import { Response, Request, NextFunction } from 'express';
import { AppLocals } from '../types/AppLocals';
import { requestDurationHistogram, totalRequestCounter } from '../lib/metricsCounters';
import { SupportedRoutes } from '../types/enums/SupportedRoutes';

/**
 * Middleware initializes infrastructure objects which will be used throughout the request lifecycle
 * @param req - Express request object
 * @param res - Express response object
 * @param next - Express next middleware function
 */
export const InitLocalsMiddleware = (req: Request, res: Response, next: NextFunction) => {
    try {
        switch(req.path) {
            // for metrics routes, no prometheus timer is needed
            case SupportedRoutes.metricsPath:
            case '/favicon.ico':
                // placeholder method to avoid checking if timer is initialized
                (res.locals as AppLocals).stopPrometheusTimer = (labels) => 0;
                break;
            // all other routes get prometheus metrics
            default:
                // The request must be processed even if Prometheus does not work
                // That's why here we wrap the Prometheus calls in try/catch
                try {
                    // counting all received requests
                    totalRequestCounter.inc({ path: req.path });

                    // starting a timer to measure request processing duration
                    // this timer will be stopped in the route handler
                    (res.locals as AppLocals).stopPrometheusTimer = requestDurationHistogram.startTimer();
                } catch(ex:any) {
                    console.error(ex);
                }
                break;
        }

        next();
    } catch(ex:any) {
        console.error('Error in InitLocalsMiddleware:', ex);
        next(ex);
    }
}