thrilltrack-explorer/docs/ERROR_BOUNDARIES.md

# Error Boundaries Implementation (P0 #5)

## ✅ Status: Complete

**Priority**: P0 - Critical (Stability)  
**Effort**: 8-12 hours  
**Date Completed**: 2025-11-03

---

## Overview

Error boundaries are React components that catch JavaScript errors in their child component tree, log the errors, and display a fallback UI instead of crashing the entire application.

**Before P0 #5**: Only 1 error boundary (`ModerationErrorBoundary`)  
**After P0 #5**: 5 specialized error boundaries covering all critical sections

---

## Error Boundary Architecture

### 1. RouteErrorBoundary (Top-Level)

**Purpose**: Last line of defense, wraps all routes  
**Location**: `src/components/error/RouteErrorBoundary.tsx`  
**Used in**: `src/App.tsx` - wraps `<Routes>`

**Features**:
- Catches route-level errors before they crash the app
- Full-screen error UI with reload/home options
- Critical severity logging
- Minimal UI to ensure maximum stability

**Usage**:
```tsx
<RouteErrorBoundary>
  <Routes>
    {/* All routes */}
  </Routes>
</RouteErrorBoundary>
```

---

### 2. AdminErrorBoundary

**Purpose**: Protects admin panel sections  
**Location**: `src/components/error/AdminErrorBoundary.tsx`  
**Used in**: Admin routes (`/admin/*`)

**Features**:
- Admin-specific error UI with shield icon
- "Back to Dashboard" recovery option
- High-priority error logging
- Section-aware error context

**Usage**:
```tsx
<Route 
  path="/admin/users" 
  element={
    <AdminErrorBoundary section="User Management">
      <AdminUsers />
    </AdminErrorBoundary>
  } 
/>
```

**Protected Sections**:
- ✅ Dashboard (`/admin`)
- ✅ Moderation Queue (`/admin/moderation`)
- ✅ Reports (`/admin/reports`)
- ✅ System Log (`/admin/system-log`)
- ✅ User Management (`/admin/users`)
- ✅ Blog Management (`/admin/blog`)
- ✅ Settings (`/admin/settings`)
- ✅ Contact Management (`/admin/contact`)
- ✅ Email Settings (`/admin/email-settings`)

---

### 3. EntityErrorBoundary

**Purpose**: Protects entity detail pages  
**Location**: `src/components/error/EntityErrorBoundary.tsx`  
**Used in**: Park, Ride, Manufacturer, Designer, Operator, Owner detail routes

**Features**:
- Entity-aware error messages
- "Back to List" navigation option
- Helpful troubleshooting suggestions
- Graceful degradation

**Usage**:
```tsx
<Route 
  path="/parks/:slug" 
  element={
    <EntityErrorBoundary entityType="park">
      <ParkDetail />
    </EntityErrorBoundary>
  } 
/>
```

**Supported Entity Types**:
- `park` → Back to `/parks`
- `ride` → Back to `/rides`
- `manufacturer` → Back to `/manufacturers`
- `designer` → Back to `/designers`
- `operator` → Back to `/operators`
- `owner` → Back to `/owners`

**Protected Routes**:
- ✅ Park Detail (`/parks/:slug`)
- ✅ Park Rides (`/parks/:parkSlug/rides`)
- ✅ Ride Detail (`/parks/:parkSlug/rides/:rideSlug`)
- ✅ Manufacturer Detail (`/manufacturers/:slug`)
- ✅ Manufacturer Rides (`/manufacturers/:manufacturerSlug/rides`)
- ✅ Manufacturer Models (`/manufacturers/:manufacturerSlug/models`)
- ✅ Model Detail (`/manufacturers/:manufacturerSlug/models/:modelSlug`)
- ✅ Model Rides (`/manufacturers/:manufacturerSlug/models/:modelSlug/rides`)
- ✅ Designer Detail (`/designers/:slug`)
- ✅ Designer Rides (`/designers/:designerSlug/rides`)
- ✅ Owner Detail (`/owners/:slug`)
- ✅ Owner Parks (`/owners/:ownerSlug/parks`)
- ✅ Operator Detail (`/operators/:slug`)
- ✅ Operator Parks (`/operators/:operatorSlug/parks`)

---

### 4. ErrorBoundary (Generic)

**Purpose**: General-purpose error boundary for any component  
**Location**: `src/components/error/ErrorBoundary.tsx`

**Features**:
- Context-aware error messages
- Customizable fallback UI
- Optional error callback
- Retry and "Go Home" options

**Usage**:
```tsx
import { ErrorBoundary } from '@/components/error';

<ErrorBoundary context="PhotoUpload">
  <PhotoUploadForm />
</ErrorBoundary>

// With custom fallback
<ErrorBoundary 
  context="ComplexChart"
  fallback={<p>Failed to load chart</p>}
  onError={(error, info) => {
    // Custom error handling
    analytics.track('chart_error', { error: error.message });
  }}
>
  <ComplexChart data={data} />
</ErrorBoundary>
```

---

### 5. ModerationErrorBoundary

**Purpose**: Protects individual moderation queue items  
**Location**: `src/components/error/ModerationErrorBoundary.tsx`  
**Status**: Pre-existing, retained

**Features**:
- Item-level error isolation
- Submission ID tracking
- Copy error details functionality
- Prevents one broken item from crashing the queue

---

## Error Boundary Hierarchy

```
App
├── RouteErrorBoundary (TOP LEVEL - catches everything)
│   └── Routes
│       ├── Admin Routes
│       │   └── AdminErrorBoundary (per admin section)
│       │       └── AdminModeration
│       │           └── ModerationErrorBoundary (per queue item)
│       │
│       ├── Entity Detail Routes
│       │   └── EntityErrorBoundary (per entity page)
│       │       └── ParkDetail
│       │
│       └── Generic Routes
│           └── ErrorBoundary (optional, as needed)
│               └── ComplexComponent
```

---

## Error Logging

All error boundaries use structured logging via `logger.error()`:

```typescript
logger.error('Component error caught by boundary', {
  context: 'PhotoUpload',
  error: error.message,
  stack: error.stack,
  componentStack: errorInfo.componentStack,
  url: window.location.href,
  userId: user?.id, // If available
});
```

**Log Severity Levels**:
- `RouteErrorBoundary`: **critical** (app-level failure)
- `AdminErrorBoundary`: **high** (admin functionality impacted)
- `EntityErrorBoundary`: **medium** (user-facing page impacted)
- `ErrorBoundary`: **medium** (component failure)
- `ModerationErrorBoundary`: **medium** (queue item failure)

---

## Recovery Options

### User Recovery Actions

Each error boundary provides appropriate recovery options:

| Boundary | Actions Available |
|----------|------------------|
| RouteErrorBoundary | Reload Page, Go Home |
| AdminErrorBoundary | Retry, Back to Dashboard, Copy Error |
| EntityErrorBoundary | Try Again, Back to List, Home |
| ErrorBoundary | Try Again, Go Home, Copy Details |
| ModerationErrorBoundary | Retry, Copy Error Details |

### Developer Recovery

In development mode, error boundaries show additional debug information:
- ✅ Full error stack trace
- ✅ Component stack trace
- ✅ Error message and context
- ✅ One-click copy to clipboard

---

## Testing Error Boundaries

### Manual Testing

1. **Force a component error**:
```tsx
const BrokenComponent = () => {
  throw new Error('Test error boundary');
  return <div>This won't render</div>;
};

// Wrap in error boundary
<ErrorBoundary context="Test">
  <BrokenComponent />
</ErrorBoundary>
```

2. **Test recovery**:
   - Click "Try Again" → Component should re-render
   - Click "Go Home" → Navigate to home page
   - Check logs for structured error data

### Automated Testing

```typescript
import { render } from '@testing-library/react';
import { ErrorBoundary } from '@/components/error';

const BrokenComponent = () => {
  throw new Error('Test error');
};

test('error boundary catches error and shows fallback', () => {
  const { getByText } = render(
    <ErrorBoundary context="Test">
      <BrokenComponent />
    </ErrorBoundary>
  );

  expect(getByText('Something Went Wrong')).toBeInTheDocument();
  expect(getByText('Test error')).toBeInTheDocument();
});
```

---

## Best Practices

### ✅ Do

- Wrap lazy-loaded routes with error boundaries
- Use specific error boundaries (Admin, Entity) when available
- Provide context for better error messages
- Log errors with structured data
- Test error boundaries regularly
- Use error boundaries for third-party components
- Add error boundaries around:
  - Form submissions
  - Data fetching components
  - Complex visualizations
  - Photo uploads
  - Editor components

### ❌ Don't

- Don't catch errors in event handlers (use try/catch instead)
- Don't use error boundaries for expected errors (validation, 404s)
- Don't nest identical error boundaries
- Don't log sensitive data in error messages
- Don't render without any error boundary (always have at least RouteErrorBoundary)

---

## Common Use Cases

### 1. Protect Heavy Components

```tsx
import { ErrorBoundary } from '@/components/error';

<ErrorBoundary context="RichTextEditor">
  <MDXEditor content={content} />
</ErrorBoundary>
```

### 2. Protect Third-Party Libraries

```tsx
<ErrorBoundary context="ChartLibrary">
  <RechartsLineChart data={data} />
</ErrorBoundary>
```

### 3. Protect User-Generated Content Rendering

```tsx
<ErrorBoundary context="UserBio">
  <ReactMarkdown>{user.bio}</ReactMarkdown>
</ErrorBoundary>
```

### 4. Protect Form Sections

```tsx
<ErrorBoundary context="ParkDetailsSection">
  <ParkDetailsForm />
</ErrorBoundary>
<ErrorBoundary context="ParkLocationSection">
  <ParkLocationForm />
</ErrorBoundary>
```

---

## Integration with Monitoring (Future)

Error boundaries are designed to integrate with error tracking services:

```typescript
// Future: Sentry integration
import * as Sentry from '@sentry/react';

componentDidCatch(error: Error, errorInfo: ErrorInfo) {
  // Automatically sent to Sentry
  Sentry.captureException(error, {
    contexts: {
      react: {
        componentStack: errorInfo.componentStack,
      },
    },
    tags: {
      errorBoundary: this.props.context,
    },
  });
}
```

---

## Metrics

### Coverage

| Category | Before P0 #5 | After P0 #5 | Status |
|----------|--------------|-------------|--------|
| Admin routes | 0% | 100% (9/9 routes) | ✅ Complete |
| Entity detail routes | 0% | 100% (14/14 routes) | ✅ Complete |
| Top-level routes | 0% | 100% | ✅ Complete |
| Queue items | 100% | 100% | ✅ Maintained |

### Impact

- **Before**: Any component error could crash the entire app
- **After**: Component errors are isolated and recoverable
- **User Experience**: Users see helpful error messages with recovery options
- **Developer Experience**: Better error logging with full context

---

## Related Documentation

- **P0 #2**: Console Statement Prevention → `docs/LOGGING_POLICY.md`
- **P0 #4**: Hardcoded Secrets Removal → (completed)
- Error Handling Patterns → `src/lib/errorHandler.ts`
- Logger Implementation → `src/lib/logger.ts`

---

## Maintenance

### Adding a New Error Boundary

1. Identify the component/section that needs protection
2. Choose appropriate error boundary type:
   - Admin section? → `AdminErrorBoundary`
   - Entity page? → `EntityErrorBoundary`
   - Generic component? → `ErrorBoundary`
3. Wrap the component in the route definition or parent component
4. Provide context for better error messages
5. Test the error boundary manually

### Updating Existing Boundaries

- Keep error messages user-friendly
- Don't expose stack traces in production
- Ensure recovery actions work correctly
- Update tests when changing boundaries

---

## Summary

✅ **5 error boundary types** covering all critical sections  
✅ **100% admin route coverage** (9/9 routes)  
✅ **100% entity route coverage** (14/14 routes)  
✅ **Top-level protection** via `RouteErrorBoundary`  
✅ **User-friendly error UIs** with recovery options  
✅ **Structured error logging** for debugging  
✅ **Development mode debugging** with stack traces  

**Result**: Application is significantly more stable and resilient to component errors. Users will never see a blank screen due to a single component failure.