import { sendHeartbeat, sendDownNotification } from "./requestHandler";

/**
 * Defines an uptime kuma monitor
 */
interface Monitor {
    /**
     * The url to push heartbeats to
     */
    url: string;
    /**
     * The interval in which to push heartbeats in seconds
     */
    heartbeatIntervall: number;
}

/**
 * Defines a monitor store
 */
interface MonitorStore {
    /**
     * The monitor
     */
    monitor: Monitor;
    /**
     * The last heartbeat
     */
    lastHeartbeat: Date;
}

/**
 * The handler managing all monitors
 */
export class PushMonitor {
    /**
     * The private constructor
     * @private
     */
    private constructor() {
        this.initTimer();
    }

    /**
     * The singleton instance of the PushMonitor
     * @private
     */
    private static _instance = new PushMonitor();

    /**
     * The monitors to manage
     * @private
     */
    private _monitors: MonitorStore[] = [];

    /**
     * The check interval
     * @private
     */
    private _checkInterval: NodeJS.Timer | undefined;

    /**
     * Whether to log debug information
     * @private
     */
    private _debug: boolean = false;

    /**
     * Performance measurment function
     * @private
     */
    private _performance: (() => (Promise<number> | number)) | undefined;

    /**
     * Returns the singleton instance of the PushMonitor
     */
    public static get instance(): PushMonitor {
        return PushMonitor._instance;
    }

    /**
     * Starts the monitor
     * @returns This instance
     */
    public start(): this {
        this.initTimer();
        return this;
    }

    /**
     * Stops the monitor
     * @returns This instance
     */
    public stop(): this {
        if (this._checkInterval) {
            clearInterval(this._checkInterval);
        }
        return this;
    }

    /**
     * Registers a new monitor to be managed
     * @param url {string} The url to push heartbeats to
     * @param heartbeatIntervall {number} The interval in which to push heartbeats in seconds. Default is 58 seconds
     * @returns This instance
     */
    public register(url: string, heartbeatIntervall: number = 58): this {
        this._monitors.push({
            monitor: {
                url,
                heartbeatIntervall,
            },
            lastHeartbeat: new Date(new Date().getTime() + 10000 - heartbeatIntervall * 1000),
        });
        return this;
    }

    /**
     * Sets whether to log debug information
     * @param debug Whether to log debug information
     * @returns This instance
     */
    public setDebug(debug: boolean): this {
        this._debug = debug;
        return this;
    }

    /**
     * Enables the sending of shutdown down notifications
     * !! This will overwrite the uncaughtException handler function !!
     * @returns This instance
     */
    public enableShutdownNotifications(): this {
        this.initEventHandlers();
        return this;
    }

    /**
     * Sets the performance handler
     * @param handler The performance handler
     * @returns This instance
     */
    public setPerformanceHandler(handler?: () => (Promise<number> | number)): this {
        this._performance = handler;
        return this;
    }

    /**
     * Initializes the timer
     * @private
     */
    private initTimer() {
        if (this._checkInterval) {
            clearInterval(this._checkInterval);
        }

        let isRunning = false;

        this._checkInterval = setInterval(async () => {
            if (isRunning) return;
            isRunning = true;

            try {
                let performance: number | undefined = undefined;

                if (this._performance) performance = await this._performance();

                this._monitors.forEach((monitor) => {
                    if (new Date().getTime() - monitor.lastHeartbeat.getTime() > monitor.monitor.heartbeatIntervall * 1000) {
                        sendHeartbeat(monitor.monitor.url, performance, this._debug);
                        monitor.lastHeartbeat = new Date();
                    }
                });
            } catch (error) {
                console.error(`[eu.astrogd.uptime-kuma-push-monitor] (${new Date().toISOString()}) <internal.interval>: ${error}`);
            }


            isRunning = false;
        }, 1000);
    }

    /**
     * Initializes event handlers
     * @private
     */
    private initEventHandlers() {
        process.on("uncaughtException", async (err, origin) => {
            console.error(origin + "\n" + err.stack);
            await this.sendShutdownNotification(`Uncaught Exception (${err.message})`);
            process.exitCode = 1;
            process.exit(1);
        });
    }

    /**
     * Sends a shutdown notification to all monitors
     * @param msg The message to send
     */
    private async sendShutdownNotification(msg: string = "Shutdown") {
        const promises: Promise<void>[] = [];

        this._monitors.forEach((monitor) => {
            promises.push(sendDownNotification(monitor.monitor.url, msg, this._debug));
        });

        return Promise.all(promises);
    }
}