#ifndef OBFUSCATE_H
#define OBFUSCATE_H

#include <stdint.h>

/* Payload uses lower 40 bits; upper 24 bits hold verification tag. */
#define OBF_PAYLOAD_BITS 40u
#define OBF_PAYLOAD_MASK ((1ULL << OBF_PAYLOAD_BITS) - 1ULL)

/* Return codes */
#define OBF_OK           0
#define OBF_ERR_NULL    -1  /* out pointer is NULL */
#define OBF_ERR_RANGE   -2  /* val exceeds encodable payload width */
#define OBF_ERR_VERIFY  -3  /* tag mismatch (wrong seed or corrupted data) */

/*
 * Encode uint64_t payload (e.g. flag bits) using seed-derived keystream.
 * seed is typically unix time in whole seconds shared by encoder and decoder.
 *
 * On success writes single uint64_t to *out and returns OBF_OK.
 */
int32_t encode(uint64_t val, uint64_t seed, uint64_t *out);

/*
 * Decode and verify. seed must match the value used at encode time.
 * On success writes recovered payload to *out and returns OBF_OK.
 */
int32_t decode(uint64_t encoded_val, uint64_t seed, uint64_t *out);

#endif /* OBFUSCATE_H */