# Nginx Load Balancer Configuration for High Scale
events {
    worker_connections 4096;
    use epoll;
    multi_accept on;
}

http {
    # Basic settings
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    server_tokens off;

    # Gzip compression
    gzip on;
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_types
        text/plain
        text/css
        text/xml
        text/javascript
        application/json
        application/javascript
        application/xml+rss
        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=chat:10m rate=5r/s;

    # Upstream servers (your Flask apps)
    upstream chatbot_backend {
        least_conn;  # Load balancing method
        server app1:8001 max_fails=3 fail_timeout=30s;
        server app2:8001 max_fails=3 fail_timeout=30s;
        server app3:8001 max_fails=3 fail_timeout=30s;
        keepalive 32;
    }

    # Main server block
    server {
        listen 80;
        server_name localhost;  # Change to your domain

        # Security headers
        add_header X-Frame-Options DENY;
        add_header X-Content-Type-Options nosniff;
        add_header X-XSS-Protection "1; mode=block";
        add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;

        # Client settings
        client_max_body_size 10M;
        client_body_timeout 60s;
        client_header_timeout 60s;

        # Proxy settings
        proxy_connect_timeout 60s;
        proxy_send_timeout 60s;
        proxy_read_timeout 60s;
        proxy_buffering on;
        proxy_buffer_size 128k;
        proxy_buffers 4 256k;
        proxy_busy_buffers_size 256k;

        # Static files
        location /static/ {
            alias /app/static/;
            expires 1y;
            add_header Cache-Control "public, immutable";
        }

        # Chat API endpoint with rate limiting
        location /chat {
            limit_req zone=chat burst=10 nodelay;
            
            proxy_pass http://chatbot_backend;
            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;
            
            # WebSocket support
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";
        }

        # General API endpoints
        location /api/ {
            limit_req zone=api burst=20 nodelay;
            
            proxy_pass http://chatbot_backend;
            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 endpoint
        location /health {
            proxy_pass http://chatbot_backend;
            access_log off;
        }

        # Main application
        location / {
            proxy_pass http://chatbot_backend;
            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;
        }

        # Error pages
        error_page 502 503 504 /50x.html;
        location = /50x.html {
            root /usr/share/nginx/html;
        }
    }

    # Logging
    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;
    error_log /var/log/nginx/error.log warn;
}