sc-mermaid: Mermaid Diagram Generator

Generate mermaid diagrams for architecture visualization and interaction flows.

Input: $ARGUMENTS

Mode Detection

Parse $ARGUMENTS to determine diagram type:

| Signal | Mode | |--------|------| | flowchart, architecture, system, component relationships | Flowchart | | sequence, flow, interaction, request/response patterns | Sequence | | Ambiguous | Ask the user or infer from context |

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Flowchart Mode

Investigation

1. Scope identification: Determine which components, services, and relationships to include
2. Architecture analysis: Read relevant files and understand data/control flow
3. Validation: Cross-reference findings against codebase to ensure accuracy

Diagram Requirements

• Use TB (top-bottom) or LR (left-right) direction based on flow complexity
• Apply the neutral theme for professional rendering
• Use semantic node shapes:
  • [Rectangle] — services, applications
  • [(Database)] — data stores (PostgreSQL, Redis, OpenSearch)
  • ((Circle)) — external services, APIs
  • [[Subroutine]] — modules, workers, background jobs
  • {Rhombus} — decision points, routing logic
  • {{Hexagon}} — gateways, proxies, middleware
• Style nodes and links using CSS classes for visual grouping
• Label every relationship with meaningful text
• Group related components with subgraphs (quote subgraph titles)

Deliverables

1. Mermaid diagram file ({descriptive-name}.mmd)
2. Syntax validation: mmdc -i <file>.mmd --parseOnly (fix errors if any)
3. Bulleted architectural explanation
4. Validation report with file path references
5. Viewing instructions (optionally render: mmdc -i <file>.mmd -o preview.png)

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Sequence Mode

Generate diagrams compatible with mermaid-ascii for terminal rendering.

Syntax Reference (mermaid-ascii parser)

Works:

sequenceDiagram           # REQUIRED first line
participant A as Alice    # aliases (optional)
"Quoted Name"             # spaces in names
A->>B: message            # solid arrow (colon REQUIRED)
A-->>B: message           # dotted arrow (colon REQUIRED)
A->>A: self               # self-message (use for notes)
%% comment                # ignored by parser

Fails:

A->B: msg     # wrong arrow (needs ->>)
A-->B: msg    # wrong arrow (needs -->>)
A->>B         # missing colon
Note over A   # not implemented
loop/alt/opt  # not implemented
activate A    # not implemented

Design Rules

1. Colon is mandatory: A->>B: text works, A->>B fails
2. Only ->> and -->>: No other arrow types parse
3. Self-messages for notes: A->>A: (thinking) instead of Note
4. Comments for structure: %% Phase 1: or %% alt: if X then Y
5. Short labels: ASCII rendering is wide; keep messages brief
6. Limit participants: 4-6 max for terminal readability

Workflow

1. Understand the flow from $ARGUMENTS or ask clarifying questions
2. Identify actors — use clear short names
3. Map interactions between them
4. Generate diagram following the template
5. Validate: cat <file> | mermaid-ascii -f -
6. Save file and show both source and ASCII render

Template

%% Flow: [title]
%% Render: cat <file> | mermaid-ascii -f -

sequenceDiagram
    participant A as ActorOne
    participant B as ActorTwo

    %% Phase 1: [description]
    A->>B: request
    B-->>A: response

Example: API Request Flow

%% Flow: API authentication
%% Render: cat api-auth.mmd | mermaid-ascii -f -

sequenceDiagram
    participant C as Client
    participant G as Gateway
    participant A as Auth
    participant S as Service

    C->>G: POST /api/data
    G->>A: validate token
    A-->>G: valid
    G->>S: forward request
    S-->>G: response
    G-->>C: 200 OK

    %% alt: invalid token
    %% A-->>G: 401
    %% G-->>C: 401 Unauthorized

Validation

Before saving, ALWAYS test with:

cat <<'EOF' | mermaid-ascii -f -
[your diagram here]
EOF

If it errors, fix the syntax. Common fixes:

• Add missing colon after target: A->>B -> A->>B:
• Fix arrow type: A->B: -> A->>B:
• Remove unsupported syntax (Notes, loops, etc.)

---

Output

Write diagram to {descriptive-name}.mmd in the current directory (or ask user for location).

Include in the file:

• Diagram code
• Architectural explanation as markdown comments
• Validation notes with file path references

$ARGUMENTS