flowchart TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Action A]
    B -->|No| D[Action B]
    C --> E[End]
    D --> E

sequenceDiagram
    participant User
    participant API
    participant Service
    User->>API: Request
    API->>Service: Process
    Service-->>API: Response
    API-->>User: Result

classDiagram
    class Brick {
        +String responsibility
        +PublicContract studs
    }
    class Module {
        +init()
        +process()
    }
    Brick <|-- Module

stateDiagram-v2
    [*] --> Planning
    Planning --> Design
    Design --> Implementation
    Implementation --> Testing
    Testing --> [*]

erDiagram
    MODULE ||--o{ FUNCTION : exports
    MODULE ||--o{ DEPENDENCY : requires
    FUNCTION }o--|| CONTRACT : implements

gantt
    title Project Timeline
    section Phase 1
    Planning :p1, 0, 30d
    Design :p2, after p1, 20d
    section Phase 2
    Implementation :p3, after p2, 40d
    Testing :p4, after p3, 25d

The authentication module handles JWT token validation. When a request arrives,
it first checks if a token exists. If not, it returns unauthorized. If it does,
it validates the token signature. If valid, it extracts the payload and continues.
If invalid, it returns forbidden. The payload is passed to the authorization
module for role-based access control.

flowchart TD
    A[Request Arrives] --> B{Token Exists?}
    B -->|No| C[Return Unauthorized]
    B -->|Yes| D{Token Valid?}
    D -->|No| E[Return Forbidden]
    D -->|Yes| F[Extract Payload]
    F --> G[Check Role-Based Access]
    G --> H{Authorized?}
    H -->|No| I[Return Access Denied]
    H -->|Yes| J[Allow Request]
    C --> K[End]
    E --> K
    I --> K
    J --> K

Module: authentication
- Exports: validate_token, TokenPayload, AuthError
- Classes: TokenPayload (user_id, role, expires_at), AuthError (message, code)
- Functions: validate_token(token, secret) -> TokenPayload
- Internal: JWT (PyJWT library), Models (TokenPayload)

classDiagram
    class AuthenticationModule {
        +validate_token(token, secret)
        +TokenPayload
        +AuthError
    }
    class TokenPayload {
        +String user_id
        +String role
        +DateTime expires_at
        +to_dict()
    }
    class AuthError {
        +String message
        +Integer code
        +__str__()
    }
    AuthenticationModule -- TokenPayload
    AuthenticationModule -- AuthError

DDD Workflow: Phase 0 (Planning) -> Phase 1 (Documentation) ->
Approval Gate -> Phase 2 (Code Planning) -> Phase 3 (Implementation) ->
Phase 4 (Testing & Cleanup) -> Complete

stateDiagram-v2
    [*] --> Planning
    Planning --> Documentation
    Documentation --> ApprovalGate
    ApprovalGate --> CodePlanning
    CodePlanning --> Implementation
    Implementation --> Testing
    Testing --> [*]

The prompt-writer agent clarifies requirements from the user. It then sends
the clarified requirements to the architect agent. The architect creates a
specification and sends it to the builder agent. The builder implements code
and sends it to the reviewer. The reviewer checks quality and sends feedback
back to the builder if issues are found, or to the user if complete.

sequenceDiagram
    actor User
    participant PromptWriter
    participant Architect
    participant Builder
    participant Reviewer

    User->>PromptWriter: Request Feature
    PromptWriter->>Architect: Clarified Requirements
    Architect->>Builder: Specification
    Builder->>Reviewer: Implementation
    Reviewer-->>Builder: Issues Found
    Builder->>Reviewer: Fixed Implementation
    Reviewer-->>User: Complete & Approved

Client requests flow through API Gateway to Services. Services can be
Authentication Service, User Service, or Data Service. All services
connect to a shared Database and Logger. Services return responses
through the API Gateway back to Client.

flowchart LR
    Client[Client]
    Gateway[API Gateway]
    Auth[Auth Service]
    User[User Service]
    Data[Data Service]
    DB[(Database)]
    Logger[Logger]

    Client <--> Gateway
    Gateway --> Auth
    Gateway --> User
    Gateway --> Data
    Auth --> DB
    User --> DB
    Data --> DB
    Auth --> Logger
    User --> Logger
    Data --> Logger

A[Rectangle]
B(Rounded Rectangle)
C{Diamond/Decision}
D[(Database)]
E[/Parallelogram Right/]
F[\Parallelogram Left\]
G[[Subroutine]]
H((Circle))

A --> B          # Arrow
A -- Text --> B  # Arrow with label
A ---|Yes| B     # Arrow with yes/no
A -->|Condition| B
A -.-> B         # Dotted line
A ==> B          # Bold arrow

classDef className fill:#f9f,stroke:#333,stroke-width:2px,color:#000
class A,B className
style A fill:#f9f,stroke:#333,stroke-width:4px

flowchart TD
    B1["Brick Module 1<br/>(Responsibility)"]
    B2["Brick Module 2<br/>(Responsibility)"]
    S1["Stud: public_function"]
    S2["Stud: public_class"]

    B1 --> S1
    B1 --> S2
    S1 -.depends on.-> B2
    B2 --> "Stud: get_data"

flowchart TD
    Start[Start] --> Q1{Condition 1?}
    Q1 -->|No| End1[End: Rejected]
    Q1 -->|Yes| Q2{Condition 2?}
    Q2 -->|No| End2[End: Review]
    Q2 -->|Yes| Q3{Condition 3?}
    Q3 -->|No| End3[End: Partial]
    Q3 -->|Yes| End4[End: Approved]

flowchart TD
    A[Execute] --> B{Error?}
    B -->|No| C[Success]
    B -->|Yes| D{Recoverable?}
    D -->|No| E[Fail]
    D -->|Yes| F[Retry]
    F --> A
    C --> G[End]
    E --> G

## System Architecture

```mermaid
flowchart TD
    ...
```

### Using with Document-Driven Development
- Create diagrams during documentation phase
- Include architecture diagrams in spec docs
- Use sequence diagrams to explain workflows
- Add state diagrams to describe state machines

### Using with Investigation Workflow
- Visualize discovered architecture
- Show data flow between components
- Map discovered dependencies
- Display call sequences between services

## Tips for Effective Diagrams

1. **Keep It Simple**: One concept per diagram
2. **Use Clear Labels**: Names should describe purpose
3. **Follow Visual Conventions**: Diamonds for decisions, circles for states
4. **Avoid Crossing Lines**: Reorganize to reduce visual clutter
5. **Logical Flow**: Top-to-bottom or left-to-right
6. **Consistent Styling**: Similar elements should look similar
7. **Legend**: Include if symbols aren't obvious
8. **Test Syntax**: Ensure Mermaid renders without errors
9. **Add Comments**: Explain non-obvious relationships
10. **Iterate**: Refine based on feedback

## Common Pitfalls to Avoid

- **Too Complex**: Diagram has too many elements (break into multiple diagrams)
- **Unclear Labels**: Node names don't describe their purpose
- **Missing Connections**: Important relationships not shown
- **Invalid Syntax**: Mermaid errors prevent rendering
- **Ambiguous Decision Points**: Yes/no paths not clearly marked
- **Crossing Arrows**: Visual confusion from overlapping connections
- **No Legend**: Symbols or colors not explained
- **Wrong Diagram Type**: Using flowchart for sequence data
- **Inconsistent Style**: Different formatting for similar elements
- **No Context**: Diagram shown without explanation

## Success Criteria

A good Mermaid diagram:
- [ ] Shows all key entities from source material
- [ ] Accurately represents relationships and flow
- [ ] Uses appropriate diagram type for content
- [ ] Clear, descriptive labels on all nodes
- [ ] Valid Mermaid syntax (renders without error)
- [ ] Readable without excessive complexity
- [ ] Supports understanding of the system
- [ ] Could be embedded in documentation
- [ ] Decision points clearly marked
- [ ] Legend included if needed
- [ ] Purpose and scope clear from context

## Related Skills

- **module-spec-generator**: Generate specs that can be visualized as class diagrams
- **Document-Driven Development**: Use diagrams in specification documents
- **Investigation Workflow**: Create architecture diagrams from discovered systems

## Output Format

Diagrams are generated in Mermaid markdown format, ready to embed:

```markdown
    ```mermaid
    [Generated Mermaid Syntax]
    ```