/**
 * @author Matthew McDole
 *
 */


function Calculate()
{
    var infix = document.getElementById('userInput').value;

    try
    {
        var postfix = InfixToPostfix(infix);
        var result = EvaluateExpression(postfix);

        document.getElementById('result').innerHTML += 'Infix: ' + infix + '<br/>';
        document.getElementById('result').innerHTML += 'Postfix: ' + postfix + '<br/>';
        document.getElementById('result').innerHTML += 'Result: ' + result + '<br/><br/>';
    }
    catch(e)
    {
        document.getElementById('result').innerHTML += e + '<br/><br/>';
    }
}



function InfixToPostfix(expression)
{
    var tokens = expression.split(/([0-9]+(?:\.[0-9]+)?|[*+-\^\/()])/);
    var outputQueue = [];
    var operatorStack = [];

    while (tokens.length != 0)
    {
        var currentToken = tokens.shift();

        if (isNumber(currentToken))
        {
            outputQueue.push(currentToken);
        }
        else if (isOperator(currentToken))
        {
            while ((getAssociativity(currentToken) == 'left' &&
                    getPrecedence(currentToken) <= getPrecedence(operatorStack[operatorStack.length-1])) ||
                   (getAssociativity(currentToken) == 'right' &&
                    getPrecedence(currentToken) < getPrecedence(operatorStack[operatorStack.length-1])))
            {
                outputQueue.push(operatorStack.pop())
            }

            operatorStack.push(currentToken);

        }
        else if (currentToken == '(')
        {
                operatorStack.push(currentToken);
        }
        else if (currentToken == ')')
        {
            while (operatorStack[operatorStack.length-1] != '(')
            {
                if (operatorStack.length == 0)
                {
                    throw("Parentheses balancing error");
                }
                outputQueue.push(operatorStack.pop());
            }
            operatorStack.pop();
        }
    }

    while (operatorStack.length != 0)
    {
        if (!operatorStack[operatorStack.length-1].match(/([()])/))
        {
            outputQueue.push(operatorStack.pop());
        }
        else
        {
            throw("Parentheses balancing error!");
        }
    }

    return outputQueue.join(" ");
}

function EvaluateExpression(expression)
{
    var tokens = expression.split(/([0-9]+(?:\.[0-9]+)?|[*+-\^\/()])/);
    var evalStack = [];

    while (tokens.length != 0)
    {
        var currentToken = tokens.shift();

        if (isNumber(currentToken))
        {
            evalStack.push(currentToken);
        }
        else if (isOperator(currentToken))
        {
            var operand2 = evalStack.pop();
            var operand1 = evalStack.pop();

            var result = PerformOperation(parseFloat(operand1), parseFloat(operand2), currentToken);
            evalStack.push(result);
        }
    }
    return evalStack.pop();
}



function isOperator(token)
{
    if (!token.match(/([*+-\^\/])/))
        return false;
    else
        return true;
}


function isNumber(token)
{
    if (!token.match(/([0-9]+)/))
        return false;
    else
        return true;
}


function getPrecedence(token)
{
    switch (token)
    {
        case '^':
            return 9;
        case '*':
        case '/':
        case '%':
            return 8;
        case '+':
        case '-':
            return 6;
        default:
            return -1;
    }
}

function getAssociativity(token)
{
    switch(token)
    {
        case '+':
        case '-':
        case '*':
        case '/':
            return 'left';
        case '^':
            return 'right';
    }

}

function PerformOperation(operand1, operand2, operator)
{
    switch(operator)
    {
        case '+':
            return operand1 + operand2;
        case '-':
            return operand1 - operand2;
        case '*':
            return operand1 * operand2;
        case '/':
            return operand1 / operand2;
        case '^':
            return Math.pow(operand1, operand2);
        default:
            return;
    }

}