Mermaid Diagrams

# Mermaid Diagrams

Create diagrams and visualizations using Mermaid markdown syntax.

## Quick Reference

Mermaid diagrams are written in markdown code blocks with `mermaid` as the language identifier.

## Flowchart

```mermaid
flowchart TD
    A[Start] --> B{Is it valid?}
    B -->|Yes| C[Process data]
    B -->|No| D[Show error]
    C --> E[Save to database]
    D --> F[Return to input]
    E --> G[End]
    F --> A
```

### Flowchart Syntax
```
flowchart TD          %% TD = top-down, LR = left-right, RL, BT
    A[Rectangle]      %% Square brackets = rectangle
    B(Rounded)        %% Parentheses = rounded rectangle
    C{Diamond}        %% Curly braces = diamond/decision
    D[[Subroutine]]   %% Double brackets = subroutine
    E[(Database)]     %% Cylinder shape
    F((Circle))       %% Double parentheses = circle
    G>Asymmetric]     %% Flag shape

    A --> B           %% Arrow
    B --- C           %% Line without arrow
    C -.-> D          %% Dotted arrow
    D ==> E           %% Thick arrow
    E --text--> F     %% Arrow with label
    F -->|label| G    %% Alternative label syntax
```

### Subgraphs
```mermaid
flowchart TB
    subgraph Frontend
        A[React App] --> B[Components]
        B --> C[Hooks]
    end
    
    subgraph Backend
        D[API Server] --> E[Database]
    end
    
    A -->|HTTP| D
```

## Sequence Diagram

```mermaid
sequenceDiagram
    participant U as User
    participant C as Client
    participant S as Server
    participant D as Database

    U->>C: Click submit
    C->>S: POST /api/data
    activate S
    S->>D: INSERT query
    D-->>S: Success
    S-->>C: 200 OK
    deactivate S
    C-->>U: Show success message
```

### Sequence Diagram Syntax
```
sequenceDiagram
    participant A as Alice
    participant B as Bob

    A->>B: Solid line with arrow
    A-->>B: Dotted line with arrow
    A-)B: Solid line with open arrow
    A--)B: Dotted line with open arrow
    
    activate B          %% Activation box
    B->>A: Response
    deactivate B
    
    Note over A,B: This is a note
    Note right of A: Note on right
    
    alt Condition true
        A->>B: Do this
    else Condition false
        A->>B: Do that
    end
    
    loop Every minute
        A->>B: Ping
    end
    
    opt Optional action
        A->>B: Maybe do this
    end
```

## Class Diagram

```mermaid
classDiagram
    class User {
        +String id
        +String name
        +String email
        +login()
        +logout()
    }
    
    class Order {
        +String id
        +Date createdAt
        +calculateTotal()
    }
    
    class Product {
        +String id
        +String name
        +Number price
    }
    
    User "1" --> "*" Order : places
    Order "*" --> "*" Product : contains
```

### Class Diagram Syntax
```
classDiagram
    class ClassName {
        +publicField
        -privateField
        #protectedField
        ~packageField
        +publicMethod()
        -privateMethod()
    }
    
    ClassA <|-- ClassB : Inheritance
    ClassC *-- ClassD : Composition
    ClassE o-- ClassF : Aggregation
    ClassG --> ClassH : Association
    ClassI ..> ClassJ : Dependency
    ClassK ..|> ClassL : Realization
```

## Entity Relationship Diagram

```mermaid
erDiagram
    USER ||--o{ ORDER : places
    ORDER ||--|{ LINE_ITEM : contains
    PRODUCT ||--o{ LINE_ITEM : "is in"
    
    USER {
        string id PK
        string email UK
        string name
        datetime created_at
    }
    
    ORDER {
        string id PK
        string user_id FK
        datetime created_at
        string status
    }
    
    PRODUCT {
        string id PK
        s