# ========================================
# NGINX PRODUCTION CONFIGURATION
# With SSL/TLS and Reverse Proxy
# ========================================

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log warn;
pid /var/run/nginx.pid;

events {
    worker_connections 4096;
    use epoll;
    multi_accept on;
}

http {
    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    # Logging format
    log_format main '$remote_addr - $remote_user [$time_local] "$request" '
                    '$status $body_bytes_sent "$http_referer" '
                    '"$http_user_agent" "$http_x_forwarded_for" '
                    'rt=$request_time uct="$upstream_connect_time" '
                    'uht="$upstream_header_time" urt="$upstream_response_time"';

    access_log /var/log/nginx/access.log main;

    # Basic settings
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    client_max_body_size 50M;

    # Gzip compression
    gzip on;
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_types text/plain text/css text/xml application/json application/javascript application/rss+xml application/atom+xml image/svg+xml;

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

    # Security headers
    add_header X-Frame-Options "SAMEORIGIN" 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;

    # Upstream backends
    upstream backend_servers {
        least_conn;
        server backend:3001 max_fails=3 fail_timeout=30s;
        keepalive 32;
    }

    upstream frontend_servers {
        least_conn;
        server frontend:3000 max_fails=3 fail_timeout=30s;
        keepalive 32;
    }

    # HTTP to HTTPS redirect
    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 http2;
        server_name _;

        # SSL Configuration
        ssl_certificate /etc/letsencrypt/live/mathplatform.com/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mathplatform.com/privkey.pem;
        ssl_trusted_certificate /etc/letsencrypt/live/mathplatform.com/chain.pem;

        # SSL Security
        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 off;
        ssl_session_cache shared:SSL:50m;
        ssl_session_timeout 1d;
        ssl_session_tickets off;
        ssl_stapling on;
        ssl_stapling_verify on;

        # Security headers
        add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;

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

        # Backend API
        location /api/ {
            limit_req zone=api burst=20 nodelay;
            
            proxy_pass http://backend_servers/;
            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_cache_bypass $http_upgrade;
            proxy_read_timeout 300s;
            proxy_connect_timeout 75s;
        }

        # Frontend
        location / {
            proxy_pass http://frontend_servers;
            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_cache_bypass $http_upgrade;
        }

        # Static files caching
        location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
            proxy_pass http://frontend_servers;
            expires 1y;
            add_header Cache-Control "public, immutable";
        }
    }
}