/**
 * @file se050_tai64n.h
 * @brief TAI64N Timestamp Encoding (WireGuard Protocol Layer)
 * RFC 7539 Section 7.2.1
 */

#ifndef SE050_TAI64N_H
#define SE050_TAI64N_H

#include <stdint.h>
#include <stddef.h>

#ifdef __cplusplus
extern "C" {
#endif

#define TAI64N_SIZE 12
#define TAI64_BASE 0x4000000000000010ULL

/**
 * @brief TAI64N timestamp structure (12 bytes)
 */
typedef struct {
    uint64_t tai64;      /* TAI64 timestamp (8 bytes) */
    uint32_t nanosec;    /* Nanoseconds (4 bytes) */
} __attribute__((packed)) tai64n_t;

/**
 * @brief Encode current time as TAI64N
 * @param out Output buffer (12 bytes)
 * @return 0 on success, -1 on error
 */
int se050_tai64n_now(uint8_t out[TAI64N_SIZE]);

/**
 * @brief Encode a TAI64N timestamp
 * @param out Output buffer (12 bytes)
 * @param seconds Unix timestamp (seconds since 1970-01-01)
 * @param nanoseconds Nanoseconds (0-999999999)
 * @return 0 on success, -1 on error
 */
int se050_tai64n_encode(uint8_t out[TAI64N_SIZE],
                        uint64_t seconds, uint32_t nanoseconds);

/**
 * @brief Decode a TAI64N timestamp
 * @param seconds Output Unix timestamp (seconds)
 * @param nanoseconds Output nanoseconds
 * @param in Input buffer (12 bytes)
 * @return 0 on success, -1 on error
 */
int se050_tai64n_decode(uint64_t *seconds, uint32_t *nanoseconds,
                        const uint8_t in[TAI64N_SIZE]);

/**
 * @brief Check if TAI64N timestamp is within acceptable window
 * @param timestamp Timestamp to check
 * @param window_sec Acceptable window in seconds
 * @return 0 if within window, -1 if too old, -2 if too far in future
 */
int se050_tai64n_check_window(const uint8_t timestamp[TAI64N_SIZE],
                              uint32_t window_sec);

#ifdef __cplusplus
}
#endif

#endif /* SE050_TAI64N_H */