flowchart LR
    %% --- 디자인 시스템 ---
    classDef pink fill:#FFCDD2,stroke:none,color:#D32F2F,rx:20,ry:20,font-weight:bold
    classDef ssl fill:#E1F5FE,stroke:#0288D1,stroke-width:2px,color:#01579B,rx:20,ry:20,font-style:italic
    classDef docker fill:#E1F5FE,stroke:#0277BD,stroke-width:2px,color:#01579B,rx:10,ry:10
    classDef coral fill:#FF8A80,stroke:none,color:white,rx:20,ry:20,font-weight:bold
    classDef ai fill:#E8F5E9,stroke:#2E7D32,stroke-width:2px,color:#1B5E20,rx:20,ry:20,font-weight:bold
    classDef plain fill:none,stroke:none,color:#5D4037,font-weight:bold

    User("👤 User"):::plain

    subgraph FE_Layer ["🌐 Frontend Edge"]
        Firebase("🔥 Firebase Hosting<br/>(Static Assets / Proxy)"):::pink
    end

    subgraph AWS_EC2 ["☁️ AWS Hardened Host (Docker Engine)"]
        direction TB
        
        %% Ingress Proxy
        subgraph Ingress ["🔒 Security Ingress"]
            Nginx_Proxy("🐳 Docker: Nginx<br/>(Reverse Proxy / SSL)"):::docker
            Cert_Bot("🔒 Certbot Sidecar"):::ssl
        end

        %% Application Mesh
        subgraph Docker_VNet ["🐳 Isolated Docker Network (Bridge)"]
            direction LR
            Node_App("🧩 Container: Node.js API"):::coral
            
            subgraph AI_Pipeline ["🤖 AI Logic"]
                AI_Handler("📡 OpenAI Agent"):::ai
            end
        end

        %% Persistence Layer
        subgraph Storage ["💾 Persistence"]
            direction LR
            DB[("🐬 MySQL 8.0")]:::coral
            Redis[("🔴 Redis 7.0")]:::coral
        end
    end

    External_AI[("🧠 OpenAI API")]:::ai

    %% --- 데이터 흐름 ---
    User -- "HTTPS Request" --> Firebase
    Firebase == "Secure Tunnel" ==> Nginx_Proxy
    
    Nginx_Proxy -- "Forward (L7)" --> Node_App
    Node_App <--> AI_Handler
    AI_Handler -. "External Call" .-> External_AI
    
    Node_App <--> DB
    Node_App <--> Redis

    %% --- 스타일 적용 ---
    linkStyle 1,2 stroke:#0288d1,stroke-width:3px
    linkStyle 4,5,6 stroke:#2E7D32,stroke-width:2px,stroke-dasharray: 4 4
    linkStyle default stroke:#FF8A80,stroke-width:2px,fill:none