# Todo App - Modern Task Manager

A beautiful, feature-rich todo application built with pure HTML, CSS, and JavaScript. No frameworks required!

## ✨ Features

### Core Functionality
- ✅ **Add, Edit, Delete Todos** - Full CRUD operations
- ✅ **Mark Complete/Incomplete** - Visual feedback with animations
- ✅ **Categories** - Personal, Work, Shopping, Health with icons
- ✅ **Priority Levels** - Low, Medium, High with color coding
- ✅ **Due Dates** - Date picker with overdue highlighting
- ✅ **Descriptions** - Optional detailed descriptions for tasks

### Organization
- 🔍 **Real-time Search** - Filter todos as you type
- 📊 **Smart Filtering** - View All, Active, or Completed todos
- ⚡ **Multiple Sort Options** - Sort by Date, Priority, or Name
- 📈 **Statistics Dashboard** - Track total, active, completed, and completion rate

### Advanced Features
- 🌙 **Dark/Light Mode** - Toggle between themes with persistence
- 📥 **Export Data** - Backup your todos as JSON
- 📤 **Import Data** - Restore from backup files
- ✅ **Bulk Actions** - Select multiple todos for batch operations
- 💾 **Auto-save** - Changes saved automatically to localStorage
- ⌨️ **Keyboard Shortcuts** - Quick actions for power users

### Security & Accessibility
- 🔒 **XSS Prevention** - All user input sanitized
- ♿ **WCAG Compliant** - ARIA labels, keyboard navigation, screen reader support
- 📱 **Fully Responsive** - Works on mobile, tablet, and desktop
- 🎨 **High Contrast** - WCAG AA compliant color contrasts

## 🚀 Quick Start

1. **Open the App**
   - Simply open `index.html` in any modern web browser
   - No build process or dependencies required!

2. **Add Your First Todo**
   - Type in the "What needs to be done?" field
   - Optionally add description, category, priority, and due date
   - Click "Add" or press Enter

3. **Manage Your Todos**
   - Click the checkbox to mark complete/incomplete
   - Click the circle icon to select for bulk actions
   - Click the trash icon to delete
   - Use filters and search to find specific todos

## ⌨️ Keyboard Shortcuts

| Key | Action |
|-----|--------|
| `N` | Focus on new todo input |
| `/` | Focus on search |
| `Escape` | Close modal / Clear selection |
| `?` | Show keyboard shortcuts |

## 🎨 Features Breakdown

### Security Features (from Critic Report)
- **XSS Prevention**: All user input sanitized using `textContent`
- **Import Validation**: File size limits (5MB), JSON schema validation
- **Safe Rendering**: No `innerHTML` used for user-generated content
- **Error Handling**: Try-catch blocks around all localStorage operations

### Accessibility Features
- **ARIA Labels**: All interactive elements properly labeled
- **Keyboard Navigation**: Full keyboard support for all actions
- **Focus Management**: Visible focus indicators, logical tab order
- **Screen Reader Support**: Semantic HTML, role attributes
- **Color Contrast**: WCAG AA compliant (4.5:1 for text)

### Data Persistence
- **localStorage**: Automatic save on every change
- **Quota Detection**: Warns user when storage is full
- **Export/Import**: JSON backup format for data portability
- **Error Recovery**: Graceful degradation if localStorage unavailable

### Responsive Design
- **Mobile**: Single column, stacked layout, touch-friendly buttons
- **Tablet**: Optimized spacing, readable fonts
- **Desktop**: Multi-column layout, hover effects
- **Breakpoints**: 768px (tablet), 480px (mobile)

## 📁 File Structure

```
todo-app-simple/
├── index.html          # Main HTML structure
├── styles.css          # All styling with dark mode support
├── app.js              # Full application logic
└── README.md           # This file
```

## 🔧 Technical Details

### Technologies Used
- **HTML5** - Semantic markup
- **CSS3** - Custom properties, Grid, Flexbox, Animations
- **Vanilla JavaScript (ES6+)** - Classes, Arrow functions, Template literals
- **localStorage API** - Client-side data persistence

### Browser Compatibility
- Chrome/Edge: Latest 2 versions
- Firefox: Latest 2 versions
- Safari: Latest 2 versions
- Mobile browsers: iOS Safari, Chrome Mobile

### Performance Optimizations
- Minimal DOM manipulation
- Event delegation for dynamic elements
- CSS animations (GPU accelerated)
- Efficient filtering and sorting algorithms
- Lazy rendering of todo items

## 🎯 Addressing Critic Report Findings

### HIGH Severity - ✅ Resolved
1. **LocalStorage Data Loss** - Export functionality, quota detection, user warnings
2. **XSS Vulnerability** - `textContent` sanitization, input validation, import sanitization
3. **Accessibility Gaps** - Full keyboard nav, ARIA labels, focus management, screen reader support
4. **Date/Time Localization** - ISO 8601 storage, localized display with `Intl.DateTimeFormat`

### MEDIUM Severity - ✅ Resolved
5. **State Race Conditions** - Immediate UI updates, no async operations
6. **Browser Compatibility** - Feature detection, graceful degradation
7. **Import/Export Security** - 5MB limit, schema validation, transactional import

### LOW Severity - ✅ Resolved
8. **UUID Generation** - Timestamp + random string collision-resistant approach
9. **Large Dataset Performance** - Efficient rendering, can handle 1000+ todos
10. **Error Handling** - Try-catch blocks, user-friendly error messages

## 🧪 Testing Checklist

### Security Tests
- [x] XSS injection prevention
- [x] Import validation (malformed JSON, oversized files)
- [x] localStorage failure handling

### Functional Tests
- [x] CRUD operations (Create, Read, Update, Delete)
- [x] Filter and sort functionality
- [x] Search functionality
- [x] Bulk operations
- [x] Export/Import

### Accessibility Tests
- [x] Keyboard navigation
- [x] Screen reader compatibility
- [x] Color contrast (WCAG AA)
- [x] Focus indicators

### Performance Tests
- [x] 100+ todos rendering
- [x] Search/filter speed
- [x] Animation smoothness

## 📊 Statistics Dashboard

The app tracks and displays:
- **Total Todos**: Overall count
- **Active Todos**: Pending tasks
- **Completed Todos**: Finished tasks
- **Completion Rate**: Percentage of completed tasks

## 🎨 Customization

### Adding New Categories
Edit the `todoCategory` select in `index.html` and update `getCategoryIcon()` in `app.js`:

```javascript
const icons = {
    personal: '🏠',
    work: '💼',
    shopping: '🛒',
    health: '💪',
    // Add your category here
};
```

### Changing Colors
Edit CSS custom properties in `styles.css`:

```css
:root {
    --primary-color: #3b82f6;
    --success-color: #10b981;
    --danger-color: #ef4444;
    /* Add your colors */
}
```

## 🔐 Privacy & Data

- All data stored locally in your browser
- No external servers or APIs
- No analytics or tracking
- Export your data anytime for backup
- Clear browser data to remove all todos

## 📝 License

Free to use and modify for personal and commercial projects.

## 🤝 Contributing

Feel free to fork, modify, and improve this application!

## 📧 Support

For issues or questions, please check the code comments or create an issue in your repository.

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**Built with ❤️ using pure HTML, CSS, and JavaScript**