# Design Document: Website Cloning Platform

## Overview

The Website Cloning Platform is a comprehensive SaaS solution that combines advanced web scraping, intelligent crawling, and AI-powered code generation to recreate websites with near 100% visual accuracy. The platform features a microservices architecture built on Node.js with Puppeteer for browser automation, Monaco Editor for the online IDE, PostgreSQL for data management, and S3 for asset storage.

## Architecture

### High-Level System Architecture

```mermaid
graph TB
    subgraph "Frontend Layer"
        UI[React Dashboard]
        IDE[Monaco Editor IDE]
        Preview[Live Preview]
    end
    
    subgraph "API Gateway"
        Gateway[Express.js Gateway]
        Auth[JWT Authentication]
        RateLimit[Rate Limiting]
    end
    
    subgraph "Core Services"
        Crawler[Intelligent Crawler]
        Scraper[Visual Scraper]
        Extractor[Asset Extractor]
        Generator[Code Generator]
        Detector[Component Detector]
    end
    
    subgraph "Processing Engine"
        Queue[Bull Queue]
        Workers[Worker Processes]
        Browser[Puppeteer Pool]
    end
    
    subgraph "Data Layer"
        DB[(PostgreSQL)]
        Cache[(Redis)]
        Storage[(S3 Storage)]
        CDN[CloudFront CDN]
    end
    
    UI --> Gateway
    IDE --> Gateway
    Preview --> Gateway
    
    Gateway --> Crawler
    Gateway --> Scraper
    Gateway --> Generator
    
    Crawler --> Queue
    Scraper --> Queue
    Extractor --> Queue
    
    Queue --> Workers
    Workers --> Browser
    Workers --> DB
    Workers --> Storage
    
    Storage --> CDN
```

### Microservices Architecture

The platform consists of the following core microservices:

1. **API Gateway Service** - Request routing, authentication, rate limiting
2. **Crawler Service** - Website discovery and mapping
3. **Scraper Service** - Visual element extraction
4. **Asset Service** - File download and optimization
5. **Generator Service** - Code generation and optimization
6. **Component Service** - UI component detection and management
7. **Project Service** - Project management and collaboration
8. **IDE Service** - Online development environment
9. **Billing Service** - Usage tracking and payment processing

## Components and Interfaces

### 1. Intelligent Crawler Component

**Purpose:** Discovers and maps website structure using breadth-first search

**Key Classes:**
```typescript
interface CrawlerConfig {
  maxDepth: number;
  maxPages: number;
  respectRobots: boolean;
  rateLimit: number;
  userAgent: string;
}

interface PageInfo {
  url: string;
  title: string;
  depth: number;
  links: string[];
  assets: AssetInfo[];
  metadata: PageMetadata;
}

class IntelligentCrawler {
  async crawlWebsite(startUrl: string, config: CrawlerConfig): Promise<SiteMap>;
  async discoverLinks(page: Page): Promise<string[]>;
  async extractPageInfo(url: string): Promise<PageInfo>;
  async respectRateLimit(): Promise<void>;
}
```

**Algorithms:**
- **BFS Link Discovery:** Systematically explores website hierarchy
- **Duplicate Detection:** Uses URL normalization and content hashing
- **Rate Limiting:** Implements exponential backoff and concurrent request limiting

### 2. Visual Scraper Component

**Purpose:** Captures visual elements and layout information with high fidelity

**Key Classes:**
```typescript
interface ScreenshotConfig {
  viewports: Viewport[];
  fullPage: boolean;
  quality: number;
  format: 'png' | 'jpeg' | 'webp';
}

interface VisualData {
  screenshots: Screenshot[];
  computedStyles: ComputedStyleMap;
  layoutMetrics: LayoutMetrics;
  animations: AnimationInfo[];
}

class VisualScraper {
  async captureVisualData(url: string, config: ScreenshotConfig): Promise<VisualData>;
  async executeJavaScript(page: Page): Promise<void>;
  async captureResponsiveBreakpoints(page: Page): Promise<ResponsiveData>;
  async extractAnimations(page: Page): Promise<AnimationInfo[]>;
}
```

### 3. Asset Extractor Component

**Purpose:** Downloads, processes, and optimizes website assets

**Key Classes:**
```typescript
interface AssetInfo {
  url: string;
  type: 'image' | 'css' | 'js' | 'font' | 'media';
  size: number;
  hash: string;
  dependencies: string[];
}

class AssetExtractor {
  async extractAllAssets(pageInfo: PageInfo): Promise<AssetInfo[]>;
  async downloadAsset(url: string): Promise<Buffer>;
  async optimizeAsset(asset: AssetInfo, buffer: Buffer): Promise<Buffer>;
  async resolveDependencies(cssContent: string): Promise<string[]>;
}
```

### 4. Code Generator Component

**Purpose:** Generates clean, semantic, and maintainable code

**Key Classes:**
```typescript
interface GenerationConfig {
  framework: 'vanilla' | 'react' | 'vue' | 'angular';
  cssFramework: 'none' | 'tailwind' | 'bootstrap';
  optimization: 'none' | 'basic' | 'aggressive';
  accessibility: boolean;
}

interface GeneratedCode {
  html: string;
  css: string;
  javascript: string;
  components: ComponentDefinition[];
  assets: AssetMapping[];
}

class CodeGenerator {
  async generateFromVisualData(visualData: VisualData, config: GenerationConfig): Promise<GeneratedCode>;
  async optimizeCSS(css: string): Promise<string>;
  async generateResponsiveCSS(breakpoints: ResponsiveData): Promise<string>;
  async createComponentStructure(elements: Element[]): Promise<ComponentDefinition[]>;
}
```

### 5. Component Detector Component

**Purpose:** Identifies and extracts reusable UI components using AI

**Key Classes:**
```typescript
interface ComponentPattern {
  type: 'navigation' | 'header' | 'footer' | 'card' | 'form' | 'button';
  selector: string;
  frequency: number;
  variations: ComponentVariation[];
}

class ComponentDetector {
  async detectComponents(dom: Document): Promise<ComponentPattern[]>;
  async analyzePatterns(elements: Element[]): Promise<ComponentPattern>;
  async extractComponentCode(pattern: ComponentPattern): Promise<ComponentDefinition>;
  async generateComponentLibrary(patterns: ComponentPattern[]): Promise<ComponentLibrary>;
}
```

## Data Models

### Core Data Structures

```typescript
// Project Management
interface CloneProject {
  id: string;
  name: string;
  sourceUrl: string;
  status: 'crawling' | 'processing' | 'generating' | 'completed' | 'failed';
  createdAt: Date;
  updatedAt: Date;
  userId: string;
  settings: ProjectSettings;
  metrics: ProjectMetrics;
}

// Site Structure
interface SiteMap {
  rootUrl: string;
  pages: PageInfo[];
  assets: AssetInfo[];
  structure: SiteStructure;
  metadata: SiteMetadata;
}

// Component System
interface ComponentDefinition {
  id: string;
  name: string;
  type: ComponentType;
  html: string;
  css: string;
  javascript?: string;
  props: ComponentProp[];
  instances: ComponentInstance[];
}

// User Management
interface User {
  id: string;
  email: string;
  subscription: SubscriptionTier;
  usage: UsageMetrics;
  projects: string[];
  settings: UserSettings;
}
```

### Database Schema

**PostgreSQL Tables:**
- `users` - User accounts and authentication
- `projects` - Clone project metadata
- `pages` - Individual page information
- `components` - Reusable component definitions
- `assets` - Asset metadata and references
- `usage_logs` - Billing and analytics data
- `collaborations` - Project sharing and permissions

## Correctness Properties

*A property is a characteristic or behavior that should hold true across all valid executions of a system-essentially, a formal statement about what the system should do. Properties serve as the bridge between human-readable specifications and machine-verifiable correctness guarantees.*

### Crawling and Discovery Properties

**Property 1: BFS Page Discovery**
*For any* website structure, the Intelligent_Crawler should discover all reachable pages in breadth-first order, ensuring systematic exploration without missing linked content.
**Validates: Requirements 1.1**

**Property 2: Rate Limiting Compliance**
*For any* crawling session, the system should respect configured rate limits and robots.txt directives, preventing server overload while maintaining crawling effectiveness.
**Validates: Requirements 1.2**

**Property 3: JavaScript Content Capture**
*For any* page with dynamic content, the Multi_Layer_Processor should capture all JavaScript-generated elements in the final scraped state.
**Validates: Requirements 1.3**

**Property 4: Complete Sitemap Generation**
*For any* crawled website, the generated sitemap should include all discovered pages with correct hierarchical relationships and no missing links.
**Validates: Requirements 1.5**

### Visual Scraping Properties

**Property 5: Multi-Viewport Screenshot Capture**
*For any* webpage and viewport configuration, the Visual_Scraper should generate screenshots for all specified viewport sizes without missing any breakpoint.
**Validates: Requirements 2.1**

**Property 6: Complete Asset Extraction**
*For any* webpage, the Asset_Extractor should successfully download all referenced assets (images, CSS, JS, fonts, media) without missing dependencies.
**Validates: Requirements 2.2**

**Property 7: CSS Dependency Resolution**
*For any* CSS file with @import statements, the Asset_Extractor should resolve and download all nested dependencies recursively.
**Validates: Requirements 2.3**

**Property 8: Responsive Breakpoint Capture**
*For any* responsive webpage, the Visual_Scraper should capture all media query breakpoints and their corresponding visual states.
**Validates: Requirements 2.4**

**Property 9: Quality-Preserving Asset Optimization**
*For any* asset optimization process, the output should maintain visual quality above acceptable thresholds while reducing file size.
**Validates: Requirements 2.5**

### Code Generation Properties

**Property 10: Semantic HTML Generation**
*For any* visual data input, the Code_Generator should produce valid, semantic HTML with proper accessibility attributes and document structure.
**Validates: Requirements 3.1**

**Property 11: CSS Modularization and Optimization**
*For any* CSS processing task, the Code_Generator should organize styles into logical modules and remove all unused rules while preserving visual appearance.
**Validates: Requirements 3.2**

**Property 12: JavaScript Module Refactoring**
*For any* page with inline JavaScript, the Code_Generator should extract and organize scripts into maintainable modules without breaking functionality.
**Validates: Requirements 3.3**

**Property 13: Responsive CSS Generation**
*For any* multi-viewport visual data, the generated CSS should work correctly across all captured device sizes and breakpoints.
**Validates: Requirements 3.4**

**Property 14: Code Documentation Generation**
*For any* complex layout structure, the Code_Generator should include explanatory comments that accurately describe the layout logic.
**Validates: Requirements 3.5**

### Component Detection Properties

**Property 15: UI Pattern Recognition**
*For any* page with repeated elements, the Component_Detector should identify all instances of the same UI pattern and mark them as reusable components.
**Validates: Requirements 4.1**

**Property 16: Component Type Classification**
*For any* detected component, the system should correctly classify it as navigation, header, footer, card, form, or other appropriate type based on its structure and context.
**Validates: Requirements 4.2**

**Property 17: Component Parameterization**
*For any* generated component, the code should accept parameters that allow customization of variable content while maintaining structure.
**Validates: Requirements 4.3**

**Property 18: Component Library Management**
*For any* project, all detected components should be properly stored, organized, and accessible through the component library interface.
**Validates: Requirements 4.4**

**Property 19: Component Instance Synchronization**
*For any* component modification, all instances of that component across the project should be updated to reflect the changes.
**Validates: Requirements 4.5**

### IDE and Collaboration Properties

**Property 20: Real-Time Preview Updates**
*For any* code modification in the IDE, the preview should update immediately to reflect the changes without manual refresh.
**Validates: Requirements 5.2**

**Property 21: Version Control Integrity**
*For any* sequence of changes, the version control system should maintain complete history and allow rollback to any previous state without data loss.
**Validates: Requirements 5.3**

**Property 22: Collaborative Editing Conflict Resolution**
*For any* concurrent editing session, the system should resolve conflicts automatically or provide clear resolution options without losing any user's work.
**Validates: Requirements 5.5**

### Project Management Properties

**Property 23: Project Structure Organization**
*For any* new project, the system should create a proper folder structure with organized asset management and clear file hierarchy.
**Validates: Requirements 6.1**

**Property 24: Project Sharing Access Control**
*For any* shared project, only authorized users should have access according to their assigned permissions level.
**Validates: Requirements 6.3**

**Property 25: Deployment-Ready Export Generation**
*For any* project export, the generated package should contain all necessary files and configurations for immediate deployment.
**Validates: Requirements 6.4**

**Property 26: Analytics Data Collection**
*For any* project activity, the system should collect and store accurate metrics including clone accuracy and performance data.
**Validates: Requirements 6.5**

### Performance and Scalability Properties

**Property 27: Parallel Processing Efficiency**
*For any* large website processing task, the system should utilize multiple concurrent workers to reduce total processing time.
**Validates: Requirements 7.1**

**Property 28: CDN Asset Distribution**
*For any* stored asset, the system should make it available through CDN endpoints for optimized global access.
**Validates: Requirements 7.2**

**Property 29: Intelligent Caching Behavior**
*For any* identical content request, the system should serve from cache rather than re-processing, reducing redundant work.
**Validates: Requirements 7.3**

**Property 30: Auto-Scaling Resource Management**
*For any* load variation, the system should automatically adjust processing resources to maintain performance while optimizing costs.
**Validates: Requirements 7.4**

**Property 31: Performance Time Constraints**
*For any* website under 100 pages, the complete cloning process should finish within 5 minutes under normal system load.
**Validates: Requirements 7.5**

### Data Storage Properties

**Property 32: PostgreSQL Data Storage**
*For any* structured project data, the system should store it in PostgreSQL with proper schema validation and referential integrity.
**Validates: Requirements 8.1**

**Property 33: S3 Asset Organization**
*For any* asset file, the system should store it in S3-compatible storage with logical organization and proper naming conventions.
**Validates: Requirements 8.2**

**Property 34: Backup and Recovery Functionality**
*For any* data backup operation, the system should create complete backups that enable point-in-time recovery without data loss.
**Validates: Requirements 8.3**

**Property 35: Data Encryption Compliance**
*For any* sensitive user data, the system should encrypt it using industry-standard methods and comply with data protection regulations.
**Validates: Requirements 8.4**

**Property 36: Data Export Portability**
*For any* user data export request, the system should generate portable formats that allow users to migrate their data to other platforms.
**Validates: Requirements 8.5**

### Security Properties

**Property 37: Multi-Factor Authentication Enforcement**
*For any* user account, the system should require and validate multi-factor authentication before granting access to sensitive operations.
**Validates: Requirements 9.1**

**Property 38: Role-Based Permission Enforcement**
*For any* project access attempt, the system should verify user permissions and only allow operations consistent with their assigned role.
**Validates: Requirements 9.2**

**Property 39: API Rate Limiting Protection**
*For any* API endpoint, the system should enforce rate limits to prevent abuse while allowing legitimate usage patterns.
**Validates: Requirements 9.3**

**Property 40: Legal Compliance Warning System**
*For any* website cloning operation, the system should display appropriate copyright and legal compliance warnings to users.
**Validates: Requirements 9.4**

**Property 41: Comprehensive Audit Logging**
*For any* user action, the system should create detailed audit logs that enable security monitoring and compliance reporting.
**Validates: Requirements 9.5**

### Billing and Monetization Properties

**Property 42: Usage-Based Billing Accuracy**
*For any* user activity, the system should accurately track usage metrics and bill according to the appropriate subscription tier limits.
**Validates: Requirements 10.1**

**Property 43: Comprehensive Usage Monitoring**
*For any* billable activity, the system should monitor and record pages cloned, storage used, and API calls made with precise accuracy.
**Validates: Requirements 10.2**

**Property 44: Detailed Billing Report Generation**
*For any* billing period, the system should generate reports containing accurate usage data and billing calculations.
**Validates: Requirements 10.3**

**Property 45: Multi-Provider Payment Processing**
*For any* payment transaction, the system should successfully process payments through multiple integrated payment providers with proper error handling.
**Validates: Requirements 10.4**

**Property 46: Free Tier Limitation Enforcement**
*For any* free tier user, the system should enforce appropriate usage limitations while providing clear upgrade paths.
**Validates: Requirements 10.5**

## Error Handling

### Error Categories and Strategies

**1. Network and Connectivity Errors**
- Implement exponential backoff for failed requests
- Provide fallback mechanisms for CDN failures
- Handle timeout scenarios gracefully with user feedback

**2. Processing and Resource Errors**
- Implement circuit breakers for overloaded services
- Provide graceful degradation when resources are limited
- Queue failed jobs for retry with appropriate delays

**3. Data Validation and Integrity Errors**
- Validate all input data at API boundaries
- Implement database constraints and transaction rollbacks
- Provide clear error messages for validation failures

**4. Authentication and Authorization Errors**
- Implement secure session management with proper timeouts
- Provide clear feedback for permission denied scenarios
- Log security-related errors for monitoring

## Testing Strategy

### Dual Testing Approach

The platform requires both unit testing and property-based testing for comprehensive coverage:

**Unit Tests:**
- Verify specific examples and edge cases
- Test integration points between microservices
- Validate error conditions and boundary cases
- Focus on concrete scenarios and known failure modes

**Property-Based Tests:**
- Verify universal properties across all inputs
- Test system behavior with randomized data
- Validate correctness properties from the design document
- Ensure comprehensive input coverage through randomization

### Property-Based Testing Configuration

**Framework:** fast-check (JavaScript/TypeScript property-based testing library)
**Configuration:**
- Minimum 100 iterations per property test
- Each test tagged with: **Feature: website-cloning-platform, Property {number}: {property_text}**
- Custom generators for domain-specific data (URLs, HTML structures, CSS rules)
- Shrinking enabled to find minimal failing examples

**Example Test Structure:**
```typescript
// Feature: website-cloning-platform, Property 1: BFS Page Discovery
fc.assert(fc.property(
  websiteStructureGenerator(),
  (website) => {
    const crawler = new IntelligentCrawler();
    const result = crawler.crawlWebsite(website.rootUrl, defaultConfig);
    return verifyBFSOrder(result.pages) && 
           verifyAllPagesFound(website, result.pages);
  }
), { numRuns: 100 });
```

### Testing Infrastructure

**Test Environment:**
- Dockerized test environment with isolated databases
- Mock external services (S3, payment providers, CDNs)
- Automated test data generation and cleanup
- Performance testing with realistic load patterns

**Continuous Integration:**
- Automated test execution on all pull requests
- Property-based test results tracked and analyzed
- Performance regression detection
- Security vulnerability scanning