```mermaid
graph TD
    %% Main system components
    Client[Chat Interface Frontend]
    Server[Flask Server]
    MongoDB[(MongoDB)]
    Neo4j[(Neo4j)]
    LLM[OpenAI LLM API]

    %% Initialization flow
    Init[System Initialization] --> |1. Start server| Server
    Server --> |2. Connect to MongoDB| MongoDB
    Server --> |3. Load or create index| IdxInit
    Server --> |4. Connect to Neo4j| Neo4j

    %% Subgraphs for clarity
    subgraph "Initialization"
        IdxInit[Initialize Global Index]
        IdxInit --> |Load existing index| LoadIdx[Load from storage]
        IdxInit --> |Build new index| BuildIdx[Process documents]
        
        BuildIdx --> LlamaParser[LlamaParse Text & Images]
        LlamaParser --> VectorIdx[Create Vector Index]
        LlamaParser --> ExtractImages[Extract Images]
        
        LoadIdx --> LoadGraph[Load GraphRAG components]
        VectorIdx --> CreateGraph[Create GraphRAG components]
        
        CreateGraph --> KGExtract[Extract entities & relations]
        KGExtract --> CommDetect[Community detection]
        CommDetect --> CommSummary[Generate community summaries]
        
        LoadGraph -.-> |Check cache| CommCache[Load community cache]
    end

    %% Chat processing flow
    Client --> |5. Send message with sessionId| Server
    Server --> |6. Get session state| SessionManager
    
    subgraph "Session Management"
        SessionManager[Session Manager]
        SessionManager --> |Check cache| MemCache[In-memory cache]
        SessionManager --> |Check DB| SessionDB[Session in MongoDB]
        SessionManager --> |Create if needed| NewSession[Create new session]
        NewSession --> NewConv[Create conversation]
    end
    
    Server --> |7. Store user message| MongoDB
    Server --> |8. Process query| Agent
    
    subgraph "Agent Workflow"
        Agent[ReAct Agent]
        Agent --> |Select tool| Tools
        
        subgraph "Query Tools"
            Tools[Query Tools]
            VectorTool[Vector Query Tool]
            GraphTool[GraphRAG Tool]
            
            Tools --> VectorTool
            Tools --> GraphTool
            
            VectorTool --> VectorRetriever[Vector Retriever]
            VectorRetriever --> VectorRank[Top-K Similarity]
            
            GraphTool --> DualRetrieval[Dual Retrieval]
            DualRetrieval --> VectorRetriever
            DualRetrieval --> GraphRetriever[Graph Community Retriever]
            
            GraphRetriever --> ExtractEntities[Extract entities]
            ExtractEntities --> MapCommunities[Map to communities]
            MapCommunities --> GetSummaries[Get community summaries]
        end
        
        VectorRank --> |Context| GenResponse[Generate Response]
        GetSummaries --> |Context| GenResponse
        GenResponse --> |Use LLM| LLM
    end
    
    Agent --> |9. Format response with sources & images| Response
    Response --> |10. Store assistant message| MongoDB
    Response --> |11. Send response to client| Client
    
    %% Image handling flow
    subgraph "Image Processing"
        ImgProcess[Image Handling]
        ExtractImages --> SaveImages[Save to images directory]
        SaveImages --> LinkToNodes[Link images to nodes]
        Client --> |12. Request images| ImgEndpoint[Image endpoint]
        ImgEndpoint --> ServeImage[Serve image files]
    end

    %% Conversation management
    subgraph "Conversation Management"
        ConvMgmt[Conversation Management]
        Client --> |List conversations| GetConvs[Get conversations]
        GetConvs --> MongoDB
        Client --> |Get messages| GetMsgs[Get messages]
        GetMsgs --> MongoDB
        Client --> |Create new conversation| CreateConv[Create conversation]
        CreateConv --> MongoDB
        Client --> |Delete conversation| DeleteConv[Delete conversation]
        DeleteConv --> MongoDB
    end

%% Styling
classDef primary fill:#3498db,stroke:#2980b9,color:white;
classDef secondary fill:#2ecc71,stroke:#27ae60,color:white;
classDef storage fill:#9b59b6,stroke:#8e44ad,color:white;
classDef apiService fill:#e74c3c,stroke:#c0392b,color:white;

class Client,Server,Agent,Response primary;
class SessionManager,Tools,ImgProcess,ConvMgmt secondary;
class MongoDB,Neo4j storage;
class LLM apiService;
```