module.exports = sanityCheck;


/**
 * Dependencies.
 */
var debug = require('debug')('JsSIP:sanityCheck');
var JsSIP_C = require('./Constants');
var SIPMessage = require('./SIPMessage');
var Utils = require('./Utils');


var message, ua, transport,
  requests = [],
  responses = [],
  all = [];


requests.push(rfc3261_8_2_2_1);
requests.push(rfc3261_16_3_4);
requests.push(rfc3261_18_3_request);
requests.push(rfc3261_8_2_2_2);

responses.push(rfc3261_8_1_3_3);
responses.push(rfc3261_18_3_response);

all.push(minimumHeaders);


function sanityCheck(m, u, t) {
  var len, pass;

  message = m;
  ua = u;
  transport = t;

  len = all.length;
  while(len--) {
    pass = all[len](message);
    if(pass === false) {
      return false;
    }
  }

  if(message instanceof SIPMessage.IncomingRequest) {
    len = requests.length;
    while(len--) {
      pass = requests[len](message);
      if(pass === false) {
        return false;
      }
    }
  }

  else if(message instanceof SIPMessage.IncomingResponse) {
    len = responses.length;
    while(len--) {
      pass = responses[len](message);
      if(pass === false) {
        return false;
      }
    }
  }

  //Everything is OK
  return true;
}


/*
 * Sanity Check for incoming Messages
 *
 * Requests:
 *  - _rfc3261_8_2_2_1_ Receive a Request with a non supported URI scheme
 *  - _rfc3261_16_3_4_ Receive a Request already sent by us
 *   Does not look at via sent-by but at jssip_id, which is inserted as
 *   a prefix in all initial requests generated by the ua
 *  - _rfc3261_18_3_request_ Body Content-Length
 *  - _rfc3261_8_2_2_2_ Merged Requests
 *
 * Responses:
 *  - _rfc3261_8_1_3_3_ Multiple Via headers
 *  - _rfc3261_18_3_response_ Body Content-Length
 *
 * All:
 *  - Minimum headers in a SIP message
 */

// Sanity Check functions for requests
function rfc3261_8_2_2_1() {
  if(message.s('to').uri.scheme !== 'sip') {
    reply(416);
    return false;
  }
}

function rfc3261_16_3_4() {
  if(!message.to_tag) {
    if(message.call_id.substr(0, 5) === ua.configuration.jssip_id) {
      reply(482);
      return false;
    }
  }
}

function rfc3261_18_3_request() {
  var len = Utils.str_utf8_length(message.body),
  contentLength = message.getHeader('content-length');

  if(len < contentLength) {
    reply(400);
    return false;
  }
}

function rfc3261_8_2_2_2() {
  var tr, idx,
    fromTag = message.from_tag,
    call_id = message.call_id,
    cseq = message.cseq;

  // Accept any in-dialog request.
  if(message.to_tag) {
    return;
  }

  // INVITE request.
  if (message.method === JsSIP_C.INVITE) {
    // If the branch matches the key of any IST then assume it is a retransmission
    // and ignore the INVITE.
    // TODO: we should reply the last response.
    if (ua.transactions.ist[message.via_branch]) {
      return false;
    }
    // Otherwise check whether it is a merged request.
    else {
      for(idx in ua.transactions.ist) {
        tr = ua.transactions.ist[idx];
        if(tr.request.from_tag === fromTag && tr.request.call_id === call_id && tr.request.cseq === cseq) {
          reply(482);
          return false;
        }
      }
    }
  }
  // Non INVITE request.
  else {
    // If the branch matches the key of any NIST then assume it is a retransmission
    // and ignore the request.
    // TODO: we should reply the last response.
    if (ua.transactions.nist[message.via_branch]) {
      return false;
    }
    // Otherwise check whether it is a merged request.
    else {
      for(idx in ua.transactions.nist) {
        tr = ua.transactions.nist[idx];
        if(tr.request.from_tag === fromTag && tr.request.call_id === call_id && tr.request.cseq === cseq) {
          reply(482);
          return false;
        }
      }
    }
  }
}

// Sanity Check functions for responses
function rfc3261_8_1_3_3() {
  if(message.getHeaders('via').length > 1) {
    debug('more than one Via header field present in the response, dropping the response');
    return false;
  }
}

function rfc3261_18_3_response() {
  var
    len = Utils.str_utf8_length(message.body),
    contentLength = message.getHeader('content-length');

    if(len < contentLength) {
      debug('message body length is lower than the value in Content-Length header field, dropping the response');
      return false;
    }
}

// Sanity Check functions for requests and responses
function minimumHeaders() {
  var
    mandatoryHeaders = ['from', 'to', 'call_id', 'cseq', 'via'],
    idx = mandatoryHeaders.length;

  while(idx--) {
    if(!message.hasHeader(mandatoryHeaders[idx])) {
      debug('missing mandatory header field : ' + mandatoryHeaders[idx] + ', dropping the response');
      return false;
    }
  }
}

// Reply
function reply(status_code) {
  var to,
    response = 'SIP/2.0 ' + status_code + ' ' + JsSIP_C.REASON_PHRASE[status_code] + '\r\n',
    vias = message.getHeaders('via'),
    length = vias.length,
    idx = 0;

  for(idx; idx < length; idx++) {
    response += 'Via: ' + vias[idx] + '\r\n';
  }

  to = message.getHeader('To');

  if(!message.to_tag) {
    to += ';tag=' + Utils.newTag();
  }

  response += 'To: ' + to + '\r\n';
  response += 'From: ' + message.getHeader('From') + '\r\n';
  response += 'Call-ID: ' + message.call_id + '\r\n';
  response += 'CSeq: ' + message.cseq + ' ' + message.method + '\r\n';
  response += '\r\n';

  transport.send(response);
}