function SDPDiffer(mySDP, otherSDP) {
    this.mySDP = mySDP;
    this.otherSDP = otherSDP;
}

/**
 * Returns map of MediaChannel that contains only media not contained in <tt>otherSdp</tt>. Mapped by channel idx.
 * @param otherSdp the other SDP to check ssrc with.
 */
SDPDiffer.prototype.getNewMedia = function() {

    // this could be useful in Array.prototype.
    function arrayEquals(array) {
        // if the other array is a falsy value, return
        if (!array)
            return false;

        // compare lengths - can save a lot of time
        if (this.length != array.length)
            return false;

        for (var i = 0, l=this.length; i < l; i++) {
            // Check if we have nested arrays
            if (this[i] instanceof Array && array[i] instanceof Array) {
                // recurse into the nested arrays
                if (!this[i].equals(array[i]))
                    return false;
            }
            else if (this[i] != array[i]) {
                // Warning - two different object instances will never be equal: {x:20} != {x:20}
                return false;
            }
        }
        return true;
    }

    var myMedias = this.mySDP.getMediaSsrcMap();
    var othersMedias = this.otherSDP.getMediaSsrcMap();
    var newMedia = {};
    Object.keys(othersMedias).forEach(function(othersMediaIdx) {
        var myMedia = myMedias[othersMediaIdx];
        var othersMedia = othersMedias[othersMediaIdx];
        if(!myMedia && othersMedia) {
            // Add whole channel
            newMedia[othersMediaIdx] = othersMedia;
            return;
        }
        // Look for new ssrcs accross the channel
        Object.keys(othersMedia.ssrcs).forEach(function(ssrc) {
            if(Object.keys(myMedia.ssrcs).indexOf(ssrc) === -1) {
                // Allocate channel if we've found ssrc that doesn't exist in our channel
                if(!newMedia[othersMediaIdx]){
                    newMedia[othersMediaIdx] = {
                        mediaindex: othersMedia.mediaindex,
                        mid: othersMedia.mid,
                        ssrcs: {},
                        ssrcGroups: []
                    };
                }
                newMedia[othersMediaIdx].ssrcs[ssrc] = othersMedia.ssrcs[ssrc];
            }
        });

        // Look for new ssrc groups across the channels
        othersMedia.ssrcGroups.forEach(function(otherSsrcGroup){

            // try to match the other ssrc-group with an ssrc-group of ours
            var matched = false;
            for (var i = 0; i < myMedia.ssrcGroups.length; i++) {
                var mySsrcGroup = myMedia.ssrcGroups[i];
                if (otherSsrcGroup.semantics == mySsrcGroup.semantics
                    && arrayEquals.apply(otherSsrcGroup.ssrcs, [mySsrcGroup.ssrcs])) {

                    matched = true;
                    break;
                }
            }

            if (!matched) {
                // Allocate channel if we've found an ssrc-group that doesn't
                // exist in our channel

                if(!newMedia[othersMediaIdx]){
                    newMedia[othersMediaIdx] = {
                        mediaindex: othersMedia.mediaindex,
                        mid: othersMedia.mid,
                        ssrcs: {},
                        ssrcGroups: []
                    };
                }
                newMedia[othersMediaIdx].ssrcGroups.push(otherSsrcGroup);
            }
        });
    });
    return newMedia;
};

/**
 * Sends SSRC update IQ.
 * @param sdpMediaSsrcs SSRCs map obtained from SDP.getNewMedia. Cntains SSRCs to add/remove.
 * @param sid session identifier that will be put into the IQ.
 * @param initiator initiator identifier.
 * @param toJid destination Jid
 * @param isAdd indicates if this is remove or add operation.
 */
SDPDiffer.prototype.toJingle = function(modify) {
    var sdpMediaSsrcs = this.getNewMedia();
    var self = this;

    // FIXME: only announce video ssrcs since we mix audio and dont need
    //      the audio ssrcs therefore
    var modified = false;
    Object.keys(sdpMediaSsrcs).forEach(function(mediaindex){
        modified = true;
        var media = sdpMediaSsrcs[mediaindex];
        modify.c('content', {name: media.mid});

        modify.c('description', {xmlns:'urn:xmpp:jingle:apps:rtp:1', media: media.mid});
        // FIXME: not completly sure this operates on blocks and / or handles different ssrcs correctly
        // generate sources from lines
        Object.keys(media.ssrcs).forEach(function(ssrcNum) {
            var mediaSsrc = media.ssrcs[ssrcNum];
            modify.c('source', { xmlns: 'urn:xmpp:jingle:apps:rtp:ssma:0' });
            modify.attrs({ssrc: mediaSsrc.ssrc});
            // iterate over ssrc lines
            mediaSsrc.lines.forEach(function (line) {
                var idx = line.indexOf(' ');
                var kv = line.substr(idx + 1);
                modify.c('parameter');
                if (kv.indexOf(':') == -1) {
                    modify.attrs({ name: kv });
                } else {
                    modify.attrs({ name: kv.split(':', 2)[0] });
                    modify.attrs({ value: kv.split(':', 2)[1] });
                }
                modify.up(); // end of parameter
            });
            modify.up(); // end of source
        });

        // generate source groups from lines
        media.ssrcGroups.forEach(function(ssrcGroup) {
            if (ssrcGroup.ssrcs.length != 0) {

                modify.c('ssrc-group', {
                    semantics: ssrcGroup.semantics,
                    xmlns: 'urn:xmpp:jingle:apps:rtp:ssma:0'
                });

                ssrcGroup.ssrcs.forEach(function (ssrc) {
                    modify.c('source', { ssrc: ssrc })
                        .up(); // end of source
                });
                modify.up(); // end of ssrc-group
            }
        });

        modify.up(); // end of description
        modify.up(); // end of content
    });

    return modified;
};

module.exports = SDPDiffer;