#include "decode_gtp.h"

#define GTP_TPDU 255
#define GTP1U_PORT 2152
#define GTP1_F_MASK 0x07

#define GTP1_GET_TYPE(gtp1_hdr) ((gtp1_hdr)->type)
#define GTP1_GET_FLAGS(gtp1_hdr) ((gtp1_hdr)->flags >> 5)
#define GTP1_GET_HLEN(gtp1_hdr) (((gtp1_hdr)->flags & GTP1_F_MASK) > 0 ? 12 : 8)

enum gtp_version_e
{
    GTP_V0 = 0,
    GTP_V1,
};

int decode_gtp(gtp_info_t *packet, const uint8_t *data, uint32_t len)
{
    if (len < sizeof(gtp1_header_t))
    {
        LOG_ERROR("Parser GTP Header: packet length too small %d", len);
        return -1;
    }

    packet->hdr = (gtp1_header_t *)data;
    if (GTP1_GET_FLAGS(packet->hdr) != GTP_V1)
    {
        LOG_ERROR("Parser GTP Header: invalid gtp flags %d", GTP1_GET_FLAGS(packet->hdr));
        return -1;
    }

    if (GTP1_GET_TYPE(packet->hdr) != GTP_TPDU)
    {
        LOG_ERROR("Parser GTP Header: invalid gtp type %d", GTP1_GET_TYPE(packet->hdr));
        return -1;
    }

    /* From 29.060: "This field shall be present if and only if any one or
     * more of the S, PN and E flags are set.".
     *
     * If any of the bit is set, then the remaining ones also have to be set.
     */
    packet->hdr_len = GTP1_GET_HLEN(packet->hdr);
    packet->payload = (uint8_t *)data + packet->hdr_len;
    packet->payload_len = len - packet->hdr_len;

    return 0;
}

int dump_gtp_info(gtp_info_t *packet, char *buff, size_t size)
{
    return snprintf(buff, size,
                    "{\"hdr_len\":%u,\"data_len\":%u}",
                    packet->hdr_len,
                    packet->payload_len);
}