events {
    worker_connections 1024;
}

http {
    # Security headers
    add_header X-Frame-Options DENY always;
    add_header X-Content-Type-Options nosniff always;
    add_header X-XSS-Protection "1; mode=block" always;
    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
    add_header Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'" always;
    add_header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload" always;

    # Hide server version
    server_tokens off;

    # Rate limiting
    limit_req_zone $binary_remote_addr zone=api:10m rate=10r/s;
    limit_req_zone $binary_remote_addr zone=ws:10m rate=5r/s;

    # Connection limiting
    limit_conn_zone $binary_remote_addr zone=conn_limit_per_ip:10m;

    # Logging
    log_format security '$remote_addr - $remote_user [$time_local] '
                       '"$request" $status $body_bytes_sent '
                       '"$http_referer" "$http_user_agent" '
                       '$request_time $upstream_response_time';

    access_log /var/log/nginx/security.log security;
    error_log /var/log/nginx/error.log warn;

    # Redirect HTTP to HTTPS
    server {
        listen 80;
        server_name _;
        return 301 https://$host$request_uri;
    }

    # HTTPS server
    server {
        listen 443 ssl http2;
        server_name ml-experiments.example.com;

        # SSL configuration
        ssl_certificate /etc/nginx/ssl/cert.pem;
        ssl_certificate_key /etc/nginx/ssl/key.pem;
        ssl_trusted_certificate /etc/nginx/ssl/ca.pem;

        # Modern SSL configuration
        ssl_protocols TLSv1.3;
        ssl_prefer_server_ciphers on;
        ssl_ciphers ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;
        ssl_session_timeout 1d;
        ssl_session_cache shared:SSL:50m;
        ssl_session_tickets off;

        # OCSP stapling
        ssl_stapling on;
        ssl_stapling_verify on;

        # Security limits
        client_max_body_size 10M;
        client_body_timeout 12s;
        client_header_timeout 12s;
        keepalive_timeout 15s;
        send_timeout 10s;
        limit_conn conn_limit_per_ip 20;

        # API endpoints
        location /health {
            proxy_pass https://api-server:9101;
            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;
            proxy_connect_timeout 5s;
            proxy_send_timeout 10s;
            proxy_read_timeout 10s;
        }

        # WebSocket endpoint with special rate limiting
        location /ws {
            limit_req zone=ws burst=10 nodelay;
            
            proxy_pass https://api-server:9101;
            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_set_header X-Forwarded-Proto $scheme;
            proxy_connect_timeout 7d;
            proxy_send_timeout 7d;
            proxy_read_timeout 7d;
            
            # WebSocket specific headers
            proxy_set_header Sec-WebSocket-Key $http_sec_websocket_key;
            proxy_set_header Sec-WebSocket-Protocol $http_sec_websocket_protocol;
            proxy_set_header Sec-WebSocket-Version $http_sec_websocket_version;
        }

        # API endpoints with rate limiting
        location /api/ {
            limit_req zone=api burst=20 nodelay;
            
            proxy_pass https://api-server:9101;
            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;
            proxy_set_header X-API-Key $http_x_api_key;
            proxy_connect_timeout 5s;
            proxy_send_timeout 10s;
            proxy_read_timeout 10s;
        }

        # Deny all other locations
        location / {
            return 404;
        }

        # Security monitoring endpoints (admin only)
        location /admin/ {
            # IP whitelist for admin access
            allow 10.0.0.0/8;
            allow 192.168.0.0/16;
            allow 172.16.0.0/12;
            deny all;
            
            proxy_pass https://api-server:9101;
            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;
        }

        # Health check for load balancers
        location /lb-health {
            access_log off;
            return 200 "healthy\n";
            add_header Content-Type text/plain;
        }
    }

    # Default server to catch unknown hosts
    server {
        listen 443 ssl http2 default_server;
        server_name _;
        
        ssl_certificate /etc/nginx/ssl/cert.pem;
        ssl_certificate_key /etc/nginx/ssl/key.pem;
        
        return 444;
    }
}