marc parser

    const lines = e.target.result.split('\n').map(line => line.trim()).filter(line => line !== '');
    const output = [];

    const regex = /^(.+?) ?: (.+?) \/ (.+?)\. - (.+?) ?: (.+?), (\d{4})\. - (.+)$/;

lines.forEach((line, index) => {
      const match = line.match(regex);

      if (match) {
        const [
          _,
          title,             // 0-24 h
          subtitle,          // Поеми
          author,            // Недялко Славов
          place,             // Пловдив
          publisher,         // Страница
          year,              // 2003
          pages              // 95 с.
        ] = match.map(m => m.trim());

        output.push(
          `Record ${index + 1}:\n` +
          `245 $a: ${title}\n` +
          `245 $b: ${subtitle}\n` +
          `245 $c: ${author}\n` +
          `260 $a: ${place}\n` +
          `260 $b: ${publisher}\n` +
          `260 $c: ${year}\n` +
          `300 $a: ${pages}\n`
        );
      } else {
        output.push(`Record ${index + 1}: Failed to parse: "${line}"\n`);
      }
    });