feat: add email-server-worker with clean template architecture

Add new email-server-worker project implementing a self-scheduling background worker pattern with HTTP monitoring. Removed all business-specific code from copied source, creating a clean, reusable template. Key features: - Self-scheduling worker loop with configurable interval - Graceful shutdown support (Docker-compatible) - Prometheus metrics collection - Health check endpoints (/healthcheck, /metrics, /ping) - Example worker template for easy customization - Comprehensive architecture documentation in CLAUDE.md The worker is now ready for email server implementation with no external dependencies on Evolution/MSSQL/ElasticSearch. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
2025-12-30 09:03:58 +01:00
parent 7a526c5a85
commit 25c2f09eef
30 changed files with 1374 additions and 17 deletions
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -8,6 +8,7 @@ This is a multi-project repository containing:
 - **web-app/**: Next.js 14 utility bills tracking application
 - **docker-stack/**: Docker Compose configurations and deployment scripts
 - **housekeeping/**: Database backup and maintenance scripts
+- **email-server-worker/**: Background worker service with HTTP health monitoring

 Each project is self-contained with its own dependencies.

@@ -29,6 +30,13 @@ All commands should be run from within the respective project directory.
 - `./db-dump--standalone.sh` - Run standalone database dump
 - See housekeeping/README.md for more details

+**Email Server Worker** (`cd email-server-worker`):
+- `npm install` - Install dependencies
+- `npm run start` - Start development server with nodemon
+- `npm run build` - Build TypeScript to JavaScript
+- `npm run test` - Run tests with Jest in watch mode
+- `npm run run-server` - Run built server from ./build directory
+
 ## Deployment Commands

 **Building Docker Image** (`cd web-app`):
@@ -91,4 +99,127 @@ export const actionName = withUser(async (user: AuthenticatedUser, ...args) => {

 ### Testing & Code Quality
 - ESLint with Next.js and Prettier configurations
- No specific test framework configured - check with user before assuming testing approach
+- No specific test framework configured - check with user before assuming testing approach
+
+## Email Server Worker Architecture
+
+The email-server-worker is a TypeScript-based background worker service that combines periodic task execution with HTTP health monitoring and metrics collection.
+
+### Tech Stack
+- **Runtime**: Node.js with TypeScript
+- **Framework**: Express for HTTP endpoints
+- **Metrics**: Prometheus (prom-client) with custom PRTG adapter
+- **Testing**: Jest with TypeScript support
+
+### Core Architecture: Worker Pattern
+
+The service implements a **self-contained worker pattern** that runs periodic background tasks while exposing HTTP endpoints for monitoring.
+
+**Entry Point** (`email-server-worker/src/entry.ts:1`):
+- Creates Express HTTP server with graceful shutdown support (stoppable)
+- Starts the worker via `startSyncWorker()` from `email-server-worker/src/workRunner.ts:134`
+- Handles SIGTERM/SIGINT for graceful shutdown (Docker-compatible)
+- Calls `disposeSyncWorker()` on shutdown to allow pending work to complete
+
+**Work Runner** (`email-server-worker/src/workRunner.ts:1`):
+The work runner implements a self-scheduling loop with the following characteristics:
+
+- **Self-Scheduling Loop**: After completing work, schedules next execution via `setTimeout(workRunner, PULL_INTERVAL)` at `email-server-worker/src/workRunner.ts:113`
+- **Graceful Shutdown**: Tracks pending work via Promise, allows in-flight operations to complete before shutdown
+- **Status Tracking**: Exports `workerRunnerInfo` with `status` and `lastWorkTime` for health monitoring
+- **Error Isolation**: Worker errors don't crash the process - caught, logged, and execution continues
+- **Metrics Integration**: Automatic Prometheus metrics collection (duration, success/failure counters)
+- **Single Work Instance**: Ensures only one work cycle runs at a time via `pendingWork` Promise
+
+Work Runner States (WorkerRunnerStatus enum):
+- `init` - Initial state before first run
+- `beginWork` - Work cycle started
+- `workDone` - Work completed successfully
+- `disposed` - Worker stopped, no longer scheduling
+- Other states track Prometheus stats updates
+
+**Worker Implementation Pattern**:
+Workers must export a `doWork` function with signature:
+```typescript
+export const doWork = async () => {
+  // Perform periodic work here
+  // Throw errors to increment failedRequestCounter
+  // Return normally to increment successfulRequestCounter
+};
+```
+
+The work runner imports and calls this function at `email-server-worker/src/workRunner.ts:88`.
+
+### Key Files & Responsibilities
+
+**Core Worker Files**:
+- `email-server-worker/src/entry.ts` - HTTP server setup, signal handling, worker lifecycle management
+- `email-server-worker/src/workRunner.ts` - Self-scheduling loop, graceful shutdown, metrics integration
+- `email-server-worker/src/app.ts` - Express app configuration, route registration
+- `email-server-worker/src/lib/logger.ts` - Debug logger factory (uses 'debug' package)
+
+**HTTP Routes** (`email-server-worker/src/routes/`):
+- `healthcheckRouter.ts` - Health check endpoint (checks worker status via `workerRunnerInfo`)
+- `metricsRouter.ts` - Prometheus metrics endpoint
+- `prtgMetricsRouter.ts` - PRTG-compatible metrics adapter
+- `pingRouter.ts` - Simple ping/pong endpoint
+- `errorRouter.ts` - Structured error handler for expected errors
+- `finalErrorRouter.ts` - Catch-all error handler for unexpected errors
+
+**Infrastructure**:
+- `email-server-worker/src/lib/metricsCounters.ts` - Prometheus counter/histogram definitions
+- `email-server-worker/src/lib/initTools.ts` - Utility functions (coalesce, etc.)
+- `email-server-worker/src/lib/serializeError.ts` - Error serialization for logging
+- `email-server-worker/src/lib/Prometheus2Prtg.ts` - Converts Prometheus metrics to PRTG XML format
+
+### Environment Variables
+
+**Required**:
+- `PULL_INTERVAL` - Milliseconds between work cycles (default: "10000")
+
+**Optional**:
+- `PORT` - HTTP server port (default: "3000")
+- `PROMETHEUS_APP_LABEL` - App label for Prometheus metrics (default: "evo-open-table-sync-svc")
+- `PROMETHEUS_HISTOGRAM_BUCKETS` - Histogram bucket sizes (default: "0.1, 0.5, 1, 5, 10")
+- `DEBUG` - Debug namespaces for console logging (e.g., "server:server")
+- `ENV` - Environment mode: "dev", "jest" (affects logging behavior)
+
+### Creating a New Worker
+
+To implement a new worker task:
+
+1. **Create worker file** (e.g., `email-server-worker/src/myWorker.ts`):
+```typescript
+export const doWork = async () => {
+  // Implement your periodic task here
+  logger.info("Work Title", "Work completed successfully");
+
+  // Throw errors to mark as failed:
+  // throw new Error("Something went wrong");
+};
+```
+
+2. **Update `workRunner.ts`** import at line 6:
+```typescript
+import { doWork } from "./myWorker";
+```
+
+3. **Add environment variables** to `email-server-worker/src/types/environment.d.ts` as needed
+
+4. **Update `package.json` metadata** if the service purpose changes (name, description)
+
+### Docker Deployment
+
+- Uses `stoppable` library for graceful shutdown (10-second timeout before force-close)
+- Health check endpoint at `/healthcheck` verifies worker is running and not stalled
+- Prometheus metrics at `/metrics` for monitoring
+- PRTG-compatible metrics at `/prtg` for legacy monitoring systems
+- Graceful shutdown ensures work in progress completes before container stops
+
+### Testing
+
+- **Framework**: Jest with esbuild-jest for TypeScript
+- **Test Location**: `email-server-worker/tests/`
+- **Mocks**: Common mocks in `email-server-worker/tests/__mocks__/` (prom-client)
+- **Test Pattern**: Co-located with source in `tests/` mirroring `src/` structure
+- **Run Tests**: `npm run test` (watch mode)
--- a/email-server-worker/.dockerignore
+++ b/email-server-worker/.dockerignore
@@ -0,0 +1,7 @@
+tests
+.git
+coverage
+node_modules
+jest.config.ts
+service-tester.sh
+build-image.sh
--- a/email-server-worker/.gitignore
+++ b/email-server-worker/.gitignore
@@ -0,0 +1,2 @@
+node_modules
+build
--- a/email-server-worker/Dockerfile
+++ b/email-server-worker/Dockerfile
@@ -0,0 +1,75 @@
+#-------------------------------------------------------------
+# Build command: docker build . -t pr-d-registry.ngit.hr/ngit/evo-open-table-sync-svc:1.0.0
+#-------------------------------------------------------------
+
+#--------------------------------------------
+# Stage: building TypeScript
+#--------------------------------------------
+FROM node:18 as build-stage
+
+ENV WORKDIR=/app
+WORKDIR /app
+
+# kopiram SSH key & known_hosts koji su potrebni za `npm i`
+# zato što `package.json` pri instalacija NGIT paketa koristi
+# SSH autentikaciju
+COPY _docker_assets/.ssh /root/.ssh
+RUN chmod 700 /root/.ssh/*
+
+COPY ./package*.json ./
+
+# instaliram pakete
+RUN npm i && npm cache clean --force
+
+COPY ./tsconfig.json ./
+COPY ./src ./src
+RUN npm run build
+
+#--------------------------------------------
+# Stage: instaliram produkcijski node_modules
+#--------------------------------------------
+FROM node:18 as package-stage
+
+WORKDIR /app
+
+COPY ./package*.json ./
+
+# instaliram SAMO produkcijske
+RUN npm i --only=production && npm cache clean --force
+
+#--------------------------------------------
+# Stage: priprema finalnog image-a
+#--------------------------------------------
+FROM gcr.io/distroless/nodejs:18 as assembly-stage
+
+WORKDIR /app
+
+ARG PORT="3000"
+ENV PORT=${PORT}
+
+# prometheus config
+ARG PROMETHEUS_APP_LABEL
+ENV PROMETHEUS_APP_LABEL=${PROMETHEUS_APP_LABEL}
+
+ARG PROMETHEUS_HISTOGRAM_BUCKETS
+ENV PROMETHEUS_HISTOGRAM_BUCKETS=${PROMETHEUS_HISTOGRAM_BUCKETS}
+
+# (optional) logiranje na stdout (moguće opcije: "server:server", "server:metrics", "server:healthcheck" )
+ARG DEBUG
+ENV DEBUG=${DEBUG}
+
+# kopiram node-modules
+COPY  --from=package-stage /app/package*.json ./
+COPY  --from=package-stage /app/node_modules ./node_modules
+
+# kopiram buildane datoteke
+COPY  --from=build-stage /app/build/ ./server
+
+# server vrtim pod ograničenim "nobody" korisnikom
+USER nobody:nobody
+
+HEALTHCHECK --interval=30s --timeout=3s --start-period=10s \
+   CMD ["/nodejs/bin/node", "./server/healthcheck.js"]
+
+# pokrećem server
+CMD ["./server/entry.js"]
--- a/email-server-worker/README.md
+++ b/email-server-worker/README.md
@@ -1,27 +1,115 @@
 # Email Server Worker

-This workspace contains the email server worker service for the Evidencija Režija tenant notification system.
+Background worker service with HTTP health monitoring and metrics collection.

-## Purpose
+## Overview

-This service manages email operations by:
- Polling MongoDB for email status changes
- Detecting unverified tenant emails (EmailStatus.Unverified)
- Sending verification emails to tenants
- Updating email status to VerificationPending
- Sending scheduled notifications (rent due, utility bills)
+This is a TypeScript-based background worker service that combines periodic task execution with HTTP health monitoring and metrics collection. It implements a self-scheduling worker pattern with graceful shutdown support.

-## Architecture
+## Features

-This is a standalone background worker service that:
- Runs independently from the Next.js web-app
- Communicates via the shared MongoDB database
- Integrates with email service provider (e.g., Mailgun, SendGrid)
+- **Periodic Task Execution**: Self-scheduling worker loop with configurable interval
+- **Graceful Shutdown**: Ensures in-flight work completes before shutdown (Docker-compatible)
+- **Health Monitoring**: HTTP health check endpoint to verify worker status
+- **Metrics Collection**: Prometheus metrics with PRTG adapter
+- **Error Isolation**: Worker errors don't crash the process

-## Setup
+## Getting Started

-TBD
+### Installation
+
+```bash
+npm install
+```
+
+### Development
+
+```bash
+npm run start  # Start with nodemon (auto-reload)
+```
+
+### Build & Run
+
+```bash
+npm run build      # Compile TypeScript
+npm run run-server # Run compiled version
+```
+
+### Testing
+
+```bash
+npm run test  # Run Jest in watch mode
+```

 ## Environment Variables

-TBD
+### Required
+
+- `PULL_INTERVAL` - Milliseconds between work cycles (default: `"10000"`)
+
+### Optional
+
+- `PORT` - HTTP server port (default: `"3000"`)
+- `PROMETHEUS_APP_LABEL` - App label for Prometheus metrics (default: `"email-server-worker"`)
+- `PROMETHEUS_HISTOGRAM_BUCKETS` - Histogram bucket sizes (default: `"0.1, 0.5, 1, 5, 10"`)
+- `DEBUG` - Debug namespaces for console logging (e.g., `"server:server"`)
+- `ENV` - Environment mode: `"dev"`, `"jest"` (affects logging)
+
+## HTTP Endpoints
+
+- `GET /healthcheck` - Health check endpoint (verifies worker is running)
+- `GET /metrics` - Prometheus metrics
+- `GET /prtg` - PRTG-compatible metrics (XML format)
+- `GET /ping` - Simple ping/pong endpoint
+
+## Creating a Worker
+
+See `src/exampleWorker.ts` for the worker template. The worker must export a `doWork` function:
+
+```typescript
+
+export const doWork = async () => {
+  // Your periodic task logic here
+  logger.info("Task Completed", "Work done successfully");
+
+  // Throw errors to mark as failed:
+  // throw new Error("Something went wrong");
+};
+```
+
+Update `src/workRunner.ts` line 6 to import your worker:
+
+```typescript
+import { doWork } from "./yourWorker";
+```
+
+## Architecture
+
+- **entry.ts** - HTTP server setup, signal handling, worker lifecycle
+- **workRunner.ts** - Self-scheduling loop, metrics, graceful shutdown
+- **app.ts** - Express app configuration, routes
+- **src/lib/** - Shared utilities (logger, metrics, etc.)
+- **src/routes/** - HTTP route handlers
+
+## Deployment
+
+The service uses the `stoppable` library for graceful shutdown with a 10-second timeout before force-closing connections. Docker containers will receive SIGTERM signals and shut down gracefully.
+
+## Logging
+
+The service supports two logging mechanisms:
+
+1. **Console Logging**: Uses the `debug` package, controlled by `DEBUG` env variable
+
+## Metrics
+
+Prometheus metrics are automatically collected:
+
+- `request_operations_total` - Total work cycles executed
+- `request_operations_ok` - Successful work cycles
+- `request_operations_failed` - Failed work cycles
+- `request_duration_seconds` - Duration histogram of work cycles
+
+## Documentation
+
+See `CLAUDE.md` in the repository root for complete architecture documentation and guidance.
--- a/email-server-worker/build-image.sh
+++ b/email-server-worker/build-image.sh
@@ -0,0 +1,30 @@
+#!/bin/bash
+
+if [ "$1" == "" ] ; then
+    printf "\nDocker image version not set - please specify the version to build"
+    printf "\n\nSyntax:\n\n    build-image.sh 1.0.0\n\n"
+    exit 1
+fi
+
+read -p "BUILD: Push new image to registry [y/n]? " -n 1 -r
+echo    # (optional) move to a new line
+
+PUSH_IMAGE_TO_REPO="$REPLY"
+
+printf "\nBUILD START ...\n\n"
+
+REGISTRY_URL=registry.ngit.hr
+IMAGE_NAME=evo-open-table-sync-svc
+IMAGE_VERSION=$1
+
+IMAGE_TAG=$REGISTRY_URL/ngit/$IMAGE_NAME:$IMAGE_VERSION
+
+docker build . -t $IMAGE_TAG
+
+# if [[ "$PUSH_IMAGE_TO_REPO" =~ ^[Yy]$ ]]
+# then
+#     printf "\nPushing image ...\n\n"
+#     docker push $IMAGE_TAG
+# fi
+
+printf "\nBUILD DONE!\n\n"
--- a/email-server-worker/jest.config.ts
+++ b/email-server-worker/jest.config.ts
@@ -0,0 +1,39 @@
+/** @type {import('jest/dist/types').InitialOptionsTsJest} */
+
+import type { Config } from 'jest/build/index';
+
+const config:Config = {
+  // preset: 'ts-jest',
+  transform: {
+    '^.+\\.tsx?$': [
+      'esbuild-jest', {
+        sourcemap:true, // bez ovog VS code umjesto originala prikazuje transpilirane datoteke
+        target:'es2020' // ovo je nužno kako bi BigInt funkcionirao
+      }]
+  },
+  maxWorkers: 4,
+  testEnvironment: 'node',
+  // The root directory that Jest should scan for tests and modules within
+  rootDir: "./",
+  // A list of paths to directories that Jest should use to search for files in
+  roots: [
+    "<rootDir>/tests",
+  ],
+  // The glob patterns Jest uses to detect test files
+  testMatch: [
+    "**/?(*.)+(spec).[tj]s?(x)",
+  ],
+  // Automatically clear mock calls and instances between every test
+  clearMocks: true,
+  // An array of regexp pattern strings that are matched against all source file paths, matched files will skip transformation
+  transformIgnorePatterns: ["/node_modules/"],
+  // An array of regexp pattern strings that are matched against all test paths, matched tests are skipped
+  testPathIgnorePatterns: ["/node_modules/", "/build/"],
+  // Indicates whether each individual test should be reported during the run
+  verbose: true,
+  setupFiles: [
+    'dotenv/config', // učitaj varijable iz .env i učini ih dostupne testiranom software-u
+  ]
+};
+
+module.exports = config;
--- a/email-server-worker/package.json
+++ b/email-server-worker/package.json
@@ -0,0 +1,49 @@
+{
+  "name": "email-server-worker",
+  "version": "0.1.0",
+  "description": "Background worker service with HTTP health monitoring and metrics collection",
+  "main": "entry.ts",
+  "scripts": {
+    "start": "nodemon ./src/entry.ts",
+    "run-server": "DEBUG=* node --enable-source-maps ./build/entry.js",
+    "build": "ttsc --project ./",
+    "test": "ENV=jest jest --watch"
+  },
+  "author": "Nikola",
+  "license": "ISC",
+  "dependencies": {
+    "debug": "^2.6.9",
+    "express": "^4.18.2",
+    "http-errors": "^1.7.2",
+    "node-fetch": "^2.6.7",
+    "prom-client": "^14.0.1",
+    "stoppable": "^1.1.0"
+  },
+  "devDependencies": {
+    "@babel/preset-typescript": "^7.18.6",
+    "@types/debug": "^4.1.7",
+    "@types/express": "^4.17.13",
+    "@types/http-errors": "^1.8.1",
+    "@types/jest": "^29.2.5",
+    "@types/node": "^16.10.2",
+    "@types/node-fetch": "^2.6.2",
+    "@types/stoppable": "^1.1.1",
+    "@types/supertest": "^2.0.11",
+    "dotenv": "^16.0.3",
+    "esbuild": "^0.16.14",
+    "esbuild-jest": "^0.5.0",
+    "jest": "^29.3.1",
+    "nodemon": "^2.0.13",
+    "supertest": "^6.3.3",
+    "ts-node": "^10.9.1",
+    "tsconfig-paths": "^4.1.2",
+    "ttypescript": "^1.5.15",
+    "typescript": "^4.9.4",
+    "typescript-transform-paths": "^3.4.4"
+  },
+  "babel": {
+    "presets": [
+      "@babel/preset-typescript"
+    ]
+  }
+}
--- a/email-server-worker/run-image.sh
+++ b/email-server-worker/run-image.sh
@@ -0,0 +1,13 @@
+#!/bin/bash
+
+if [ "$1" == "" ] ; then
+    printf "\nNisi zadao verziju Docker image-a koji treba pokrenuti"
+    printf "\n\nSintaksa:\n\n    run-image.sh 1.0.0\n\n"
+    exit 1
+fi
+
+IMAGE_TAG=pr-d-registry.ngit.hr/ngit/evo-open-table-sync-svc:$1
+
+docker run -p 3000:3000 \
+   --env DEBUG=* \
+   $IMAGE_TAG
--- a/email-server-worker/src/app.ts
+++ b/email-server-worker/src/app.ts
@@ -0,0 +1,34 @@
+import express from 'express';
+import createError from 'http-errors';
+
+import { errorRouter } from './routes/errorRouter';
+import { finalErrorRouter } from './routes/finalErrorRouter';
+import { metricsRouter } from './routes/metricsRouter';
+import { pingRouter } from './routes/pingRouter';
+import { healthcheckRouter } from './routes/healthcheckRouter';
+
+import { SupportedRoutes } from './types/enums/SupportedRoutes';
+
+const app = express();
+
+// u slučaju kada se server vrti iza proxy-a
+// ovaj flag će natjerati Express da informacije poput
+// IP adrese klijenta, protokola uzima iz X-Forward-*
+// HTTP header polja, koja postavlja proxy
+app.set('trust proxy', true);
+
+// prometheus sa ove rute dohvaća zadnje važeću statistiku
+app.use(SupportedRoutes.metricsPath, metricsRouter);
+app.use(SupportedRoutes.ping, pingRouter);
+app.use(SupportedRoutes.healthcheck, healthcheckRouter);
+
+// default handler
+app.use((req, res, next) => next(createError(404)));
+
+// error handler za sve predviđene greške
+app.use(errorRouter);
+
+// error router za nepredviđene greške
+app.use(finalErrorRouter);
+
+export default app;
--- a/email-server-worker/src/entry.ts
+++ b/email-server-worker/src/entry.ts
@@ -0,0 +1,122 @@
+import app from './app';
+import http from 'http';
+import stoppable  from 'stoppable';
+
+import { createLogger } from './lib/logger';
+import { disposeSyncWorker, startSyncWorker } from './workRunner';
+const logger = createLogger("server:server");
+
+/**
+* Normalize a port into a number, string, or false.
+*/
+const normalizePort = (val:string):string|number|boolean => {
+  const port = parseInt(val, 10);
+
+  if (isNaN(port)) {
+    // named pipe
+    return val;
+  }
+
+  if (port >= 0) {
+    // port number
+    return port;
+  }
+
+  return false;
+};
+
+/**
+* Event listener for HTTP server "error" event.
+*/
+const onError = (error:any):void => {
+  if (error.syscall !== 'listen') {
+    throw error;
+  }
+
+  const bind = typeof port === 'string'
+    ? 'Pipe ' + port
+    : 'Port ' + port;
+
+  // handle specific listen errors with friendly messages
+  switch (error.code) {
+    case 'EACCES':
+      console.error(bind + ' requires elevated privileges');
+      process.exit(1);
+      break;
+    case 'EADDRINUSE':
+      console.error(bind + ' is already in use');
+      process.exit(1);
+      break;
+    default:
+      throw error;
+  }
+};
+
+/**
+* Event listener for HTTP server "listening" event.
+*/
+const onListening = ():void => {
+  const addr = server.address();
+  const bind = typeof addr === 'string'
+    ? 'pipe ' + addr
+    : 'port ' + addr?.port;
+  logger(`⚡️[server]: Server is running at ${bind}`);
+};
+
+/**
+* Get port from environment and store in Express.
+*/
+const port:number|string|boolean = normalizePort(process.env.PORT || '3000');
+
+/**
+* How long should stoppable wait before it starts force-closing connections
+* @description wait max 10 seconds - needs to be shorter than `healthcheck.timeout` (=15sec)
+*/
+const FORCE_STOP_TIMEOUT = 10000;
+
+/**
+* Create HTTP server.
+*/
+const server = stoppable( http.createServer(app), FORCE_STOP_TIMEOUT );
+
+// Listen on provided port, on all network interfaces.
+server.listen(port);
+server.on('error', onError);
+server.on('listening', onListening);
+
+/**
+ * Starting sync worker process
+ */
+startSyncWorker();
+
+// quit on ctrl-c when running docker in terminal
+// (signal neće biti registriran ako je server pokrenuti via `npm` ili `nodemon` - mora biti pokrenuti izravno via Node)
+process.on('SIGINT', () => {
+    logger('Got SIGINT (aka ctrl-c in docker). Graceful shutdown ', new Date().toISOString());
+    shutdown();
+});
+
+// quit properly on docker stop
+// (signal neće biti registriran ako je server pokrenuti via `npm` ili `nodemon` - mora biti pokrenuti izravno via Node)
+process.on('SIGTERM', () => {
+    logger('Got SIGTERM (docker container stop). Graceful shutdown ', new Date().toISOString());
+    shutdown();
+});
+
+// shut down server
+const shutdown = async () => {
+  
+  await disposeSyncWorker();
+
+  // NOTE: server.close is for express based apps
+  // If using hapi, use `server.stop`
+  server.close((err) => {
+    if (err) {
+      console.error(err);
+      process.exitCode = 1;
+    } else {
+      logger('Exiting server process...');
+    }
+    process.exit();
+  });
+};
--- a/email-server-worker/src/exampleWorker.ts
+++ b/email-server-worker/src/exampleWorker.ts
@@ -0,0 +1,33 @@
+/**
+ * Example worker implementation
+ *
+ * This is a placeholder worker that demonstrates the worker pattern.
+ * Replace this with your actual worker implementation.
+ *
+ * The worker is called periodically by workRunner.ts based on PULL_INTERVAL.
+ *
+ * @throws Error to increment failedRequestCounter in Prometheus
+ * @returns Promise that resolves when work is complete (increments successfulRequestCounter)
+ */
+export const doWork = async () => {
+    const startTime = Date.now();
+
+    // TODO: Implement your periodic worker logic here
+    // Examples:
+    // - Fetch data from external API
+    // - Process queued tasks from database
+    // - Send scheduled emails
+    // - Clean up expired records
+    // - Sync data between systems
+
+    const workDuration = Date.now() - startTime;
+
+    // Log success (only in non-test environments)
+    if (process.env.ENV !== "jest") {
+        const logMessage = `Example worker completed in ${workDuration}ms`;
+        console.log(logMessage);
+    }
+
+    // Note: Throw errors to mark work as failed:
+    // throw new Error("Something went wrong");
+};
--- a/email-server-worker/src/healthcheck.ts
+++ b/email-server-worker/src/healthcheck.ts
@@ -0,0 +1,29 @@
+import { createLogger } from "./lib/logger";
+
+import http, { IncomingMessage } from "http";
+const logger = createLogger("server:healthcheck");
+
+const options = {
+    host: "localhost",
+    port: "3000",
+    timeout: 2000,
+    path: '/healthcheck/'
+};
+
+const request = http.request(options, (res:IncomingMessage) => {
+
+    logger(`Healthcheck: STATUS ${res.statusCode}`);
+
+    if (res.statusCode == 200) {
+        process.exit(0);
+    } else {
+        process.exit(1);
+    }
+});
+
+request.on("error", function (err:any) {
+    logger("Healthcheck: ERROR");
+    process.exit(1);
+});
+
+request.end();
--- a/email-server-worker/src/lib/initTools.ts
+++ b/email-server-worker/src/lib/initTools.ts
@@ -0,0 +1,8 @@
+
+/**
+ * Za neinicijaliziranu env varijablu vraća default vrijednost
+ * @param value vrijednost env varijable
+ * @param defaultValue default vrijednost
+ * @returns 
+ */
+export const coalesce = (value:string|undefined, defaultValue:string):string => value===undefined ? defaultValue : (value==="" ? defaultValue : value);
--- a/email-server-worker/src/lib/logger.ts
+++ b/email-server-worker/src/lib/logger.ts
@@ -0,0 +1,21 @@
+import debug from 'debug';
+
+/**
+ * Logs to console / stdout
+ * @param namespace 
+ * @returns instance of Debug
+ */
+export const createLogger = (namespace:string):debug.Debugger => {
+    const dbg = debug(namespace);
+
+    const rx = /nodemon/gi;
+    
+    if(rx.test(process.env?.npm_lifecycle_script ?? "")) {
+        // When started via nodemon:
+        // forcing the use of console insted of stdout
+        // -> nodemon doesn't work with stdout
+        dbg.log = console.log.bind(console);
+    }
+
+    return(dbg);
+};
--- a/email-server-worker/src/lib/metricsCounters.ts
+++ b/email-server-worker/src/lib/metricsCounters.ts
@@ -0,0 +1,50 @@
+import { Counter, Histogram, register } from 'prom-client';
+import { coalesce } from './initTools';
+
+/** Histogram Buckets */
+const PROMETHEUS_HISTOGRAM_BUCKETS = coalesce(process.env.PROMETHEUS_HISTOGRAM_BUCKETS, "0.1, 0.5, 1, 5, 10");
+
+/** Labela kojom želimo da bude označena metrika prikupljena na ovom web servisu */
+const PROMETHEUS_APP_LABEL = coalesce(process.env.PROMETHEUS_APP_LABEL, 'email-server-worker');
+
+// na "app" labele ćemo razdvajanje rezultata u Grafani
+register.setDefaultLabels({ app: PROMETHEUS_APP_LABEL });
+
+/**
+ * Broji koliko je ukupno zahtjeva zaprimljeno za obradu
+ */
+ export const totalRequestCounter = new Counter({
+    name: "request_operations_total",
+    help: "ukupan broj zaprimljenih zahtjeva",
+    /** countere razdvajamo po vrsti zahtjeva */
+    labelNames: ['path'],
+});
+
+/**
+ * Broji zahtjeve koji su uspješno obrađeni
+ */
+export const successfulRequestCounter = new Counter({
+    name: "request_operations_ok",
+    help: "broj zahtjeva koji su uspješno obrađeni",
+    /** countere razdvajamo po vrsti zahtjeva */
+    labelNames: ['path'],
+});
+
+/**
+ * Broji zahtjeve kod čije obrade je došlo do greške
+ */
+export const failedRequestCounter = new Counter({
+    name: "request_operations_failed",
+    help: "broj zahtjeva kod čije obrade je došlo do greške",
+    /** countere razdvajamo po vrsti zahtjeva i rezultatu izvođenja */
+    labelNames: ["path", "status"],
+});
+
+/** Histogram mjeri koliko traje obrada pristiglog zahtjeva */
+export const requestDurationHistogram = new Histogram({
+    name: "request_duration_seconds",
+    help: "Trajanje request-a u sekundama",
+    /** countere razdvajamo po vrsti zahtjeva i rezultatu izvođenja */
+    labelNames: ["path", "status"],
+    buckets: PROMETHEUS_HISTOGRAM_BUCKETS?.split(',').map((el) => parseFloat(el))
+});
--- a/email-server-worker/src/lib/serializeError.ts
+++ b/email-server-worker/src/lib/serializeError.ts
@@ -0,0 +1,19 @@
+
+
+/**
+ * This function serializes an error object into a string that can be logged
+ * @param ex error object
+ * @returns string
+ * @description SQL Server may generate more than one error for one request so you can access preceding errors with `err.precedingErrors`, while the `ex` itself is a generic error without any useful information
+ */
+export const serializeError = (ex:Error | Error & { precedingErrors?:Error[] }):string => {
+    const { name, message, stack, precedingErrors } = (ex as Error & { precedingErrors?:Error[] });
+
+    // SQL Server may generate more than one error for one request so you can access preceding errors with `ex.precedingErrors`,
+    // while the `ex` itself is a generic error without any useful information
+    if(precedingErrors) {
+        return(serializeError(precedingErrors[0]));
+    }
+
+    return `${name}:${message}`;
+}
--- a/email-server-worker/src/routes/errorRouter.ts
+++ b/email-server-worker/src/routes/errorRouter.ts
@@ -0,0 +1,81 @@
+import { ErrorRequestHandler, Request, Response } from "express";
+import createHttpError, { HttpError } from "http-errors";
+import { createLogger } from '../lib/logger';
+import { NgitLocals } from "../types/NgitLocals";
+import { failedRequestCounter } from "../lib/metricsCounters";
+import { SupportedRoutes } from "../types/enums/SupportedRoutes";
+
+const consoleLog = createLogger("server:server");
+
+/**
+ * Router koji se zadnji poziva, a koji sastavlja odgovor u slučaju greške
+ * @param err 
+ * @param req 
+ * @param res 
+ * @param next 
+ */
+export const errorRouter:ErrorRequestHandler = async (err:HttpError, req, res, next) => {
+
+    const requestPath = req.path as SupportedRoutes;
+
+    // kako je ovaj error handler dosta složen, moguće je da negdje baci grešku
+    // > zato je zamotan u try-catch
+    // > na taj način osiguravam da neće srušiti cijeli proces
+    try {
+
+        let { name:errorLogName, message:errorLogText } = err;
+        let responseBody:string = "";
+
+        switch(err.status) {
+            case 400:
+                responseBody = 'bad request';
+                break;
+            case 401:
+                responseBody = 'unauthorized';
+                break;
+            case 403:
+                responseBody = 'forbidden';
+                break;
+            case 404:
+                consoleLog(`page not found ${req.method} ${requestPath}`)
+                responseBody = 'page not found';
+                errorLogText = `page ${requestPath} not found`;
+                break;
+            case 500:
+                responseBody = "internal server error";
+                errorLogText = err.message;
+                break;
+            default:
+                responseBody = err.name;
+                errorLogText = `err.status=${err.status};err.name=${err.name};err.message=${err.message}`;
+        }
+
+        consoleLog(`${errorLogName}:${errorLogText}`);
+        
+        // `headersSent` će biti TRUE ako je router kod kojeg se dogodila greška već poslao header-e
+        // > ako ih probam ponovo postaviti, to će baciti grešku ... a to ovdje mogu izbjeći
+        if(!res.headersSent) {
+            res.status(err.status);
+            res.setHeader('Content-Type', "text/html");
+            res.end(responseBody);
+        } else {
+            // AKO nije pozvan `end` - pozovi ga i završi obradu zahtjeva
+            // ... u suprotnom će konekcija ostati otvorena do timeout-a
+            if(!res.writableEnded) {
+                res.end();
+            }
+        }
+
+    } catch(ex:any) {
+        // ovu grešku će obraditi `finalErrorRouter`
+        next(createHttpError(500, ex));
+    }
+
+    // ne mogu dopustiti da prometheus client sruši server
+    try  {
+        failedRequestCounter.inc({ path: requestPath, status: err.status });
+        (res.locals as NgitLocals).stopPrometheusTimer({ path: req.path, status: err.status });
+    } catch(ex:any) {
+        console.error(ex);
+    }
+};
--- a/email-server-worker/src/routes/finalErrorRouter.ts
+++ b/email-server-worker/src/routes/finalErrorRouter.ts
@@ -0,0 +1,34 @@
+import { ErrorRequestHandler, Request, Response } from "express";
+import { HttpError } from "http-errors";
+import { createLogger } from '../lib/logger';
+import { NgitLocals } from "../types/NgitLocals";
+
+const consoleLog = createLogger("server:server");
+
+/**
+ * Router koji se izvršava u slučaju grube greške koja nije obrađena nigdje prije
+ * @param err error objekt
+ * @param req express request
+ * @param res express response
+ * @param next 
+ */
+export const finalErrorRouter:ErrorRequestHandler = async (err:HttpError, req, res, next) => {
+
+    const errorLogText:string = JSON.stringify({ message:err.message, name:err.name, stack:err.stack });
+
+    consoleLog(`Server Error ${err.status}\n${errorLogText}`);          
+
+    // `headersSent` će biti TRUE ako je router kod kojeg se dogodila greška već poslao header-e
+    // > ako ih probam ponovo postaviti, to će baciti grešku i u ovom slučaju SRUŠITI SERVER - to ne smijemo dopustiti
+    if(!res.headersSent) {
+        res.status(err.status);
+        res.setHeader('Content-Type', "text/html");
+        res.end(`unhandled server error`);
+    } else {
+        // AKO nije pozvan `end` - pozovi ga i završi obradu zahtjeva
+        // ... u suprotnom će konekcija ostati otvorena do timeout-a
+        if(!res.writableEnded) {
+            res.end();
+        }
+    }
+};
--- a/email-server-worker/src/routes/healthcheckRouter.ts
+++ b/email-server-worker/src/routes/healthcheckRouter.ts
@@ -0,0 +1,35 @@
+import { RequestHandler, Router } from "express";
+import { workerRunnerInfo } from "../workRunner";
+import { coalesce } from "../lib/initTools";
+
+const PULL_INTERVAL = parseInt(coalesce(process.env.PULL_INTERVAL, "10000"));
+
+/** Maximum time between two worker jobs */
+const MAX_WORKER_LATENCY = PULL_INTERVAL * 2.5;
+
+/**
+ * Router koji se izvršava u slučaju grube greške koja nije obrađena nigdje prije
+ * @param req express request
+ * @param res express response
+ * @param next 
+ */
+export const healthcheckRouter:RequestHandler = async (req, res, next) => {
+    const workerLatency = Date.now() - workerRunnerInfo.lastWorkTime;
+
+    if(workerLatency > MAX_WORKER_LATENCY) {
+        const msg = `No work done in ${workerLatency}ms. Last worker status = "${workerRunnerInfo.status}"`;
+
+        console.warn(msg)
+
+        res.status(500);
+        res.setHeader('Content-Type', 'text/plain');
+        res.end(msg);
+    } else {
+        res.status(200);
+        res.setHeader('Content-Type', 'text/plain');
+        res.end('OK');
+    }
+};
+
+export const pingRouter = Router();
+pingRouter.get('/', healthcheckRouter);
--- a/email-server-worker/src/routes/metricsRouter.ts
+++ b/email-server-worker/src/routes/metricsRouter.ts
@@ -0,0 +1,19 @@
+import { Router, NextFunction, Request, Response } from "express";
+import createError from 'http-errors';
+import { register } from 'prom-client';
+import { createLogger } from '../lib/logger';
+
+const logger = createLogger("server:metrics");
+
+export const metricsRouter = Router();
+
+metricsRouter.get('/', async (req:Request, res:Response, next:NextFunction) => {
+    // ne mogu dopustiti da prometheus client sruši server
+    try {
+        logger(`⚡️[server]: GET /metrics`);
+        res.set('Content-Type', register.contentType);
+        res.end(await register.metrics());
+    } catch(ex:any) {
+        next(createError(500, (ex as Error).message));
+    }
+});
--- a/email-server-worker/src/routes/pingRouter.ts
+++ b/email-server-worker/src/routes/pingRouter.ts
@@ -0,0 +1,16 @@
+import { RequestHandler, Router } from "express";
+
+/**
+ * Router koji se izvršava u slučaju grube greške koja nije obrađena nigdje prije
+ * @param req express request
+ * @param res express response
+ * @param next 
+ */
+export const pingRequestHandler:RequestHandler = async (req, res, next) => {
+    res.status(200);
+    res.setHeader('Content-Type', 'text/plain');
+    res.end('PONG');
+};
+
+export const pingRouter = Router();
+pingRouter.get('/', pingRequestHandler);
--- a/email-server-worker/src/types/NgitLocals.ts
+++ b/email-server-worker/src/types/NgitLocals.ts
@@ -0,0 +1,7 @@
+import { LabelValues } from "prom-client";
+
+/** data assignet to `express.response.locals` */
+export type NgitLocals = {
+    /** Prometheus client timer */
+    stopPrometheusTimer: (labels?: LabelValues<"path"|"status">) => number,
+};
--- a/email-server-worker/src/types/enums/SupportedRoutes.ts
+++ b/email-server-worker/src/types/enums/SupportedRoutes.ts
@@ -0,0 +1,5 @@
+export enum SupportedRoutes {
+    metricsPath='/metrics',
+    ping='/ping',
+    healthcheck='/healthcheck',
+}
--- a/email-server-worker/src/types/environment.d.ts
+++ b/email-server-worker/src/types/environment.d.ts
@@ -0,0 +1,29 @@
+
+declare global {
+    namespace NodeJS {
+        interface ProcessEnv  {
+            /**
+             * (optional) environment u kojem se proces vrti
+             * @default undefined
+             * */
+            ENV?:"dev"|"jest"
+            /**
+             * (optional) App label to be used in Prometheus (Grafana)
+             * @default "email-server-worker"
+             * */
+            PROMETHEUS_APP_LABEL?: string
+            /**
+             * (optional) Prometheus histogram bucket sizes (grafana)
+             * @default "0.1, 0.5, 1, 5, 10"
+             * */
+            PROMETHEUS_HISTOGRAM_BUCKETS?: string
+            /**
+             * (required) Pull interval in milliseconds - how often should worker cycle run
+             * @default "10000"
+             * */
+            PULL_INTERVAL:string
+        }
+    }
+}
+
+export {}
--- a/email-server-worker/src/workRunner.ts
+++ b/email-server-worker/src/workRunner.ts
@@ -0,0 +1,165 @@
+import { failedRequestCounter, requestDurationHistogram, successfulRequestCounter, totalRequestCounter } from "./lib/metricsCounters";
+import { coalesce } from "./lib/initTools";
+import { createLogger } from "./lib/logger";
+import { serializeError } from "./lib/serializeError";
+import { doWork } from "./exampleWorker";
+
+/** time between two pull operations */
+const PULL_INTERVAL = parseInt(coalesce(process.env.PULL_INTERVAL, "10000"));
+const consoleLog = createLogger("server:server");
+
+/** Writes entry to log */
+const logWrite = (logTitle:string, logMessage:string) => {
+    consoleLog(`${logTitle}: ${logMessage}}`);
+}
+
+/** Writes error to log */
+const logError = (ex: any) => 
+    logWrite(serializeError(ex), "error");
+
+/**
+ * zastavica za zaustavljanje sinhronizacije
+ */
+let disposed:boolean = false;
+/** is worker started - prevents multiple starts */
+let workerStarted:boolean = false;
+/** Promise which is resolved once the pending work in progress is completed */
+let pendingWork:Promise<void>|undefined;
+/** Worker re-run timeout */
+let pendingTimeout:NodeJS.Timeout|undefined;
+
+/** Enumeracija pojedinih statusa obrade jednog work-a */
+export enum WorkerRunnerStatus {
+    init="init",
+    disposed="disposed",
+    beginWork="beginWork",
+    updatedStats1="updatedStats1",
+    updatedStats2="updatedStats2",
+    stoppedStatTimer="stoppedStatTimer",
+    workDone="workDone",
+    newIntervalScheduled="newIntervalScheduled",
+    currentWorkResolved="currentWorkResolved",
+}
+
+/** Info o statusu workera */
+export type WorkerRunnerInfo = {
+    /** zadnje izvršena readnja */
+    status: WorkerRunnerStatus,
+    /** vrijeme kada je worker zadnji puta pokrenut */
+    lastWorkTime: number,
+}
+
+/** Info o statusu workera, koji koristi healthcheck kako bi vidio da li stvar funkcionira */
+export const workerRunnerInfo:WorkerRunnerInfo = {
+    status: WorkerRunnerStatus.init,
+    lastWorkTime: Date.now()
+}
+
+export const workRunner = async () => {
+
+    pendingTimeout = undefined;
+    workerRunnerInfo.lastWorkTime = Date.now();
+    workerRunnerInfo.status = WorkerRunnerStatus.beginWork;
+
+    // AKO je modul zaustavljen
+    // -> nemoj se pokrenuti
+    if(disposed) {
+        workerRunnerInfo.status = WorkerRunnerStatus.disposed;
+        return;
+    }
+
+    // kreiram Promise koji omogućuje da dispose zna
+    // pričekati da worker završi sa poslom (ako je u tom trenutku aktivan)
+    pendingWork = new Promise(async (resolve) => {
+
+        try {
+            totalRequestCounter.inc();
+
+            const stopPrometheusTimer = requestDurationHistogram.startTimer();
+
+            workerRunnerInfo.status = WorkerRunnerStatus.updatedStats1;
+            
+            try {
+                // ne dopuštam da stvar sruši worker
+                await doWork();
+
+                workerRunnerInfo.status = WorkerRunnerStatus.workDone;
+
+                // ažuriram statistiku
+                successfulRequestCounter.inc();
+
+                workerRunnerInfo.status = WorkerRunnerStatus.updatedStats2;
+            } catch(ex:any) {
+
+                // ažuriram statistiku
+                failedRequestCounter.inc();
+                logError(ex);
+            }
+
+            stopPrometheusTimer();
+
+            workerRunnerInfo.status = WorkerRunnerStatus.stoppedStatTimer;
+        } catch(ex:any) {
+            logError(ex);
+        }
+    
+        // nemoj pokrenuti timer ako je worker u međuvremenu disposed
+        if(!disposed) {
+            // pull again after timeout
+            pendingTimeout = setTimeout(workRunner, PULL_INTERVAL);
+            workerRunnerInfo.status = WorkerRunnerStatus.newIntervalScheduled;
+        } else {
+            logWrite("Info", "... exiting worker loop");
+        }
+
+        resolve();
+
+        workerRunnerInfo.status = WorkerRunnerStatus.currentWorkResolved;
+
+        pendingWork = undefined;
+    });
+    
+    // this is an async function which must return a promise
+    // > so return the promise which will be resolved once the work is done
+    return(pendingWork);
+};
+
+/**
+ * Starts the worker
+ */
+export const startSyncWorker = () => {
+    if(!workerStarted && !disposed) {
+        workerStarted = true;
+        workRunner();
+        logWrite("Info", "Worker Started");
+    };
+}
+
+/**
+ * Stops and disposes the worker
+ */
+export const disposeSyncWorker = async () => {
+    logWrite("Info", "Disposing worker ...");
+
+    disposed = true;
+
+    // preventing timer from trigger another work cycle
+    if(pendingTimeout) {
+        clearTimeout(pendingTimeout);
+    }
+
+    // IF no work is currently in progress
+    // > return a resolved promise
+    if(!pendingWork) {
+        return(Promise.resolve());
+    }
+
+    await pendingWork;
+
+    logWrite("Info", "Worker disposed!");
+}
+
+/** Ovo se koristi samo za Unit Testing */
+export const reset_dispose = () => {
+    disposed = false;
+}
--- a/email-server-worker/tests/mocks/prom-client.ts
+++ b/email-server-worker/tests/mocks/prom-client.ts
@@ -0,0 +1,29 @@
+import { LabelValues } from "prom-client";
+
+export class Counter {
+    public inc() {
+
+    }
+}
+
+export class Histogram<T extends string> {
+    startTimer(labels?: LabelValues<T>): (labels?: LabelValues<T>) => void {
+        return((labels?: LabelValues<T>) => { });
+    }
+}
+
+class Register {
+    public setDefaultLabels(labels: Object) {
+
+    }
+
+    public metrics(): Promise<string> {
+        return(Promise.resolve(""));
+    }
+
+    public get contentType() {
+        return("");
+    }
+}
+
+export const register = new Register();
--- a/email-server-worker/tests/helpers/mockHttpContext.ts
+++ b/email-server-worker/tests/helpers/mockHttpContext.ts
@@ -0,0 +1,33 @@
+import { Request, Response, NextFunction } from 'express';
+import { NgitLocals } from "../../src/types/NgitLocals";
+
+interface IMockHttpContext {
+  reqPath?:string
+  headersSent?:boolean
+  writableEnded?:boolean
+  method?:string
+}
+
+export const mockHttpContext = ({reqPath="/", headersSent=false, writableEnded=false, method="GET"}:IMockHttpContext|undefined = {}) => {
+    const req = {
+      path:reqPath,
+      method,
+      url:`https://localhost${reqPath}`,
+      params: {},
+    } as unknown as Request;
+  
+    const res = {
+      end: jest.fn(),
+      status: jest.fn(),
+      setHeader: jest.fn(),
+      locals: {
+        stopPrometheusTimer: jest.fn(),
+      } as unknown as NgitLocals,
+      headersSent,
+      writableEnded,
+    } as unknown as Response;
+
+    const next:NextFunction = jest.fn();
+  
+    return({req,res,next})
+  }
--- a/email-server-worker/tests/routers/errorRouter.spec.ts
+++ b/email-server-worker/tests/routers/errorRouter.spec.ts
@@ -0,0 +1,118 @@
+
+import { errorRouter } from '../../src/routes/errorRouter';
+import createError from "http-errors";
+import { mockHttpContext } from "../helpers/mockHttpContext";
+
+describe("errorRouter", () => {
+
+    beforeEach(() => {
+      mockWrite.mockClear();
+    });
+
+    test("u slučaju greške 404 mora vratiti string poruku 'page not found'", async () => {
+        const err = createError(404)
+        const {req,res,next} = mockHttpContext();
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.status).toHaveBeenCalledWith(404);
+        expect(res.setHeader).toHaveBeenCalledWith('Content-Type', "text/html");
+        expect(res.end).toHaveBeenCalledWith("page not found");
+      });
+
+      test("u slučaju greške 404 mora logirati request, response i tekst greške", async () => {
+        const err = createError(404)
+        const reqPath = "/neki-path/";
+        const {req,res,next} = mockHttpContext({ reqPath });
+        
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.locals.logger.info).toHaveBeenCalledWith("response", "page not found");
+        expect(res.locals.logger.error).toHaveBeenCalledWith(err.name, "page "+req.path+" not found");
+      });
+
+      test("ako su header-i već poslani, ne smiju biti poslani još jednom", async () => {
+        const err = createError(404)
+        const {req,res,next} = mockHttpContext({ headersSent:true, writableEnded:true });
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.status).not.toHaveBeenCalled();
+        expect(res.setHeader).not.toHaveBeenCalled();
+        expect(res.end).not.toHaveBeenCalled();
+      });
+
+      test("ako NIJE već pozvana [end] metoda, treba je pozvati", async () => {
+        const err = createError(404)
+        const {req,res,next} = mockHttpContext({ headersSent:true, writableEnded:false });
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.status).not.toHaveBeenCalled();
+        expect(res.setHeader).not.toHaveBeenCalled();
+        expect(res.end).toHaveBeenCalled();
+      });
+  
+      test("mora zaustaviti Prometheus Timer", async () => {
+        const err = createError(404)
+        const {req,res,next} = mockHttpContext({ headersSent:true, writableEnded:false });
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.locals.stopPrometheusTimer).toHaveBeenCalled();
+      });
+
+      test("u slučaju greške 500 mora vratiti string poruku 'internal server error'", async () => {
+        const err = createError(500)
+        const {req,res,next} = mockHttpContext();
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.status).toHaveBeenCalledWith(500);
+        expect(res.setHeader).toHaveBeenCalledWith('Content-Type', "text/html");
+        expect(res.end).toHaveBeenCalledWith("internal server error");
+      });
+
+      test("u slučaju greške 400 mora vratiti string poruku 'bad request' i logirati grešku", async () => {
+        const errorMessage = "mock error text 1";
+        const err = createError(400, errorMessage);
+        const {req,res,next} = mockHttpContext();
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.status).toHaveBeenCalledWith(400);
+        expect(res.setHeader).toHaveBeenCalledWith('Content-Type', "text/html");
+        expect(res.end).toHaveBeenCalledWith("bad request");
+
+        expect(res.locals.logger.errorwrite).toHaveBeenCalledWith(err.name, errorMessage);
+      });
+
+      test("u slučaju greške 401 mora vratiti string poruku 'unauthorized' i logirati grešku", async () => {
+        const errorMessage = "mock error text 2";
+        const err = createError(401, errorMessage)
+        const {req,res,next} = mockHttpContext();
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.status).toHaveBeenCalledWith(401);
+        expect(res.setHeader).toHaveBeenCalledWith('Content-Type', "text/html");
+        expect(res.end).toHaveBeenCalledWith("unauthorized");
+
+        expect(res.locals.logger.error).toHaveBeenCalledWith(err.name, errorMessage);
+      });
+
+      test("u slučaju greške 403 mora vratiti string poruku 'forbidden' i logirati grešku", async () => {
+        const errorMessage = "mock error text 3";
+        const err = createError(403, errorMessage);
+        const {req,res,next} = mockHttpContext();
+  
+        await errorRouter(err, req, res, next);
+  
+        expect(res.status).toHaveBeenCalledWith(403);
+        expect(res.setHeader).toHaveBeenCalledWith('Content-Type', "text/html");
+        expect(res.end).toHaveBeenCalledWith("forbidden");
+
+        expect(res.locals.logger.error).toHaveBeenCalledWith(err.name, errorMessage);
+      });
+});
--- a/email-server-worker/tsconfig.json
+++ b/email-server-worker/tsconfig.json
@@ -0,0 +1,36 @@
+{
+  "compilerOptions": {
+    "target": "es2020", // https://github.com/microsoft/TypeScript/wiki/Node-Target-Mapping
+    "module": "commonjs",
+    "esModuleInterop": true, // solves the problem regarding the default importa vs importa *
+    "strict": true,
+    "sourceMap": true, // please do create source maps
+    "skipLibCheck": true, // don't verify typescript of 3rd party modules
+    "rootDir": "src", // root directory under which source files are located - it's subtree will be mirrored in "outDir"
+    "outDir": "build", // where the build files should be stored
+// "baseUrl" ---- se NE SMIJE koristiti
+// POJAŠNJENJE: ako zadamo "baseUrl" Intellisense će početi kod autocompletion-a (Ctrl+Space)
+//              umjesto relativnih insertirati apsolutni path do modula,
+//              a takav path nije dobar za build niti debugging
+//      "baseUrl": "./", // set a base directory to resolve non-absolute module names - This must be specified if "paths" is used
+    "paths": {
+    },
+    "plugins": [
+      {
+        // Slijedeće je namijenjeno BUILD projekta
+        // POJAŠNJENJE: build tadi `ttypescript`
+        //              koji ne zna interpretirati što je podešeno pod "path"
+        //              > to za njega rješava "typescript-transform-paths"
+        "transform": "typescript-transform-paths"
+      }
+    ]
+  },
+  "include": ["src/**/*"], // location of files which need to be compiled
+  // Slijedeće je namijenjeno DEBUGGING servera u VS Code-u
+  // POJAŠNJENJE: kod debugginga modul se pokreće pomoću `ts-node`,
+  //              koji ne zna sam interpretirati što je podešeno pod "paths"
+  //              > to za njega rješava "tsconfig-paths/register"
+  "ts-node": {
+    "require": ["tsconfig-paths/register"]
+  },
+}