import { ImportError } from '../shared/errors';

/**
 * Keep angle brackets inside quoted attributes inert for the bounded lexical
 * readers. This is not a sanitizer: values and entities remain unchanged apart
 * from those delimiters. Raw-text elements and comments are never interpreted
 * as nested tags. The original document remains untouched.
 */
export function protectHtmlAttributeMarkup(text: string, allowIncompleteFinalTag = false): string {
  const output: string[] = [];
  let copied = 0;
  let position = 0;
  while ((position = text.indexOf('<', position)) >= 0) {
    if (text.startsWith('<!--', position)) {
      const end = text.indexOf('-->', position + 4);
      position = end < 0 ? text.length : end + 3;
      continue;
    }
    const opening = /^<\/?([a-z][\w:-]*)(?=[\s/>])/i.exec(text.slice(position, position + 256));
    if (!opening) { position++; continue; }
    const start = position;
    const previousOutputLength = output.length;
    const previousCopied = copied;
    let quote = '';
    let expectingValue = false;
    let unquotedValue = false;
    let closed = false;
    for (position += opening[0].length; position < text.length; position++) {
      const character = text[position];
      if (quote) {
        if (character === quote) quote = '';
        else if (character === '<' || character === '>') {
          output.push(text.slice(copied, position), character === '<' ? '&lt;' : '&gt;');
          copied = position + 1;
        }
      } else if (character === '>') { position++; closed = true; break; }
      else if (unquotedValue) {
        if (/\s/.test(character)) unquotedValue = false;
      } else if (expectingValue) {
        if (/\s/.test(character)) continue;
        expectingValue = false;
        if (character === '"' || character === "'") quote = character;
        else unquotedValue = true;
      } else if (character === '=') expectingValue = true;
    }
    // Bounded text fragments may end within a tag even though the complete
    // document was valid. Drop only that unfinished tag, never expose its tail.
    if (!closed && allowIncompleteFinalTag) return output.slice(0, previousOutputLength).join('') + text.slice(previousCopied, start);
    if (!closed && quote) throw new ImportError('HTML enthält ein nicht abgeschlossenes Attribut.', [{
      severity: 'error', code: 'html-unclosed-attribute', stage: 'structure-decoding',
      message: 'Eine Attributzeichenkette endet nicht innerhalb des HTML-Dokuments.'
    }]);
    if (text[start + 1] !== '/' && /^(script|style|textarea|title|xmp|iframe|noembed|noframes)$/i.test(opening[1])) {
      const closing = new RegExp('</' + opening[1] + '\\s*>', 'ig');
      closing.lastIndex = position;
      const end = closing.exec(text);
      position = end ? end.index + end[0].length : text.length;
    }
  }
  return output.length ? output.join('') + text.slice(copied) : text;
}