#pragma once

// A QR encoder, for getting a crash report off a machine whose network stack is
// dead.
//
// A panic report is worth nothing if it cannot leave the machine, and at panic
// time there is no network, no filesystem write that can be trusted, and often
// no second machine on the desk. A phone camera is a working out-of-band
// channel that needs no drivers on our side at all. See docs/architecture/graphics.md.
//
// Deliberately small, in three ways:
//
//   - Byte mode only. The report is arbitrary bytes; alphanumeric mode would
//     pack tighter but only for a restricted character set.
//   - Error correction level L only. The screen is a clean, evenly lit,
//     high-contrast source -- the failure mode QR's stronger levels protect
//     against (dirt, print damage, curved packaging) does not apply.
//   - Versions 1 to 6 only. Version 7 is where QR starts requiring an extra
//     18-bit version-information block in two more places on the symbol, and
//     version 10 is where the character count field grows and the alignment
//     pattern grid becomes 2-dimensional. Stopping at 6 avoids both, and
//     134 bytes is a large crash report.
//
// If a payload ever needs more than 134 bytes, the honest fix is to shorten the
// report -- not to reach for version 10 and its two extra tables.

#define QR_MAX_VERSION 6
#define QR_MAX_SIZE    (17 + 4 * QR_MAX_VERSION)   // 41 modules per side
#define QR_MAX_BYTES   134

struct qr {
  int size;                              // modules per side; 0 if unencoded
  unsigned char mod[QR_MAX_SIZE][QR_MAX_SIZE];   // 1 = dark
  unsigned char fn[QR_MAX_SIZE][QR_MAX_SIZE];    // 1 = function pattern
};

// Encode len bytes into q. Picks the smallest version that fits.
// Returns 0, or -1 if len > QR_MAX_BYTES.
int qr_encode(struct qr *q, const unsigned char *data, int len);

// Largest payload, in bytes, for a given version (1..QR_MAX_VERSION).
int qr_capacity(int version);