

define(function() {
  
  // regular expression for removing double slashes
  // eg http://www.example.com//my///url/here -> http://www.example.com/my/url/here
  var slashes = /([^:])\/+/g
  var removeDoubleSlashes = function(uri) {
    return uri.replace(slashes, '$1/');
  }

  // given a relative URI, and two absolute base URIs, convert it from one base to another
  var protocolRegEx = /[^\:\/]*:\/\/([^\/])*/;
  var absUrlRegEx = /^(\/|data:)/;
  function convertURIBase(uri, fromBase, toBase) {
    if (uri.match(absUrlRegEx) || uri.match(protocolRegEx))
      return uri;
    uri = removeDoubleSlashes(uri);
    // if toBase specifies a protocol path, ensure this is the same protocol as fromBase, if not
    // use absolute path at fromBase
    var toBaseProtocol = toBase.match(protocolRegEx);
    var fromBaseProtocol = fromBase.match(protocolRegEx);
    if (fromBaseProtocol && (!toBaseProtocol || toBaseProtocol[1] != fromBaseProtocol[1] || toBaseProtocol[2] != fromBaseProtocol[2]))
      return absoluteURI(uri, fromBase);
    
    else {
      return relativeURI(absoluteURI(uri, fromBase), toBase);
    }
  };
  
  // given a relative URI, calculate the absolute URI
  function absoluteURI(uri, base) {
    if (uri.substr(0, 2) == './')
      uri = uri.substr(2);

    // absolute urls are left in tact
    if (uri.match(absUrlRegEx) || uri.match(protocolRegEx))
      return uri;
    
    var baseParts = base.split('/');
    var uriParts = uri.split('/');
    
    baseParts.pop();
    
    while (curPart = uriParts.shift())
      if (curPart == '..')
        baseParts.pop();
      else
        baseParts.push(curPart);
    
    return baseParts.join('/');
  };


  // given an absolute URI, calculate the relative URI
  function relativeURI(uri, base) {
    
    // reduce base and uri strings to just their difference string
    var baseParts = base.split('/');
    baseParts.pop();
    base = baseParts.join('/') + '/';
    i = 0;
    while (base.substr(i, 1) == uri.substr(i, 1))
      i++;
    while (base.substr(i, 1) != '/')
      i--;
    base = base.substr(i + 1);
    uri = uri.substr(i + 1);

    // each base folder difference is thus a backtrack
    baseParts = base.split('/');
    var uriParts = uri.split('/');
    out = '';
    while (baseParts.shift())
      out += '../';
    
    // finally add uri parts
    while (curPart = uriParts.shift())
      out += curPart + '/';
    
    return out.substr(0, out.length - 1);
  };
  
  var normalizeCSS = function(source, fromBase, toBase) {

    fromBase = removeDoubleSlashes(fromBase);
    toBase = removeDoubleSlashes(toBase);

    var urlRegEx = /@import\s*("([^"]*)"|'([^']*)')|url\s*\((?!#)\s*(\s*"([^"]*)"|'([^']*)'|[^\)]*\s*)\s*\)/ig;
    var result, url, source;

    while (result = urlRegEx.exec(source)) {
      url = result[3] || result[2] || result[5] || result[6] || result[4];
      var newUrl;
      newUrl = convertURIBase(url, fromBase, toBase);
      var quoteLen = result[5] || result[6] ? 1 : 0;
      source = source.substr(0, urlRegEx.lastIndex - url.length - quoteLen - 1) + newUrl + source.substr(urlRegEx.lastIndex - quoteLen - 1);
      urlRegEx.lastIndex = urlRegEx.lastIndex + (newUrl.length - url.length);
    }
    
    return source;
  };
  
  normalizeCSS.convertURIBase = convertURIBase;
  normalizeCSS.absoluteURI = absoluteURI;
  normalizeCSS.relativeURI = relativeURI;
  
  return normalizeCSS;
});
//>>excludeEnd('excludeRequireCss')
