#include <stdio.h>

#include <osmocom/core/bits.h>
#include <osmocom/core/crc32gen.h>

/* x24 + x23 + x21 + x20 + x19 + x17 + x16 + x15 + x13 + x8 + x7 + x5 + x4 + x2 + 1 */
static const struct osmo_crc32gen_code fcs = {
        .bits = 24,
        .poly = 0xbba1b5,
        .init = 0xffffff,
        .remainder = 0xffffff,
};

static int
rlp_process_frame(pbit_t *frame)
{
        ubit_t fbits[240];
        int crc;

        /* Decode to bits */
        osmo_pbit2ubit_ext(fbits, 0, frame, 0, 240, 1);

        /* Check CRC */
        crc = osmo_crc32gen_check_bits(&fcs, fbits, 216, fbits+216);
        if (crc)
                return -1;

        /* Frame type */
        if (!memcmp(&fbits[3], "\x01\x01\x01\x01\x01\x01", 6))
        {
                const char *m_names[32] = {
                        [ 0] = "UI",
                        [ 3] = "DM",
                        [ 7] = "SABM",
                        [ 8] = "DISC",
                        [12] = "UA",
                        [15] = "NULL",
                        [17] = "REMAP",
                        [23] = "XID",
                        [29] = "TEST",
                };
                int M;

                M = (frame[1] & 0x7c) >> 2;

                printf(" U  : %s\n",
                        m_names[M]
                );

                if (M == 23) {
                        int i;
                        for (i=0; i<30; i++)
                                printf("%02x", frame[i]);
                        printf("\n");
                }

        }
        else if (!memcmp(&fbits[3], "\x00\x01\x01\x01\x01\x01", 6))
        {
                const char *s_names[4] = { "RR", "RNR", "REJ", "SREJ" };
                int nr;

                nr = (frame[1] >> 5) | ((frame[2] & 0x3f) << 3);

                printf(" S  : %4s - N(R) = %3d\n",
                        s_names[(frame[0] & 0x06) >> 1],
                        nr
                );
        }
        else
        {
                const char *s_names[4] = { "RR", "RNR", "REJ", "SREJ" };
                int ns, nr;

                ns = frame[0] | ((frame[1] & 1) << 8);
                nr = (frame[1] >> 5) | ((frame[2] & 0x3f) << 3);
                printf("I+S : %4s - N(R) = %3d  N(S) = %3d\n",
                        s_names[(frame[0] & 0x06) >> 1],
                        nr, ns
                );

                {
                        int i;
                        printf("data: ");
                        for (i=3; i<27; i++)
                                printf("%02x", frame[i]);
                        printf("\n");
                }
        }

        return 0;

}

int main(int argc, char *argv[])
{
        FILE *fh;
        pbit_t frame[30];

        fh = fopen(argv[1], "rb");
        if (!fh)
                return -1;

        while (!feof(fh)) {
                fread(frame, 30, 1, fh);
                rlp_process_frame(frame);
        }

        fclose(fh);

        return 0;

}