#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 two 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.
//
// Every version, 1 to 40. It stopped at 6 -- 134 bytes, enough for the crash
// card -- until PSOGM mode wanted the log itself off the machine, a page of it
// per symbol: version 40 at level L carries 2,953 bytes. A struct qr is
// therefore about 62 KB; keep one static, never on a stack.

#define QR_MAX_VERSION 40
#define QR_MAX_SIZE    (17 + 4 * QR_MAX_VERSION)   // 177 modules per side
#define QR_MAX_BYTES   2953

// The crash card on the PSOGM stays small, so a phone reads it from across a
// desk: a version-6 symbol at most.
#define QR_CARD_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);