upstream backend_upstream {
    # Docker Compose DNS resolves by service name (backend), not container name
    server backend:3000;
    keepalive 32;
}

server {
    listen 80;
    server_name _;

    root /usr/share/nginx/html;
    index index.html;

    # gzip compression
    gzip on;
    gzip_types text/plain text/css application/json application/javascript text/xml application/xml text/javascript image/svg+xml;
    gzip_min_length 256;

    # SPA fallback
    location / {
        try_files $uri $uri/ /index.html;
    }

    # API reverse proxy
    location /api {
        proxy_pass http://backend_upstream;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_read_timeout 180s;
    }

    # Health check proxy
    location /health {
        proxy_pass http://backend_upstream/health;
    }

    # WebSocket proxy
    location /ws {
        proxy_pass http://backend_upstream;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
    }

    # Cache static assets
    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
        expires 30d;
        add_header Cache-Control "public, immutable";
    }
}