DiceRoller = {

   regExp: /([\d]+)d([\d]+)(([\-\+])([\d]+))?/gi,

      parseInput:function(strIn)

      {

        var retStr = {error: false, message: ""};

        var str = strIn;

       var matches = (this.regExp.exec(str));

       if ( matches === null ||  str != matches[0] )

       {

         retStr.error = true;

         retStr.message = "input doesn't match pattern";

       } else if ( parseInt(matches[1], 10) === 0 || parseInt(matches[2], 10) === 0)

       {

         retStr.error = true;

         retStr.message = "sides of dice and rolls can't be zero";

       } else {

         retStr.numSides = parseInt(matches[2], 10);

         retStr.numDices = parseInt(matches[1], 10);

         if (! matches[3] )

         { 

           retStr.modifier = 0;

         }else{

           retStr.modifier = parseInt(matches[5], 10) *  ( matches[4] == "-" ? -1 : 1) ;

         }

         retStr.rolls = [];

         retStr.total=retStr.modifier;

         for ( var i = 0; i < retStr.numDices; i++)

         {

             retStr.rolls.push(this.performRoll(retStr.numSides));

            retStr.total+=retStr.rolls[retStr.rolls.length-1];

         }

       }

        return retStr;

      },

   performRoll: function(sides)

   {

     return Math.floor(Math.random()*sides+1);

   }, 

   driveRolls: function(input, output)

   {

     var str = document.getElementById(input).value;

      var outElm = document.getElementById(output);

     var res = this.parseInput(str);

     if ( res.error )

     {

      outElm.innerHTML = ("Error has occured:" + res.message);

     } else {

      var outStr =[];

       outStr.push("You have rolled " +      

                   (res.numDices == 1 ? "a " : res.numDices + " ") + res.numSides + " sided " + 

                   (res.numDices==1? "die" : "dice" ));

       for ( var i = 0; i < res.rolls.length; i++)

       {

         outStr.push("Roll #" + (i+1) + ": " + res.rolls[i]);

       }

       if ( res.modifier !== 0)

       {

         outStr.push("You had a " + res.modifier + " modifier.");

       }

       outStr.push("For a Total of: " + res.total);

       outElm.innerHTML = outStr.join("<br />");

     }

   }

    };