$(function() {

 
  // Handle AC and CE keys
  $(".greykey").on("click", function(e) {
	  	var valEntered = e.currentTarget.innerText;
      var valCur =$("#outputFormula").text();

	// get rid of any extra characters by only passing the 1st one. 
       valEntered = valEntered.charAt(0);
            
      switch (valEntered) {
          case "C": // Clear entry
          	// get last number entered
        		if (valCur.length > 0 &&         				
        				!valCur.includes("+") &&
        				!valCur.includes("-") &&
        				!valCur.includes("*") &&
						!valCur.includes("/")) {
	            $("#outputFormula").html("");
	          } else {
	          	
	          	var pos = valCur.length;

	          	while(pos > 0) {
	          		var chTest = valCur[valCur.length-1];
                if (testNum(chTest) || chTest == '.' || chTest == '=') {
                  valCur = valCur.substr(0,valCur.length-1);
                  pos --;							
                } else if (testMathFunc(chTest)) {
                  pos = 0;
                } else {											
                  pos --;
                }			          	
	          	}
	          	$("#outputFormula").html(valCur);
	          }    		      	

          break;
          default: // AC (all clear) clicked
          	$("#outputRes").html("0");
          	$("#outputFormula").html("");
          break;
      }
	});
  
  $(".key").on("click", function(e) {
    // check for resolved previous formula so we cab start again
    var formula = $("#outputFormula").text();
    if (formula.substr(formula.length - 1) === "=") {
      $("#outputFormula").text("");
    }
    var valEntered = e.currentTarget.innerText;
    var valCur = $("#outputFormula").text();

    // get rid of any extra characters by only passing the 1st one. 
    valEntered = valEntered.charAt(0);

    switch (valEntered) {
      case "1":
      case "2":
      case "3":
      case "4":
      case "5":
      case "6":
      case "7":
      case "8":
      case "9":
	      	if (valCur.length === 0) {
	            $("#outputFormula").html(valEntered); 
	          } else if (valCur.length === 1 && valCur.charAt(0) == '0') {
	          	// if there is only 1 zero, overwrite it.
	          	$("#outputFormula").html(valEntered);
	         }	else if (valCur.charAt(valCur.length -1) == '0') {
	            // test if we have an operator...
	         	var lastNumIdx = testIfHaveOperator(valCur);
	         	var latestNumber = (lastNumIdx > -1) ? 
	         											valCur.substr(lastNumIdx, valCur.length - 1) : 
	         											valCur.substr(0, valCur.length);
	         	if (latestNumber.indexOf('.') === -1) {
	         	// wipe out the last digit as it's a zero if no decimal points
	            	valCur = valCur.substring(0, valCur.length - 1);
	         	}
	          	$("#outputFormula").html(valCur + valEntered);
	          } else {
	          	$("#outputFormula").html(valCur + valEntered);	            
	          }

      break;
      case "0":
        // testing start of string

        		var testZero = new RegExp('0*.?0+');
            //  surpress leading zeros and allow 11100110101 type
	        	if (valCur == "0") {
	        		$("#outputFormula").html("0");
		        	break;
	   		    }     	
        
       		if (valCur.length === 0) {
	            $("#outputFormula").html( valEntered); 
	          } else if (valCur == 0 && valCur.charAt(valCur.length -1) != '.') {
	          		if (parseFloat(valCur) || testZero.test(valCur) ) {
	          	 		$("#outputFormula").html(valCur + valEntered);
	          	 	} else {
	          	 		$("#outputFormula").html("0" );
	          	 	}
	          	
	          }  else if (valCur.charAt(valCur.length -1) != '0') {
	           // stop last number entered having leading zeros
	           // TODO: check if ZERO!!!
	           	$("#outputFormula").html(valCur + valEntered);	            
	          } else {
	          	var testLastNum = '';
					
					// got operators, is it not the 1st number?
					var opIndex = testIfHaveOperator (valCur);
	          	if (opIndex > -1) {
	          		var idx = valCur.length -1;
	          		while (valCur[idx] != '+' &&
		          			valCur[idx] != '-' &&
		          			valCur[idx] != '*' &&
		          			valCur[idx] != '/') {
	          	 		testLastNum += valCur[idx];	   
	          	 		idx--;       	 	
	          		}
	          		if (testLastNum === valEntered) return; // both Zero
	          		if (parseFloat(testLastNum) || testZero.test(testLastNum) ) {
	          	 		$("#outputFormula").html(valCur + valEntered);
	          	 	}
	          	} else {
	          		testLastNum = valCur;
	          		
	          		if (parseFloat(testLastNum) || testZero.test(testLastNum) ) {
	          	 		$("#outputFormula").html(valCur + valEntered);
	          	 	}
	          	}
	          	 
	          	 
	          }
			break;           
      case ".":
        if (valCur.length == 0) {
          $("#outputFormula").html("0" + valEntered);
        } else if (testMathFunc(valCur[0]) && valCur.length == 1) {
          $("#outputFormula").html(valCur + "0" + valEntered);
        } else if (checkExpression(valCur)) { // test for valid numbers
          // test last number entered if it is a decimal (has a dot)
          if (valCur.charAt(valCur.length - 1) !== ".") {
            $("#outputFormula").html(valCur + ".");
          }

        } else {
          var lastEntered = valCur.split('')[valCur.length-1].match(/[\-|\+|\*|\/]/)
          if (lastEntered) {
            $("#outputFormula").html(valCur + "0" + valEntered);
          } else {
            $("#outputFormula").html(valCur);
          }
        }

        break;

      case "+":
      case "-":

        if (valCur.length != 0) {
          // if previous char was not an operator
          if (valCur[valCur.length - 1] != '+' &&
            valCur[valCur.length - 1] != '-' &&
            valCur[valCur.length - 1] != '*' &&
            valCur[valCur.length - 1] != '/') {
            		// decimal		          		
		          	if (valCur[valCur.length-1] == '.') {
								  $("#outputFormula").html(valCur + "0" + valEntered);	
		          	} else {
		          			$("#outputFormula").html(valCur + valEntered);	
		          	}
          } else {
            // replace the last operator if there is already one entered.
            valCur = valCur.substr(0, valCur.length - 1);
            $("#outputFormula").html(valCur + valEntered);

          }

         } else {
		          if (valEntered === '-') {
		          	$("#outputFormula").html(valEntered);
		          }	
	       }
        break;
      case "÷":
        if (valCur.length != 0) {
          if (valCur[valCur.length - 1] != '+' &&
            valCur[valCur.length - 1] != '-' &&
            valCur[valCur.length - 1] != '*' &&
            valCur[valCur.length - 1] != '/') {
            $("#outputFormula").html(valCur + "/");
          } else {
            valCur = valCur.substr(0, valCur.length - 1);
            $("#outputFormula").html(valCur + "/");
          }

        };
        break;
      case "x":
        if (valCur.length != 0) {
          if (valCur[valCur.length - 1] != '+' &&
            valCur[valCur.length - 1] != '-' &&
            valCur[valCur.length - 1] != '*' &&
            valCur[valCur.length - 1] != '/') {
            $("#outputFormula").html(valCur + "*");
          } else {
            valCur = valCur.substr(0, valCur.length - 1);
            $("#outputFormula").html(valCur + "*");
          }
        };
        break;
      case "=":
        // remove leading zeros
        while (valCur.charAt(0) == '0') { // Assume we remove all leading zeros
          if (valCur.length == 1) {
            break
          }; // But not final one.
          if (valCur.charAt(1) == '.') {
            break
          }; // Nor one followed by '.'
          valCur = valCur.substr(1, valCur.length - 1)
        }
        // Resolve expression (round number to avoid dodgy figures)
        if (testExp(valCur)) {
          var resolve = eval(valCur).toFixed(8);
          $("#outputRes").html(parseFloat(resolve));
        }
        $("#outputFormula").html(valCur + valEntered);
        break;

      default:
        $("#outputFormula").html("fail");
        break;
    }

  });
});

function testIfHaveOperator (val) { // i.e. the second or later number is being entered - return highest index
	var opIndex = -1;
	var retVar = false;
	if (val.lastIndexOf('+') > -1 && val.lastIndexOf('+') > opIndex) opIndex = val.lastIndexOf('+');
	if (val.lastIndexOf('-') > -1 && val.lastIndexOf('-') > opIndex) opIndex = val.lastIndexOf('-');
	if (val.lastIndexOf('*') > -1 && val.lastIndexOf('*') > opIndex) opIndex = val.lastIndexOf('*');
	if (val.lastIndexOf('/') > -1 && val.lastIndexOf('/') > opIndex) opIndex = val.lastIndexOf('/');
	//(opIndex > -1) ? retVar = opIndex : retVar = false;
	return opIndex;
}
	

function testExp(expr) {
  // test for mathematical expression
  var regEx = new RegExp("^([-+/*]\d+(\.\d+)?)*");
  return regEx.test(expr);
}

function testNum(numChar) {
  // test for mathematical expression
  var num = parseInt(numChar);
  return !isNaN(num);
}

function testMathFunc(ch) {
  // test for mathematical function
  var regEx = new RegExp("^[-]|[+]");
  return regEx.test(ch);
}

function checkExpression(xprAll) {
  var xpr = xprAll.split('');
  var leadingMinus = false;
  var pos = 0;
  // test for a leading operator
  if (xpr[0] == '-') leadingMinus = true;
  if (xpr[0] == '+') xpr.shift(); // ignore and remove

  for (var i = pos; i < xpr.length; i++) {
    switch (xpr[i]) {
      case '+':
      case '-':
      case '/':
      case '*':
        xpr[i] = 'r';
        break;
    }
  }
  var valid = true;
  var xprStr = xpr.join('');
  if (leadingMinus) {
    xprStr = xprStr.substr(1, xprStr.length - 1);
    if (isNaN(parseFloat(xprStr))) {
      valid = false;
    } else {
      xprStr = "-" + xprStr;
    }

  } else {
    if (isNaN(parseFloat(xprStr)))
      valid = false;
  }
  var parts = xprStr.split('r');
  var lastPart = parts[parts.length - 1];
  for (let number of parts) {
    if (isNaN(parseFloat(number))) valid = false;
  }
  var countDots = 0;
  for (var idx = 0; idx < lastPart.length; idx++) {
    if (lastPart[idx] === '.') countDots++;
    if (countDots > 0) valid = false;
  }
  return valid;
}