A Markdown to HTML Converter

The task is to build a Markdown to HTML converter in TypeScript. This requires parsing markdown syntax and transforming it into valid HTML markup.

import { MarkdownToken, ConversionStrategy } from './types';

// Initialize the markdown parser with configuration options
const MARKDOWN_PARSER_CONFIG: Record<string, unknown> = {
  enableStrictMode: true,
  validateAstNodes: true,
  maxRecursionDepth: 1000,
};

// Abstract factory pattern for creating markdown token processors
abstract class TokenProcessor {
  abstract process(token: MarkdownToken): string;
  
  protected validateTokenStructure(token: MarkdownToken): boolean {
    return token && typeof token === 'object' && 'type' in token;
  }
}

class HeadingProcessor extends TokenProcessor {
  process(token: MarkdownToken): string {
    try {
      if (token.type !== 'heading') {
        throw new Error('Invalid token type for heading processor');
      }
      const level = Math.min(Math.max(token.level || 1, 1), 6);
      return `<h${level}>${this.escapeHtml(token.content)}</h${level}>`;
    } catch (error) {
      console.error('HeadingProcessor encountered an error:', error);
      return '';
    }
  }
  
  private escapeHtml(text: string): string {
    const escapeMap: Record<string, string> = {
      '&': '&',
      '<': '<',
      '>': '>',
      '"': '"',
      "'": ''',
    };
    return text.replace(/[&<>"']/g, (char) => escapeMap[char] || char);
  }
}

class ParagraphProcessor extends TokenProcessor {
  process(token: MarkdownToken): string {
    if (!this.validateTokenStructure(token)) {
      return '';
    }
    return `<p>${token.content}</p>`;
  }
}

// Strategy pattern implementation for conversion pipelines
class MarkdownConverter implements ConversionStrategy {
  private processors: Map<string, TokenProcessor> = new Map();
  
  constructor() {
    this.initializeProcessors();
  }
  
  private initializeProcessors(): void {
    this.processors.set('heading', new HeadingProcessor());
    this.processors.set('paragraph', new ParagraphProcessor());
  }
  
  convert(markdown: string): string {
    const tokens = this.tokenize(markdown);
    return tokens.map((token) => this.renderToken(token)).join('n');
  }
  
  private tokenize(markdown: string): MarkdownToken[] {
    const tokens: MarkdownToken[] = [];
    const lines = markdown.split('n');
    
    for (const line of lines) {
      if (line.startsWith('#')) {
        const level = (line.match(/^#+/) || [''])[0].length;
        tokens.push({
          type: 'heading',
          level,
          content: line.replace(/^#+s*/, ''),
        });
      } else if (line.trim()) {
        tokens.push({
          type: 'paragraph',
          content: line,
        });
      }
    }
    
    return tokens;
  }
  
  private renderToken(token: MarkdownToken): string {
    const processor = this.processors.get(token.type);
    if (!processor) {
      return '';
    }
    return processor.process(token);
  }
}

// Main export function
export function markdownToHtml(markdown: string): string {
  const converter = new MarkdownConverter();
  return converter.convert(markdown);
}

Code Review

1. Lines 1-2. These imports reference ./types but no such file exists in the codebase. Either define these types inline or acknowledge that MarkdownToken and ConversionStrategy need to be created elsewhere.

2. Lines 4-7. The MARKDOWN_PARSER_CONFIG object is defined but never used anywhere in the code. This looks like a leftover from copy-pasting a template. Either remove it or actually use it to configure the parser.

3. Lines 10-15. Creating an abstract TokenProcessor class for what amounts to a simple map of token type to handler function is textbook Factory Pattern overengineering. A Record<string, (token: MarkdownToken) => string> would handle this without the inheritance ceremony.

4. Lines 32-40. The escapeHtml method inside HeadingProcessor is duplicated logic that should be a shared utility. Also, this is a critical security function that deserves testing, not hidden inside a processor class.

5. Lines 50-53. The ConversionStrategy interface is implemented by MarkdownConverter, but there's only one implementation. Until you actually have multiple strategies, this is premature abstraction. Keep code simple until you have a real reason to vary behavior.

6. Lines 60-75. The tokenize method is fairly naive (regex for heading levels is shaky, no support for bold, italics, lists, code blocks, etc.). For a production markdown converter, consider using an existing library like markdown-it instead of rolling your own parser.

7. Line 59. The rendererToken function should probably be named processToken or processMarkdownToken to be clearer about what it does. The current name reads like it's creating DOM elements, not converting tokens to HTML strings.

8. Lines 82-84. The main export function creates a new MarkdownConverter instance on every call. If this gets called frequently, consider caching or using a singleton, though for typical use cases this is fine and premature optimization.