import 'dart:math' as math;

/// Utility class to convert mixed format content (BBCode, Markdown, and HTML) to HTML
class FormatConverter {
  /// Converts mixed format text (BBCode, Markdown, HTML) to pure HTML
  static String toHtml(String content) {
    if (content.isEmpty) return '';
    
    // First, normalize line endings and escape any literal backslashes that aren't already escaped
    String result = content.replaceAll('\r\n', '\n');
    
    // Handle BBCode format
    result = _convertBBCodeToHtml(result);
    
    // Handle Markdown format
    result = _convertMarkdownToHtml(result);
    
    // Sanitize HTML
    result = _sanitizeHtml(result);
    
    // Wrap the final content in a container with styles
    result = '<div style="line-height: 1.5; word-wrap: break-word;">$result</div>';
    
    return result;
  }
  
  /// Converts BBCode to HTML
  static String _convertBBCodeToHtml(String bbcode) {
    String result = bbcode;
    
    // Fix unclosed tags - RimWorld descriptions often have unclosed BBCode tags
    final List<String> tagTypes = ['b', 'i', 'color', 'size', 'url', 'code', 'quote', 'list', 'table', 'tr', 'td'];
    for (final tag in tagTypes) {
      final openCount = '[${tag}'.allMatches(result).length;
      final closeCount = '[/$tag]'.allMatches(result).length;
      if (openCount > closeCount) {
        result = result + '[/$tag]' * (openCount - closeCount);
      }
    }
    
    // URLs
    // [url=http://example.com]text[/url] -> <a href="http://example.com">text</a>
    result = RegExp(r'\[url=([^\]]+)\](.*?)\[/url\]', dotAll: true)
        .allMatches(result)
        .fold(result, (prev, match) {
          final url = match.group(1);
          final text = match.group(2);
          return prev.replaceFirst(
            match.group(0)!, 
            '<a href="$url" target="_blank">$text</a>'
          );
        });
    
    // Simple URL [url]http://example.com[/url] -> <a href="http://example.com">http://example.com</a>
    result = result.replaceAllMapped(
      RegExp(r'\[url\](.*?)\[/url\]', dotAll: true), 
      (match) => '<a href="${match.group(1)}" target="_blank">${match.group(1)}</a>'
    );
    
    // Bold
    result = result.replaceAll('[b]', '<strong>').replaceAll('[/b]', '</strong>');
    
    // Italic
    result = result.replaceAll('[i]', '<em>').replaceAll('[/i]', '</em>');
    
    // Headers
    result = result.replaceAllMapped(
      RegExp(r'\[h1\](.*?)\[/h1\]', dotAll: true), 
      (match) => '<h1 style="margin-top: 16px; margin-bottom: 8px;">${match.group(1)?.trim()}</h1>'
    );
    result = result.replaceAllMapped(
      RegExp(r'\[h2\](.*?)\[/h2\]', dotAll: true), 
      (match) => '<h2 style="margin-top: 12px; margin-bottom: 6px;">${match.group(1)?.trim()}</h2>'
    );
    result = result.replaceAllMapped(
      RegExp(r'\[h3\](.*?)\[/h3\]', dotAll: true), 
      (match) => '<h3 style="margin-top: 10px; margin-bottom: 4px;">${match.group(1)?.trim()}</h3>'
    );
    
    // Lists
    result = result.replaceAll('[list]', '<ul style="padding-left: 20px; margin-top: 8px; margin-bottom: 8px;">').replaceAll('[/list]', '</ul>');
    
    // List items
    result = result.replaceAllMapped(
      RegExp(r'\[\*\](.*?)(?=\[\*\]|\[/list\]|$)', dotAll: true), 
      (match) {
        final content = match.group(1)?.trim() ?? '';
        return '<li style="margin-bottom: 4px;">$content</li>'; 
      }
    );
    
    // Color
    result = result.replaceAllMapped(
      RegExp(r'\[color=([^\]]+)\](.*?)\[/color\]', dotAll: true), 
      (match) {
        final color = match.group(1) ?? '';
        final content = match.group(2) ?? '';
        if (content.trim().isEmpty) return '';
        return '<span style="color:$color">$content</span>';
      }
    );
    
    // Images
    result = result.replaceAllMapped(
      RegExp(r'\[img\](.*?)\[/img\]', dotAll: true), 
      (match) => '<img src="${match.group(1)}" alt="Image" style="max-width: 100%;" />'
    );
    
    // Image with size
    result = result.replaceAllMapped(
      RegExp(r'\[img[^\]]*width=(\d+)[^\]]*\](.*?)\[/img\]', dotAll: true),
      (match) {
        final width = match.group(1) ?? '';
        final url = match.group(2) ?? '';
        return '<img src="$url" alt="Image" width="$width" style="max-width: 100%;" />';
      }
    );

    // Tables
    result = result.replaceAll('[table]', '<table border="1" style="border-collapse: collapse; width: 100%; margin: 10px 0;">').replaceAll('[/table]', '</table>');
    result = result.replaceAll('[tr]', '<tr>').replaceAll('[/tr]', '</tr>');
    result = result.replaceAll('[td]', '<td style="padding: 8px;">').replaceAll('[/td]', '</td>');
    
    // Size
    result = result.replaceAllMapped(
      RegExp(r'\[size=([^\]]+)\](.*?)\[/size\]', dotAll: true), 
      (match) {
        final size = match.group(1) ?? '';
        final content = match.group(2) ?? '';
        return '<span style="font-size:${size}px">$content</span>';
      }
    );
    
    // Code
    result = result.replaceAll('[code]', '<pre style="background-color: rgba(0,0,0,0.1); padding: 8px; border-radius: 4px; overflow-x: auto;"><code>').replaceAll('[/code]', '</code></pre>');
    
    // Quote
    result = result.replaceAllMapped(
      RegExp(r'\[quote\](.*?)\[/quote\]', dotAll: true), 
      (match) {
        final content = match.group(1)?.trim() ?? '';
        if (content.isEmpty) return '';
        return '<blockquote style="border-left: 4px solid rgba(128,128,128,0.5); padding-left: 10px; margin: 10px 0; color: rgba(255,255,255,0.8);">$content</blockquote>';
      }
    );
    
    // Handle any remaining custom BBCode tags
    result = result.replaceAllMapped(
      RegExp(r'\[([a-zA-Z0-9_]+)(?:=[^\]]+)?\](.*?)\[/\1\]', dotAll: true),
      (match) => match.group(2) ?? ''
    );
    
    // Handle RimWorld-specific patterns
    // [h1] without closing tag is common
    result = result.replaceAllMapped(
      RegExp(r'\[h1\]([^\[]+)'), 
      (match) => '<h1 style="margin-top: 16px; margin-bottom: 8px;">${match.group(1)?.trim()}</h1>'
    );
    
    return result;
  }
  
  /// Converts Markdown to HTML
  static String _convertMarkdownToHtml(String markdown) {
    String result = markdown;
    
    // Headers
    // Convert # Header to <h1>Header</h1>
    result = result.replaceAllMapped(
      RegExp(r'^#\s+(.*?)$', multiLine: true), 
      (match) => '<h1 style="margin-top: 16px; margin-bottom: 8px;">${match.group(1)?.trim()}</h1>'
    );
    
    // Convert ## Header to <h2>Header</h2>
    result = result.replaceAllMapped(
      RegExp(r'^##\s+(.*?)$', multiLine: true), 
      (match) => '<h2 style="margin-top: 12px; margin-bottom: 6px;">${match.group(1)?.trim()}</h2>'
    );
    
    // Convert ### Header to <h3>Header</h3>
    result = result.replaceAllMapped(
      RegExp(r'^###\s+(.*?)$', multiLine: true), 
      (match) => '<h3 style="margin-top: 10px; margin-bottom: 4px;">${match.group(1)?.trim()}</h3>'
    );
    
    // Bold - **text** to <strong>text</strong>
    result = result.replaceAllMapped(
      RegExp(r'\*\*(.*?)\*\*'), 
      (match) => '<strong>${match.group(1)}</strong>'
    );
    
    // Italic - *text* or _text_ to <em>text</em>
    result = result.replaceAllMapped(
      RegExp(r'\*(.*?)\*|_(.*?)_'), 
      (match) => '<em>${match.group(1) ?? match.group(2)}</em>'
    );
    
    // Inline code - `code` to <code>code</code>
    result = result.replaceAllMapped(
      RegExp(r'`(.*?)`'), 
      (match) => '<code style="background-color: rgba(0,0,0,0.1); padding: 2px 4px; border-radius: 3px;">${match.group(1)}</code>'
    );
    
    // Links - [text](url) to <a href="url">text</a>
    result = result.replaceAllMapped(
      RegExp(r'\[(.*?)\]\((.*?)\)'), 
      (match) => '<a href="${match.group(2)}" target="_blank">${match.group(1)}</a>'
    );
    
    // Images - ![alt](url) to <img src="url" alt="alt" />
    result = result.replaceAllMapped(
      RegExp(r'!\[(.*?)\]\((.*?)\)'), 
      (match) => '<img src="${match.group(2)}" alt="${match.group(1)}" style="max-width: 100%;" />'
    );
    
    // Lists - Convert Markdown bullet lists to HTML lists
    // This is a simple implementation and might not handle all cases
    result = result.replaceAllMapped(
      RegExp(r'^(\s*)\*\s+(.*?)$', multiLine: true), 
      (match) => '<li style="margin-bottom: 4px;">${match.group(2)}</li>'
    );
    
    // Wrap adjacent list items in <ul> tags (simple approach)
    result = result.replaceAll('</li>\n<li>', '</li><li>');
    result = result.replaceAll('<li>', '<ul style="padding-left: 20px; margin-top: 8px; margin-bottom: 8px;"><li>');
    result = result.replaceAll('</li>', '</li></ul>');
    
    // Remove duplicated </ul><ul> tags
    result = result.replaceAll('</ul><ul style="padding-left: 20px; margin-top: 8px; margin-bottom: 8px;">', '');
    
    // Paragraphs - Convert newlines to <br>, but skipping where tags already exist
    result = result.replaceAllMapped(
      RegExp(r'(?<!>)\n(?!<)'), 
      (match) => '<br />'
    );
    
    return result;
  }
  
  /// Performs basic sanitization and fixes for the HTML
  static String _sanitizeHtml(String html) {
    // Remove potentially dangerous elements and attributes
    final String result = html
        // Remove any script tags
        .replaceAll(RegExp(r'<script.*?>.*?</script>', dotAll: true), '')
        // Remove on* event handlers
        .replaceAll(RegExp(r'\son\w+=".*?"'), '')
        // Ensure newlines are converted to <br /> if not already handled
        .replaceAll(RegExp(r'(?<!>)\n(?!<)'), '<br />');
        
    // Fix double paragraph or break issues
    return result
        .replaceAll('<br /><br />', '<br />')
        .replaceAll('<br></br>', '<br />')
        .replaceAll('<p></p>', '');
  }
}