();

    console.log("App Insights enabled.");
    return true;
};

const startServer = async (config) => {
    const serverOptions = {
        dev: config.env === "development",
        dir: ".",
        quiet: false,
    };

    const app = next(serverOptions);
    await app.prepare(); // prepare BEFORE starting the server

    const handleNextRequests = app.getRequestHandler();

    const srv = createServer((req, res) => {
        if (config.useAppInsights) {
            appInsights.defaultClient.trackNodeHttpRequest({
                request: req,
                response: res,
            });
        }

        handleNextRequests(req, res);
    });

    await new Promise((resolve, reject) => {
        srv.on("error", reject);
        srv.on("listening", () => resolve());
        srv.listen(config.port, config.hostname);
    });

    // Graceful shutdown handling
    process.on("SIGTERM", () => {
        console.log("Received SIGTERM, shutting down gracefully...");
        srv.close(() => {
            console.log("Server closed.");
            process.exit(0);
        });
    });

    return app;
};

// App configuration
const startTime = Date.now();
const serverConfig = {
    hostname: "0.0.0.0", // Required for Azure App Service
    port: parseInt(process.env.PORT, 10) || 3000,
    env: process.env.APP_ENV || process.env.NODE_ENV || "production",
    useAppInsights: initAppInsights(
        process.env.NEXT_PUBLIC_APPINSIGHTS_INSTRUMENTATIONKEY
    ),
};

startServer(serverConfig)
    .then(() => {
        console.log(
            `Server ready on http://${serverConfig.hostname}:${serverConfig.port} [${serverConfig.env}]`
        );

        if (serverConfig.useAppInsights) {
            const duration = Date.now() - startTime;
            appInsights.defaultClient.trackMetric({
                name: "Server Startup Time",
                value: duration,
            });
        }
    })
    .catch((err) => {
        console.error("Server failed to start:", err);
        process.exit(1);
    });