const iconv = require('iconv-lite');

/**
 * Decodes MIME encoded-words (e.g. =?UTF-8?B?...?= or =?ISO-8859-1?Q?...?=)
 */
function decodeMimeWords(str) {
  if (!str || typeof str !== 'string') return str || '';
  if (!str.includes('=?')) return str;

  return str.replace(/=\?([^?]+)\?([BQbq])\?([^?]+)\?=/g, (fullMatch, charset, encoding, data) => {
    try {
      const cs = charset.toLowerCase();
      const enc = encoding.toUpperCase();

      let buf;
      if (enc === 'B') {
        buf = Buffer.from(data, 'base64');
      } else if (enc === 'Q') {
        const qDec = data.replace(/_/g, ' ').replace(/=([0-9A-Fa-f]{2})/g, (_, hex) => String.fromCharCode(parseInt(hex, 16)));
        buf = Buffer.from(qDec, 'binary');
      }

      if (buf) {
        if (iconv.encodingExists(cs)) {
          return iconv.decode(buf, cs);
        } else {
          return buf.toString('utf-8');
        }
      }
    } catch (_) {
      return fullMatch;
    }
    return fullMatch;
  });
}

/**
 * Decodes raw Quoted-Printable strings (e.g. =E0=E8=E9=F9 or =C3=A8)
 */
function decodeQuotedPrintable(str, charset = 'utf-8') {
  if (!str || typeof str !== 'string') return str || '';
  if (!/=(?:[0-9A-Fa-f]{2}|\r?\n)/.test(str)) return str;

  try {
    const cleaned = str.replace(/=\r?\n/g, '');
    const bytes = [];
    for (let i = 0; i < cleaned.length; i++) {
      if (cleaned[i] === '=' && i + 2 < cleaned.length && /[0-9A-Fa-f]{2}/.test(cleaned.substring(i + 1, i + 3))) {
        bytes.push(parseInt(cleaned.substring(i + 1, i + 3), 16));
        i += 2;
      } else {
        bytes.push(cleaned.charCodeAt(i));
      }
    }
    const buf = Buffer.from(bytes);
    if (iconv.encodingExists(charset)) {
      return iconv.decode(buf, charset);
    }
    return buf.toString('utf-8');
  } catch (_) {
    return str;
  }
}

/**
 * Main text decoder & Mojibake repair utility
 */
function cleanAndDecodeText(rawInput, contentTypeHint = '') {
  if (!rawInput && rawInput !== 0) return '';

  let text = '';

  // 1. Buffer / Base64 / String normalization
  if (Buffer.isBuffer(rawInput)) {
    let charset = 'utf-8';
    const match = (contentTypeHint || '').match(/charset=["']?([^"';\s]+)/i);
    if (match && match[1]) charset = match[1].toLowerCase();

    try {
      if (iconv.encodingExists(charset)) {
        text = iconv.decode(rawInput, charset);
      } else {
        text = rawInput.toString('utf-8');
      }
    } catch (_) {
      text = rawInput.toString('utf-8');
    }
  } else if (typeof rawInput === 'string') {
    const cleaned = rawInput.replace(/\s+/g, '');
    if (cleaned.length > 20 && cleaned.length % 4 === 0 && /^[A-Za-z0-9+/]*={0,2}$/.test(cleaned)) {
      try {
        const buf = Buffer.from(cleaned, 'base64');
        const utfStr = buf.toString('utf-8');
        // Only accept base64 decode if result doesn't look like corrupted binary noise
        if (utfStr && !utfStr.includes('\uFFFD')) {
          text = utfStr;
        } else {
          text = rawInput;
        }
      } catch (_) {
        text = rawInput;
      }
    } else {
      text = rawInput;
    }
  } else {
    return String(rawInput);
  }

  // 2. Decode MIME words (e.g. =?UTF-8?B?...?= or =?ISO-8859-1?Q?...?=)
  if (text.includes('=?')) {
    text = decodeMimeWords(text);
  }

  // 3. Decode Quoted-Printable if present (and not inside HTML tags)
  if (/=(?:[0-9A-Fa-f]{2})/.test(text) && !text.includes('<html') && !text.includes('<div') && !text.includes('<p>')) {
    text = decodeQuotedPrintable(text);
  }

  // 4. Fix Mojibake / Double-UTF-8 / Win1252 / ISO-8859-1 mis-decoding
  if (/(?:Ã[\s\xa0¡-ÿ]|â€[™œ]|–|Â[°©®])/.test(text)) {
    try {
      const reEncoded = iconv.encode(text, 'win1252');
      const repaired = iconv.decode(reEncoded, 'utf-8');
      if (repaired && !repaired.includes('\uFFFD')) {
        text = repaired;
      }
    } catch (_) {}
  }

  // 6. Clean stray Mojibake/control characters like ý, ÿ, or U+FFFD () replacement symbols
  if (/[ýÿ\uFFFD]/.test(text)) {
    text = text.replace(/ý{1,}/g, '')
               .replace(/ÿ{1,}/g, '')
               .replace(/\uFFFD{1,}/g, '');
  }

  return text;
}

module.exports = {
  cleanAndDecodeText,
  decodeMimeWords,
  decodeQuotedPrintable
};