# Frontend Refactoring Quick Start Guide

## 🚀 What Changed?

Your frontend has been refactored to improve maintainability, type safety, and code organization. Here's what you need to know.

---

## 📦 New Shared Utilities

### 1. useLocalStorage Hook

**Import:**
```typescript
import { useLocalStorage } from '@/hooks';
```

**Usage:**
```typescript
// Instead of managing localStorage manually...
const [value, setValue, removeValue] = useLocalStorage<MyType>('storage-key', defaultValue);

// Works just like useState, but persists automatically!
setValue({ ...value, updated: true });
```

**Features:**
- Type-safe
- Automatic JSON serialization
- Error handling built-in
- Returns remove function as third element

---

### 2. useApi Hook

**Import:**
```typescript
import { useApi } from '@/hooks';
```

**Usage:**
```typescript
// Manages loading, error, and data states automatically
const { data, loading, error, execute } = useApi(
  (id: number) => apiService.getData(id),
  {
    onSuccess: (data) => console.log('Success!', data),
    onError: (error) => console.error('Error:', error)
  }
);

// Later in your component...
<button onClick={() => execute(123)}>Load Data</button>

{loading && <Spinner />}
{error && <ErrorMessage>{error}</ErrorMessage>}
{data && <DataDisplay data={data} />}
```

**Features:**
- Automatic request cancellation on unmount
- Prevents memory leaks
- Consistent loading/error patterns

---

### 3. Formatting Utilities

**Import:**
```typescript
import { formatCurrency, formatPercent, formatNumber, formatPriceChange } from '@/utils/indicators';
```

**Usage:**
```typescript
// Currency formatting (handles null/undefined)
formatCurrency(1234.56)  // "$1,234.56"
formatCurrency(null)     // "—"

// Percentage with sign
formatPercent(5.25)      // "+5.25%"
formatPercent(-2.5)      // "-2.50%"

// Number formatting
formatNumber(1234.567)   // "1,234.57"

// Price change with color
const { text, color } = formatPriceChange(5.25);
// { text: "+5.25", color: "text-green-400" }
```

**Replace these patterns:**
```typescript
// ❌ Old way
const formatNumber = (value?: number | null) => {
  if (value === undefined || value === null) return '—';
  return new Intl.NumberFormat('en-US', { maximumFractionDigits: 2 }).format(value);
};

// ✅ New way
import { formatNumber } from '@/utils/indicators';
```

---

### 4. Modal Components

**Import:**
```typescript
import { Modal, ConfirmModal, AlertModal } from '@/components/shared/Modal';
```

**Replace `confirm()`:**
```typescript
// ❌ Old way
if (confirm('Are you sure you want to delete this?')) {
  handleDelete();
}

// ✅ New way
const [showConfirm, setShowConfirm] = useState(false);

<ConfirmModal
  isOpen={showConfirm}
  onClose={() => setShowConfirm(false)}
  onConfirm={handleDelete}
  title="Delete Item"
  message="Are you sure you want to delete this?"
  variant="danger"
/>
```

**Replace `alert()`:**
```typescript
// ❌ Old way
alert('Success! Your changes have been saved.');

// ✅ New way
const [showAlert, setShowAlert] = useState(false);

<AlertModal
  isOpen={showAlert}
  onClose={() => setShowAlert(false)}
  title="Success"
  message="Your changes have been saved."
  variant="success"
/>
```

**Custom Modal:**
```typescript
<Modal isOpen={open} onClose={() => setOpen(false)} title="Custom Dialog" size="lg">
  <p>Your custom content here</p>
  <div className="flex gap-2 mt-4">
    <button onClick={handleAction}>Action</button>
    <button onClick={() => setOpen(false)}>Cancel</button>
  </div>
</Modal>
```

**Modal Props:**
- `size`: 'sm' | 'md' | 'lg' | 'xl'
- `showCloseButton`: boolean (default: true)
- `closeOnEscape`: boolean (default: true)
- `closeOnBackdropClick`: boolean (default: true)

---

## 🏗️ New Component Structure

### DailyTradingPlan Refactored

**Location changed:**
```typescript
// ❌ Old import
import DailyTradingPlan from './components/DailyTradingPlan';

// ✅ New import
import DailyTradingPlan from './components/features/trading/DailyTradingPlan';
```

**Props unchanged** - no breaking changes!

**Internal structure:**
```
DailyTradingPlan/
├── index.tsx                    # Main container
├── types.ts                     # TypeScript interfaces
├── usePlanGeneration.ts         # AI logic hook
├── PlanHeader.tsx               # Sub-component
├── PlanBiasSelector.tsx         # Sub-component
├── PlanRiskParameters.tsx       # Sub-component
└── PlanKeyLevelsEditor.tsx      # Sub-component
```

---

## 🎨 Patterns to Follow

### 1. Component Organization

```
components/
├── features/              # Feature-specific components
│   ├── trading/
│   ├── analytics/
│   ├── ai/
│   └── journal/
├── shared/                # Reusable UI components
│   ├── Modal.tsx
│   ├── Button.tsx
│   └── Input.tsx
└── layout/                # Layout components
    └── DashboardLayout.tsx
```

### 2. Component File Structure

For complex components, create a directory:
```
MyComponent/
├── index.tsx              # Main container
├── types.ts               # TypeScript interfaces
├── useMyLogic.ts          # Custom hooks
├── SubComponentA.tsx      # Sub-component
└── SubComponentB.tsx      # Sub-component
```

Export from `index.tsx`:
```typescript
export default function MyComponent() { ... }
export type { MyComponentProps } from './types';
```

### 3. Custom Hooks Pattern

```typescript
// useMyFeature.ts
import { useState, useCallback } from 'react';

export interface UseMyFeatureReturn {
  data: MyData | null;
  loading: boolean;
  error: string | null;
  execute: () => Promise<void>;
  reset: () => void;
}

export function useMyFeature(): UseMyFeatureReturn {
  const [data, setData] = useState<MyData | null>(null);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);

  const execute = useCallback(async () => {
    setLoading(true);
    setError(null);
    try {
      const result = await fetchData();
      setData(result);
    } catch (err) {
      setError(err instanceof Error ? err.message : 'Unknown error');
    } finally {
      setLoading(false);
    }
  }, []);

  const reset = useCallback(() => {
    setData(null);
    setError(null);
  }, []);

  return { data, loading, error, execute, reset };
}
```

### 4. TypeScript Best Practices

```typescript
// ✅ Do: Explicit interfaces
interface MyComponentProps {
  value: number;
  onChange: (value: number) => void;
  label?: string;
}

// ✅ Do: Explicit return types
function MyComponent({ value, onChange, label }: MyComponentProps): JSX.Element {
  const handleChange = useCallback((newValue: number): void => {
    onChange(newValue);
  }, [onChange]);

  return <div>...</div>;
}

// ❌ Don't: Use 'any'
const [data, setData] = useState<any>(null);  // Bad!

// ✅ Do: Use proper types
interface MyData {
  id: number;
  name: string;
}
const [data, setData] = useState<MyData | null>(null);  // Good!
```

---

## 🔧 Migration Checklist

When refactoring a component:

- [ ] Move to appropriate feature directory
- [ ] Extract types to `types.ts`
- [ ] Extract business logic to custom hooks
- [ ] Split into sub-components (if > 250 lines)
- [ ] Replace `localStorage` patterns with `useLocalStorage`
- [ ] Replace direct API calls with `useApi`
- [ ] Replace `alert`/`confirm` with Modal components
- [ ] Use formatting utilities from `@/utils/indicators`
- [ ] Remove all `any` types
- [ ] Add explicit return types
- [ ] Wrap callbacks in `useCallback`
- [ ] Wrap expensive calculations in `useMemo`
- [ ] Add ARIA attributes for accessibility
- [ ] Update imports in parent components

---

## 🧪 Testing Your Changes

### Quick Smoke Test:
```bash
cd frontend
npm run build
```

Should compile without TypeScript errors!

### Runtime Test:
```bash
npm run dev
```

Check:
1. Component loads without errors
2. State updates work
3. localStorage persists
4. Modals open/close correctly
5. No console warnings

---

## 📚 Additional Resources

- [React Hooks Documentation](https://react.dev/reference/react)
- [TypeScript Handbook](https://www.typescriptlang.org/docs/)
- [ARIA Authoring Practices](https://www.w3.org/WAI/ARIA/apg/)

---

## ❓ FAQ

**Q: Can I still use the old DailyTradingPlan import?**
A: No, update imports to the new location. The old file will be removed.

**Q: Do I need to refactor all components at once?**
A: No! Refactor incrementally. Start with components you're actively working on.

**Q: What if I need localStorage outside a component?**
A: Create a separate utility function or use the hook in the nearest parent component.

**Q: Should I use ConfirmModal for every confirmation?**
A: Yes! It provides better UX and accessibility than native `confirm()`.

**Q: Can I customize Modal appearance?**
A: Yes! The Modal component uses Tailwind classes. Extend or override as needed.

---

## 🆘 Getting Help

If you encounter issues:

1. Check TypeScript errors in your IDE
2. Review the summary document: `WEEK1_2_REFACTORING_SUMMARY.md`
3. Look at refactored DailyTradingPlan as an example
4. Ask the team!

---

**Last Updated:** Week 1-2 Refactoring
**Next Update:** Week 3-4 (TradingJournal & AITradingCoach refactoring)
