Enterprise and Production Considerations

// bundle-optimizer.js
var BundleOptimizer = {
    // Analyze bundle composition
    analyzeBundle: function() {
        // Use webpack-bundle-analyzer or similar
        return {
            total: 250, // KB
            polyfills: 120, // KB
            application: 100, // KB
            vendor: 30 // KB
        };
    },
    
    // Calculate optimal polyfill strategy
    optimizeStrategy: function() {
        var analysis = this.analyzeBundle();
        var recommendations = [];
        
        // Check if polyfills are too large
        var polyfillPercentage = (analysis.polyfills / analysis.total) * 100;
        
        if (polyfillPercentage > 40) {
            recommendations.push({
                issue: 'Polyfills exceed 40% of bundle',
                solution: 'Implement differential serving',
                savings: Math.round(analysis.polyfills * 0.6) + ' KB'
            });
        }
        
        // Check for tree-shaking opportunities
        recommendations.push({
            issue: 'Potential unused polyfills',
            solution: 'Use core-js with useBuiltIns: "usage"',
            savings: Math.round(analysis.polyfills * 0.3) + ' KB'
        });
        
        // Compression recommendations
        recommendations.push({
            issue: 'Uncompressed assets',
            solution: 'Enable Brotli compression',
            savings: Math.round(analysis.total * 0.7) + ' KB (transfer size)'
        });
        
        return recommendations;
    },
    
    // Generate optimized bundle configuration
    generateConfig: function() {
        return {
            modern: {
                target: 'es2015',
                polyfills: [
                    'Promise.allSettled',
                    'String.matchAll'
                ],
                size: '80 KB',
                browsers: '>0.5%, not dead, supports es6-module'
            },
            
            legacy: {
                target: 'es5',
                polyfills: [
                    'core-js/stable',
                    'regenerator-runtime',
                    'whatwg-fetch',
                    'intersection-observer'
                ],
                size: '220 KB',
                browsers: 'ie 11, > 0.5%'
            },
            
            savings: {
                modernBrowsers: '140 KB saved (64%)',
                avgUser: '90 KB saved (41%)'
            }
        };
    }
};

// Webpack plugin for size budget enforcement
class PolyfillBudgetPlugin {
    constructor(options) {
        this.maxSize = options.maxSize || 100 * 1024; // 100 KB default
        this.maxPolyfillPercentage = options.maxPolyfillPercentage || 30;
    }
    
    apply(compiler) {
        compiler.hooks.afterEmit.tap('PolyfillBudgetPlugin', (compilation) => {
            var polyfillSize = 0;
            var totalSize = 0;
            
            Object.keys(compilation.assets).forEach((filename) => {
                var size = compilation.assets[filename].size();
                totalSize += size;
                
                if (filename.includes('polyfill')) {
                    polyfillSize += size;
                }
            });
            
            var percentage = (polyfillSize / totalSize) * 100;
            
            console.log('\n📦 Bundle Size Analysis:');
            console.log('  Total: ' + (totalSize / 1024).toFixed(2) + ' KB');
            console.log('  Polyfills: ' + (polyfillSize / 1024).toFixed(2) + ' KB (' + percentage.toFixed(1) + '%)');
            
            if (polyfillSize > this.maxSize) {
                compilation.errors.push(
                    new Error('Polyfill bundle exceeds size budget: ' + 
                             (polyfillSize / 1024).toFixed(2) + ' KB > ' + 
                             (this.maxSize / 1024).toFixed(2) + ' KB')
                );
            }
            
            if (percentage > this.maxPolyfillPercentage) {
                compilation.warnings.push(
                    new Error('Polyfills exceed ' + this.maxPolyfillPercentage + 
                             '% of total bundle (' + percentage.toFixed(1) + '%)')
                );
            }
        });
    }
}

// Usage in webpack.config.js
module.exports = {
    plugins: [
        new PolyfillBudgetPlugin({
            maxSize: 100 * 1024, // 100 KB
            maxPolyfillPercentage: 30 // 30%
        })
    ],
    
    performance: {
        maxEntrypointSize: 250 * 1024,
        maxAssetSize: 100 * 1024,
        hints: 'warning'
    }
};

// performance-monitor.js
var PolyfillPerformanceMonitor = {
    metrics: {},
    
    // Mark polyfill loading start
    markStart: function(polyfillName) {
        performance.mark('polyfill-' + polyfillName + '-start');
    },
    
    // Mark polyfill loading end
    markEnd: function(polyfillName) {
        performance.mark('polyfill-' + polyfillName + '-end');
        
        performance.measure(
            'polyfill-' + polyfillName,
            'polyfill-' + polyfillName + '-start',
            'polyfill-' + polyfillName + '-end'
        );
        
        var measure = performance.getEntriesByName('polyfill-' + polyfillName)[0];
        
        this.metrics[polyfillName] = {
            duration: measure.duration,
            startTime: measure.startTime
        };
        
        console.log('Polyfill ' + polyfillName + ' loaded in ' + 
                   measure.duration.toFixed(2) + 'ms');
    },
    
    // Measure method performance
    measureMethod: function(nativeFn, polyfillFn, iterations) {
        iterations = iterations || 10000;
        
        // Measure native
        var nativeStart = performance.now();
        for (var i = 0; i < iterations; i++) {
            nativeFn();
        }
        var nativeDuration = performance.now() - nativeStart;
        
        // Measure polyfill
        var polyfillStart = performance.now();
        for (var i = 0; i < iterations; i++) {
            polyfillFn();
        }
        var polyfillDuration = performance.now() - polyfillStart;
        
        var slowdown = polyfillDuration / nativeDuration;
        
        return {
            native: nativeDuration,
            polyfill: polyfillDuration,
            slowdown: slowdown,
            acceptable: slowdown < 2
        };
    },
    
    // Monitor FCP impact
    measureFCPImpact: function() {
        if (!window.PerformanceObserver) {
            return;
        }
        
        var observer = new PerformanceObserver(function(list) {
            list.getEntries().forEach(function(entry) {
                if (entry.name === 'first-contentful-paint') {
                    console.log('FCP: ' + entry.startTime.toFixed(2) + 'ms');
                    
                    // Check if polyfills delayed FCP
                    var polyfillMarks = performance.getEntriesByType('mark')
                        .filter(function(mark) {
                            return mark.name.includes('polyfill');
                        });
                    
                    var polyfillTime = 0;
                    polyfillMarks.forEach(function(mark) {
                        if (mark.startTime < entry.startTime) {
                            polyfillTime += mark.duration || 0;
                        }
                    });
                    
                    var impact = (polyfillTime / entry.startTime) * 100;
                    console.log('Polyfill impact on FCP: ' + impact.toFixed(1) + '%');
                }
            });
        });
        
        observer.observe({ entryTypes: ['paint'] });
    },
    
    // Generate performance report
    generateReport: function() {
        var report = {
            totalPolyfillTime: 0,
            polyfills: [],
            recommendations: []
        };
        
        Object.keys(this.metrics).forEach(function(name) {
            var metric = this.metrics[name];
            report.totalPolyfillTime += metric.duration;
            
            report.polyfills.push({
                name: name,
                duration: metric.duration.toFixed(2) + 'ms',
                startTime: metric.startTime.toFixed(2) + 'ms'
            });
            
            // Recommendations
            if (metric.duration > 50) {
                report.recommendations.push({
                    polyfill: name,
                    issue: 'Slow loading (>50ms)',
                    solution: 'Consider lazy loading or removing'
                });
            }
        }.bind(this));
        
        // Overall assessment
        if (report.totalPolyfillTime > 100) {
            report.recommendations.push({
                issue: 'Total polyfill time exceeds 100ms',
                solution: 'Use differential serving to reduce polyfills for modern browsers'
            });
        }
        
        return report;
    },
    
    // Send metrics to analytics
    sendToAnalytics: function() {
        var report = this.generateReport();
        
        // Send to Google Analytics, custom endpoint, etc.
        if (typeof gtag !== 'undefined') {
            gtag('event', 'polyfill_performance', {
                total_time: report.totalPolyfillTime,
                polyfill_count: report.polyfills.length
            });
        }
        
        console.log('Performance Report:', report);
    }
};

// Usage
PolyfillPerformanceMonitor.markStart('Promise');
import('es6-promise/auto').then(function() {
    PolyfillPerformanceMonitor.markEnd('Promise');
});

// Monitor FCP impact
PolyfillPerformanceMonitor.measureFCPImpact();

// Generate report on page load
window.addEventListener('load', function() {
    setTimeout(function() {
        PolyfillPerformanceMonitor.sendToAnalytics();
    }, 1000);
});

// memory-monitor.js
var MemoryMonitor = {
    snapshots: [],
    
    // Take memory snapshot (Chrome only)
    takeSnapshot: function() {
        if (!performance.memory) {
            console.warn('performance.memory not available');
            return null;
        }
        
        var snapshot = {
            timestamp: Date.now(),
            usedJSHeapSize: performance.memory.usedJSHeapSize,
            totalJSHeapSize: performance.memory.totalJSHeapSize,
            jsHeapSizeLimit: performance.memory.jsHeapSizeLimit
        };
        
        this.snapshots.push(snapshot);
        return snapshot;
    },
    
    // Analyze memory growth
    analyzeGrowth: function() {
        if (this.snapshots.length < 2) {
            return null;
        }
        
        var first = this.snapshots[0];
        var last = this.snapshots[this.snapshots.length - 1];
        
        var growth = last.usedJSHeapSize - first.usedJSHeapSize;
        var duration = last.timestamp - first.timestamp;
        var growthRate = growth / duration; // bytes per ms
        
        return {
            growth: (growth / 1024 / 1024).toFixed(2) + ' MB',
            duration: (duration / 1000).toFixed(2) + ' seconds',
            growthRate: (growthRate * 1000).toFixed(2) + ' KB/s',
            isLeaking: growthRate > 100 // >100 KB/s sustained growth
        };
    },
    
    // Test for memory leaks
    testForLeaks: function(testFn, iterations) {
        iterations = iterations || 1000;
        
        // Force GC before test (requires --expose-gc flag)
        if (global.gc) {
            global.gc();
        }
        
        this.takeSnapshot();
        
        // Run test function multiple times
        for (var i = 0; i < iterations; i++) {
            testFn();
        }
        
        // Force GC after test
        if (global.gc) {
            global.gc();
        }
        
        setTimeout(function() {
            this.takeSnapshot();
            var analysis = this.analyzeGrowth();
            
            console.log('Memory Leak Test Results:');
            console.log('  Growth: ' + analysis.growth);
            console.log('  Rate: ' + analysis.growthRate);
            console.log('  Leaking: ' + (analysis.isLeaking ? 'YES ⚠️' : 'NO ✓'));
        }.bind(this), 1000);
    },
    
    // Monitor continuous memory usage
    startMonitoring: function(interval) {
        interval = interval || 5000; // 5 seconds
        
        this.monitoringInterval = setInterval(function() {
            var snapshot = this.takeSnapshot();
            
            if (snapshot) {
                var usedMB = (snapshot.usedJSHeapSize / 1024 / 1024).toFixed(2);
                var totalMB = (snapshot.totalJSHeapSize / 1024 / 1024).toFixed(2);
                var percentage = ((snapshot.usedJSHeapSize / snapshot.totalJSHeapSize) * 100).toFixed(1);
                
                console.log('Memory: ' + usedMB + ' MB / ' + totalMB + ' MB (' + percentage + '%)');
                
                // Alert if memory is high
                if (percentage > 80) {
                    console.warn('⚠️  High memory usage: ' + percentage + '%');
                }
            }
        }.bind(this), interval);
    },
    
    stopMonitoring: function() {
        if (this.monitoringInterval) {
            clearInterval(this.monitoringInterval);
        }
    }
};

// Memory-efficient polyfill patterns
var MemoryEfficientPolyfills = {
    // Use WeakMap to avoid memory leaks
    createPrivateStorage: function() {
        if (typeof WeakMap !== 'undefined') {
            return new WeakMap();
        } else {
            // Fallback: use regular object with cleanup
            var storage = {};
            var counter = 0;
            
            return {
                set: function(key, value) {
                    if (!key.__memoryId) {
                        key.__memoryId = 'id_' + (++counter);
                    }
                    storage[key.__memoryId] = value;
                },
                get: function(key) {
                    return key.__memoryId ? storage[key.__memoryId] : undefined;
                },
                delete: function(key) {
                    if (key.__memoryId) {
                        delete storage[key.__memoryId];
                    }
                }
            };
        }
    },
    
    // Object pooling for frequently created objects
    createObjectPool: function(createFn, resetFn) {
        var pool = [];
        var maxSize = 100;
        
        return {
            acquire: function() {
                if (pool.length > 0) {
                    return pool.pop();
                } else {
                    return createFn();
                }
            },
            
            release: function(obj) {
                if (pool.length < maxSize) {
                    resetFn(obj);
                    pool.push(obj);
                }
            }
        };
    }
};

// Test for memory leaks
MemoryMonitor.testForLeaks(function() {
    // Test Promise polyfill for leaks
    new Promise(function(resolve) {
        resolve('test');
    }).then(function(result) {
        return result;
    });
}, 1000);

// Start continuous monitoring
MemoryMonitor.startMonitoring(10000);

// polyfill-monitoring.js
var PolyfillMonitoring = {
    // Track which polyfills were loaded
    loadedPolyfills: [],
    
    // Track polyfill errors
    polyfillErrors: [],
    
    // Initialize monitoring
    init: function(config) {
        this.config = config || {};
        
        // Set up error tracking
        this.setupErrorTracking();
        
        // Track polyfill metadata
        this.trackPolyfillMetadata();
        
        // Send initial load event
        this.trackEvent('polyfills_initialized', {
            userAgent: navigator.userAgent,
            viewport: window.innerWidth + 'x' + window.innerHeight
        });
    },
    
    // Set up global error tracking
    setupErrorTracking: function() {
        var self = this;
        
        // Catch unhandled errors
        window.addEventListener('error', function(event) {
            // Check if error is polyfill-related
            if (event.filename && event.filename.includes('polyfill')) {
                self.trackPolyfillError({
                    message: event.message,
                    filename: event.filename,
                    lineno: event.lineno,
                    colno: event.colno,
                    stack: event.error ? event.error.stack : null
                });
            }
        });
        
        // Catch unhandled promise rejections
        window.addEventListener('unhandledrejection', function(event) {
            self.trackPolyfillError({
                message: 'Unhandled Promise Rejection',
                reason: event.reason,
                promise: event.promise
            });
        });
    },
    
    // Track polyfill loading
    trackPolyfillLoad: function(polyfillName, loadTime, success) {
        this.loadedPolyfills.push({
            name: polyfillName,
            loadTime: loadTime,
            success: success,
            timestamp: Date.now()
        });
        
        // Send to monitoring service
        this.trackEvent('polyfill_loaded', {
            polyfill: polyfillName,
            loadTime: loadTime,
            success: success
        });
        
        // Track in Sentry
        if (window.Sentry) {
            Sentry.addBreadcrumb({
                category: 'polyfill',
                message: 'Loaded ' + polyfillName,
                level: success ? 'info' : 'error',
                data: { loadTime: loadTime }
            });
        }
    },
    
    // Track polyfill errors
    trackPolyfillError: function(errorInfo) {
        this.polyfillErrors.push({
            ...errorInfo,
            timestamp: Date.now(),
            userAgent: navigator.userAgent
        });
        
        console.error('Polyfill Error:', errorInfo);
        
        // Send to Sentry
        if (window.Sentry) {
            Sentry.captureException(new Error(errorInfo.message), {
                tags: {
                    type: 'polyfill_error',
                    polyfill: errorInfo.filename || 'unknown'
                },
                extra: errorInfo
            });
        }
        
        // Send to custom endpoint
        this.sendToEndpoint('/api/polyfill-errors', errorInfo);
    },
    
    // Track polyfill metadata
    trackPolyfillMetadata: function() {
        var metadata = {
            browser: this.detectBrowser(),
            features: this.detectFeatureSupport(),
            polyfillsNeeded: this.detectPolyfillsNeeded()
        };
        
        // Set Sentry context
        if (window.Sentry) {
            Sentry.setContext('polyfills', metadata);
        }
        
        // Send to analytics
        this.trackEvent('polyfill_metadata', metadata);
    },
    
    // Detect browser
    detectBrowser: function() {
        var ua = navigator.userAgent;
        var browsers = {
            chrome: /Chrome\/(\d+)/.exec(ua),
            firefox: /Firefox\/(\d+)/.exec(ua),
            safari: /Version\/(\d+).*Safari/.exec(ua),
            edge: /Edg\/(\d+)/.exec(ua),
            ie: /MSIE (\d+)|Trident.*rv:(\d+)/.exec(ua)
        };
        
        for (var name in browsers) {
            if (browsers[name]) {
                return {
                    name: name,
                    version: browsers[name][1] || browsers[name][2]
                };
            }
        }
        
        return { name: 'unknown', version: 'unknown' };
    },
    
    // Detect feature support
    detectFeatureSupport: function() {
        return {
            Promise: typeof Promise !== 'undefined',
            fetch: typeof fetch !== 'undefined',
            IntersectionObserver: typeof IntersectionObserver !== 'undefined',
            ResizeObserver: typeof ResizeObserver !== 'undefined',
            CustomElements: typeof customElements !== 'undefined',
            Map: typeof Map !== 'undefined',
            Set: typeof Set !== 'undefined',
            Symbol: typeof Symbol !== 'undefined'
        };
    },
    
    // Detect which polyfills are needed
    detectPolyfillsNeeded: function() {
        var support = this.detectFeatureSupport();
        var needed = [];
        
        Object.keys(support).forEach(function(feature) {
            if (!support[feature]) {
                needed.push(feature);
            }
        });
        
        return needed;
    },
    
    // Track custom event
    trackEvent: function(eventName, data) {
        // Google Analytics
        if (typeof gtag !== 'undefined') {
            gtag('event', eventName, data);
        }
        
        // Datadog RUM
        if (window.DD_RUM) {
            window.DD_RUM.addAction(eventName, data);
        }
        
        console.log('Event:', eventName, data);
    },
    
    // Send data to custom endpoint
    sendToEndpoint: function(endpoint, data) {
        if (typeof fetch !== 'undefined') {
            fetch(endpoint, {
                method: 'POST',
                headers: { 'Content-Type': 'application/json' },
                body: JSON.stringify(data)
            }).catch(function(error) {
                console.error('Failed to send monitoring data:', error);
            });
        }
    },
    
    // Generate monitoring report
    generateReport: function() {
        return {
            loadedPolyfills: this.loadedPolyfills,
            errors: this.polyfillErrors,
            browser: this.detectBrowser(),
            features: this.detectFeatureSupport(),
            summary: {
                totalPolyfills: this.loadedPolyfills.length,
                totalErrors: this.polyfillErrors.length,
                avgLoadTime: this.loadedPolyfills.reduce(function(sum, p) {
                    return sum + (p.loadTime || 0);
                }, 0) / this.loadedPolyfills.length
            }
        };
    }
};

// Initialize monitoring
PolyfillMonitoring.init({
    sentryDsn: 'https://your-sentry-dsn',
    customEndpoint: '/api/monitoring'
});

// Track polyfill loading
PolyfillMonitoring.trackPolyfillLoad('Promise', 25, true);
PolyfillMonitoring.trackPolyfillLoad('fetch', 18, true);

// deployment-manager.js
var PolyfillDeployment = {
    // Current polyfill version
    version: '1.2.3',
    
    // Canary configuration
    canary: {
        enabled: false,
        percentage: 10, // 10% of users
        duration: 3600000, // 1 hour
        startTime: null
    },
    
    // Feature flags
    flags: {
        'new-promise-polyfill': false,
        'experimental-fetch': false
    },
    
    // Initialize deployment
    init: function() {
        // Check if user is in canary group
        var isCanary = this.isCanaryUser();
        
        if (isCanary) {
            console.log('User in canary group, loading new polyfills');
            this.loadCanaryPolyfills();
        } else {
            console.log('User in stable group, loading stable polyfills');
            this.loadStablePolyfills();
        }
        
        // Track deployment version
        this.trackDeploymentMetrics();
    },
    
    // Check if user is in canary group
    isCanaryUser: function() {
        if (!this.canary.enabled) {
            return false;
        }
        
        // Check if canary period expired
        if (this.canary.startTime) {
            var elapsed = Date.now() - this.canary.startTime;
            if (elapsed > this.canary.duration) {
                return false;
            }
        }
        
        // Use consistent hashing based on user ID or session
        var userId = this.getUserId();
        var hash = this.hashCode(userId);
        var bucket = Math.abs(hash % 100);
        
        return bucket < this.canary.percentage;
    },
    
    // Get or generate user ID
    getUserId: function() {
        var userId = localStorage.getItem('userId');
        if (!userId) {
            userId = 'user_' + Date.now() + '_' + Math.random();
            localStorage.setItem('userId', userId);
        }
        return userId;
    },
    
    // Simple hash function
    hashCode: function(str) {
        var hash = 0;
        for (var i = 0; i < str.length; i++) {
            var char = str.charCodeAt(i);
            hash = ((hash << 5) - hash) + char;
            hash = hash & hash;
        }
        return hash;
    },
    
    // Load canary polyfills
    loadCanaryPolyfills: function() {
        var version = this.version + '-canary';
        
        return Promise.all([
            this.loadVersionedPolyfill('promise', version),
            this.loadVersionedPolyfill('fetch', version)
        ]).then(function() {
            console.log('Canary polyfills loaded');
            this.trackEvent('canary_polyfills_loaded');
        }.bind(this));
    },
    
    // Load stable polyfills
    loadStablePolyfills: function() {
        return Promise.all([
            this.loadVersionedPolyfill('promise', this.version),
            this.loadVersionedPolyfill('fetch', this.version)
        ]).then(function() {
            console.log('Stable polyfills loaded');
            this.trackEvent('stable_polyfills_loaded');
        }.bind(this));
    },
    
    // Load versioned polyfill
    loadVersionedPolyfill: function(name, version) {
        var url = '/polyfills/' + name + '.' + version + '.js';
        
        return new Promise(function(resolve, reject) {
            var script = document.createElement('script');
            script.src = url;
            script.async = true;
            
            script.onload = function() {
                console.log('Loaded:', name, 'v' + version);
                resolve();
            };
            
            script.onerror = function() {
                console.error('Failed to load:', name, 'v' + version);
                // Fallback to stable version
                if (version.includes('canary')) {
                    console.log('Falling back to stable version');
                    PolyfillDeployment.loadVersionedPolyfill(name, PolyfillDeployment.version)
                        .then(resolve)
                        .catch(reject);
                } else {
                    reject(new Error('Failed to load polyfill: ' + name));
                }
            };
            
            document.head.appendChild(script);
        });
    },
    
    // Track deployment metrics
    trackDeploymentMetrics: function() {
        var metrics = {
            version: this.version,
            isCanary: this.isCanaryUser(),
            browser: navigator.userAgent,
            timestamp: Date.now()
        };
        
        // Send to monitoring service
        this.trackEvent('deployment_metrics', metrics);
    },
    
    // Track event
    trackEvent: function(eventName, data) {
        if (typeof gtag !== 'undefined') {
            gtag('event', eventName, data);
        }
    }
};

// CI/CD deployment script (Node.js)
// deploy-polyfills.js
const fs = require('fs');
const path = require('path');

class PolyfillDeployer {
    constructor(config) {
        this.config = config;
        this.version = require('./package.json').version;
    }
    
    async deploy() {
        console.log('Deploying polyfills version:', this.version);
        
        // 1. Build polyfills
        await this.buildPolyfills();
        
        // 2. Run tests
        await this.runTests();
        
        // 3. Create versioned files
        await this.createVersionedFiles();
        
        // 4. Deploy to CDN
        await this.deployToCDN();
        
        // 5. Enable canary release
        await this.enableCanary();
        
        console.log('Deployment complete!');
    }
    
    async buildPolyfills() {
        console.log('Building polyfills...');
        // Run webpack/rollup build
    }
    
    async runTests() {
        console.log('Running tests...');
        // Run test suite
    }
    
    async createVersionedFiles() {
        console.log('Creating versioned files...');
        
        const files = ['promise.js', 'fetch.js', 'polyfills.js'];
        
        files.forEach(file => {
            const source = path.join('dist', file);
            const dest = path.join('dist', file.replace('.js', `.${this.version}.js`));
            fs.copyFileSync(source, dest);
            console.log('Created:', dest);
        });
    }
    
    async deployToCDN() {
        console.log('Deploying to CDN...');
        // Upload to S3/CloudFront/etc
    }
    
    async enableCanary() {
        console.log('Enabling canary release (10%)...');
        // Update feature flag or config
    }
}

// Usage
// node deploy-polyfills.js
const deployer = new PolyfillDeployer({
    cdn: 'https://cdn.example.com',
    canaryPercentage: 10
});

deployer.deploy();

// ab-testing.js
var PolyfillABTest = {
    // Test configuration
    tests: {
        'polyfill-loading-strategy': {
            variants: ['control', 'minimal', 'lazy', 'differential'],
            distribution: [25, 25, 25, 25], // Equal distribution
            startDate: new Date('2025-01-01'),
            endDate: new Date('2025-01-31')
        }
    },
    
    // Initialize A/B test
    init: function(testName) {
        var test = this.tests[testName];
        if (!test) {
            console.error('Test not found:', testName);
            return;
        }
        
        // Check if test is active
        var now = new Date();
        if (now < test.startDate || now > test.endDate) {
            console.log('Test not active, using control');
            return this.loadVariant(testName, 'control');
        }
        
        // Get or assign user to variant
        var variant = this.getUserVariant(testName, test);
        console.log('User assigned to variant:', variant);
        
        // Load appropriate polyfills
        return this.loadVariant(testName, variant);
    },
    
    // Get user's variant assignment
    getUserVariant: function(testName, test) {
        var storageKey = 'ab_test_' + testName;
        var assigned = localStorage.getItem(storageKey);
        
        if (assigned && test.variants.includes(assigned)) {
            return assigned;
        }
        
        // Assign variant based on distribution
        var random = Math.random() * 100;
        var cumulative = 0;
        
        for (var i = 0; i < test.variants.length; i++) {
            cumulative += test.distribution[i];
            if (random < cumulative) {
                assigned = test.variants[i];
                break;
            }
        }
        
        localStorage.setItem(storageKey, assigned);
        return assigned;
    },
    
    // Load polyfills for variant
    loadVariant: function(testName, variant) {
        var strategies = {
            'control': this.loadControlPolyfills.bind(this),
            'minimal': this.loadMinimalPolyfills.bind(this),
            'lazy': this.loadLazyPolyfills.bind(this),
            'differential': this.loadDifferentialPolyfills.bind(this)
        };
        
        var startTime = performance.now();
        
        return strategies[variant]().then(function() {
            var loadTime = performance.now() - startTime;
            
            // Track variant metrics
            this.trackVariantMetrics(testName, variant, {
                loadTime: loadTime,
                timestamp: Date.now()
            });
            
            return variant;
        }.bind(this));
    },
    
    // Load all polyfills (control)
    loadControlPolyfills: function() {
        return Promise.all([
            import('core-js/stable'),
            import('regenerator-runtime/runtime'),
            import('whatwg-fetch'),
            import('intersection-observer')
        ]);
    },
    
    // Load minimal polyfills
    loadMinimalPolyfills: function() {
        var polyfills = [];
        
        if (!window.Promise) {
            polyfills.push(import('es6-promise/auto'));
        }
        
        if (!window.fetch) {
            polyfills.push(import('whatwg-fetch'));
        }
        
        return Promise.all(polyfills);
    },
    
    // Load lazy polyfills
    loadLazyPolyfills: function() {
        // Load critical polyfills immediately
        var critical = this.loadMinimalPolyfills();
        
        // Lazy load others during idle time
        if ('requestIdleCallback' in window) {
            requestIdleCallback(function() {
                if (!window.IntersectionObserver) {
                    import('intersection-observer');
                }
            });
        }
        
        return critical;
    },
    
    // Load differential polyfills
    loadDifferentialPolyfills: function() {
        var isModern = this.detectModernBrowser();
        
        if (isModern) {
            // Modern browsers: minimal polyfills
            return this.loadMinimalPolyfills();
        } else {
            // Legacy browsers: full polyfills
            return this.loadControlPolyfills();
        }
    },
    
    // Detect modern browser
    detectModernBrowser: function() {
        return (
            'Promise' in window &&
            'fetch' in window &&
            'assign' in Object &&
            'from' in Array
        );
    },
    
    // Track variant metrics
    trackVariantMetrics: function(testName, variant, metrics) {
        var data = {
            test: testName,
            variant: variant,
            ...metrics,
            userAgent: navigator.userAgent,
            viewport: window.innerWidth + 'x' + window.innerHeight
        };
        
        // Send to analytics
        if (typeof gtag !== 'undefined') {
            gtag('event', 'ab_test_variant', data);
        }
        
        // Track in Datadog
        if (window.DD_RUM) {
            window.DD_RUM.addAction('ab_test_variant', data);
        }
        
        // Track performance metrics
        this.trackPerformanceMetrics(testName, variant);
    },
    
    // Track performance metrics for variant
    trackPerformanceMetrics: function(testName, variant) {
        // Wait for page load
        window.addEventListener('load', function() {
            setTimeout(function() {
                var metrics = {
                    test: testName,
                    variant: variant,
                    fcp: this.getFCP(),
                    lcp: this.getLCP(),
                    tti: this.getTTI(),
                    bundleSize: this.getBundleSize()
                };
                
                console.log('A/B Test Metrics:', metrics);
                
                // Send to analytics
                if (typeof gtag !== 'undefined') {
                    gtag('event', 'ab_test_metrics', metrics);
                }
            }.bind(this), 1000);
        }.bind(this));
    },
    
    getFCP: function() {
        var fcp = performance.getEntriesByName('first-contentful-paint')[0];
        return fcp ? fcp.startTime : null;
    },
    
    getLCP: function() {
        // Simplified LCP measurement
        var lcpEntries = performance.getEntriesByType('largest-contentful-paint');
        return lcpEntries.length > 0 ? lcpEntries[lcpEntries.length - 1].startTime : null;
    },
    
    getTTI: function() {
        // Simplified TTI measurement
        return performance.timing.domInteractive - performance.timing.navigationStart;
    },
    
    getBundleSize: function() {
        // Calculate total bundle size
        var resources = performance.getEntriesByType('resource');
        var totalSize = 0;
        
        resources.forEach(function(resource) {
            if (resource.name.includes('.js')) {
                totalSize += resource.transferSize || 0;
            }
        });
        
        return totalSize;
    }
};

// Initialize A/B test
PolyfillABTest.init('polyfill-loading-strategy').then(function(variant) {
    console.log('A/B test initialized with variant:', variant);
    
    // Initialize app
    initApp();
});