# Error Handling System - Flow Diagram

## Request Processing Flow

```
┌─────────────────────────────────────────────────────────────────┐
│                      Incoming HTTP Request                       │
└─────────────────────────────────┬───────────────────────────────┘
                                  │
                                  ▼
┌─────────────────────────────────────────────────────────────────┐
│               Vendor Context Middleware (FIRST)                  │
│  - Detects vendor from domain/subdomain/path                    │
│  - Sets request.state.vendor                                     │
│  - Sets request.state.vendor_context                            │
└─────────────────────────────────┬───────────────────────────────┘
                                  │
                                  ▼
┌─────────────────────────────────────────────────────────────────┐
│                Context Detection Middleware (NEW)                │
│  - Detects request context type                                 │
│  - Sets request.state.context_type                              │
│    • API, ADMIN, VENDOR_DASHBOARD, SHOP, FALLBACK             │
└─────────────────────────────────┬───────────────────────────────┘
                                  │
                                  ▼
┌─────────────────────────────────────────────────────────────────┐
│                    Route Handler Execution                       │
│  - Process business logic                                        │
│  - May throw exceptions                                          │
└─────────────────────────────────┬───────────────────────────────┘
                                  │
                    ┌─────────────┴─────────────┐
                    │                           │
                    ▼                           ▼
            ┌──────────────┐          ┌──────────────┐
            │   Success    │          │   Exception  │
            │   Response   │          │    Raised    │
            └──────────────┘          └──────┬───────┘
                                             │
                                             ▼
            ┌────────────────────────────────────────────────────────┐
            │              Exception Handler                         │
            │  - WizamartException                                   │
            │  - HTTPException                                       │
            │  - RequestValidationError                             │
            │  - Generic Exception                                   │
            │  - 404 Not Found                                       │
            └────────────────────┬───────────────────────────────────┘
                                 │
                   ┌─────────────┴────────────┐
                   │                          │
                   ▼                          ▼
        ┌──────────────────┐      ┌──────────────────┐
        │  Special Case:   │      │  General Error   │
        │  401 on HTML     │      │   Handling       │
        │  → Redirect to   │      │                  │
        │     Login        │      │                  │
        └──────────────────┘      └─────────┬────────┘
                                            │
                              ┌─────────────┴─────────────┐
                              │                           │
                              ▼                           ▼
                    ┌──────────────────┐      ┌──────────────────┐
                    │   API Request?   │      │  HTML Request?   │
                    │   /api/* path    │      │  GET + text/html │
                    └────────┬─────────┘      └─────────┬────────┘
                             │                          │
                             ▼                          ▼
                  ┌──────────────────┐      ┌──────────────────────────┐
                  │  Return JSON     │      │   Error Page Renderer    │
                  │  Response        │      │                          │
                  │  {               │      │  - Detect context type   │
                  │    error_code,   │      │  - Select template       │
                  │    message,      │      │  - Prepare data          │
                  │    status_code   │      │  - Render HTML           │
                  │  }               │      └──────────┬───────────────┘
                  └──────────────────┘                 │
                                                       ▼
                                        ┌──────────────────────────────┐
                                        │   Template Selection         │
                                        │                              │
                                        │   Priority:                  │
                                        │   1. {context}/errors/{code} │
                                        │   2. {context}/errors/generic│
                                        │   3. shared/{code}-fallback  │
                                        │   4. shared/generic-fallback │
                                        └──────────┬───────────────────┘
                                                   │
                                    ┌──────────────┼──────────────┐
                                    │              │              │
                                    ▼              ▼              ▼
                          ┌─────────────┐ ┌─────────────┐ ┌─────────────┐
                          │    Admin    │ │   Vendor    │ │    Shop     │
                          │    Error    │ │    Error    │ │    Error    │
                          │    Page     │ │    Page     │ │    Page     │
                          │             │ │             │ │  (Themed)   │
                          └─────────────┘ └─────────────┘ └─────────────┘
```

---

## Context Detection Logic

```
┌──────────────────────────────────────────────────────────────────┐
│                     Request Arrives                               │
│                     (host + path)                                 │
└────────────────────────────┬─────────────────────────────────────┘
                             │
                             ▼
                   ┌──────────────────┐
                   │  Path starts     │───YES───→ API Context
                   │  with /api/ ?    │           (Always JSON)
                   └────────┬─────────┘
                            │ NO
                            ▼
                   ┌──────────────────┐
                   │  Host starts     │───YES───→ ADMIN Context
                   │  with admin.     │           (Admin Portal)
                   │  OR path starts  │
                   │  with /admin ?   │
                   └────────┬─────────┘
                            │ NO
                            ▼
                   ┌──────────────────┐
                   │  Path starts     │───YES───→ VENDOR_DASHBOARD Context
                   │  with /vendor/ ? │           (Vendor Management)
                   └────────┬─────────┘
                            │ NO
                            ▼
                   ┌──────────────────┐
                   │  Vendor object   │───YES───→ SHOP Context
                   │  in request      │           (Customer Storefront)
                   │  state?          │
                   └────────┬─────────┘
                            │ NO
                            ▼
                   ┌──────────────────┐
                   │   FALLBACK       │
                   │   Context        │
                   │   (Unknown)      │
                   └──────────────────┘
```

---

## Template Selection Example

For a 404 error in ADMIN context:

```
1. Check: app/templates/admin/errors/404.html       ✓ EXISTS → USE THIS
2. Check: app/templates/admin/errors/generic.html   (skipped)
3. Check: app/templates/shared/404-fallback.html    (skipped)
4. Check: app/templates/shared/generic-fallback.html (skipped)
```

For a 429 error in SHOP context (not created yet):

```
1. Check: app/templates/shop/errors/429.html        ✗ Missing
2. Check: app/templates/shop/errors/generic.html    ✗ Missing
3. Check: app/templates/shared/429-fallback.html    ✗ Missing
4. Check: app/templates/shared/generic-fallback.html ✓ EXISTS → USE THIS
```

---

## Error Response Types

```
┌──────────────────────────────────────────────────────────────────┐
│                       Request Type                                │
└───────────┬─────────────┬───────────────────┬─────────────────────┘
            │             │                   │
            ▼             ▼                   ▼
    ┌────────────┐ ┌────────────┐    ┌──────────────┐
    │    API     │ │  HTML Page │    │  401 on HTML │
    │  Request   │ │  Request   │    │     Page     │
    └──────┬─────┘ └──────┬─────┘    └──────┬───────┘
           │              │                  │
           ▼              ▼                  ▼
    ┌────────────┐ ┌────────────┐    ┌──────────────┐
    │   JSON     │ │  Rendered  │    │   Redirect   │
    │  Response  │ │   HTML     │    │  to Login    │
    │            │ │   Error    │    │              │
    │ {          │ │   Page     │    │  302 Found   │
    │  error_code│ │            │    │  Location:   │
    │  message   │ │ Context-   │    │  /admin/login│
    │  status    │ │  aware     │    │  /vendor/login│
    │  details   │ │  template  │    │  /shop/login │
    │ }          │ │            │    │              │
    └────────────┘ └────────────┘    └──────────────┘
```

---

## Example Scenarios

### Scenario 1: API 404 Error
```
Request: GET /api/v1/admin/vendors/999
Context: API
Result:  JSON { "error_code": "VENDOR_NOT_FOUND", ... }
```

### Scenario 2: Admin Page 404 Error
```
Request: GET /admin/nonexistent
         Accept: text/html
Context: ADMIN
Result:  HTML admin/errors/404.html
```

### Scenario 3: Shop Page 500 Error
```
Request: GET /products/123 (on vendor1.platform.com)
         Accept: text/html
Context: SHOP (vendor detected)
Result:  HTML shop/errors/500.html (with vendor theme)
```

### Scenario 4: Unauthorized Access to Admin
```
Request: GET /admin/settings
         Accept: text/html
         No valid session
Context: ADMIN
Result:  302 Redirect to /admin/login
```

---

## Debug Information Display

```
┌──────────────────────────────────────────────────────────────┐
│                    Error Page Display                         │
└──────────────────────┬───────────────────────────────────────┘
                       │
           ┌───────────┴───────────┐
           │                       │
           ▼                       ▼
    ┌──────────────┐      ┌──────────────┐
    │  Admin User  │      │  Other Users │
    │  (Context:   │      │  (Vendor,    │
    │   ADMIN)     │      │   Shop)      │
    └──────┬───────┘      └──────┬───────┘
           │                     │
           ▼                     ▼
    ┌──────────────┐      ┌──────────────┐
    │ Debug Info   │      │  No Debug    │
    │   SHOWN:     │      │  Info:       │
    │ • Path       │      │              │
    │ • Error code │      │ Only user-   │
    │ • Details    │      │ friendly     │
    │ • Stack      │      │ message      │
    └──────────────┘      └──────────────┘
```

---

## File Organization

```
app/
├── exceptions/
│   ├── handler.py              # Exception handlers (refactored)
│   ├── error_renderer.py       # NEW: Renders error pages
│   └── base.py                 # Base exceptions
│
├── templates/
│   ├── admin/
│   │   └── errors/             # NEW: Admin error pages
│   │       ├── base.html       # Base template
│   │       ├── 404.html        # Specific errors
│   │       └── generic.html    # Catch-all
│   │
│   ├── vendor/
│   │   └── errors/             # TODO: Vendor error pages
│   │
│   ├── shop/
│   │   └── errors/             # TODO: Shop error pages (themed)
│   │
│   └── shared/
│       └── *-fallback.html     # Shared fallback error pages

middleware/
├── vendor_context.py           # Vendor detection (existing)
├── context_middleware.py       # NEW: Context detection
└── theme_context.py            # Theme loading (existing)
```

---

## Benefits Summary

✅ **Separation of Concerns**: HTML templates separate from handler logic  
✅ **Context-Aware**: Different error pages for different areas  
✅ **Maintainable**: Easy to update individual error pages  
✅ **Scalable**: Easy to add new contexts or error types  
✅ **Professional**: Polished error pages matching area design  
✅ **Flexible**: Fallback mechanism ensures errors always render  
✅ **Secure**: Debug info only shown to admins  
✅ **Themed**: Shop errors can use vendor branding (Phase 3)  

---

This flow ensures that:
1. API calls ALWAYS get JSON responses
2. HTML page requests get appropriate error pages
3. Each context (admin/vendor/shop) has its own error design
4. Fallback mechanism prevents broken error pages
5. 401 errors redirect to appropriate login pages
