import QRCode from "qrcode";

/**
 * QR matrix builder for documents printed by `@react-pdf/renderer`.
 *
 * ## Why the matrix, and not a PNG
 *
 * A QR could be embedded as an image, but a matrix renders as pure
 * VECTOR — one `<Rect>` per dark module — which is strictly better
 * here:
 *
 *   - it stays crisp at any print size or DPI, with no resampling
 *   - it adds ~30 shapes rather than a compressed image blob, so the
 *     PDF stays small
 *   - it does not depend on react-pdf's raster image path at all.
 *     That path was exactly what the old `pdf().toString()` pipeline
 *     silently corrupted (see the note at the top of `render.tsx`),
 *     and vector content is immune to it.
 *
 * ## What the QR carries
 *
 * Currently just the delivery note number, e.g. `DN26100401`.
 *
 * SECURITY NOTE — this is a deliberate product decision, not an
 * oversight. The number is a daily sequential counter (`DN{YY}{MM}{DD}{NN}`
 * starting at 01), so it is fully enumerable: anyone can guess every
 * delivery note that will ever exist. A QR carrying the bare number,
 * pointed at an upload endpoint, is therefore a signature-forgery
 * vector.
 *
 * That is acceptable *today* because the intended consumer is a
 * closed, logged-in internal app on the office network, not the public
 * internet. If this QR is ever exposed to customers, or the scan
 * target is ever made reachable without a login, the fix is to encode
 * an unguessable per-note token instead — e.g.
 * `DN26100401.<base64url(HMAC-SHA256(noteId, SIGNING_SECRET))[0..22]>`,
 * which needs no new column because it is recomputed rather than
 * stored. Raise it before the surface changes, not after.
 */
export type QrMatrix = {
  /** Modules per side, excluding the quiet zone. A version-1 code is 21. */
  size: number;
  /** Row-major, length `size * size`. `true` = dark module. */
  modules: boolean[];
  /**
   * QR spec requires 4 modules of light margin on every side, and
   * scanners rely on it. Without it a code sitting against other ink
   * on the page fails to decode, so the padding is part of the
   * contract, not decoration.
   */
  quietZone: number;
};

/**
 * Encode `text` as a QR matrix.
 *
 * Error correction `M` (~15%) is the deliberate middle: enough to keep
 * the code readable through a thermal-grade print, a fingerprint smear
 * and a bent-in-a-pocket scan, without inflating the module count (and
 * so the physical size) the way `H` would for a payload this short.
 */
export function buildQrMatrix(text: string): QrMatrix {
  const trimmed = text.trim();
  if (!trimmed) {
    throw new Error("buildQrMatrix: refusing to encode an empty string");
  }
  const qr = QRCode.create(trimmed, { errorCorrectionLevel: "M" });
  const size = qr.modules.size;
  // `qr.modules.data` is a FLAT row-major Uint8Array of size*size.
  // (It is not an array of rows — `data[r]` is a single module, which
  // is a trap worth naming.)
  const modules: boolean[] = new Array(size * size);
  for (let i = 0; i < modules.length; i++) {
    modules[i] = qr.modules.data[i] === 1;
  }
  return { size, modules, quietZone: 4 };
}