# ┌──────────────────────────────────────────────────────────┐
# │  Docker Compose — Multi-Container Orchestration         │
# │                                                        │
# │  WHAT IS DOCKER COMPOSE?                               │
# │  A tool to define and run multi-container apps.        │
# │  Instead of running 3 separate `docker run` commands   │
# │  for MongoDB, Backend, and Frontend, you define them   │
# │  all in this ONE file and run `docker-compose up`.     │
# │                                                        │
# │  NETWORKING:                                           │
# │  Docker Compose creates a virtual network. Containers  │
# │  can reach each other by SERVICE NAME (e.g., the       │
# │  backend connects to "mongodb" not "localhost").       │
# │                                                        │
# │  DEPENDS_ON:                                           │
# │  Controls startup order. Backend waits for MongoDB.    │
# │  Frontend waits for Backend.                           │
# └──────────────────────────────────────────────────────────┘

services:
  # ── MongoDB Database ─────────────────────────────────────
  # The data layer — stores all todo items
  mongodb:
    image: mongo:7                      # Official MongoDB 7 image
    container_name: todo-mongodb
    restart: unless-stopped             # Auto-restart unless manually stopped
    ports:
      - "27017:27017"                   # Host:Container port mapping
    volumes:
      - mongodb_data:/data/db           # Persist data across container restarts
    environment:
      MONGO_INITDB_DATABASE: todoapp    # Create this database on first start
    healthcheck:
      test: ["CMD", "mongosh", "--eval", "db.adminCommand('ping')"]
      interval: 10s
      timeout: 5s
      retries: 5
      start_period: 30s
    networks:
      - todo-network

  # ── Backend API ──────────────────────────────────────────
  # The logic layer — handles business logic & database queries
  backend:
    build:
      context: ./backend
      dockerfile: Dockerfile
    container_name: todo-backend
    restart: unless-stopped
    ports:
      - "4000:4000"
    environment:
      - PORT=4000
      - MONGO_URI=mongodb://mongodb:27017/todoapp  # "mongodb" = service name above
      - NODE_ENV=production
      - CORS_ORIGIN=*
    depends_on:
      mongodb:
        condition: service_healthy      # Wait for MongoDB health check to pass
    healthcheck:
      test: ["CMD", "wget", "-qO-", "http://localhost:4000/health"]
      interval: 15s
      timeout: 5s
      retries: 3
      start_period: 15s
    networks:
      - todo-network

  # ── Frontend UI ──────────────────────────────────────────
  # The presentation layer — React app served via Nginx
  frontend:
    build:
      context: ./client
      dockerfile: Dockerfile
    container_name: todo-frontend
    restart: unless-stopped
    ports:
      - "3000:80"                       # Access at http://localhost:3000
    depends_on:
      backend:
        condition: service_healthy      # Wait for Backend health check
    networks:
      - todo-network

# ── Named Volumes ──────────────────────────────────────────
# Docker manages these volumes. Data persists even after
# `docker-compose down` (use `down -v` to delete volumes too)
volumes:
  mongodb_data:
    driver: local

# ── Networks ───────────────────────────────────────────────
# Custom bridge network — all services can communicate
# by service name (DNS resolution handled by Docker)
networks:
  todo-network:
    driver: bridge