upstream backend {
    server backend:3000;
    keepalive 32;            # reuse connections to backend
}

upstream frontend {
    server frontend:80;
    keepalive 16;
}

# Shared proxy settings
proxy_http_version 1.1;
proxy_set_header Connection "";          # enable keepalive to upstreams
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_set_header X-Forwarded-Proto $scheme;

# Buffer settings — prevent 502s when backend is slow to respond
proxy_buffering on;
proxy_buffer_size 16k;
proxy_buffers 8 16k;
proxy_busy_buffers_size 32k;

# Redirect HTTP → HTTPS
server {
    listen 80;
    server_name _;

    location /.well-known/acme-challenge/ {
        root /var/www/certbot;
    }

    location / {
        return 301 https://$host$request_uri;
    }
}

# HTTPS server
server {
    listen 443 ssl;
    # Replace with your hostname:
    server_name staging.example.com;

    # --- TLS certificates ---
    ssl_certificate     /etc/letsencrypt/live/staging.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/staging.example.com/privkey.pem;

    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers 'ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384';
    ssl_prefer_server_ciphers on;
    ssl_session_cache shared:SSL:10m;
    ssl_session_timeout 1d;
    ssl_session_tickets off;

    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains" always;
    add_header X-Content-Type-Options nosniff always;
    add_header X-Frame-Options SAMEORIGIN always;

    # --- Rate limit zone (10 req/s per IP for API) ---
    limit_req_zone $binary_remote_addr zone=api_limit:10m rate=10r/s;

    # --- API routes → backend ---
    location /api/ {
        limit_req zone=api_limit burst=30 nodelay;

        proxy_pass http://backend;
        proxy_read_timeout 30s;
        proxy_connect_timeout 5s;
        proxy_send_timeout 15s;
    }

    # AI endpoints → longer timeouts
    location /api/investment-planning/recommendations {
        proxy_pass http://backend;
        proxy_read_timeout 180s;
        proxy_connect_timeout 10s;
        proxy_send_timeout 30s;
    }

    location /api/health-scores/calculate {
        proxy_pass http://backend;
        proxy_read_timeout 180s;
        proxy_connect_timeout 10s;
        proxy_send_timeout 30s;
    }

    # --- Static frontend → built React assets ---
    location / {
        proxy_pass http://frontend;
        proxy_read_timeout 10s;
        proxy_connect_timeout 5s;

        # Cache static assets aggressively at the proxy level
        proxy_cache_bypass $http_upgrade;
    }
}