// Supported clients: iOS Safari, Android Chrome, PC Chrome/Edge/Firefox.
// Gated on required API presence; anything missing → hard stop.
export function supported(): string | null {
  if (typeof window === 'undefined') return 'window unavailable';
  if (typeof createImageBitmap !== 'function') return 'createImageBitmap';
  if (typeof Worker === 'undefined') return 'Worker';
  if (typeof indexedDB === 'undefined') return 'IndexedDB';
  const hasOffscreen =
    typeof OffscreenCanvas !== 'undefined' &&
    typeof OffscreenCanvas.prototype.convertToBlob === 'function';
  const hasCanvasBlob =
    typeof HTMLCanvasElement !== 'undefined' &&
    typeof HTMLCanvasElement.prototype.toBlob === 'function';
  if (!hasOffscreen && !hasCanvasBlob) return 'canvas PNG encode';
  const ua = navigator.userAgent;
  const isIOS = /iPad|iPhone|iPod/.test(ua) || (navigator.platform === 'MacIntel' && navigator.maxTouchPoints > 1);
  const isAndroid = /Android/i.test(ua);
  const isSafari = /Safari/i.test(ua) && !/Chrome|CriOS|Edg|Firefox|FxiOS/i.test(ua);
  const isChrome = /Chrome|CriOS/i.test(ua) && !/Edg/i.test(ua);
  const isEdge = /Edg/i.test(ua);
  const isFirefox = /Firefox|FxiOS/i.test(ua);
  if (isIOS && isSafari) return null;
  if (isAndroid && isChrome) return null;
  if (!isIOS && !isAndroid && (isChrome || isEdge || isFirefox)) return null;
  return 'unsupported browser';
}

// v4 UUID. crypto.randomUUID() is only guaranteed on secure contexts
// (HTTPS/localhost); the UAT host is plain HTTP on a LAN IP, where it is
// undefined. Fall back to crypto.getRandomValues (available on HTTP) so the
// client-generated ids (APP-20) work in both contexts.
export function uuid(): string {
  const c = globalThis.crypto;
  if (c && typeof c.randomUUID === 'function') return c.randomUUID();
  if (c && typeof c.getRandomValues === 'function') {
    const b = new Uint8Array(16);
    c.getRandomValues(b);
    b[6] = (b[6] & 0x0f) | 0x40; // version 4
    b[8] = (b[8] & 0x3f) | 0x80; // variant 10
    const h = Array.from(b, (x) => x.toString(16).padStart(2, '0')).join('');
    return `${h.slice(0, 8)}-${h.slice(8, 12)}-${h.slice(12, 16)}-${h.slice(16, 20)}-${h.slice(20)}`;
  }
  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (ch) => {
    const r = (Math.random() * 16) | 0;
    const v = ch === 'x' ? r : (r & 0x3) | 0x8;
    return v.toString(16);
  });
}