#ifndef VL_PROTOCOL_H
#define VL_PROTOCOL_H
#include <stddef.h>
#include <stdint.h>
#include "mbedtls/md.h"

/* All functions return 0 on success, nonzero on failure. Not board firmware.
 * String outputs include NUL, binary outputs do not. Never transmit the NUL.
 * Caller owns buffers; inputs/outputs must not overlap. */
int vl_key_from_hex(const char *hex, uint8_t key[32]);
/* rng must fill ALL n bytes from the hardware/OS secure RNG; return 0 or fail. */
typedef int (*vl_rng_fn)(void *context, uint8_t *bytes, size_t n);
int vl_nonce(vl_rng_fn rng, void *context, char out[23]);
int vl_uuid4(vl_rng_fn rng, void *context, char out[37]);
int vl_sha256_hex(const void *bytes, size_t length, char out[65]);
int vl_http_sign(const uint8_t key[32], const char *method, const char *path,
                 const char *device_id, const char *key_version,
                 const char *timestamp_ms, const char *nonce,
                 const char *request_id, const void *body, size_t body_length,
                 char signature_hex[65]);
int vl_ble_pack(const void *json_utf8, size_t length,
                uint8_t *frame, size_t capacity, size_t *frame_length);
/* Stream OTA bytes with bounded memory. Always call mbedtls_md_free after
 * begin, even if an update/finish fails. Do not begin twice on a live context. */
int vl_sha256_begin(mbedtls_md_context_t *context);
int vl_sha256_update(mbedtls_md_context_t *context, const void *bytes, size_t n);
int vl_sha256_finish(mbedtls_md_context_t *context, char out[65]);
/* Read already downloaded bytes (e.g. flash/file): 0=success, *n=0 means EOF.
 * On each call write at most capacity bytes; return nonzero on I/O failure. */
typedef int (*vl_read_fn)(void *context, uint8_t *out, size_t capacity, size_t *n);
int vl_ota_verify(vl_read_fn read, void *context, uint64_t expected_size,
                  const char *expected_sha256);
#endif