/* eslint-env node */
"use strict";

// SDP helpers.
var SDPUtils = {};

// Generate an alphanumeric identifier for cname or mids.
// TODO: use UUIDs instead? https://gist.github.com/jed/982883
SDPUtils.generateIdentifier = function() {
  return Math.random()
    .toString(36)
    .substr(2, 10);
};

// The RTCP CNAME used by all peerconnections from the same JS.
SDPUtils.localCName = SDPUtils.generateIdentifier();

// Splits SDP into lines, dealing with both CRLF and LF.
SDPUtils.splitLines = function(blob) {
  return blob
    .trim()
    .split("\n")
    .map(function(line) {
      return line.trim();
    });
};
// Splits SDP into sessionpart and mediasections. Ensures CRLF.
SDPUtils.splitSections = function(blob) {
  var parts = blob.split("\nm=");
  return parts.map(function(part, index) {
    return (index > 0 ? "m=" + part : part).trim() + "\r\n";
  });
};

// returns the session description.
SDPUtils.getDescription = function(blob) {
  var sections = SDPUtils.splitSections(blob);
  return sections && sections[0];
};

// returns the individual media sections.
SDPUtils.getMediaSections = function(blob) {
  var sections = SDPUtils.splitSections(blob);
  sections.shift();
  return sections;
};

// Returns lines that start with a certain prefix.
SDPUtils.matchPrefix = function(blob, prefix) {
  return SDPUtils.splitLines(blob).filter(function(line) {
    return line.indexOf(prefix) === 0;
  });
};

// Parses an ICE candidate line. Sample input:
// candidate:702786350 2 udp 41819902 8.8.8.8 60769 typ relay raddr 8.8.8.8
// rport 55996"
SDPUtils.parseCandidate = function(line) {
  var parts;
  // Parse both variants.
  if (line.indexOf("a=candidate:") === 0) {
    parts = line.substring(12).split(" ");
  } else {
    parts = line.substring(10).split(" ");
  }

  var candidate = {
    foundation: parts[0],
    component: parseInt(parts[1], 10),
    protocol: parts[2].toLowerCase(),
    priority: parseInt(parts[3], 10),
    ip: parts[4],
    address: parts[4], // address is an alias for ip.
    port: parseInt(parts[5], 10),
    // skip parts[6] == 'typ'
    type: parts[7],
  };

  for (var i = 8; i < parts.length; i += 2) {
    switch (parts[i]) {
      case "raddr":
        candidate.relatedAddress = parts[i + 1];
        break;
      case "rport":
        candidate.relatedPort = parseInt(parts[i + 1], 10);
        break;
      case "tcptype":
        candidate.tcpType = parts[i + 1];
        break;
      case "ufrag":
        candidate.ufrag = parts[i + 1]; // for backward compability.
        candidate.usernameFragment = parts[i + 1];
        break;
      default:
        // extension handling, in particular ufrag
        candidate[parts[i]] = parts[i + 1];
        break;
    }
  }
  return candidate;
};

// Translates a candidate object into SDP candidate attribute.
SDPUtils.writeCandidate = function(candidate) {
  var sdp = [];
  sdp.push(candidate.foundation);
  sdp.push(candidate.component);
  sdp.push(candidate.protocol.toUpperCase());
  sdp.push(candidate.priority);
  sdp.push(candidate.address || candidate.ip);
  sdp.push(candidate.port);

  var type = candidate.type;
  sdp.push("typ");
  sdp.push(type);
  if (type !== "host" && candidate.relatedAddress && candidate.relatedPort) {
    sdp.push("raddr");
    sdp.push(candidate.relatedAddress);
    sdp.push("rport");
    sdp.push(candidate.relatedPort);
  }
  if (candidate.tcpType && candidate.protocol.toLowerCase() === "tcp") {
    sdp.push("tcptype");
    sdp.push(candidate.tcpType);
  }
  if (candidate.usernameFragment || candidate.ufrag) {
    sdp.push("ufrag");
    sdp.push(candidate.usernameFragment || candidate.ufrag);
  }
  return "candidate:" + sdp.join(" ");
};

// Parses an ice-options line, returns an array of option tags.
// a=ice-options:foo bar
SDPUtils.parseIceOptions = function(line) {
  return line.substr(14).split(" ");
};

// Parses an rtpmap line, returns RTCRtpCoddecParameters. Sample input:
// a=rtpmap:111 opus/48000/2
SDPUtils.parseRtpMap = function(line) {
  var parts = line.substr(9).split(" ");
  var parsed = {
    payloadType: parseInt(parts.shift(), 10), // was: id
  };

  parts = parts[0].split("/");

  parsed.name = parts[0];
  parsed.clockRate = parseInt(parts[1], 10); // was: clockrate
  parsed.channels = parts.length === 3 ? parseInt(parts[2], 10) : 1;
  // legacy alias, got renamed back to channels in ORTC.
  parsed.numChannels = parsed.channels;
  return parsed;
};

// Generate an a=rtpmap line from RTCRtpCodecCapability or
// RTCRtpCodecParameters.
SDPUtils.writeRtpMap = function(codec) {
  var pt = codec.payloadType;
  if (codec.preferredPayloadType !== undefined) {
    pt = codec.preferredPayloadType;
  }
  var channels = codec.channels || codec.numChannels || 1;
  return (
    "a=rtpmap:" +
    pt +
    " " +
    codec.name +
    "/" +
    codec.clockRate +
    (channels !== 1 ? "/" + channels : "") +
    "\r\n"
  );
};

// Parses an a=extmap line (headerextension from RFC 5285). Sample input:
// a=extmap:2 urn:ietf:params:rtp-hdrext:toffset
// a=extmap:2/sendonly urn:ietf:params:rtp-hdrext:toffset
SDPUtils.parseExtmap = function(line) {
  var parts = line.substr(9).split(" ");
  return {
    id: parseInt(parts[0], 10),
    direction: parts[0].indexOf("/") > 0 ? parts[0].split("/")[1] : "sendrecv",
    uri: parts[1],
  };
};

// Generates a=extmap line from RTCRtpHeaderExtensionParameters or
// RTCRtpHeaderExtension.
SDPUtils.writeExtmap = function(headerExtension) {
  return (
    "a=extmap:" +
    (headerExtension.id || headerExtension.preferredId) +
    (headerExtension.direction && headerExtension.direction !== "sendrecv"
      ? "/" + headerExtension.direction
      : "") +
    " " +
    headerExtension.uri +
    "\r\n"
  );
};

// Parses an ftmp line, returns dictionary. Sample input:
// a=fmtp:96 vbr=on;cng=on
// Also deals with vbr=on; cng=on
SDPUtils.parseFmtp = function(line) {
  var parsed = {};
  var kv;
  var parts = line.substr(line.indexOf(" ") + 1).split(";");
  for (var j = 0; j < parts.length; j++) {
    kv = parts[j].trim().split("=");
    parsed[kv[0].trim()] = kv[1];
  }
  return parsed;
};

// Generates an a=ftmp line from RTCRtpCodecCapability or RTCRtpCodecParameters.
SDPUtils.writeFmtp = function(codec) {
  var line = "";
  var pt = codec.payloadType;
  if (codec.preferredPayloadType !== undefined) {
    pt = codec.preferredPayloadType;
  }
  if (codec.parameters && Object.keys(codec.parameters).length) {
    var params = [];
    Object.keys(codec.parameters).forEach(function(param) {
      if (codec.parameters[param]) {
        params.push(param + "=" + codec.parameters[param]);
      } else {
        params.push(param);
      }
    });
    line += "a=fmtp:" + pt + " " + params.join(";") + "\r\n";
  }
  return line;
};

// Parses an rtcp-fb line, returns RTCPRtcpFeedback object. Sample input:
// a=rtcp-fb:98 nack rpsi
SDPUtils.parseRtcpFb = function(line) {
  var parts = line.substr(line.indexOf(" ") + 1).split(" ");
  return {
    type: parts.shift(),
    parameter: parts.join(" "),
  };
};
// Generate a=rtcp-fb lines from RTCRtpCodecCapability or RTCRtpCodecParameters.
SDPUtils.writeRtcpFb = function(codec) {
  var lines = "";
  var pt = codec.payloadType;
  if (codec.preferredPayloadType !== undefined) {
    pt = codec.preferredPayloadType;
  }
  if (codec.rtcpFeedback && codec.rtcpFeedback.length) {
    // FIXME: special handling for trr-int?
    codec.rtcpFeedback.forEach(function(fb) {
      lines +=
        "a=rtcp-fb:" +
        pt +
        " " +
        fb.type +
        (fb.parameter && fb.parameter.length ? " " + fb.parameter : "") +
        "\r\n";
    });
  }
  return lines;
};

// Parses an RFC 5576 ssrc media attribute. Sample input:
// a=ssrc:3735928559 cname:something
SDPUtils.parseSsrcMedia = function(line) {
  var sp = line.indexOf(" ");
  var parts = {
    ssrc: parseInt(line.substr(7, sp - 7), 10),
  };
  var colon = line.indexOf(":", sp);
  if (colon > -1) {
    parts.attribute = line.substr(sp + 1, colon - sp - 1);
    parts.value = line.substr(colon + 1);
  } else {
    parts.attribute = line.substr(sp + 1);
  }
  return parts;
};

SDPUtils.parseSsrcGroup = function(line) {
  var parts = line.substr(13).split(" ");
  return {
    semantics: parts.shift(),
    ssrcs: parts.map(function(ssrc) {
      return parseInt(ssrc, 10);
    }),
  };
};

// Extracts the MID (RFC 5888) from a media section.
// returns the MID or undefined if no mid line was found.
SDPUtils.getMid = function(mediaSection) {
  var mid = SDPUtils.matchPrefix(mediaSection, "a=mid:")[0];
  if (mid) {
    return mid.substr(6);
  }
};

SDPUtils.parseFingerprint = function(line) {
  var parts = line.substr(14).split(" ");
  return {
    algorithm: parts[0].toLowerCase(), // algorithm is case-sensitive in Edge.
    value: parts[1],
  };
};

// Extracts DTLS parameters from SDP media section or sessionpart.
// FIXME: for consistency with other functions this should only
//   get the fingerprint line as input. See also getIceParameters.
SDPUtils.getDtlsParameters = function(mediaSection, sessionpart) {
  var lines = SDPUtils.matchPrefix(
    mediaSection + sessionpart,
    "a=fingerprint:"
  );
  // Note: a=setup line is ignored since we use the 'auto' role.
  // Note2: 'algorithm' is not case sensitive except in Edge.
  return {
    role: "auto",
    fingerprints: lines.map(SDPUtils.parseFingerprint),
  };
};

// Serializes DTLS parameters to SDP.
SDPUtils.writeDtlsParameters = function(params, setupType) {
  var sdp = "a=setup:" + setupType + "\r\n";
  params.fingerprints.forEach(function(fp) {
    sdp += "a=fingerprint:" + fp.algorithm + " " + fp.value + "\r\n";
  });
  return sdp;
};

// Parses a=crypto lines into
//   https://rawgit.com/aboba/edgertc/master/msortc-rs4.html#dictionary-rtcsrtpsdesparameters-members
SDPUtils.parseCryptoLine = function(line) {
  var parts = line.substr(9).split(" ");
  return {
    tag: parseInt(parts[0], 10),
    cryptoSuite: parts[1],
    keyParams: parts[2],
    sessionParams: parts.slice(3),
  };
};

SDPUtils.writeCryptoLine = function(parameters) {
  return (
    "a=crypto:" +
    parameters.tag +
    " " +
    parameters.cryptoSuite +
    " " +
    (typeof parameters.keyParams === "object"
      ? SDPUtils.writeCryptoKeyParams(parameters.keyParams)
      : parameters.keyParams) +
    (parameters.sessionParams ? " " + parameters.sessionParams.join(" ") : "") +
    "\r\n"
  );
};

// Parses the crypto key parameters into
//   https://rawgit.com/aboba/edgertc/master/msortc-rs4.html#rtcsrtpkeyparam*
SDPUtils.parseCryptoKeyParams = function(keyParams) {
  if (keyParams.indexOf("inline:") !== 0) {
    return null;
  }
  var parts = keyParams.substr(7).split("|");
  return {
    keyMethod: "inline",
    keySalt: parts[0],
    lifeTime: parts[1],
    mkiValue: parts[2] ? parts[2].split(":")[0] : undefined,
    mkiLength: parts[2] ? parts[2].split(":")[1] : undefined,
  };
};

SDPUtils.writeCryptoKeyParams = function(keyParams) {
  return (
    keyParams.keyMethod +
    ":" +
    keyParams.keySalt +
    (keyParams.lifeTime ? "|" + keyParams.lifeTime : "") +
    (keyParams.mkiValue && keyParams.mkiLength
      ? "|" + keyParams.mkiValue + ":" + keyParams.mkiLength
      : "")
  );
};

// Extracts all SDES paramters.
SDPUtils.getCryptoParameters = function(mediaSection, sessionpart) {
  var lines = SDPUtils.matchPrefix(mediaSection + sessionpart, "a=crypto:");
  return lines.map(SDPUtils.parseCryptoLine);
};

// Parses ICE information from SDP media section or sessionpart.
// FIXME: for consistency with other functions this should only
//   get the ice-ufrag and ice-pwd lines as input.
SDPUtils.getIceParameters = function(mediaSection, sessionpart) {
  var ufrag = SDPUtils.matchPrefix(
    mediaSection + sessionpart,
    "a=ice-ufrag:"
  )[0];
  var pwd = SDPUtils.matchPrefix(mediaSection + sessionpart, "a=ice-pwd:")[0];
  if (!(ufrag && pwd)) {
    return null;
  }
  return {
    usernameFragment: ufrag.substr(12),
    password: pwd.substr(10),
  };
};

// Serializes ICE parameters to SDP.
SDPUtils.writeIceParameters = function(params) {
  return (
    "a=ice-ufrag:" +
    params.usernameFragment +
    "\r\n" +
    "a=ice-pwd:" +
    params.password +
    "\r\n"
  );
};

// Parses the SDP media section and returns RTCRtpParameters.
SDPUtils.parseRtpParameters = function(mediaSection) {
  var description = {
    codecs: [],
    headerExtensions: [],
    fecMechanisms: [],
    rtcp: [],
  };
  var lines = SDPUtils.splitLines(mediaSection);
  var mline = lines[0].split(" ");
  for (var i = 3; i < mline.length; i++) {
    // find all codecs from mline[3..]
    var pt = mline[i];
    var rtpmapline = SDPUtils.matchPrefix(
      mediaSection,
      "a=rtpmap:" + pt + " "
    )[0];
    if (rtpmapline) {
      var codec = SDPUtils.parseRtpMap(rtpmapline);
      var fmtps = SDPUtils.matchPrefix(mediaSection, "a=fmtp:" + pt + " ");
      // Only the first a=fmtp:<pt> is considered.
      codec.parameters = fmtps.length ? SDPUtils.parseFmtp(fmtps[0]) : {};
      codec.rtcpFeedback = SDPUtils.matchPrefix(
        mediaSection,
        "a=rtcp-fb:" + pt + " "
      ).map(SDPUtils.parseRtcpFb);
      description.codecs.push(codec);
      // parse FEC mechanisms from rtpmap lines.
      switch (codec.name.toUpperCase()) {
        case "RED":
        case "ULPFEC":
          description.fecMechanisms.push(codec.name.toUpperCase());
          break;
        default:
          // only RED and ULPFEC are recognized as FEC mechanisms.
          break;
      }
    }
  }
  SDPUtils.matchPrefix(mediaSection, "a=extmap:").forEach(function(line) {
    description.headerExtensions.push(SDPUtils.parseExtmap(line));
  });
  // FIXME: parse rtcp.
  return description;
};

// Generates parts of the SDP media section describing the capabilities /
// parameters.
SDPUtils.writeRtpDescription = function(kind, caps) {
  var sdp = "";

  // Build the mline.
  sdp += "m=" + kind + " ";
  sdp += caps.codecs.length > 0 ? "9" : "0"; // reject if no codecs.
  sdp += " UDP/TLS/RTP/SAVPF ";
  sdp +=
    caps.codecs
      .map(function(codec) {
        if (codec.preferredPayloadType !== undefined) {
          return codec.preferredPayloadType;
        }
        return codec.payloadType;
      })
      .join(" ") + "\r\n";

  sdp += "c=IN IP4 0.0.0.0\r\n";
  sdp += "a=rtcp:9 IN IP4 0.0.0.0\r\n";

  // Add a=rtpmap lines for each codec. Also fmtp and rtcp-fb.
  caps.codecs.forEach(function(codec) {
    sdp += SDPUtils.writeRtpMap(codec);
    sdp += SDPUtils.writeFmtp(codec);
    sdp += SDPUtils.writeRtcpFb(codec);
  });
  var maxptime = 0;
  caps.codecs.forEach(function(codec) {
    if (codec.maxptime > maxptime) {
      maxptime = codec.maxptime;
    }
  });
  if (maxptime > 0) {
    sdp += "a=maxptime:" + maxptime + "\r\n";
  }
  sdp += "a=rtcp-mux\r\n";

  if (caps.headerExtensions) {
    caps.headerExtensions.forEach(function(extension) {
      sdp += SDPUtils.writeExtmap(extension);
    });
  }
  // FIXME: write fecMechanisms.
  return sdp;
};

// Parses the SDP media section and returns an array of
// RTCRtpEncodingParameters.
SDPUtils.parseRtpEncodingParameters = function(mediaSection) {
  var encodingParameters = [];
  var description = SDPUtils.parseRtpParameters(mediaSection);
  var hasRed = description.fecMechanisms.indexOf("RED") !== -1;
  var hasUlpfec = description.fecMechanisms.indexOf("ULPFEC") !== -1;

  // filter a=ssrc:... cname:, ignore PlanB-msid
  var ssrcs = SDPUtils.matchPrefix(mediaSection, "a=ssrc:")
    .map(function(line) {
      return SDPUtils.parseSsrcMedia(line);
    })
    .filter(function(parts) {
      return parts.attribute === "cname";
    });
  var primarySsrc = ssrcs.length > 0 && ssrcs[0].ssrc;
  var secondarySsrc;

  var flows = SDPUtils.matchPrefix(mediaSection, "a=ssrc-group:FID").map(
    function(line) {
      var parts = line.substr(17).split(" ");
      return parts.map(function(part) {
        return parseInt(part, 10);
      });
    }
  );
  if (flows.length > 0 && flows[0].length > 1 && flows[0][0] === primarySsrc) {
    secondarySsrc = flows[0][1];
  }

  description.codecs.forEach(function(codec) {
    if (codec.name.toUpperCase() === "RTX" && codec.parameters.apt) {
      var encParam = {
        ssrc: primarySsrc,
        codecPayloadType: parseInt(codec.parameters.apt, 10),
      };
      if (primarySsrc && secondarySsrc) {
        encParam.rtx = { ssrc: secondarySsrc };
      }
      encodingParameters.push(encParam);
      if (hasRed) {
        encParam = JSON.parse(JSON.stringify(encParam));
        encParam.fec = {
          ssrc: primarySsrc,
          mechanism: hasUlpfec ? "red+ulpfec" : "red",
        };
        encodingParameters.push(encParam);
      }
    }
  });
  if (encodingParameters.length === 0 && primarySsrc) {
    encodingParameters.push({
      ssrc: primarySsrc,
    });
  }

  // we support both b=AS and b=TIAS but interpret AS as TIAS.
  var bandwidth = SDPUtils.matchPrefix(mediaSection, "b=");
  if (bandwidth.length) {
    if (bandwidth[0].indexOf("b=TIAS:") === 0) {
      bandwidth = parseInt(bandwidth[0].substr(7), 10);
    } else if (bandwidth[0].indexOf("b=AS:") === 0) {
      // use formula from JSEP to convert b=AS to TIAS value.
      bandwidth =
        parseInt(bandwidth[0].substr(5), 10) * 1000 * 0.95 - 50 * 40 * 8;
    } else {
      bandwidth = undefined;
    }
    encodingParameters.forEach(function(params) {
      params.maxBitrate = bandwidth;
    });
  }
  return encodingParameters;
};

// parses http://draft.ortc.org/#rtcrtcpparameters*
SDPUtils.parseRtcpParameters = function(mediaSection) {
  var rtcpParameters = {};

  // Gets the first SSRC. Note tha with RTX there might be multiple
  // SSRCs.
  var remoteSsrc = SDPUtils.matchPrefix(mediaSection, "a=ssrc:")
    .map(function(line) {
      return SDPUtils.parseSsrcMedia(line);
    })
    .filter(function(obj) {
      return obj.attribute === "cname";
    })[0];
  if (remoteSsrc) {
    rtcpParameters.cname = remoteSsrc.value;
    rtcpParameters.ssrc = remoteSsrc.ssrc;
  }

  // Edge uses the compound attribute instead of reducedSize
  // compound is !reducedSize
  var rsize = SDPUtils.matchPrefix(mediaSection, "a=rtcp-rsize");
  rtcpParameters.reducedSize = rsize.length > 0;
  rtcpParameters.compound = rsize.length === 0;

  // parses the rtcp-mux attrіbute.
  // Note that Edge does not support unmuxed RTCP.
  var mux = SDPUtils.matchPrefix(mediaSection, "a=rtcp-mux");
  rtcpParameters.mux = mux.length > 0;

  return rtcpParameters;
};

// parses either a=msid: or a=ssrc:... msid lines and returns
// the id of the MediaStream and MediaStreamTrack.
SDPUtils.parseMsid = function(mediaSection) {
  var parts;
  var spec = SDPUtils.matchPrefix(mediaSection, "a=msid:");
  if (spec.length === 1) {
    parts = spec[0].substr(7).split(" ");
    return { stream: parts[0], track: parts[1] };
  }
  var planB = SDPUtils.matchPrefix(mediaSection, "a=ssrc:")
    .map(function(line) {
      return SDPUtils.parseSsrcMedia(line);
    })
    .filter(function(msidParts) {
      return msidParts.attribute === "msid";
    });
  if (planB.length > 0) {
    parts = planB[0].value.split(" ");
    return { stream: parts[0], track: parts[1] };
  }
};

// SCTP
// parses draft-ietf-mmusic-sctp-sdp-26 first and falls back
// to draft-ietf-mmusic-sctp-sdp-05
SDPUtils.parseSctpDescription = function(mediaSection) {
  var mline = SDPUtils.parseMLine(mediaSection);
  var maxSizeLine = SDPUtils.matchPrefix(mediaSection, "a=max-message-size:");
  var maxMessageSize;
  if (maxSizeLine.length > 0) {
    maxMessageSize = parseInt(maxSizeLine[0].substr(19), 10);
  }
  if (isNaN(maxMessageSize)) {
    maxMessageSize = 65536;
  }
  var sctpPort = SDPUtils.matchPrefix(mediaSection, "a=sctp-port:");
  if (sctpPort.length > 0) {
    return {
      port: parseInt(sctpPort[0].substr(12), 10),
      protocol: mline.fmt,
      maxMessageSize,
    };
  }
  var sctpMapLines = SDPUtils.matchPrefix(mediaSection, "a=sctpmap:");
  if (sctpMapLines.length > 0) {
    var parts = SDPUtils.matchPrefix(mediaSection, "a=sctpmap:")[0]
      .substr(10)
      .split(" ");
    return {
      port: parseInt(parts[0], 10),
      protocol: parts[1],
      maxMessageSize,
    };
  }
};

// SCTP
// outputs the draft-ietf-mmusic-sctp-sdp-26 version that all browsers
// support by now receiving in this format, unless we originally parsed
// as the draft-ietf-mmusic-sctp-sdp-05 format (indicated by the m-line
// protocol of DTLS/SCTP -- without UDP/ or TCP/)
SDPUtils.writeSctpDescription = function(media, sctp) {
  var output = [];
  if (media.protocol !== "DTLS/SCTP") {
    output = [
      "m=" + media.kind + " 9 " + media.protocol + " " + sctp.protocol + "\r\n",
      "c=IN IP4 0.0.0.0\r\n",
      "a=sctp-port:" + sctp.port + "\r\n",
    ];
  } else {
    output = [
      "m=" + media.kind + " 9 " + media.protocol + " " + sctp.port + "\r\n",
      "c=IN IP4 0.0.0.0\r\n",
      "a=sctpmap:" + sctp.port + " " + sctp.protocol + " 65535\r\n",
    ];
  }
  if (sctp.maxMessageSize !== undefined) {
    output.push("a=max-message-size:" + sctp.maxMessageSize + "\r\n");
  }
  return output.join("");
};

// Generate a session ID for SDP.
// https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-20#section-5.2.1
// recommends using a cryptographically random +ve 64-bit value
// but right now this should be acceptable and within the right range
SDPUtils.generateSessionId = function() {
  return Math.floor((Math.random() * 4294967296) + 1);
};

// Write boilder plate for start of SDP
// sessId argument is optional - if not supplied it will
// be generated randomly
// sessVersion is optional and defaults to 2
// sessUser is optional and defaults to 'thisisadapterortc'
SDPUtils.writeSessionBoilerplate = function(sessId, sessVer, sessUser) {
  var sessionId;
  var version = sessVer !== undefined ? sessVer : 2;
  if (sessId) {
    sessionId = sessId;
  } else {
    sessionId = SDPUtils.generateSessionId();
  }
  var user = sessUser || "thisisadapterortc";
  // FIXME: sess-id should be an NTP timestamp.
  return (
    "v=0\r\n" +
    "o=" +
    user +
    " " +
    sessionId +
    " " +
    version +
    " IN IP4 127.0.0.1\r\n" +
    "s=-\r\n" +
    "t=0 0\r\n"
  );
};

SDPUtils.writeMediaSection = function(transceiver, caps, type, stream) {
  var sdp = SDPUtils.writeRtpDescription(transceiver.kind, caps);

  // Map ICE parameters (ufrag, pwd) to SDP.
  sdp += SDPUtils.writeIceParameters(
    transceiver.iceGatherer.getLocalParameters()
  );

  // Map DTLS parameters to SDP.
  sdp += SDPUtils.writeDtlsParameters(
    transceiver.dtlsTransport.getLocalParameters(),
    type === "offer" ? "actpass" : "active"
  );

  sdp += "a=mid:" + transceiver.mid + "\r\n";

  if (transceiver.direction) {
    sdp += "a=" + transceiver.direction + "\r\n";
  } else if (transceiver.rtpSender && transceiver.rtpReceiver) {
    sdp += "a=sendrecv\r\n";
  } else if (transceiver.rtpSender) {
    sdp += "a=sendonly\r\n";
  } else if (transceiver.rtpReceiver) {
    sdp += "a=recvonly\r\n";
  } else {
    sdp += "a=inactive\r\n";
  }

  if (transceiver.rtpSender) {
    // spec.
    var msid =
      "msid:" + stream.id + " " + transceiver.rtpSender.track.id + "\r\n";
    sdp += "a=" + msid;

    // for Chrome.
    sdp += "a=ssrc:" + transceiver.sendEncodingParameters[0].ssrc + " " + msid;
    if (transceiver.sendEncodingParameters[0].rtx) {
      sdp +=
        "a=ssrc:" + transceiver.sendEncodingParameters[0].rtx.ssrc + " " + msid;
      sdp +=
        "a=ssrc-group:FID " +
        transceiver.sendEncodingParameters[0].ssrc +
        " " +
        transceiver.sendEncodingParameters[0].rtx.ssrc +
        "\r\n";
    }
  }
  // FIXME: this should be written by writeRtpDescription.
  sdp +=
    "a=ssrc:" +
    transceiver.sendEncodingParameters[0].ssrc +
    " cname:" +
    SDPUtils.localCName +
    "\r\n";
  if (transceiver.rtpSender && transceiver.sendEncodingParameters[0].rtx) {
    sdp +=
      "a=ssrc:" +
      transceiver.sendEncodingParameters[0].rtx.ssrc +
      " cname:" +
      SDPUtils.localCName +
      "\r\n";
  }
  return sdp;
};

// Gets the direction from the mediaSection or the sessionpart.
SDPUtils.getDirection = function(mediaSection, sessionpart) {
  // Look for sendrecv, sendonly, recvonly, inactive, default to sendrecv.
  var lines = SDPUtils.splitLines(mediaSection);
  for (var i = 0; i < lines.length; i++) {
    switch (lines[i]) {
      case "a=sendrecv":
      case "a=sendonly":
      case "a=recvonly":
      case "a=inactive":
        return lines[i].substr(2);
      default:
      // FIXME: What should happen here?
    }
  }
  if (sessionpart) {
    return SDPUtils.getDirection(sessionpart);
  }
  return "sendrecv";
};

SDPUtils.getKind = function(mediaSection) {
  var lines = SDPUtils.splitLines(mediaSection);
  var mline = lines[0].split(" ");
  return mline[0].substr(2);
};

SDPUtils.isRejected = function(mediaSection) {
  return mediaSection.split(" ", 2)[1] === "0";
};

SDPUtils.parseMLine = function(mediaSection) {
  var lines = SDPUtils.splitLines(mediaSection);
  var parts = lines[0].substr(2).split(" ");
  return {
    kind: parts[0],
    port: parseInt(parts[1], 10),
    protocol: parts[2],
    fmt: parts.slice(3).join(" "),
  };
};

SDPUtils.parseOLine = function(mediaSection) {
  var line = SDPUtils.matchPrefix(mediaSection, "o=")[0];
  var parts = line.substr(2).split(" ");
  return {
    username: parts[0],
    sessionId: parts[1],
    sessionVersion: parseInt(parts[2], 10),
    netType: parts[3],
    addressType: parts[4],
    address: parts[5],
  };
};

// a very naive interpretation of a valid SDP.
SDPUtils.isValidSDP = function(blob) {
  if (typeof blob !== "string" || blob.length === 0) {
    return false;
  }
  var lines = SDPUtils.splitLines(blob);
  for (var i = 0; i < lines.length; i++) {
    if (lines[i].length < 2 || lines[i].charAt(1) !== "=") {
      return false;
    }
    // TODO: check the modifier a bit more.
  }
  return true;
};

// Expose public methods.
if (typeof module === "object") {
  module.exports = SDPUtils;
}