NFC

Copyfunction describe(record) {
  if (record.recordType === 'text') return new TextDecoder(record.encoding).decode(record.data);
  if (record.recordType === 'url' || record.recordType === 'absolute-url') return new TextDecoder().decode(record.data);
  if (record.recordType === 'mime') return record.mediaType + ' (' + record.data.byteLength + ' bytes)';
  return record.recordType;
}

var scanStop = null;

document.getElementById('read').addEventListener('click', async function () {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  var reader = new NDEFReader();
  scanStop = new AbortController();
  reader.onreading = function (e) {
    showStatus('Tag ' + e.serialNumber + ': ' + e.message.records.map(describe).join(' | '));
  };
  reader.onreadingerror = function () { showStatus('That tag holds no NFC data this phone can read.'); };
  try {
    await reader.scan({ signal: scanStop.signal });
    showStatus('Hold a tag to the back of the phone.');
  } catch (err) {
    showStatus('NFC error: ' + err.name + ' ' + err.message);   // NotReadableError = NFC switched off
  }
});

document.getElementById('stop').addEventListener('click', function () {
  if (scanStop) scanStop.abort();   // the standard way to stop scanning
});

Copyasync function writeTag(kind, value) {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  var reader = new NDEFReader();
  showStatus('Tap a tag to write it...');
  try {
    if (kind === 'text') await reader.write(value);   // same as { records: [{ recordType: 'text', data: value }] }
    else await reader.write({ records: [{ recordType: 'url', data: value }] }, { overwrite: false });
    showStatus('Tag written.');
  } catch (err) {
    showStatus('Write failed: ' + err.name + ' ' + err.message);   // NotAllowedError: read-only, or overwrite:false on a used tag
  }
}

Copyasync function lockTag() {
  if (!('NDEFReader' in window)) return;
  if (!confirm('Lock the next tag you tap? It can never be changed again.')) return;
  try { await new NDEFReader().makeReadOnly(); showStatus('Tag locked.'); }
  catch (err) { showStatus('Lock failed: ' + err.message); }
}

Copyvar controller = null;

async function writeWithCancel(text) {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  controller = new AbortController();
  showStatus('Tap a tag to write it... (or press Cancel)');
  try {
    await new NDEFReader().write(text, { signal: controller.signal });
    showStatus('Tag written.');
  } catch (err) {
    showStatus(err.name === 'AbortError' ? 'Cancelled.' : 'Write failed: ' + err.message);
  }
}

document.getElementById('cancel').addEventListener('click', function () {
  if (controller) controller.abort();
});

Copyasync function writeWithTimeout(url, ms) {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  var controller = new AbortController();
  var timer = setTimeout(function () { controller.abort(); }, ms);
  showStatus('Tap a tag within ' + Math.round(ms / 1000) + ' seconds...');
  try {
    await new NDEFReader().write({ records: [{ recordType: 'url', data: url }] }, { signal: controller.signal });
    showStatus('Tag written.');
  } catch (err) {
    showStatus(err.name === 'AbortError' ? 'Timed out. Tap Write to try again.' : 'Write failed: ' + err.message);
  } finally {
    clearTimeout(timer);
  }
}

Copyvar pendingTagOp = null;

window.addEventListener('hashchange', function () {
  if (pendingTagOp) { pendingTagOp.abort(); pendingTagOp = null; }
});

document.getElementById('lock').addEventListener('click', function () {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  if (pendingTagOp) pendingTagOp.abort();
  var controller = pendingTagOp = new AbortController();
  showStatus('Tap the tag to lock it...');
  new NDEFReader().makeReadOnly({ signal: controller.signal })
    .then(function () { showStatus('Tag locked.'); })
    .catch(function (err) { if (err.name !== 'AbortError') showStatus('Lock failed: ' + err.message); })
    .finally(function () { if (pendingTagOp === controller) pendingTagOp = null; });
});

Copydocument.getElementById('publish-tag').addEventListener('click', async function () {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  if (!confirm('Write and lock this tag? A locked tag can never be changed.')) return;
  var reader = new NDEFReader();
  try {
    showStatus('Tap the tag to write it...');
    await reader.write({ records: [{ recordType: 'url', data: 'https://example.com/item/42' }] });
    showStatus('Now tap the same tag again to lock it...');
    await reader.makeReadOnly();
    showStatus('Tag written and locked.');
  } catch (err) {
    showStatus('Failed: ' + err.message);
  }
});

Copyasync function lockTag() {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  if (!confirm('Lock this tag for good? It can never be changed again.')) return;
  var controller = new AbortController();
  var timer = setTimeout(function () { controller.abort(); }, 20000);
  showStatus('Tap the tag to lock it...');
  try {
    await new NDEFReader().makeReadOnly({ signal: controller.signal });
    showStatus('Tag locked.');
  } catch (err) {
    if (err.name === 'AbortError') showStatus('No tag was tapped. Try again when ready.');
    else if (err.name === 'NotAllowedError') showStatus('This kind of tag cannot be locked.');
    else showStatus('Lock failed: ' + err.message);
  } finally {
    clearTimeout(timer);
  }
}

Copyasync function checkThenLock(expectedUrl) {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  var reader = new NDEFReader();
  var scanning = new AbortController();
  var lockBtn = document.getElementById('lock-btn');
  reader.onreading = function (e) {
    var rec = e.message.records.find(function (r) { return r.recordType === 'url'; });
    var url = rec ? new TextDecoder().decode(rec.data) : null;
    showStatus(url ? 'Tag points to ' + url : 'This tag holds no link.');
    lockBtn.disabled = url !== expectedUrl;
  };
  await reader.scan({ signal: scanning.signal });
  showStatus('Hold the tag to the phone to check it.');

  lockBtn.onclick = async function () {
    if (!confirm('Lock this tag? It can never be changed again.')) return;
    scanning.abort();
    showStatus('Tap the tag again to lock it...');
    try { await reader.makeReadOnly(); showStatus('Tag locked.'); }
    catch (err) { showStatus('Lock failed: ' + err.message); }
  };
}

Copyasync function startReading() {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  try {
    await new NDEFReader().scan();
    showStatus('Hold a tag to the back of the phone.');
  } catch (err) {
    if (err.name === 'NotReadableError') showStatus('Turn on NFC in the phone settings, then try again.');
    else if (err.name === 'NotSupportedError') showStatus('This phone has no NFC.');
    else showStatus('NFC error: ' + err.message);
  }
}

Copyasync function nfcStatus() {
  if (!('NDEFReader' in window)) return 'none';
  var probe = new AbortController();
  try {
    await new NDEFReader().scan({ signal: probe.signal });
    return 'on';
  } catch (err) {
    return err.name === 'NotReadableError' ? 'off' : 'none';
  } finally {
    probe.abort();
  }
}

async function refreshNfcUi() {
  var state = await nfcStatus();
  document.getElementById('nfc-panel').hidden = state !== 'on';
  document.getElementById('nfc-off-hint').hidden = state !== 'off';
}

refreshNfcUi();
document.addEventListener('visibilitychange', function () {
  if (document.visibilityState === 'visible') refreshNfcUi(); // back from the phone settings
});

Copyvar tagScreen = null;

async function openTagScreen() {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  tagScreen = new AbortController();
  var reader = new NDEFReader();
  reader.onreading = function (e) {
    var n = e.message.records.length;
    showStatus(n ? 'Tag ' + e.serialNumber + ' holds ' + n + ' record(s).' : 'This tag is empty.');
  };
  reader.onreadingerror = function () { showStatus('This tag cannot be read. Try another one.'); };
  try {
    await reader.scan({ signal: tagScreen.signal });
    showStatus('Hold a tag to the back of the phone.');
  } catch (err) {
    showStatus(err.name === 'NotReadableError' ? 'NFC is off. Turn it on in the phone settings.' : 'NFC error: ' + err.message);
  }
}

function closeTagScreen() {
  if (tagScreen) { tagScreen.abort(); tagScreen = null; }
}

Copydocument.getElementById('write-table-tag').addEventListener('click', async function () {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  showStatus('Tap a tag to write it...');
  try {
    await new NDEFReader().write({
      records: [
        { recordType: 'url', data: 'https://example.com/menu' },
        { recordType: 'text', data: 'Table 12', lang: 'en' },
        { recordType: 'mime', mediaType: 'application/json',
          data: new TextEncoder().encode(JSON.stringify({ table: 12 })) }
      ]
    });
    showStatus('Tag written.');
  } catch (err) {
    showStatus('Write failed: ' + err.message);
  }
});

Copyasync function writeToBlankTag(url) {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  showStatus('Tap a blank tag...');
  try {
    await new NDEFReader().write(
      { records: [{ recordType: 'url', data: url }] },
      { overwrite: false }
    );
    showStatus('Tag written.');
  } catch (err) {
    if (err.name === 'NotAllowedError') showStatus('That tag already holds data or is locked. Use a blank tag.');
    else if (err.name === 'NetworkError') showStatus('Hold the tag still until it is written.');
    else showStatus('Write failed: ' + err.message);
  }
}

Copydocument.getElementById('write-poster').addEventListener('click', async function () {
  if (!('NDEFReader' in window)) { showStatus('NFC is not available in this app.'); return; }
  showStatus('Tap a tag to write the poster...');
  try {
    await new NDEFReader().write({
      records: [{
        recordType: 'smart-poster',
        data: { records: [
          { recordType: 'url', data: 'https://example.com/events/spring-fair' },
          { recordType: 'text', data: 'Spring Fair tickets', lang: 'en' }
        ] }
      }]
    });
    showStatus('Poster tag written.');
  } catch (err) {
    showStatus(err.name === 'NotSupportedError' ? 'This tag is too small or cannot hold NFC data.' : 'Write failed: ' + err.message);
  }
});

Copyfunction nfcReady() {
  if (!window.AndroidNFC || typeof window.AndroidNFC.startScan !== 'function') return false;
  return window.AndroidNFC.startScan();
}

document.getElementById('scan-tag').addEventListener('click', async function () {
  if (!nfcReady()) { showStatus('Turn on NFC in the phone settings, then try again.'); return; }
  var reader = new NDEFReader();
  reader.addEventListener('reading', function (e) { showStatus('Tag ' + e.serialNumber); });
  await reader.scan();
  showStatus('Hold a tag to the back of the phone.');
});

Copydocument.getElementById('write-pass').addEventListener('click', async function () {
  if (!window.AndroidNFC || typeof window.AndroidNFC.startScan !== 'function') {
    showStatus('NFC is not available in this app.');
    return;
  }
  if (!window.AndroidNFC.startScan()) { showStatus('NFC is off, or this phone has no NFC.'); return; }
  showStatus('Tap a tag to write it...');
  try {
    await new NDEFReader().write('Visitor pass #1042');
    showStatus('Tag written.');
  } catch (err) {
    showStatus('Write failed: ' + err.message);
  }
});

Copyvar retry = document.getElementById('nfc-retry');
retry.addEventListener('click', function () {
  if (!window.AndroidNFC || typeof window.AndroidNFC.startScan !== 'function') {
    showStatus('NFC is not available in this app.');
    return;
  }
  if (window.AndroidNFC.startScan()) {
    retry.hidden = true;
    document.getElementById('nfc-panel').hidden = false;
    startReading(); // your own NDEFReader.scan() code
  } else {
    showStatus('NFC is still off, or this phone has no NFC.');
  }
});