ISO 14443A, ISO 15693 & NFC NDEF Protocols

// Encodes a standard NFC Forum NDEF URI Record for NTAG213 chips
export function encodeNdefUri(url: string): Uint8Array {
  const uriPrefixMap: Record<string, number> = {
    'http://www.': 0x01,
    'https://www.': 0x02,
    'http://': 0x03,
    'https://': 0x04,
    'tel:': 0x05,
    'mailto:': 0x06
  };

  let prefixCode = 0x00;
  let trimmedUrl = url;

  for (const [prefix, code] of Object.entries(uriPrefixMap)) {
    if (url.startsWith(prefix)) {
      prefixCode = code;
      trimmedUrl = url.slice(prefix.length);
      break;
    }
  }

  const urlBytes = new TextEncoder().encode(trimmedUrl);
  const payloadLength = 1 + urlBytes.length;

  // NDEF Record Header: MB=1, ME=1, CF=0, SR=1, IL=0, TNF=0x01 (NFC Well Known)
  const header = 0xD1; 
  const typeLength = 0x01; // 'U' for URI
  const typeByte = 0x55;   // ASCII 'U'

  const ndefMessage = new Uint8Array([
    0x03, // NDEF Message TLV Tag
    payloadLength + 4, // TLV Length
    header,
    typeLength,
    payloadLength,
    typeByte,
    prefixCode,
    ...urlBytes,
    0xFE // Terminator TLV
  ]);

  return ndefMessage;
}