/**
 * peachQR.ts — render a Peach binary payload as a printable QR code.
 *
 * The spec (§4) calls for a proprietary dense matrix format with custom
 * anchor patterns and Reed-Solomon ECC tuned for high-capacity payloads.
 * That decoder is non-trivial (perspective correction + ECC + camera
 * frame analysis) and is genuinely out of scope for v2.5.0. For now the
 * print-backup path uses a standard QR code via the bundled `qrcode`
 * package with byte-mode segments and low ECC for maximum capacity.
 *
 * Standard QR (v40, ECC level L) caps at 2,953 binary bytes — that
 * covers the common case (vaults up to roughly 100 entries). Larger
 * vaults are advised to use PeachScript instead. The full proprietary
 * matrix code (20 KB capacity, custom Reed-Solomon, four-anchor
 * orientation) is a follow-up; the call sites below already separate
 * "encode" from "render", so swapping in the spec-compliant codec later
 * does not require touching the UI layer.
 */

import QRCode from "qrcode";

/** Approximate binary capacity for standard QR Version 40, ECC level L. */
export const QR_MAX_BYTES = 2953;

export interface PeachQROptions {
  /** Pixel width of one matrix module. Higher = larger PNG. Default 6. */
  scale?: number;
  /** White margin in modules around the code. Default 4. */
  margin?: number;
}

/**
 * Render a binary payload to a black-and-white QR canvas. Throws
 * `QR_PAYLOAD_TOO_LARGE` if the payload exceeds standard QR capacity —
 * callers should fall back to PeachScript in that case.
 */
export async function renderPeachQR(
  payload: Uint8Array,
  opts: PeachQROptions = {}
): Promise<HTMLCanvasElement> {
  if (payload.length > QR_MAX_BYTES) {
    throw new Error("QR_PAYLOAD_TOO_LARGE");
  }

  const canvas = document.createElement("canvas");
  await QRCode.toCanvas(
    canvas,
    [{ data: payload, mode: "byte" }],
    {
      errorCorrectionLevel: "L",
      margin: opts.margin ?? 4,
      scale: opts.scale ?? 6,
      color: { dark: "#000000", light: "#ffffff" },
    }
  );
  return canvas;
}

/** Convenience: PNG data URL ready for download. */
export async function renderPeachQRDataURL(
  payload: Uint8Array,
  opts: PeachQROptions = {}
): Promise<string> {
  if (payload.length > QR_MAX_BYTES) {
    throw new Error("QR_PAYLOAD_TOO_LARGE");
  }
  return QRCode.toDataURL([{ data: payload, mode: "byte" }], {
    errorCorrectionLevel: "L",
    margin: opts.margin ?? 4,
    scale: opts.scale ?? 6,
    color: { dark: "#000000", light: "#ffffff" },
  });
}