---
description: 
globs: 
alwaysApply: true
---
# Performance Optimizer

```yaml
name: Performance Optimizer
description: Analyzes code for performance issues and suggests improvements
author: Cursor AI
version: 1.0.0
tags:
  - performance
  - optimization
  - analysis
activation:
  always: true
  event:
    - file_change
    - pull_request
    - command
triggers:
  - file.modified
  - pull_request.created
  - pull_request.updated
  - command: "optimize_performance"
```

## Rule Definition

This rule analyzes code changes for potential performance issues and suggests optimizations.

## Performance Analysis Logic

```javascript
// Main function to analyze code for performance issues
function analyzePerformance(files, codebase) {
  const issues = [];
  const suggestions = [];
  let score = 100; // Start with perfect score
  
  // Process each file
  for (const file of files) {
    const fileIssues = findPerformanceIssues(file, codebase);
    if (fileIssues.length > 0) {
      issues.push(...fileIssues);
      
      // Reduce score based on severity of issues
      score -= fileIssues.reduce((total, issue) => total + issue.severity, 0);
      
      // Generate optimization suggestions
      const fileSuggestions = generateOptimizationSuggestions(file, fileIssues, codebase);
      suggestions.push(...fileSuggestions);
    }
  }
  
  // Ensure score doesn't go below 0
  score = Math.max(0, score);
  
  return {
    score,
    issues,
    suggestions,
    summary: generatePerformanceSummary(score, issues, suggestions)
  };
}

// Find performance issues in a file
function findPerformanceIssues(file, codebase) {
  const issues = [];
  
  // Check file based on its type
  if (file.path.includes('.ts') || file.path.includes('.js')) {
    issues.push(...findJavaScriptPerformanceIssues(file));
  } else if (file.path.includes('.java')) {
    issues.push(...findJavaPerformanceIssues(file));
  } else if (file.path.includes('.css')) {
    issues.push(...findCssPerformanceIssues(file));
  }
  
  return issues;
}

// Find performance issues in JavaScript/TypeScript files
function findJavaScriptPerformanceIssues(file) {
  const issues = [];
  const content = file.content;
  
  // Check for common JavaScript performance issues
  
  // 1. Nested loops with high complexity (O(n²) or worse)
  if (/for\s*\([^)]*\)\s*\{[^}]*for\s*\([^)]*\)/g.test(content)) {
    issues.push({
      type: 'nested_loops',
      lineNumber: findLineNumber(content, /for\s*\([^)]*\)\s*\{[^}]*for\s*\([^)]*\)/g),
      description: 'Nested loops detected, which may cause O(n²) time complexity',
      severity: 8,
      suggestion: 'Consider refactoring to reduce time complexity, possibly using maps/sets'
    });
  }
  
  // 2. Large array operations without memoization
  if (/\.map\(.*\.filter\(|\.filter\(.*\.map\(/g.test(content)) {
    issues.push({
      type: 'chained_array_operations',
      lineNumber: findLineNumber(content, /\.map\(.*\.filter\(|\.filter\(.*\.map\(/g),
      description: 'Chained array operations may cause performance issues with large datasets',
      severity: 5,
      suggestion: 'Consider combining operations or using a different data structure'
    });
  }
  
  // 3. Frequent DOM manipulations
  if (/document\.getElement(s?)By|querySelector(All)?/g.test(content) && 
      content.match(/document\.getElement(s?)By|querySelector(All)?/g).length > 5) {
    issues.push({
      type: 'frequent_dom_manipulation',
      lineNumber: findLineNumber(content, /document\.getElement(s?)By|querySelector(All)?/g),
      description: 'Frequent DOM manipulations can cause layout thrashing',
      severity: 7,
      suggestion: 'Batch DOM manipulations or use DocumentFragment'
    });
  }
  
  // 4. Memory leaks in event listeners
  if (/addEventListener\(/g.test(content) && 
      !/removeEventListener\(/g.test(content)) {
    issues.push({
      type: 'potential_memory_leak',
      lineNumber: findLineNumber(content, /addEventListener\(/g),
      description: 'Event listener without corresponding removal may cause memory leaks',
      severity: 6,
      suggestion: 'Add corresponding removeEventListener calls where appropriate'
    });
  }
  
  // Add more JavaScript-specific performance checks here
  
  return issues;
}

// Find performance issues in Java files
function findJavaPerformanceIssues(file) {
  const issues = [];
  const content = file.content;
  
  // Check for common Java performance issues
  
  // 1. Inefficient string concatenation
  if (/String.*\+= |String.*= .*\+ /g.test(content)) {
    issues.push({
      type: 'inefficient_string_concat',
      lineNumber: findLineNumber(content, /String.*\+= |String.*= .*\+ /g),
      description: 'Inefficient string concatenation in loops',
      severity: 4,
      suggestion: 'Use StringBuilder instead of string concatenation'
    });
  }
  
  // 2. Unclosed resources
  if (/new FileInputStream|new Connection/g.test(content) &&
      !/try\s*\([^)]*\)/g.test(content)) {
    issues.push({
      type: 'unclosed_resources',
      lineNumber: findLineNumber(content, /new FileInputStream|new Connection/g),
      description: 'Resources may not be properly closed',
      severity: 7,
      suggestion: 'Use try-with-resources to ensure proper resource closure'
    });
  }
  
  // Add more Java-specific performance checks here
  
  return issues;
}

// Find performance issues in CSS files
function findCssPerformanceIssues(file) {
  const issues = [];
  const content = file.content;
  
  // Check for common CSS performance issues
  
  // 1. Overqualified selectors
  if (/div\.[a-zA-Z0-9_-]+|ul\.[a-zA-Z0-9_-]+/g.test(content)) {
    issues.push({
      type: 'overqualified_selectors',
      lineNumber: findLineNumber(content, /div\.[a-zA-Z0-9_-]+|ul\.[a-zA-Z0-9_-]+/g),
      description: 'Overqualified selectors may impact rendering performance',
      severity: 3,
      suggestion: 'Use more efficient selectors, avoiding element type with class'
    });
  }
  
  // 2. Universal selectors
  if (/\*\s*\{/g.test(content)) {
    issues.push({
      type: 'universal_selector',
      lineNumber: findLineNumber(content, /\*\s*\{/g),
      description: 'Universal selectors can be very slow, especially in large documents',
      severity: 5,
      suggestion: 'Replace universal selectors with more specific ones'
    });
  }
  
  // Add more CSS-specific performance checks here
  
  return issues;
}

// Find line number for a regex match
function findLineNumber(content, regex) {
  const match = content.match(regex);
  if (!match) return 0;
  
  const index = content.indexOf(match[0]);
  return content.substring(0, index).split('\n').length;
}

// Generate optimization suggestions based on issues found
function generateOptimizationSuggestions(file, issues, codebase) {
  const suggestions = [];
  
  for (const issue of issues) {
    const suggestion = {
      file: file.path,
      issue: issue.type,
      description: issue.suggestion,
      lineNumber: issue.lineNumber,
      code: issue.suggestion // This would be actual code in a real implementation
    };
    
    suggestions.push(suggestion);
  }
  
  return suggestions;
}

// Generate a summary of the performance analysis
function generatePerformanceSummary(score, issues, suggestions) {
  const criticalIssues = issues.filter(issue => issue.severity >= 7).length;
  const majorIssues = issues.filter(issue => issue.severity >= 4 && issue.severity < 7).length;
  const minorIssues = issues.filter(issue => issue.severity < 4).length;
  
  return {
    score,
    issues: {
      total: issues.length,
      critical: criticalIssues,
      major: majorIssues,
      minor: minorIssues
    },
    suggestions: suggestions.length,
    recommendation: getPerformanceRecommendation(score)
  };
}

// Get a recommendation based on the performance score
function getPerformanceRecommendation(score) {
  if (score >= 90) {
    return "Code looks good performance-wise. Only minor optimizations possible.";
  } else if (score >= 70) {
    return "Some performance issues found. Consider addressing them before deploying.";
  } else if (score >= 50) {
    return "Significant performance issues detected. Optimizations strongly recommended.";
  } else {
    return "Critical performance issues found. The code may perform poorly in production.";
  }
}

// Run on activation
function activate(context) {
  // Register event handlers
  context.on('file.modified', (event) => {
    const file = context.getFileContent(event.file.path);
    const codebase = context.getCodebase();
    return analyzePerformance([file], codebase);
  });
  
  context.on('pull_request.created', (event) => {
    const files = context.getPullRequestFiles(event.pullRequest.id);
    const codebase = context.getCodebase();
    return analyzePerformance(files, codebase);
  });
  
  context.on('pull_request.updated', (event) => {
    const files = context.getPullRequestFiles(event.pullRequest.id);
    const codebase = context.getCodebase();
    return analyzePerformance(files, codebase);
  });
  
  context.registerCommand('optimize_performance', (args) => {
    const filePath = args.file || context.getCurrentFilePath();
    if (!filePath) {
      return {
        status: "error",
        message: "No file specified"
      };
    }
    
    const file = context.getFileContent(filePath);
    const codebase = context.getCodebase();
    return analyzePerformance([file], codebase);
  });
}

// Export functions
module.exports = {
  activate,
  analyzePerformance,
  findPerformanceIssues,
  generateOptimizationSuggestions,
  generatePerformanceSummary
};
```

## When It Runs

This rule can be triggered:
- When code changes might impact performance
- When a pull request is created or updated
- When a developer runs the `optimize_performance` command in Cursor
- Before deploying to production environments

## Usage Example

1. Make code changes to a file
2. Run `optimize_performance` in Cursor
3. Review the performance analysis
4. Implement the suggested optimizations
5. Re-run the analysis to confirm improvements

## Performance Optimization Best Practices

### JavaScript/TypeScript

- Avoid nested loops when possible
- Use appropriate data structures (Map, Set) for lookups
- Minimize DOM manipulations
- Use event delegation instead of multiple event listeners
- Memoize expensive function calls
- Use requestAnimationFrame for animations

### Java

- Use StringBuilder for string concatenation
- Use try-with-resources for proper resource management
- Avoid excessive object creation
- Choose appropriate collections (ArrayList, HashMap) based on use-case
- Use primitive types where possible instead of wrapper classes

### CSS

- Avoid universal selectors and deeply nested selectors
- Minimize the use of expensive properties (box-shadow, border-radius, etc.)
- Prefer class selectors over tag selectors
- Use CSS containment where appropriate