फ़ाइलें: एक बार में एक फ़ाइल

Copyfunction exportCsv(rows) {
  const csv = rows.map(function (r) { return r.join(','); }).join('\n');
  const b64 = btoa(unescape(encodeURIComponent(csv)));          // UTF-8 safe
  if (window.AppMint && typeof AppMint.downloadFile === 'function') {
    AppMint.downloadFile(b64, 'Ledger_Q3.csv', 'text/csv');
  } else {
    const a = document.createElement('a');                       // a normal browser
    a.href = 'data:text/csv;base64,' + b64;
    a.download = 'Ledger_Q3.csv';
    a.click();
  }
}

Copyconst png = document.querySelector('canvas').toDataURL('image/png');
AppMint.downloadFile(png, 'Chart.png');

const blob = new Blob([JSON.stringify(state)], { type: 'application/json' });
AppMint.downloadFile(blob, 'Backup.json');                        // same as AppMint.saveBlob

Copyasync function downloadInvoice(id) {
  const res = await fetch('/api/invoices/' + id + '?format=base64');
  const body = await res.json();                                  // { base64: 'JVBERi0x…' }
  if (!window.AppMint || typeof AppMint.downloadFile !== 'function') {
    location.href = 'data:application/pdf;base64,' + body.base64;
    return;
  }
  AppMint.downloadFile(body.base64, 'Invoice_' + id, 'application/pdf');   // saved as Invoice_<id>.pdf
}

Copy// earlier: preview.src = URL.createObjectURL(editedImageBlob);
document.getElementById('save-photo').addEventListener('click', function () {
  const preview = document.getElementById('preview');
  if (window.AppMint && typeof AppMint.downloadFile === 'function') {
    AppMint.downloadFile(preview.src, 'Edited_Photo.jpg');
  }
});

Copyasync function saveReport() {
  const blob = await makePdfBlob();                    // e.g. jsPDF: doc.output('blob')
  if (window.AppMint && typeof AppMint.saveBlob === 'function') {
    AppMint.saveBlob(blob, 'Site_Report_2026-08.pdf');
    return;
  }
  const url = URL.createObjectURL(blob);               // a normal browser
  const a = document.createElement('a');
  a.href = url;
  a.download = 'Site_Report_2026-08.pdf';
  a.click();
  setTimeout(function () { URL.revokeObjectURL(url); }, 10000);
}

Copyconst file = new File(['name,score\n'], 'Scores.csv', { type: 'text/csv' });
AppMint.saveBlob(file);            // saved as Scores.csv

Copyasync function saveStatement(month, token) {
  const res = await fetch('/api/statements/' + month, {
    headers: { Authorization: 'Bearer ' + token }
  });
  if (!res.ok) { alert('Could not fetch the statement (' + res.status + ')'); return; }
  const blob = await res.blob();
  if (window.AppMint && typeof AppMint.saveBlob === 'function') {
    AppMint.saveBlob(blob, 'Statement_' + month + '.pdf');
  }
}

Copyasync function exportAll(notes) {
  const zip = new JSZip();
  notes.forEach(function (n) { zip.file(n.title + '.txt', n.body); });
  zip.file('index.json', JSON.stringify(notes.map(function (n) { return n.title; })));
  const blob = await zip.generateAsync({ type: 'blob' });
  if (window.AppMint && typeof AppMint.saveBlob === 'function') {
    AppMint.saveBlob(blob, 'Notes_' + new Date().toISOString().slice(0, 10) + '.zip');
  }
}

Copyconst blob = new Blob([csvText], { type: 'text/csv' });
const url = URL.createObjectURL(blob);
if (window.AppMint && typeof AppMint.setDownloadName === 'function') {
  AppMint.setDownloadName(url, 'Invoice_0042.csv');
}
location.href = url;           // saved as Invoice_0042.csv, not "download.csv"

Copyfunction previewPdf(pdfBlob, invoiceNo) {
  const url = URL.createObjectURL(pdfBlob);
  if (window.AppMint && typeof AppMint.setDownloadName === 'function') {
    AppMint.setDownloadName(url, 'Invoice_' + invoiceNo + '.pdf');
  }
  window.open(url, '_blank');
}

Copyconst dataUrl = chart.toBase64Image();         // e.g. Chart.js: 'data:image/png;base64,…'
if (window.AppMint && typeof AppMint.setDownloadName === 'function') {
  AppMint.setDownloadName(dataUrl, 'Sales_by_month.png');
}
const link = document.getElementById('chart-link');
link.href = dataUrl;                           // a tap on this link saves Sales_by_month.png
link.textContent = 'Save chart';

Copyfunction copyFile(fromUri, toPath) {
  if (!window.WebToApkFS) return { ok: false, error: 'not in the app' };
  const step = WebToApkFS.maxChunkSize() || 1048576;   // fall back to 1 MB pieces
  let offset = 0;
  for (;;) {
    const r = WebToApkFS.readBytes(fromUri, offset, step);
    if (!r.ok) return r;
    if (r.bytesRead > 0) {
      const w = WebToApkFS.writeBytes(toPath, r.base64, offset, offset === 0 ? 'truncate' : 'patch');
      if (!w.ok) return w;
    }
    offset += r.bytesRead;
    if (r.eof || r.bytesRead <= 0) return { ok: true, size: offset };
  }
}

Copyfunction readWithProgress(uri, onProgress) {
  const info = WebToApkFS.stat(uri);
  if (!info.ok) return info;
  const step = WebToApkFS.maxChunkSize() || 1048576;
  const steps = Math.max(1, Math.ceil(info.size / step));
  for (let i = 0; i < steps; i++) {
    const r = WebToApkFS.readBytes(uri, i * step, step);
    if (!r.ok) return r;
    onProgress(Math.round(((i + 1) / steps) * 100), r.base64);
  }
  return { ok: true, size: info.size };
}

Copyfunction appendBytes(path, bytes) {                    // bytes: a Uint8Array
  const step = WebToApkFS.maxChunkSize();
  if (!step) return { ok: false, error: 'not in the app' };
  for (let at = 0; at < bytes.length; at += step) {
    const piece = bytes.subarray(at, at + step);
    let bin = '';
    for (let i = 0; i < piece.length; i += 0x8000) bin += String.fromCharCode.apply(null, piece.subarray(i, i + 0x8000));
    const w = WebToApkFS.writeBytes(path, btoa(bin), 0, 'append');   // 'append' ignores the offset
    if (!w.ok) return w;
  }
  return { ok: true };
}

Copyasync function openOneFile() {
  if (!window.WebToApkFS) { alert('Open this page in the app to pick a file.'); return; }
  const f = await WebToApkFS.pickFile('application/pdf');   // '' = any file, 'image/*' = pictures
  if (!f.ok) {
    if (f.error !== 'cancelled') alert('Cannot open a file: ' + f.error);
    return;
  }
  console.log(f.name, f.size + ' bytes', f.mime);
  localStorage.setItem('lastFile', f.uri);   // the grant survives a restart
}

Copyconst uri = localStorage.getItem('lastFile');
if (uri && window.WebToApkFS) {
  const info = WebToApkFS.stat(uri);
  if (info.ok) console.log('still here:', info.name);
  else console.log('file is gone or access was removed:', info.error);
}

Copyasync function importTable() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('text/*');        // CSV and TSV files are both text/*
  if (!f.ok) {
    if (f.error === 'busy') return;                     // a picker is already open
    if (f.error !== 'cancelled') alert('Cannot open a file: ' + f.error);
    return;
  }
  if (!/\.(csv|tsv)$/i.test(f.name)) {
    WebToApkFS.releaseFile(f.uri);
    alert(f.name + ' is not a CSV or TSV file.');
    return;
  }
  const r = WebToApkFS.readAll(f.uri);
  if (r.ok) showTable(atob(r.base64), f.name.toLowerCase().endsWith('.tsv') ? '\t' : ',');
  WebToApkFS.releaseFile(f.uri);
}

Copyasync function showPicture() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('image/*');
  if (!f.ok) return;
  const r = WebToApkFS.readAll(f.uri);
  if (!r.ok) { alert('Read failed: ' + r.error); return; }
  document.getElementById('photo').src = 'data:' + f.mime + ';base64,' + r.base64;
}

Copyfunction readUtf8(pathOrUri) {
  const r = WebToApkFS.readAll(pathOrUri);
  if (!r.ok) throw new Error(r.error);
  const bytes = Uint8Array.from(atob(r.base64), function (c) { return c.charCodeAt(0); });
  return new TextDecoder('utf-8').decode(bytes);
}

Copyasync function checksum() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('');
  if (!f.ok) return;
  const r = WebToApkFS.readAll(f.uri);
  if (!r.ok) { alert('Read failed: ' + r.error); return; }
  const bytes = Uint8Array.from(atob(r.base64), function (c) { return c.charCodeAt(0); });
  const hash = new Uint8Array(await crypto.subtle.digest('SHA-256', bytes));
  const hex = Array.from(hash, function (b) { return b.toString(16).padStart(2, '0'); }).join('');
  console.log(f.name, r.size + ' bytes', hex);
}

Copyasync function checkPng() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('image/*');
  if (!f.ok) return;
  const r = WebToApkFS.readBytes(f.uri, 0, 65536);
  if (!r.ok) { alert('Read failed: ' + r.error); return; }
  const head = atob(r.base64).slice(1, 4);
  console.log(head === 'PNG' ? 'a PNG' : 'not a PNG', '- file is', r.size, 'bytes');
}

Copyfunction eachChunk(uri, onChunk) {
  const step = WebToApkFS.maxChunkSize() || 1048576;
  let offset = 0;
  for (;;) {
    const r = WebToApkFS.readBytes(uri, offset, step);
    if (!r.ok) return r;                 // stop on the first error
    onChunk(r.base64, offset);
    offset += r.bytesRead;
    if (r.eof || r.bytesRead <= 0) return { ok: true, size: offset };
  }
}

Copyfunction readMp3Title(uri) {
  const info = WebToApkFS.stat(uri);
  if (!info.ok || info.size < 128) return null;
  const r = WebToApkFS.readBytes(uri, info.size - 128, 128);
  if (!r.ok) return null;
  const tail = atob(r.base64);
  if (tail.slice(0, 3) !== 'TAG') return null;          // no old-style tag in this file
  return tail.slice(3, 33).replace(/\0+$/, '').trim();  // bytes 3-32 hold the title
}

Copyfunction loadSecret() {
  if (!window.WebToApkFS || !window.AppMintKeystore || !AppMintKeystore.isAvailable()) return null;
  const out = WebToApkFS.readSealed('secret.bin', 'vault');
  if (out.ok) {
    const bytes = Uint8Array.from(atob(out.base64), function (c) { return c.charCodeAt(0); });
    return new TextDecoder().decode(bytes);
  }
  if (out.error === 'auth-required') {
    alert('Unlock your phone, then try again.');
  } else if (out.error === 'no-such-key') {
    alert('This note was deleted.');
  } else {
    alert('Could not open the note: ' + out.error);
  }
  return null;
}

Copyfunction loadSettings() {
  const defaults = { theme: 'light', pinHint: '' };
  const out = WebToApkFS.readSealed('settings.sealed', 'settings');
  if (!out.ok) {
    if (out.error === 'not-found') return defaults;      // nothing saved yet
    throw new Error('Settings could not be opened: ' + out.error);
  }
  const bytes = Uint8Array.from(atob(out.base64), function (c) { return c.charCodeAt(0); });
  return Object.assign(defaults, JSON.parse(new TextDecoder().decode(bytes)));
}

Copyfunction rekey(path, oldAlias, newAlias) {
  const plain = WebToApkFS.readSealed(path, oldAlias);
  if (!plain.ok) return plain;
  if (!AppMintKeystore.hasKey(newAlias)) {
    const k = AppMintKeystore.generateKey(newAlias, {});
    if (!k.ok) return k;
  }
  const w = WebToApkFS.writeSealed(path, plain.base64, newAlias);
  if (!w.ok) return w;
  AppMintKeystore.deleteKey(oldAlias);                  // only after the new copy is written
  return { ok: true };
}

Copyasync function importOnce() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('text/csv');
  if (!f.ok) return;
  const r = WebToApkFS.readAll(f.uri);
  if (r.ok) importCsv(atob(r.base64));
  WebToApkFS.releaseFile(f.uri);       // done with it: do not keep the grant
}

Copyasync function chooseDefaultFile() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('');
  if (!f.ok) return;
  const old = localStorage.getItem('defaultFile');
  if (old && old !== f.uri) WebToApkFS.releaseFile(old);
  localStorage.setItem('defaultFile', f.uri);
}

Copyfunction forgetRecentFiles() {
  const recent = JSON.parse(localStorage.getItem('recentFiles') || '[]');
  let released = 0;
  for (const uri of recent) {
    if (WebToApkFS.releaseFile(uri)) released++;       // false: already gone or never granted
  }
  localStorage.removeItem('recentFiles');
  console.log('released', released, 'of', recent.length);
}

Copyasync function showInfo() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('');
  if (!f.ok) return;
  const info = WebToApkFS.stat(f.uri);
  if (!info.ok) { alert('Cannot read file info: ' + info.error); return; }
  console.log(info.name, info.size + ' bytes', info.mime,
              new Date(info.lastModified).toLocaleString(),
              info.canWrite ? 'writable' : 'read only');
}

Copyconst info = WebToApkFS.stat('photos/cover.jpg');
if (info.ok && !info.isDirectory) console.log('cover is', info.size, 'bytes');

Copyfunction importIfChanged(uri) {
  const info = WebToApkFS.stat(uri);
  if (!info.ok) return 'gone: ' + info.error;
  const seen = JSON.parse(localStorage.getItem('lastImport') || '{}');
  if (seen.size === info.size && seen.lastModified === info.lastModified) return 'unchanged';
  const r = WebToApkFS.readAll(uri);
  if (!r.ok) return 'read failed: ' + r.error;
  importData(atob(r.base64));
  localStorage.setItem('lastImport', JSON.stringify({ size: info.size, lastModified: info.lastModified }));
  return 'imported';
}

Copyfunction bytesToBase64(bytes) {
  let s = '';
  for (let i = 0; i < bytes.length; i += 0x8000) {
    s += String.fromCharCode.apply(null, bytes.subarray(i, i + 0x8000));
  }
  return btoa(s);
}

async function saveNote(text) {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('text/plain');
  if (!f.ok) return;
  const r = WebToApkFS.writeAll(f.uri, bytesToBase64(new TextEncoder().encode(text)));
  if (r.ok) console.log('saved', r.bytesWritten, 'bytes');
  else alert('Could not save: ' + r.error);
}

Copyconst b64 = document.querySelector('canvas').toDataURL('image/png').split(',')[1];
const r = WebToApkFS.writeAll('drawings/sketch.png', b64);
if (!r.ok) alert('Could not save: ' + r.error);

Copyasync function backup(data) {
  if (!window.WebToApkFS || !WebToApkFS.isAvailable()) return;
  if (!WebToApkFS.hasAccess()) {
    const a = await WebToApkFS.requestAccess();
    if (!a.success) return;
  }
  const bytes = new TextEncoder().encode(JSON.stringify(data));
  let bin = '';
  for (let i = 0; i < bytes.length; i += 0x8000) bin += String.fromCharCode.apply(null, bytes.subarray(i, i + 0x8000));
  const r = WebToApkFS.writeAll('backup.json', btoa(bin));
  if (!r.ok) { alert('Backup failed: ' + r.error); return; }
  const info = WebToApkFS.stat('backup.json');
  console.log('backup is', info.ok ? info.size : '?', 'bytes');
}

Copyconst r = WebToApkFS.writeBytes(fileUri, btoa('ABCD'), 100, 'patch');
if (r.ok) console.log('file is now', r.size, 'bytes');
else alert('Write failed: ' + r.error);

Copyconst csv = 'name,score\nAsha,12\n';
const r = WebToApkFS.writeBytes('exports/scores.csv', btoa(csv), 0, 'truncate');
if (!r.ok) alert('Could not save: ' + r.error);

Copyconst line = new Date().toISOString() + ' opened\n';
WebToApkFS.writeBytes('log.txt', btoa(line), 0, 'append');

Copyfunction saveSecret(text) {
  if (!window.WebToApkFS || !window.AppMintKeystore || !AppMintKeystore.isAvailable()) {
    alert('Secure storage is not available in this build.');
    return false;
  }
  if (!AppMintKeystore.hasKey('vault')) {
    const k = AppMintKeystore.generateKey('vault', {});
    if (!k.ok) { alert('Could not create key: ' + k.error); return false; }
  }
  const bytes = new TextEncoder().encode(text);
  let bin = '';
  for (let i = 0; i < bytes.length; i++) bin += String.fromCharCode(bytes[i]);
  const r = WebToApkFS.writeSealed('secret.bin', btoa(bin), 'vault');
  if (!r.ok) alert('Could not save: ' + r.error);
  return r.ok;
}

CopyAppMintKeystore.deleteKey('vault');   // secret.bin can never be decrypted again
WebToApkFS.delete('secret.bin');

Copyasync function sealPhoto(file) {                  // a File from <input type="file" accept="image/*">
  if (!window.WebToApkFS || !window.AppMintKeystore || !AppMintKeystore.isAvailable()) return false;
  if (!WebToApkFS.hasAccess()) {
    const g = await WebToApkFS.requestAccess();
    if (!g.success) return false;
  }
  if (!AppMintKeystore.hasKey('vault')) AppMintKeystore.generateKey('vault', {});
  const dataUrl = await new Promise(function (resolve, reject) {
    const fr = new FileReader();
    fr.onload = function () { resolve(fr.result); };
    fr.onerror = reject;
    fr.readAsDataURL(file);
  });
  const b64 = dataUrl.slice(dataUrl.indexOf(',') + 1);
  const r = WebToApkFS.writeSealed('photo-' + Date.now() + '.sealed', b64, 'vault');
  if (!r.ok) alert('Not saved: ' + r.error);
  return r.ok;
}

Copyif (!AppMintKeystore.hasKey('diary')) {
  AppMintKeystore.generateKey('diary', { requireAuth: true, authValiditySeconds: 300 });
}

function saveDiary(entry) {
  const b64 = btoa(unescape(encodeURIComponent(JSON.stringify(entry))));   // UTF-8 safe
  const r = WebToApkFS.writeSealed('diary.bin', b64, 'diary');
  if (r.ok) return true;
  if (r.error === 'auth-required') showMessage('Unlock your phone again, then tap Save.');
  else if (r.error === 'key-invalidated') showMessage('Your screen lock changed, so this key no longer works.');
  else showMessage('Could not save: ' + r.error);
  return false;
}

Copy<button id="save">Download report</button>
<script>
document.getElementById('save').addEventListener('click', function () {
  const blob = new Blob(['Name,Total\nAsha,120\n'], { type: 'text/csv' });
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'Report_2026-08.csv';     // this is the name the user sees
  document.body.appendChild(a);
  a.click();                             // caught by the app, saved to Downloads
  a.remove();
});
</script>

Copyconst a = document.createElement('a');
a.href = canvas.toDataURL('image/png');
a.download = 'Drawing.png';
a.click();

if (typeof saveAs === 'function') saveAs(blob, 'Backup.json');   // FileSaver.js
if (navigator.msSaveBlob) navigator.msSaveBlob(blob, 'Backup.json');

Copyconst pdfUrl = URL.createObjectURL(pdfBlob);
const w = window.open(pdfUrl);    // never null in the app, so no "popup blocked" message

Copy<input type="file" id="pics" accept="image/*" multiple>
<div id="preview"></div>
<script>
document.getElementById('pics').addEventListener('change', function (e) {
  const box = document.getElementById('preview');
  for (let i = 0; i < e.target.files.length; i++) {
    const img = document.createElement('img');
    img.src = URL.createObjectURL(e.target.files[i]);
    img.style.width = '100px';
    box.appendChild(img);
  }
});
</script>

Copy<input type="file" id="snap" accept="image/*" capture="environment">
<input type="file" id="clip" accept="video/*" capture="environment">
<script>
document.getElementById('snap').addEventListener('change', function (e) {
  const photo = e.target.files[0];
  if (!photo) return;                        // user closed the camera
  const form = new FormData();
  form.append('photo', photo);
  fetch('/api/upload', { method: 'POST', body: form });
});
</script>

Copy<input type="file" accept=".pdf,.csv,application/json" multiple>

Copylet handle = null;

document.getElementById('open').addEventListener('click', async () => {
  try {
    [handle] = await showOpenFilePicker({
      types: [{ description: 'Text', accept: { 'text/plain': ['.txt', '.md'] } }]
    });
    const file = await handle.getFile();
    editor.value = await file.text();
    title.textContent = file.name;
  } catch (e) {
    if (e.name !== 'AbortError') alert('Could not open: ' + e.message);
  }
});

document.getElementById('save').addEventListener('click', async () => {
  if (!handle) handle = await showSaveFilePicker({ suggestedName: 'note.txt' });
  const w = await handle.createWritable();   // writes go to a copy…
  await w.write(editor.value);
  await w.close();                           // …that replaces the file only here
});

document.getElementById('export').addEventListener('click', async () => {
  const dir = await showDirectoryPicker({ mode: 'readwrite' });
  const out = await dir.getFileHandle('export.csv', { create: true });
  const w = await out.createWritable();
  await w.write(csvText);
  await w.close();
  for await (const [name, entry] of dir.entries()) console.log(entry.kind, name);
});

Copydocument.getElementById('add-photos').addEventListener('click', async () => {
  try {
    const handles = await showOpenFilePicker({
      multiple: true,
      startIn: 'pictures',
      types: [{ description: 'Images', accept: { 'image/*': ['.jpg', '.jpeg', '.png', '.webp'] } }]
    });
    for (const h of handles) {
      const img = document.createElement('img');
      img.src = URL.createObjectURL(await h.getFile());
      gallery.appendChild(img);
    }
  } catch (e) {
    if (e.name !== 'AbortError') alert('Could not open: ' + e.message);
  }
});

Copyasync function appendLine(handle, line) {      // handle from showOpenFilePicker / showSaveFilePicker
  const size = (await handle.getFile()).size;
  const w = await handle.createWritable({ keepExistingData: true });
  await w.seek(size);
  await w.write(line + '\n');
  await w.close();
}

Copy// Tiny IndexedDB helpers (idb-keyval's get/set work the same way).
function db() {
  return new Promise((ok, fail) => {
    const r = indexedDB.open('backup-settings', 1);
    r.onupgradeneeded = () => r.result.createObjectStore('kv');
    r.onsuccess = () => ok(r.result);
    r.onerror = () => fail(r.error);
  });
}
async function kvGet(key) {
  const d = await db();
  return new Promise((ok, fail) => {
    const r = d.transaction('kv').objectStore('kv').get(key);
    r.onsuccess = () => ok(r.result);
    r.onerror = () => fail(r.error);
  });
}
async function kvSet(key, value) {
  const d = await db();
  return new Promise((ok, fail) => {
    const t = d.transaction('kv', 'readwrite');
    t.objectStore('kv').put(value, key);
    t.oncomplete = () => ok();
    t.onerror = () => fail(t.error);
  });
}

// "Choose backup folder" button (the picker needs a tap).
document.getElementById('choose-folder').addEventListener('click', async () => {
  try {
    const dir = await showDirectoryPicker({ mode: 'readwrite', startIn: 'documents' });
    await kvSet('backupDir', dir);
    status.textContent = 'Backups go to ' + dir.name;
  } catch (e) {
    if (e.name !== 'AbortError') status.textContent = 'Could not choose: ' + e.message;
  }
});

// Called after every workout, and on a timer: no tap needed once the folder is chosen.
async function autoBackup(data) {
  const dir = await kvGet('backupDir');
  if (!dir) return 'no folder chosen yet';
  if ((await dir.queryPermission({ mode: 'readwrite' })) !== 'granted') {
    return 'folder access was removed: tap "Choose backup folder" again';
  }
  const file = await dir.getFileHandle('backup-' + new Date().toISOString().slice(0, 10) + '.json', { create: true });
  const w = await file.createWritable();
  await w.write(JSON.stringify(data));
  await w.close();
  return 'saved ' + file.name;
}

Copydocument.getElementById('reconnect').addEventListener('click', async () => {
  const dir = await kvGet('backupDir');
  if (dir && (await dir.requestPermission({ mode: 'readwrite' })) === 'granted') {
    status.textContent = 'Backups go to ' + dir.name + ' again';
  } else {
    status.textContent = 'Choose a backup folder';
  }
});

Copydocument.getElementById('clean').addEventListener('click', async () => {
  const dir = await showDirectoryPicker({ mode: 'readwrite' });
  let removed = 0;
  for await (const entry of dir.values()) {
    if (entry.kind === 'file' && entry.name.endsWith('.tmp')) {
      await dir.removeEntry(entry.name);
      removed++;
    } else if (entry.kind === 'directory' && entry.name === 'cache') {
      await dir.removeEntry(entry.name, { recursive: true });
      removed++;
    }
  }
  alert(removed + ' item(s) removed');
});

Copyconst blob = new Blob([csvText], { type: 'text/csv' });
const a = document.createElement('a');
a.href = URL.createObjectURL(blob);
a.download = 'Report.csv';
a.click();   // lands in Downloads as "Report.csv"

Copycanvas.toBlob(function (blob) {
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'drawing.png';
  a.click();
  setTimeout(function () { URL.revokeObjectURL(a.href); }, 10000);
}, 'image/png');

Copyfunction exportBackup(data) {
  const blob = new Blob([JSON.stringify(data, null, 2)], { type: 'application/json' });
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'backup-' + new Date().toISOString().slice(0, 10) + '.json';
  document.body.appendChild(a);
  a.click();
  a.remove();
  showMessage('Backup saved to Downloads.');
}

Copyconst blob = new Blob([csvText], { type: 'text/csv' });
const a = document.createElement('a');
a.href = URL.createObjectURL(blob);
a.download = 'Report.csv';
a.click();   // lands in Downloads as "Report.csv"

Copycanvas.toBlob(function (blob) {
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'drawing.png';
  a.click();
  setTimeout(function () { URL.revokeObjectURL(a.href); }, 10000);
}, 'image/png');

Copyfunction exportBackup(data) {
  const blob = new Blob([JSON.stringify(data, null, 2)], { type: 'application/json' });
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'backup-' + new Date().toISOString().slice(0, 10) + '.json';
  document.body.appendChild(a);
  a.click();
  a.remove();
  showMessage('Backup saved to Downloads.');
}

Copyconst blob = new Blob([csvText], { type: 'text/csv' });
const a = document.createElement('a');
a.href = URL.createObjectURL(blob);
a.download = 'Report.csv';
a.click();   // lands in Downloads as "Report.csv"

Copycanvas.toBlob(function (blob) {
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'drawing.png';
  a.click();
  setTimeout(function () { URL.revokeObjectURL(a.href); }, 10000);
}, 'image/png');

Copyfunction exportBackup(data) {
  const blob = new Blob([JSON.stringify(data, null, 2)], { type: 'application/json' });
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'backup-' + new Date().toISOString().slice(0, 10) + '.json';
  document.body.appendChild(a);
  a.click();
  a.remove();
  showMessage('Backup saved to Downloads.');
}

Copyconst blob = new Blob([csvText], { type: 'text/csv' });
const a = document.createElement('a');
a.href = URL.createObjectURL(blob);
a.download = 'Report.csv';
a.click();   // lands in Downloads as "Report.csv"

Copycanvas.toBlob(function (blob) {
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'drawing.png';
  a.click();
  setTimeout(function () { URL.revokeObjectURL(a.href); }, 10000);
}, 'image/png');

Copyfunction exportBackup(data) {
  const blob = new Blob([JSON.stringify(data, null, 2)], { type: 'application/json' });
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = 'backup-' + new Date().toISOString().slice(0, 10) + '.json';
  document.body.appendChild(a);
  a.click();
  a.remove();
  showMessage('Backup saved to Downloads.');
}

Copyconst dir = await showDirectoryPicker();
const photos = await dir.getDirectoryHandle('photos', { create: true });
const file = await photos.getFileHandle('list.json', { create: true });

Copyasync function exists(dir, name) {
  try {
    await dir.getFileHandle(name);                     // no {create} = look up only
    return true;
  } catch (e) {
    if (e.name === 'NotFoundError') return false;
    if (e.name === 'TypeMismatchError') return true;   // a folder already has that name
    throw e;
  }
}

Copyasync function saveSettings(root, settings) {
  const config = await root.getDirectoryHandle('config', { create: true });
  const file = await config.getFileHandle('settings.json', { create: true });
  const w = await file.createWritable();
  await w.write(JSON.stringify(settings, null, 2));
  await w.close();
}
// root = await showDirectoryPicker()  (from a button tap)

Copyconst [handle] = await showOpenFilePicker();
const file = await handle.getFile();
console.log(file.name, file.size, await file.text());

Copydocument.querySelector('#choose').addEventListener('click', async function () {
  const [handle] = await showOpenFilePicker({ types: [{ accept: { 'image/*': [] } }] });
  const file = await handle.getFile();                    // a real File, streamed from the app
  const img = document.querySelector('#preview');
  if (img.src) URL.revokeObjectURL(img.src);
  img.src = URL.createObjectURL(file);
  img.alt = file.name + ' (' + file.type + ')';
});

Copyasync function reloadIfChanged(handle, lastSeen) {
  try {
    const file = await handle.getFile();
    if (file.lastModified === lastSeen) return null;      // unchanged
    return { data: JSON.parse(await file.text()), lastModified: file.lastModified };
  } catch (e) {
    if (e.name === 'NotFoundError') alert(handle.name + ' was moved or deleted.');
    else throw e;
    return null;
  }
}

Copyconst dir = await showDirectoryPicker();
for await (const [name, entry] of dir.entries()) console.log(entry.kind, name);

Copyasync function countFiles(dir) {
  let n = 0;
  for await (const entry of dir.values()) {
    if (entry.kind === 'file') n++;
    else n += await countFiles(entry);                 // entry is a FileSystemDirectoryHandle
  }
  return n;
}
document.querySelector('#scan').addEventListener('click', async function () {
  const dir = await showDirectoryPicker();
  console.log(dir.name, 'holds', await countFiles(dir), 'files');
});

Copydocument.querySelector('#open-album').addEventListener('click', async function () {
  const dir = await showDirectoryPicker({ startIn: 'pictures' });
  const names = [];
  for await (const name of dir.keys()) {
    if (/\.(jpe?g|png|webp)$/i.test(name)) names.push(name);
  }
  names.sort(function (a, b) { return a.localeCompare(b); });
  renderAlbum(dir, names);                             // dir.getFileHandle(name) opens each one
});

Copyconst dir = await kvGet('backupDir');                 // a handle stored in IndexedDB earlier
if ((await dir.queryPermission({ mode: 'readwrite' })) === 'granted') {
  const f = await dir.getFileHandle('backup.json', { create: true });
  const w = await f.createWritable();
  await w.write(JSON.stringify(state));
  await w.close();
}

Copydocument.getElementById('reconnect').addEventListener('click', async () => {
  const dir = await kvGet('backupDir');
  const state = await dir.requestPermission({ mode: 'readwrite' });   // 'granted' | 'denied'
  status.textContent = state === 'granted' ? 'Backups resumed' : 'Choose a backup folder';
});

Copyconst [handle] = await showOpenFilePicker({ types: [{ accept: { 'image/*': ['.png', '.jpg'] } }] });
const file = await handle.getFile();

Copydocument.querySelector('#export').addEventListener('click', async function () {
  try {
    const handle = await showSaveFilePicker({
      suggestedName: 'report.csv',
      types: [{ description: 'CSV', accept: { 'text/csv': ['.csv'] } }]
    });
    const w = await handle.createWritable();
    await w.write(buildCsv());
    await w.close();
  } catch (e) {
    if (e.name !== 'AbortError') alert('Export failed: ' + e.message);   // AbortError = cancelled
  }
});

Copydocument.querySelector('#add-photos').addEventListener('click', async function () {
  let handles;
  try {
    handles = await showOpenFilePicker({
      multiple: true,
      startIn: 'pictures',
      types: [{ accept: { 'image/*': ['.jpg', '.jpeg', '.png', '.webp'] } }]
    });
  } catch (e) { return; }                                 // cancelled or already open
  for (const h of handles) addToGallery(await h.getFile());
});

Copyconst dir = await showDirectoryPicker();
await dir.removeEntry('old-drafts', { recursive: true });

Copyasync function deleteFile(dir, name) {
  try {
    await dir.removeEntry(name);
  } catch (e) {
    if (e.name !== 'NotFoundError') throw e;   // NotFoundError: nothing left to delete
  }
}

Copyasync function removeFolder(dir, name) {
  try {
    await dir.removeEntry(name);                          // succeeds for an empty folder
  } catch (e) {
    if (e.name !== 'InvalidModificationError') throw e;
    if (!confirm('"' + name + '" is not empty. Delete it and everything inside?')) return false;
    await dir.removeEntry(name, { recursive: true });
  }
  return true;
}

Copyconst w = await handle.createWritable();
try { await w.write(await buildExport()); await w.close(); }
catch (e) { await w.abort(); }

Copylet cancelled = false;
document.getElementById('cancel').onclick = function () { cancelled = true; };

async function exportAll(handle, pages) {
  const w = await handle.createWritable();
  for (const page of pages) {
    if (cancelled) { await w.abort(); return 'cancelled'; }   // the file keeps its old content
    await w.write(await renderPage(page));
  }
  await w.close();
  return 'saved';
}

Copyconst ctl = new AbortController();
document.getElementById('stop').onclick = function () { ctl.abort(); };

async function downloadInto(handle, url) {
  const res = await fetch(url);
  if (!res.ok) throw new Error('HTTP ' + res.status);
  const w = await handle.createWritable();
  try {
    await res.body.pipeTo(w, { signal: ctl.signal });     // closes the file when the body ends
    return 'saved';
  } catch (e) {
    return e.name === 'AbortError' ? 'stopped, file unchanged' : 'failed: ' + e.message;
  }
}

Copyconst w = await handle.createWritable();
await w.write(json);
await w.close();   // nothing changes on disk before this

Copyasync function saveText(handle, text) {
  const w = await handle.createWritable();
  await w.write(text);
  try {
    await w.close();
    return true;
  } catch (e) {
    if (e.name === 'InvalidModificationError') alert('This file\'s app cannot make it shorter. Save a copy instead.');
    else if (e.name === 'NoModificationAllowedError') alert('This file cannot be changed.');
    else alert('Save failed: ' + e.message);
    return false;
  }
}

Copyasync function saveRows(handle, rows) {
  const w = await handle.createWritable();
  await w.write('id,name,total\n');
  for (const r of rows) await w.write(r.id + ',' + r.name + ',' + r.total + '\n');
  console.log('before close:', (await handle.getFile()).size, 'bytes (old file)');
  await w.close();
  console.log('after close:', (await handle.getFile()).size, 'bytes');
}

Copyconst handle = await showSaveFilePicker({ suggestedName: 'report.csv' });
const w = await handle.createWritable({ keepExistingData: false });
await w.write('a,b\n1,2\n');
await w.close();

Copyasync function appendLine(handle, line) {
  const size = (await handle.getFile()).size;
  const w = await handle.createWritable({ keepExistingData: true });
  await w.seek(size);                                     // write after the old content
  await w.write(new Date().toISOString() + ' ' + line + '\n');
  await w.close();                                        // only now does the file change
}

Copydocument.querySelector('#save-png').addEventListener('click', async function () {
  const handle = await showSaveFilePicker({
    suggestedName: 'drawing.png',
    types: [{ accept: { 'image/png': ['.png'] } }]
  });
  const blob = await new Promise(function (r) { document.querySelector('canvas').toBlob(r, 'image/png'); });
  const w = await handle.createWritable();
  try {
    await w.write(blob);
    await w.close();
  } catch (e) {
    try { await w.abort(); } catch (x) {}                 // nothing reaches the file before close()
    alert('Could not save: ' + e.message);
  }
});

Copyconst w = await handle.createWritable({ keepExistingData: true });
await w.truncate(0);
await w.write('fresh start');
await w.close();

Copyasync function keepFirstKilobyte(handle) {
  const w = await handle.createWritable({ keepExistingData: true });
  await w.truncate(1000);   // a file shorter than this grows instead (see the next example)
  await w.close();
}

Copyasync function makeEmptySlotFile(handle, slots, slotSize) {
  const w = await handle.createWritable();
  await w.truncate(slots * slotSize);                  // e.g. 100 slots of 256 bytes, all zero
  await w.write({ type: 'write', position: 0, data: new Uint8Array([1, 0, 0, 0]) });
  await w.close();
  console.log('file is now', (await handle.getFile()).size, 'bytes');
}

Copyconst w = await handle.createWritable({ keepExistingData: true });
await w.write({ type: 'write', position: 0, data: new Blob(['HEADER\n']) });
await w.close();

Copydocument.getElementById('addLine').addEventListener('click', async () => {
  const [handle] = await showOpenFilePicker({
    types: [{ description: 'Text', accept: { 'text/plain': ['.txt', '.log'] } }]
  });
  const size = (await handle.getFile()).size;
  const w = await handle.createWritable({ keepExistingData: true });
  await w.seek(size);                                   // start writing after the old content
  await w.write(new Date().toISOString() + ' checked in\n');
  await w.close();
});

Copydocument.getElementById('saveDrawing').addEventListener('click', async () => {
  const handle = await showSaveFilePicker({
    suggestedName: 'drawing.png',
    types: [{ description: 'PNG image', accept: { 'image/png': ['.png'] } }]
  });
  const blob = await new Promise(function (ok) { document.querySelector('canvas').toBlob(ok, 'image/png'); });
  const w = await handle.createWritable();
  await w.write(blob);
  await w.close();
});

Copyconst step = window.WebToApkFS ? WebToApkFS.maxChunkSize() : 0;

Copylet step = 1048576;
if (window.WebToApk && typeof WebToApk.getMaxIoChunkSize === 'function') {
  step = Number(WebToApk.getMaxIoChunkSize()) || step;
}
console.log('read/write up to', step, 'bytes per call');

Copyfunction plannedSteps(fileUri) {
  const step = WebToApkFS.maxChunkSize();          // 0 when the helper is not available
  const info = WebToApkFS.stat(fileUri);
  if (!step || !info.ok) return 0;
  const steps = Math.max(1, Math.ceil(info.size / step));
  document.querySelector('#progress').max = steps;
  return steps;
}

Copyfunction copyFile(fromUri, toPath) {
  const step = WebToApkFS.maxChunkSize() || 1048576;
  let offset = 0;
  for (;;) {
    const r = WebToApkFS.readBytes(fromUri, offset, step);
    if (!r.ok) return r;
    const w = WebToApkFS.writeBytes(toPath, r.base64, offset, offset === 0 ? 'truncate' : 'patch');
    if (!w.ok) return w;
    offset += r.bytesRead;
    if (r.eof || r.bytesRead <= 0) return { ok: true, bytes: offset };
  }
}
// copyFile(pickedUri, 'photo-backup.jpg')  (a file in the granted folder)

Copyconst f = await WebToApkFS.pickFile('image/*');
if (f.ok) console.log('picked', f.name, f.uri);

Copyfunction pickRaw(mime) {
  return new Promise(function (resolve) {
    if (!window.WebToApk || typeof WebToApk.pickFile !== 'function') { resolve(null); return; }
    const myId = 'pick_' + Date.now();
    window.WebToApkOnFilePickResult = function (success, fileJson, requestId) {
      if (requestId !== myId) return;
      const r = JSON.parse(fileJson);           // fileJson is a string
      resolve(success && r.ok ? r : null);      // null = cancelled or not allowed
    };
    WebToApk.pickFile(myId, mime || '');        // '' = any file
  });
}

Copydocument.querySelector('#attach').addEventListener('click', async function () {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('application/pdf');
  if (!f.ok) {
    if (f.error === 'cancelled' || f.error === 'busy') return;   // user closed it / one already open
    alert('Could not open the file picker: ' + f.error);         // 'disabled', 'no-picker', ...
    return;
  }
  document.querySelector('#attachment').textContent =
    f.name + ' (' + Math.round(f.size / 1024) + ' KB)';
  localStorage.setItem('attachmentUri', f.uri);   // the grant is kept across restarts
});

Copyasync function openTextFile() {
  if (!window.WebToApkFS) return;
  const f = await WebToApkFS.pickFile('text/*');
  if (!f.ok) return;
  const r = WebToApkFS.readAll(f.uri);            // {ok, base64, size} or {ok:false, error}
  if (!r.ok) { alert('Could not read ' + f.name + ': ' + r.error); return; }
  const bytes = Uint8Array.from(atob(r.base64), function (c) { return c.charCodeAt(0); });
  document.querySelector('#editor').value = new TextDecoder('utf-8').decode(bytes);
  document.querySelector('#editor').dataset.uri = f.uri;   // save back to the same file later
}

Copyconst r = WebToApkFS.readBytes(fileUri, 0, 65536);
if (r.ok) console.log(r.bytesRead, 'bytes read, end of file:', r.eof);

Copyif (window.WebToApk && typeof WebToApk.readFileBase64 === 'function') {
  const r = JSON.parse(WebToApk.readFileBase64(fileUri, 0, 0));   // length 0 = up to 4 MB
  if (r.ok) {
    const bytes = Uint8Array.from(atob(r.base64), function (c) { return c.charCodeAt(0); });
    console.log('first byte', bytes[0], 'of', r.size);
  } else {
    console.log('read failed:', r.error);
  }
}

Copyfunction isPng(fileUri) {
  const r = WebToApkFS.readBytes(fileUri, 0, 8);
  if (!r.ok || r.bytesRead < 8) return false;
  const head = atob(r.base64);
  const sig = [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a];
  return sig.every(function (b, i) { return head.charCodeAt(i) === b; });
}

Copyfunction scanInChunks(fileUri, onChunk) {
  const step = WebToApkFS.maxChunkSize() || 1048576;
  let offset = 0;
  for (;;) {
    const r = WebToApkFS.readBytes(fileUri, offset, step);
    if (!r.ok) throw new Error('read failed: ' + r.error);
    onChunk(r.base64);                                    // process this piece, then drop it
    offset += r.bytesRead;
    document.querySelector('#progress').value = r.size ? offset / r.size : 1;
    if (r.eof || r.bytesRead <= 0) break;
  }
  return offset;                                          // total bytes read
}

Copyif (window.WebToApkFS) WebToApkFS.releaseFile(fileUri);

Copyif (window.WebToApk && typeof WebToApk.releaseFileAccess === 'function') {
  const released = WebToApk.releaseFileAccess(fileUri) === 'true';   // a string, not a boolean
  console.log(released ? 'access released' : 'nothing to release');
}

Copyfunction rememberRecent(uri) {
  let recent = JSON.parse(localStorage.getItem('recentFiles') || '[]');
  recent = [uri].concat(recent.filter(function (u) { return u !== uri; }));
  while (recent.length > 10) {
    const dropped = recent.pop();
    if (window.WebToApkFS) WebToApkFS.releaseFile(dropped);   // Android caps kept grants
  }
  localStorage.setItem('recentFiles', JSON.stringify(recent));
}

Copydocument.querySelector('#close-doc').addEventListener('click', function () {
  const uri = localStorage.getItem('openDocUri');
  if (uri && window.WebToApkFS) {
    const released = WebToApkFS.releaseFile(uri);   // true / false, already a boolean
    console.log(released ? 'grant released' : 'no grant was held for this file');
  }
  localStorage.removeItem('openDocUri');
  document.querySelector('#editor').value = '';
});

Copyconst info = WebToApkFS.stat(fileUri);
if (info.ok) console.log(info.name, info.size);

Copyif (window.WebToApk && typeof WebToApk.statFile === 'function') {
  const info = JSON.parse(WebToApk.statFile(fileUri));   // or 'notes/today.txt' in the granted folder
  if (info.ok) console.log(info.name, info.size + ' bytes', info.mime, info.canWrite);
  else console.log('stat failed:', info.error);
}

Copyconst MAX_BYTES = 20 * 1024 * 1024;
function canImport(fileUri) {
  const info = WebToApkFS.stat(fileUri);
  if (!info.ok) { alert('File not available: ' + info.error); return false; }
  if (info.size > MAX_BYTES) {
    alert(info.name + ' is ' + Math.round(info.size / 1048576) + ' MB; the limit is 20 MB.');
    return false;
  }
  return true;
}

Copyfunction checkExportFolder() {
  const info = WebToApkFS.stat('exports');          // a path relative to the granted folder
  const btn = document.querySelector('#save-here');
  if (!info.ok) {                                    // 'not-found' = the folder is not there yet
    btn.textContent = 'Create "exports" and save';
    return WebToApkFS.mkdir('exports');
  }
  btn.disabled = !(info.isDirectory && info.canWrite);
  console.log('exports last changed', new Date(info.lastModified).toLocaleString());
  return true;
}

Copyconst r = WebToApkFS.writeBytes(fileUri, btoa('hello'), 0, 'truncate');
if (r.ok) console.log('saved', r.bytesWritten, 'bytes');

Copyif (window.WebToApk && typeof WebToApk.writeFileBase64 === 'function') {
  const r = JSON.parse(WebToApk.writeFileBase64('notes/today.txt', btoa('Buy milk\n'), 0, 'append'));
  if (!r.ok) console.log('write failed:', r.error);
  else console.log('file is now', r.size, 'bytes');
}

Copydocument.querySelector('#save').addEventListener('click', async function () {
  const f = await WebToApkFS.pickFile('image/png');
  if (!f.ok) return;
  const base64 = document.querySelector('canvas').toDataURL('image/png').split(',')[1];
  const r = WebToApkFS.writeAll(f.uri, base64);   // truncates, then writes in 4 MB chunks
  if (r.ok) console.log('saved', r.bytesWritten, 'bytes to', f.name);
  else alert('Save failed: ' + r.error);
});

Copyfunction zeroFill(fileUri) {
  const info = WebToApkFS.stat(fileUri);
  if (!info.ok) return false;
  const slice = 32768;
  for (let at = 0; at < info.size; at += slice) {
    const len = Math.min(slice, info.size - at);
    const zeros = btoa(String.fromCharCode.apply(null, new Uint8Array(len)));
    const w = WebToApkFS.writeBytes(fileUri, zeros, at, 'patch');   // the rest of the file is kept
    if (!w.ok || w.bytesWritten !== len) { console.log('write failed at', at, w.error); return false; }
  }
  return true;   // each call is fsync'ed before it answers
}