/**
 * Copyright (c) 2019-2021 Chris Hiszpanski. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 */

#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "err.h"
#include "log.h"
#include "sdp.h"

#define STRINGIFY(x) #x
#define TOSTRING(x) STRINGIFY(x)

/**
 * Parse group attribute
 *
 * Format is:
 *
 *     a=group:BUNDLE <mid> <mid> ...
 *
 * Only the BUNDLE semantics value is supported.
 *
 * \param sdp[out] SDP structure updated with bundle id tags.
 * \param value[in] NULL-terminated string containing SDP attribute line value
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_attr_group(struct sdp *sdp, char *val) {
    char *id = val;

    val = strsep(&id, " ");

    if (0 == strcmp("BUNDLE", val)) {
        for (int i = 0; id && i < SDP_MAX_BUNDLE_IDS; i++) {
            strncpy(sdp->mid[i], strsep(&id, " "), SDP_MAX_BUNDLE_ID_SIZE);
        }
    }
    return 0;
}

static int sdp_parse_attr_msid_semantic(struct sdp *sdp, const char *val) {
    /* not implemented */
    return 0;
}

static int sdp_parse_attr_rtcp(struct sdp *sdp, const char *val) {
    /* not implemented */
    return 0;
}

static int sdp_parse_attr_ice_ufrag(struct sdp *sdp, const char *val) {
    if (sdp->ufrag != strncpy(sdp->ufrag, val, sizeof(sdp->ufrag))) {
        return -1;
    }
    return 0;
}

static int sdp_parse_attr_ice_password(struct sdp *sdp, const char *val) {
    if (sdp->pwd != strncpy(sdp->pwd, val, sizeof(sdp->pwd))) {
        return -1;
    }
    return 0;
}

static int sdp_parse_attr_ice_options(struct sdp *sdp, const char *val) {
    if (0 == strcmp("trickle", val)) {
        sdp->ice_options.trickle = true;
    }
    return 0;
}

/**
 * Parse fingerprint
 *
 * Only SHA-256 fingerprint is supported.
 *
 * \param[out] sdp SDP structure updated with parsed content.
 * \param[in]  val NULL-terminated string.
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_attr_fingerprint(struct sdp *sdp, char *val) {
    char *fingerprint = val;

    val = strsep(&fingerprint, " ");

    if (fingerprint) {
        if (0 == strcmp("sha-256", val)) {
            if (32 != sscanf(fingerprint,
                "%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:"
                "%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:"
                "%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:"
                "%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX:%2hhX",
                &sdp->fingerprint.sha256[0],  &sdp->fingerprint.sha256[1],
                &sdp->fingerprint.sha256[2],  &sdp->fingerprint.sha256[3],
                &sdp->fingerprint.sha256[4],  &sdp->fingerprint.sha256[5],
                &sdp->fingerprint.sha256[6],  &sdp->fingerprint.sha256[7],
                &sdp->fingerprint.sha256[8],  &sdp->fingerprint.sha256[9],
                &sdp->fingerprint.sha256[10], &sdp->fingerprint.sha256[11],
                &sdp->fingerprint.sha256[12], &sdp->fingerprint.sha256[13],
                &sdp->fingerprint.sha256[14], &sdp->fingerprint.sha256[15],
                &sdp->fingerprint.sha256[16], &sdp->fingerprint.sha256[17],
                &sdp->fingerprint.sha256[18], &sdp->fingerprint.sha256[19],
                &sdp->fingerprint.sha256[20], &sdp->fingerprint.sha256[21],
                &sdp->fingerprint.sha256[22], &sdp->fingerprint.sha256[23],
                &sdp->fingerprint.sha256[24], &sdp->fingerprint.sha256[25],
                &sdp->fingerprint.sha256[26], &sdp->fingerprint.sha256[27],
                &sdp->fingerprint.sha256[28], &sdp->fingerprint.sha256[29],
                &sdp->fingerprint.sha256[30], &sdp->fingerprint.sha256[31]
            )) {
                return -URTC_ERR_SDP_MALFORMED;
            }
        } else {
            return -URTC_ERR_SDP_UNSUPPORTED_FINGERPRINT_ALGO;
        }
    } else {
        return -URTC_ERR_SDP_MALFORMED;
    }

    return 0;
}

static int sdp_parse_attr_setup(struct sdp *sdp, const char *val) {
    /* not implemented */
    return 0;
}

static int sdp_parse_attr_mid(struct sdp *sdp, const char *val) {
    /* not implemented */
    return 0;
}

static int sdp_parse_attr_extmap(struct sdp *sdp, const char *val) {
    /* not implemented */
    return 0;
}

/**
 * Parse RTP map
 *
 * Expected format is:
 * 
 *     <payload type> <encoding name>/<clock rate> [/<encoding parameters>]
 *
 * \param[out] sdp SDP structure updated with parsed content.
 * \param[in]  val NULL-terminated string.
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_attr_rtpmap(struct sdp *sdp, char *val) {
    if (!val) return -URTC_ERR_SDP_MALFORMED;

    unsigned int pt;                    // payload type
    char         en[10];                // encoding name
    unsigned int cr;                    // clock rate
    
    if (3 != sscanf(val, "%3d %9[a-zA-Z0-9]%*c%5d", &pt, en, &cr)) {
        return -URTC_ERR_SDP_MALFORMED_ATTRIBUTE;
    }

    if (0 == strcmp("H264", en)) {
        for (int i = 0; i < sdp->video.count; i++) {
            if (sdp->video.params[i].type == pt) {
                sdp->video.params[i].clock = cr;
                sdp->video.params[i].codec = SDP_CODEC_H264;
            }
        }
    }

    return 0;
}

static int sdp_parse_attr_rtcp_feedback(struct sdp *sdp, const char *val) {
    /* not implemented */
    return 0;
}

static int sdp_parse_attr_fmtp(struct sdp *sdp, const char *val) {
    /* not implemented */
    return 0;
}

/**
 * Parse SDP attribute line
 *
 * \param sdp[out] SDP structure updated with parsed content
 * \param attr[in] NULL-terminated SDP attribute string (after "a=")
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_attribute(struct sdp *sdp, char *attr) {
    char *value = attr;

    // Find colon separating attribute from value
    attr = strsep(&value, ":");

    if (value) {
        if (0 == strcmp("group", attr)) {
            return sdp_parse_attr_group(sdp, value);
        } else if (0 == strcmp("msid-semantic", attr)) {
            return sdp_parse_attr_msid_semantic(sdp, value);
        } else if (0 == strcmp("rtcp", attr)) {
            return sdp_parse_attr_rtcp(sdp, value);
        } else if (0 == strcmp("ice-ufrag", attr)) {
            return sdp_parse_attr_ice_ufrag(sdp, value);
        } else if (0 == strcmp("ice-pwd", attr)) {
            return sdp_parse_attr_ice_password(sdp, value);
        } else if (0 == strcmp("ice-options", attr)) {
            return sdp_parse_attr_ice_options(sdp, value);
        } else if (0 == strcmp("fingerprint", attr)) {
            return sdp_parse_attr_fingerprint(sdp, value);
        } else if (0 == strcmp("setup", attr)) {
            return sdp_parse_attr_setup(sdp, value);
        } else if (0 == strcmp("mid", attr)) {
            return sdp_parse_attr_mid(sdp, value);
        } else if (0 == strcmp("extmap", attr)) {
            return sdp_parse_attr_extmap(sdp, value);
        } else if (0 == strcmp("rtpmap", attr)) {
            return sdp_parse_attr_rtpmap(sdp, value);
        } else if (0 == strcmp("rtcp-fb", attr)) {
            return sdp_parse_attr_rtcp_feedback(sdp, value);
        } else if (0 == strcmp("fmtp", attr)) {
            return sdp_parse_attr_fmtp(sdp, value);
        }
    } else /* flag */ {
        if (0 == strcmp("recvonly", attr)) {
            sdp->mode = SDP_MODE_RECEIVE_ONLY;
        } else if (0 == strcmp("sendonly", attr)) {
            sdp->mode = SDP_MODE_SEND_ONLY;
        } else if (0 == strcmp("sendrecv", attr)) {
            sdp->mode = SDP_MODE_SEND_AND_RECEIVE;
        } else if (0 == strcmp("rtcp-mux", attr)) {
            sdp->rtcp_mux = true;
        } else if (0 == strcmp("rtcp-rsize", attr)) {
            sdp->rtcp_rsize = true;
        }
    }

    return 0;
}

/**
 * Parse media description line
 *
 * Format is:
 *
 *     m=<audio|video> <port> UDP/TLS/RTP/SAVPF <n> ...
 *
 * Only the UDP/TLS/RTP/SAVPF transport protocol is supported.
 *
 * \param sdp[out] SDP structure updated with username, session id and
 *                 session version.
 * \param value[in] NULL-terminated string containing SDP line value
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_media_description(struct sdp *sdp, char *value) {
    char *next = value;

    value = strsep(&next, " ");

    if (0 == strcmp("audio", value)) {
        /* not implemented */
    } else if (0 == strcmp("video", value)) {
        if (!next) return -URTC_ERR_SDP_MALFORMED_MEDIA;

        /* get port */
        value = strsep(&next, " ");
        if (1 != sscanf(value, "%5hd", &sdp->video.port)) {
            return -URTC_ERR_SDP_MALFORMED_MEDIA;
        }
        if (!next) return -URTC_ERR_SDP_MALFORMED_MEDIA;

        /* get protocol: only "UDP/TLS/RTP/SAVPF" supported */
        value = strsep(&next, " ");
        if (0 != strcmp("UDP/TLS/RTP/SAVPF", value)) {
            return -URTC_ERR_SDP_UNSUPPORTED_MEDIA_PROTOCOL;
        }
        if (!next) return -URTC_ERR_SDP_MALFORMED_MEDIA;

        /* get RTP payload types */
        sdp->video.count = 0;
        for (
            value = strsep(&next, " ");
            value && sdp->video.count < SDP_MAX_RTP_PAYLOAD_TYPES;
            value = strsep(&next, " ")
        ) {
            unsigned int *v = &sdp->video.params[sdp->video.count].type;
            if (1 != sscanf(value, "%3d", v)) {
                return -URTC_ERR_SDP_MALFORMED_MEDIA;
            }
            sdp->video.count++;
        }

    } else if (0 == strcmp("text", value)) {
        /* ignore */
    } else if (0 == strcmp("message", value)) {
        /* ignore */
    } else if (0 == strcmp("application", value)) {
        /* ignore */
    } else {
        return -URTC_ERR_SDP_UNSUPPORTED_MEDIA_TYPE;
    }

    return 0;
}

static int sdp_parse_connection_data(struct sdp *sdp, const char *value) {
    return 0;
}

/**
 * Parse version line
 *
 * Format is:
 *
 *     v=0
 *
 * Only version zero is supported. Anything else is an error.
 *
 * \param value[in] NULL-terminated string containing SDP line value
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_version(struct sdp *sdp, const char *value) {
    if (0 != strcmp("0", value)) {
        return -URTC_ERR_SDP_MALFORMED_VERSION;
    }
    sdp->version = 0;

    return 0;
}

/**
 * Parse origin line
 *
 * Format is:
 *
 *     o=<username> <sess-id> <sess-version> <nettype> <addrtype>
 *       <unicast-address>
 *
 * <nettype> <addrtype> and <unicast-address> are ignored.
 *
 * \param sdp[out] SDP structure updated with username, session id and
 *                 session version.
 * \param value[in] NULL-terminated string containing SDP line value
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_origin(struct sdp *sdp, const char *value) {
    if (3 != sscanf(value,
        "%" TOSTRING(SDP_MAX_USERNAME_SIZE) "s "
        "%" TOSTRING(SDP_MAX_SESSION_ID_SIZE) "[0-9] "
        "%" TOSTRING(SDP_MAX_SESSION_VERSION_SIZE) "[0-9] "
        "IN IP4 127.0.0.1",
        sdp->username,
        sdp->session_id,
        sdp->session_version
    )) {
        return -URTC_ERR_SDP_MALFORMED_ORIGIN;
    }

    return 0;
}

static int sdp_parse_session_name(struct sdp *sdp, const char *value) {
    return 0;
}

/**
 * Parse timing line
 *
 * Format is:
 *
 *     t=<start-time> <stop-time>
 *
 * \param sdp[out] SDP structure updated with start and stop time
 * \param value[in] NULL-terminated string containing SDP line value
 *
 * \return 0 on success. Negative on error.
 */
static int sdp_parse_timing(struct sdp *sdp, const char *value) {
    if (2 != sscanf(value, "%10lli %10lli",
        (unsigned long long *)&sdp->start_time,
        (unsigned long long *)&sdp->stop_time
    )) {
        return -URTC_ERR_SDP_MALFORMED_TIMING;
    }

    return 0;
}

/**
 * Parse a line of SDP
 *
 * \param sdp[out] SDP structure to be updated with parsed information
 * \param line[in] NULL-terminated string containing one line of SDP
 *
 * \return 0 on success, negative on error.
 */
static int sdp_parse_line(struct sdp *sdp, char *line) {
    if (!line) return -URTC_ERR_BAD_ARGUMENT;
    if (0 == strlen(line)) return 0;
    if (strlen(line) < 3) return -URTC_ERR_SDP_MALFORMED;
    if ('=' != line[1]) return -URTC_ERR_SDP_MALFORMED;

    char type = line[0];
    char *value = line + 2;

    switch (type) {
    case 'a':
        return sdp_parse_attribute(sdp, value);
    case 'c':
        return sdp_parse_connection_data(sdp, value);
    case 'o':
        return sdp_parse_origin(sdp, value);
    case 'm':
        return sdp_parse_media_description(sdp, value);
    case 's':
        return sdp_parse_session_name(sdp, value);
    case 't':
        return sdp_parse_timing(sdp, value);
    case 'v':
        return sdp_parse_version(sdp, value);
    default:
        /* ignore unsupported types */
        return 0;
    }
}


int sdp_parse(struct sdp *dst, const char *str) {
    if (!str) return -URTC_ERR_BAD_ARGUMENT;
    if (!dst) return -URTC_ERR_BAD_ARGUMENT;

    err_t retval = 0;

    /* make a malleable copy of string for parser */
    char *copy = malloc(strlen(str));
    if (copy) {
        strcpy(copy, str);

        for (char *in = copy, *line = strsep(&in, "\r\n"); in; line = strsep(&in, "\r\n")) {
            retval = sdp_parse_line(dst, line);
            if (retval != 0) {
                urtc_log(URTC_ERROR, "sdp_parse_line returned %i for %s", retval, line);
                break;
            }
        }

        free(copy);
    } else {
        return -URTC_ERR_INSUFFICIENT_MEMORY;
    }

    return retval;
}

int sdp_serialize(char *dst, size_t len, const struct sdp *src) {
    int n;

    // sanity check
    if (!dst) return -URTC_ERR_BAD_ARGUMENT;
    if (!src) return -URTC_ERR_BAD_ARGUMENT;

    // write version
    n = snprintf(dst, len, "v=%u\n", src->version);
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write originator and session identifier
    n = snprintf(dst, len,
        "o=- %s 0 IN IP4 127.0.0.1\n",
        src->session_id
    );
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write session name
    n = snprintf(dst, len, "s=%s\n",
        0 == strlen(src->session_name) ? " " : src->session_name);
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write uri
    n = snprintf(dst, len, "u=http://www.liburtc.org\n");
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write time descriptor
    n = snprintf(dst, len, "t=%" PRIu64 " %" PRIu64 "\n",
        src->start_time, src->stop_time);
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write session attribute
    n = snprintf(dst, len, "a=group:BUNDLE");
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;
    for (int i = 0; i < SDP_MAX_BUNDLE_IDS; i++) {
        if (strlen(src->mid[i]) > 0) {
            n = snprintf(dst, len, " %s", src->mid[i]);
            if (n < 0) return -URTC_ERR_SDP_MALFORMED;
            if (n >= len) return -URTC_ERR_SDP_MALFORMED;
            dst += n;
            len -= n;
        }
    }
    n = snprintf(dst, len, "\n");
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write video media description
    if (src->video.count > 0) {
        n = snprintf(
            dst, len, "m=video %hd UDP/TLS/RTP/SAVPF", src->video.port
        );
        if (n < 0) return -URTC_ERR_SDP_MALFORMED;
        if (n >= len) return -URTC_ERR_SDP_MALFORMED;
        dst += n;
        len -= n;
        for (int i = 0; i < src->video.count; i++) {
            if (src->video.params[i].codec == SDP_CODEC_H264) {
                n = snprintf(dst, len, " %d", src->video.params[i].type);
                if (n < 0) return -URTC_ERR_SDP_MALFORMED;
                if (n > len) return -URTC_ERR_SDP_MALFORMED;
                dst += n;
                len -= n;
            }
        }
        n = snprintf(dst, len, "\n");
        if (n < 0) return -URTC_ERR_SDP_MALFORMED;
        if (n >= len) return -URTC_ERR_SDP_MALFORMED;
        dst += n;
        len -= n;
    }

    // TODO write rtcp attribute

    // write connection information (TODO IPv6)
    n = snprintf(dst, len, "c=IN IP4 0.0.0.0\n");
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write media attribute: ice ufrag
    n = snprintf(dst, len, "a=ice-ufrag:%s\n", src->ufrag);
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write media attribute: ice pwd
    n = snprintf(dst, len, "a=ice-pwd:%s\n", src->pwd);
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write media attribute: trickle ICE
    if (src->ice_options.trickle) {
        n = snprintf(dst, len, "a=ice-options:trickle\n");
        if (n < 0) return -URTC_ERR_SDP_MALFORMED;
        if (n >= len) return -URTC_ERR_SDP_MALFORMED;
        dst += n;
        len -= n;
    }

    // write media attribute: fingerprint
    n = snprintf(dst, len,
        "a=fingerprint:sha-256 "
        "%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:"
        "%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:"
        "%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:"
        "%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX:%02hhX\n",
        src->fingerprint.sha256[0], src->fingerprint.sha256[1],
        src->fingerprint.sha256[2], src->fingerprint.sha256[3],
        src->fingerprint.sha256[4], src->fingerprint.sha256[5],
        src->fingerprint.sha256[6], src->fingerprint.sha256[7],
        src->fingerprint.sha256[8], src->fingerprint.sha256[9],
        src->fingerprint.sha256[10], src->fingerprint.sha256[11],
        src->fingerprint.sha256[12], src->fingerprint.sha256[13],
        src->fingerprint.sha256[14], src->fingerprint.sha256[15],
        src->fingerprint.sha256[16], src->fingerprint.sha256[17],
        src->fingerprint.sha256[18], src->fingerprint.sha256[19],
        src->fingerprint.sha256[20], src->fingerprint.sha256[21],
        src->fingerprint.sha256[22], src->fingerprint.sha256[23],
        src->fingerprint.sha256[24], src->fingerprint.sha256[25],
        src->fingerprint.sha256[26], src->fingerprint.sha256[27],
        src->fingerprint.sha256[28], src->fingerprint.sha256[29],
        src->fingerprint.sha256[30], src->fingerprint.sha256[31]
    );
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // TODO write setup, mid

    // write media attribute: mode
    switch (src->mode) {
        case SDP_MODE_RECEIVE_ONLY:
            n = snprintf(dst, len, "a=recvonly\n");
            break;
        case SDP_MODE_SEND_ONLY:
            n = snprintf(dst, len, "a=sendonly\n");
            break;
        case SDP_MODE_SEND_AND_RECEIVE:
            n = snprintf(dst, len, "a=sendrecv\n");
            break;
        default:
            return -URTC_ERR_SDP_MALFORMED;
            break;
    }
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    // write media attribute: rtcp mux
    if (src->rtcp_mux) {
        n = snprintf(dst, len, "a=rtcp-mux\n");
        if (n < 0) return -URTC_ERR_SDP_MALFORMED;
        if (n >= len) return -URTC_ERR_SDP_MALFORMED;
        dst += n;
        len -= n;
    }

    // write media attribute: rtcp rsize
    if (src->rtcp_rsize) {
        n = snprintf(dst, len, "a=rtcp-rsize\n");
        if (n < 0) return -URTC_ERR_SDP_MALFORMED;
        if (n >= len) return -URTC_ERR_SDP_MALFORMED;
        dst += n;
        n -= n;
    }

    // write dynamic profiles
    for (int i = 0; i < src->video.count; i++) {
        if (src->video.params[i].codec == SDP_CODEC_H264) {
            n = snprintf(dst, len, "a=rtpmap:%d H264/%d\n",
                src->video.params[i].type,
                src->video.params[i].clock
            );
            if (n < 0) return -URTC_ERR_SDP_MALFORMED;
            if (n >= len) return -URTC_ERR_SDP_MALFORMED;
            dst += n;
            len -= n;
        }
    }

    // write media attribute: media id
    // TODO fix hardcoded media id
    n = snprintf(dst, len, "a=mid:video\n");
    if (n < 0) return -URTC_ERR_SDP_MALFORMED;
    if (n >= len) return -URTC_ERR_SDP_MALFORMED;
    dst += n;
    len -= n;

    return 0;
}

/* vim: set expandtab ts=8 sw=4 tw=0 : */