Back-end Challenge V2

.vscode/extensions.json

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+{
+  "recommendations": [
+    "esbenp.prettier-vscode",
+    "ms-vscode.vscode-typescript-next"
+  ]
+}

.vscode/settings.json

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+{
+  "editor.defaultFormatter": "esbenp.prettier-vscode",
+  "editor.formatOnSave": true
+}

back-end-challenge-v2-solution/.env.example

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+MONGODB_URI=mongodb://localhost:27017
+MONGODB_DATABASE=dynamox
+PORT=3000

back-end-challenge-v2-solution/.gitignore

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+node_modules
+.env
+dist

back-end-challenge-v2-solution/.nvmrc

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+v24.14.1

back-end-challenge-v2-solution/.prettierignore

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+dist

back-end-challenge-v2-solution/.prettierrc

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+{}

back-end-challenge-v2-solution/README.md

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+# Back-end Challenge V2 Solution
+
+Implementation of `back-end-challenge-v2.md` using Node.js, Express, MongoDB, and Jest.
+
+**All commands in this README must be run from the back-end-challenge-v2-solution directory.**
+
+## Overview
+
+This API allows clients to:
+
+- create a time series
+- retrieve a full time series
+- retrieve time series metrics
+- delete a time series
+- count how many time series are stored
+
+The public API contract is standardized in `snake_case`.
+
+## Stack
+
+- Node.js
+- TypeScript
+- Express
+- MongoDB with Mongoose
+- Zod for validation
+- Jest + Supertest for tests
+- Docker for local MongoDB
+
+## Deployed API
+
+The application is also deployed as a bonus feature.
+
+Base URL:
+
+```text
+https://developer-challenges-n2rp.onrender.com
+```
+
+Health check:
+
+```text
+https://developer-challenges-n2rp.onrender.com/health
+```
+
+Note:
+
+- the deployed version uses free-tier cloud services
+- response times may vary due to shared infrastructure, cold starts, and network latency between the application and the managed database
+- local execution is a more reliable reference for evaluating the application itself than the free-tier deployment environment
+
+## Prerequisites
+
+Make sure the following tools are installed on your machine:
+
+- `nvm` or another Node.js version manager
+- Node.js
+- npm
+- Docker
+- Docker Compose
+
+This repository includes a [.nvmrc](.nvmrc) file. If you use `nvm`, run:
+
+```bash
+nvm use
+```
+
+If the required Node.js version is not installed yet, run:
+
+```bash
+nvm install
+nvm use
+```
+
+## Implemented User Stories
+
+- store a raw time series
+- retrieve a full time series
+- retrieve metrics for a time series
+- delete a time series
+- retrieve the total number of stored time series
+
+## Endpoints
+
+### `POST /api/series`
+
+Creates a new time series.
+
+Example payload:
+
+```json
+{
+  "series_id": "S1",
+  "unit": "C",
+  "points": [
+    {
+      "timestamp": "2024-01-01T00:00:00.000Z",
+      "value": 10
+    }
+  ]
+}
+```
+
+Example response:
+
+```json
+{
+  "series_id": "S1",
+  "created_at": "2026-04-04T16:16:11.845Z"
+}
+```
+
+### `GET /api/series/:series_id`
+
+Returns the full time series.
+
+### `GET /api/series/:series_id/metrics`
+
+Returns metrics for the time series.
+
+Example response:
+
+```json
+{
+  "series_id": "S1",
+  "unit": "C",
+  "total_points": 3,
+  "min_value": 10,
+  "max_value": 30,
+  "average_value": 20,
+  "first_timestamp": "2024-01-01T00:00:00.000Z",
+  "last_timestamp": "2024-01-03T00:00:00.000Z"
+}
+```
+
+### `DELETE /api/series/:series_id`
+
+Deletes a time series.
+
+Expected response:
+
+- `204 No Content`
+
+### `GET /api/series/count`
+
+Returns the total number of stored time series.
+
+Example response:
+
+```json
+{
+  "total_series": 5
+}
+```
+
+### `GET /health`
+
+Returns the basic application and MongoDB connection status.
+
+## Validation Rules
+
+- `series_id` must be a non-empty string
+- `unit` must be a non-empty string
+- `points` must contain at least one item
+- `points` must contain at most `2000` items
+- `timestamp` must use ISO 8601 format
+- timestamps must be unique within the same time series
+- `series_id` must be unique per series
+- JSON request payloads above `512kb` are rejected with `413 Payload Too Large`
+
+Notes:
+
+- repeated timestamps are allowed across different time series
+- series uniqueness is enforced by `seriesId`
+
+## How to Run
+
+### 1. Install the correct Node.js version
+
+If you use `nvm`:
+
+```bash
+nvm install
+nvm use
+```
+
+### 2. Install dependencies
+
+```bash
+npm install
+```
+
+### 3. Configure the environment
+
+Copy `.env.example` to `.env` and adjust values if needed.
+
+Available variables:
+
+```env
+MONGODB_URI=mongodb://localhost:27017
+MONGODB_DATABASE=dynamox
+PORT=3000
+```
+
+### 4. Start MongoDB
+
+```bash
+npm run db:start
+```
+
+### 5. Start the application in development mode
+
+```bash
+npm run dev
+```
+
+By default, the API will be available at:
+
+```text
+http://localhost:3000
+```
+
+### 6. Build and start the application
+
+Compile the project:
+
+```bash
+npm run build
+```
+
+Start the compiled server:
+
+```bash
+npm start
+```
+
+## Running Tests
+
+```bash
+npm test
+```
+
+Or in watch mode:
+
+```bash
+npm run test:watch
+```
+
+## Project Structure
+
+```text
+src/
+  config/
+  controllers/
+  dto/
+  errors/
+  middlewares/
+  models/
+  routes/
+  services/
+```
+
+## Implementation Decisions
+
+- the HTTP contract uses `snake_case`
+- the internal domain and model representation use `camelCase`
+- response serialization is handled in the DTO layer
+- `seriesId` has a unique index in MongoDB
+- metrics are calculated in memory after retrieving the full series
+- request size and number of points are bounded to keep ingestion latency under control
+
+## Test Coverage
+
+- invalid payload validation
+- duplicate timestamp validation within the same time series
+- maximum points validation for time series creation
+- time series creation
+- time series count
+- full time series retrieval by `series_id`
+- time series metrics retrieval
+- time series deletion
+- `400`, `404`, and `413` scenarios
+- service tests and HTTP tests with Supertest

back-end-challenge-v2-solution/docker-compose.yml

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+services:
+  mongodb:
+    image: mongo:7.0
+    ports:
+      - "27017:27017"
+    volumes:
+      - mongodb_data:/data/db
+
+volumes:
+  mongodb_data:

back-end-challenge-v2-solution/jest.config.ts

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+import type { Config } from "jest";
+
+const config: Config = {
+  testEnvironment: "node",
+  extensionsToTreatAsEsm: [".ts"],
+  transform: {
+    "^.+\\.ts$": [
+      "ts-jest",
+      {
+        useESM: true,
+        diagnostics: {
+          ignoreCodes: [151002],
+        },
+      },
+    ],
+  },
+  moduleNameMapper: {
+    "^(\\.{1,2}/.*)\\.js$": "$1",
+  },
+};
+
+export default config;