agentsqripts/lib/performance/async-patterns/detectors/detectAsyncCallbacks.js

Comprehensive static code analysis toolkit for identifying technical debt, security vulnerabilities, performance issues, and code quality problems

/**
 * @file Detect legacy callback-based async patterns for modernization
 * @description Single responsibility: Identify callback patterns that could benefit from async/await
 * 
 * This detector analyzes JavaScript code for legacy callback-based asynchronous patterns,
 * particularly Node.js-style error-first callbacks and nested callback structures
 * (callback hell). It helps identify opportunities to modernize codebases with
 * Promise-based patterns and async/await syntax for improved maintainability.
 * 
 * Design rationale:
 * - Focuses on two main problematic patterns: error-first callbacks and callback nesting
 * - Uses regex pattern matching for efficient detection across large codebases
 * - Provides specific modernization recommendations based on detected patterns
 * - Categorizes issues by severity to help prioritize refactoring efforts
 */

/**
 * Detect callback-based async patterns that could be modernized
 * 
 * Technical function: Scans code lines for legacy callback patterns and nesting issues
 * 
 * Implementation rationale:
 * - Line-by-line analysis provides precise location information for issues
 * - Regex patterns efficiently identify callback signatures and nesting structures
 * - Severity differentiation helps prioritize refactoring (callback hell > simple callbacks)
 * - Comprehensive issue objects provide context and actionable recommendations
 * 
 * Pattern detection strategy:
 * - Error-first callback pattern: `function(err, ...)` or `(err, ...)` arrow functions
 * - Nested callback detection: Multiple function declarations within single line
 * - Whitespace normalization handles various coding styles and formatting
 * - Conservative matching prevents false positives while catching common patterns
 * 
 * Regex pattern breakdown:
 * - `\w+\s*\([^)]*,\s*function\s*\(\s*err\s*,`: Named function with error-first callback
 * - `\w+\s*\([^)]*,\s*\(\s*err\s*,`: Function call with arrow function error-first callback
 * - `function\s*\([^)]*\)\s*{.*function\s*\([^)]*\)\s*{`: Nested function declarations
 * 
 * Severity classification rationale:
 * - Callback patterns (LOW): Modernization improves maintainability but not critical
 * - Callback hell (MEDIUM): Significantly impacts code readability and error handling
 * - Effort estimates based on typical refactoring complexity for each pattern type
 * 
 * Modernization recommendations:
 * - Simple callbacks: Use util.promisify() or native Promise-based APIs
 * - Callback hell: Refactor to async/await with proper error handling
 * - Focus on maintainability improvements rather than performance gains
 * 
 * Performance considerations:
 * - O(n) time complexity for single pass through all code lines
 * - Regex compilation cached by JavaScript engine for repeated patterns
 * - Memory usage scales linearly with number of detected issues
 * - Early continue optimization when no patterns match
 * 
 * Limitations and trade-offs:
 * - Line-based analysis may miss multi-line callback patterns
 * - Regex matching may have false positives in comments or strings
 * - Simple pattern detection chosen over AST parsing for performance
 * - Focus on common Node.js patterns rather than all possible callback styles
 * 
 * Alternative approaches considered:
 * - AST-based analysis: Rejected for performance overhead in large codebases
 * - Multi-line pattern detection: Rejected for complexity vs benefit trade-off
 * - Framework-specific callback detection: Rejected to maintain general applicability
 * 
 * @param {string[]} lines - Array of code lines to analyze for callback patterns
 * @param {string} filePath - File path for issue location reporting
 * @returns {Array<Object>} Array of detected callback-related issues with modernization recommendations
 * @example
 *   // For: fs.readFile('file.txt', function(err, data) { ... })
 *   [{
 *     type: 'callback_pattern',
 *     severity: 'LOW',
 *     location: 'src/file.js:10',
 *     description: 'Callback-based async pattern - consider modernizing to async/await',
 *     recommendation: 'Consider using promisify() or native Promise-based APIs'
 *   }]
 */
function detectAsyncCallbacks(lines, filePath) {
  const issues = [];
  
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    const lineNumber = i + 1;
    const trimmed = line.trim();
    
    // Node.js callback patterns
    if (/\w+\s*\([^)]*,\s*function\s*\(\s*err\s*,/.test(trimmed) ||
        /\w+\s*\([^)]*,\s*\(\s*err\s*,/.test(trimmed)) {
      issues.push({
        type: 'callback_pattern',
        severity: 'LOW',
        category: 'Async',
        location: `${filePath}:${lineNumber}`,
        line: lineNumber,
        code: trimmed,
        description: 'Callback-based async pattern - consider modernizing to async/await',
        summary: 'Legacy callback pattern detected',
        recommendation: 'Consider using promisify() or native Promise-based APIs',
        effort: 2,
        impact: 'Modernizes codebase and improves error handling',
        estimatedSavings: 'improved maintainability'
      });
    }
    
    // Nested callbacks (callback hell)
    if (/function\s*\([^)]*\)\s*{.*function\s*\([^)]*\)\s*{/.test(trimmed)) {
      issues.push({
        type: 'callback_hell',
        severity: 'MEDIUM',
        category: 'Async',
        location: `${filePath}:${lineNumber}`,
        line: lineNumber,
        code: trimmed,
        description: 'Nested callbacks detected - callback hell pattern',
        summary: 'Callback hell pattern',
        recommendation: 'Refactor to async/await or Promise chains',
        effort: 3,
        impact: 'Significantly improves code readability and maintainability',
        estimatedSavings: 'major maintainability improvement'
      });
    }
  }
  
  return issues;
}

module.exports = detectAsyncCallbacks;