import QRCode from "qrcode";

/**
 * The single QR encoder for this project.
 *
 * ONE encoder feeds two surfaces — the SVG badge on screen and the vector PDF — so a
 * badge can never be printed with a different code than the one displayed. That drift
 * is the one failure this whole feature must not have: a badge whose printed code
 * differs from its on-screen code identifies the wrong person.
 *
 * `qrcode` is used rather than `react-qr-code` because we need the raw MODULE MATRIX,
 * not a rendered widget: the PDF draws each dark module as a real rectangle, which
 * keeps the printed QR vector-sharp at any printer resolution.
 */

// High correction on purpose: a badge is scanned off a lanyard, and the realistic
// failure modes are a scratch, a smear of mud, or a fold. H tolerates ~30% damage.
const EC_LEVEL = "H" as const;

export type QrMatrix = {
  /** Modules per side, e.g. 29. */
  size: number;
  /** Row-major, 1 = dark. */
  data: Uint8Array;
};

export function qrMatrix(payload: string): QrMatrix {
  const qr = QRCode.create(payload, { errorCorrectionLevel: EC_LEVEL });
  return { size: qr.modules.size, data: qr.modules.data };
}

/** Is a module at (x, y) dark? */
export function isDark(m: QrMatrix, x: number, y: number): boolean {
  return m.data[y * m.size + x] === 1;
}

/**
 * A QR as an inline SVG path, with the quiet zone baked in.
 *
 * `d` is a run of `M x y h w v h ... z` rectangles — one per dark module, each a
 * single filled square. One path element instead of hundreds of <rect>s keeps the DOM
 * small when a page shows a badge per mechanic.
 */
export function qrSvgPath(m: QrMatrix, quiet = 2): { d: string; viewBox: number } {
  const span = m.size + quiet * 2;
  const parts: string[] = [];
  for (let y = 0; y < m.size; y++) {
    let run = 0;
    for (let x = 0; x <= m.size; x++) {
      const dark = x < m.size && isDark(m, x, y);
      if (dark) {
        run++;
      } else if (run > 0) {
        // Merge horizontally adjacent dark modules into one rect — far fewer path
        // commands, and visually identical.
        parts.push(`M${x - run + quiet} ${y + quiet}h${run}v1h-${run}z`);
        run = 0;
      }
    }
  }
  return { d: parts.join(""), viewBox: span };
}