events {}

http {
    upstream dotnet_app {
        server dotnet-1;
        server dotnet-2;
    }

    upstream java_app {
        server java-1;
        server java-2;
    }

    # Map the header to the chosen upstream
    map $http_x_app_type $app_upstream {
        dotnet dotnet_app;
        java   java_app;
        default "";
    }

    server {
        listen 80;

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

        #
        # 1) If header is present -> route here
        #
        location @proxy_handler {
            proxy_pass http://$app_upstream;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }

        #
        # 2) Default location for all requests
        #
        location / {
            # If upstream selected -> jump to proxy handler
            error_page 418 = @proxy_handler;

            if ($app_upstream != "") {
                return 418;
            }

            # Otherwise serve index.html or static files
            try_files $uri $uri/ /index.html;
        }
    }
}