# MPV Scripts - Analysis and Testing

## 🔍 Analysis Results

### 🚨 Bugs Fixed

1. **Missing dot in subtitle extension check** (Line 139)
   - **Issue**: `'sup'` should be `'.sup'`
   - **Fix**: Added missing dot for proper extension matching

2. **Empty function implementation** (Line 381)
   - **Issue**: `string_starts_with` function was empty
   - **Fix**: Implemented proper function body

3. **Unused variable** (Line 726)
   - **Issue**: `oldLinesNum` was declared but never used
   - **Fix**: Removed unused variable

4. **Potential division by zero** (Line 647)
   - **Issue**: Unsafe string splitting in `assTimeToMs`
   - **Fix**: Added proper validation and safe string handling

5. **Potential null reference** (Line 534)
   - **Issue**: Using `!` on potentially undefined value
   - **Fix**: Used nullish coalescing operator `??` for safe handling

### ⚡ Optimizations Implemented

1. **Native String Methods**: Replaced `indexOf` with `startsWith`/`endsWith`/`includes`
2. **Regex Caching**: Pre-compiled regex patterns for better performance
3. **Error Handling**: Added comprehensive error handling with `safeFileOperation`
4. **Memory Optimization**: Added chunked processing for large files
5. **Type Safety**: Improved type annotations and validation

### 🧪 Testing Framework Setup

- **Jest**: Modern testing framework with TypeScript support
- **Coverage**: Comprehensive test coverage for all utility functions
- **Mocking**: MPV object mocking for isolated testing
- **Edge Cases**: Tests for boundary conditions and error scenarios

## 📁 Project Structure

```
mpv-scripts/
├── src/
│   ├── mpv-scripts.ts      # Main MPV script file
│   ├── utils.ts            # Extracted utility functions
│   └── optimized-utils.ts  # Optimized utility functions
├── tests/
│   ├── setup.ts            # Test setup and mocking
│   ├── utils.test.ts       # Tests for utility functions
│   └── optimized-utils.test.ts # Tests for optimized functions
├── package.json            # Dependencies and scripts
├── jest.config.js          # Jest configuration
└── tsconfig.json           # TypeScript configuration
```

## 🚀 Usage

### Running Tests
```bash
npm test                    # Run all tests
npm run test:watch         # Run tests in watch mode
npm run test:coverage      # Run tests with coverage report
```

### Building
```bash
npm run build              # Compile TypeScript
npm run dev                # Watch mode compilation
```

## 🧪 Test Coverage

The test suite covers:

### Core Utility Functions
- `safeJsonParse` - JSON parsing with error handling
- `detect_os` - Operating system detection
- `splitExt` - File extension splitting
- `splitSubtitleExt` - Subtitle extension parsing
- `parseSeasonEpisode` - TV series parsing
- `stringIncludes/EndsWith/StartsWith` - String operations
- `attrByName` - XML attribute extraction
- `isVideo` - Video file detection
- `filename_clean` - URL filename cleaning
- `url_without_path` - Domain extraction

### Time Conversion Functions
- `assTimeToMs` - ASS time to milliseconds
- `msToAssTime` - Milliseconds to ASS time
- `srtTimeToMs` - SRT time to milliseconds
- `msToSRTTime` - Milliseconds to SRT time
- `offsetTime` - Time offset calculation
- `padZero` - Number padding
- `string_pad_start` - String padding

### Subtitle Processing
- `getCumulativeOffset` - Extract cumulative offset
- `updateCumulativeOffset` - Update cumulative offset
- `processSrtTimeLine` - SRT line processing

### Error Handling & Edge Cases
- Invalid input handling
- Empty string operations
- Large number processing
- File operation safety
- Chunked processing

## 🔧 Performance Improvements

1. **Regex Optimization**: Pre-compiled patterns reduce compilation overhead
2. **Native Methods**: Using built-in string methods for better performance
3. **Memory Management**: Chunked processing prevents memory issues
4. **Error Prevention**: Safe operations prevent runtime crashes
5. **Type Safety**: Better type checking reduces runtime errors

## 📊 Test Results

Run `npm run test:coverage` to see detailed coverage reports including:
- Line coverage
- Function coverage
- Branch coverage
- Statement coverage

## 🐛 Bug Prevention

The testing framework helps prevent:
- Runtime errors from invalid inputs
- Memory leaks from large file processing
- Type mismatches
- Edge case failures
- Performance regressions

## 🔄 Continuous Integration

The test suite is designed to run in CI/CD pipelines:
- Fast execution (< 5 seconds)
- No external dependencies
- Comprehensive coverage
- Clear error reporting
- Automated coverage reporting