/**
 *     SIMPLE POCKET CALCULATOR
 *       for freeCodeCamp.com
 *
 * --------------------------------------
 *   !!! NOW RESPONSIVE !!!
 *   Scales down on small devices,
 * try resizing your page to 300px width
 * --------------------------------------
 */

$(document).ready(function() {

  var current_out = []; // display digits, as an array of chars
  var active_operator; // char in [+-*/] representing the last op button pushed
  var previous_operand; // float -the first operand for chaining ops 

  // Custom base logarithm
  // Math.log10 is unsupported in old browsers
  function getBaseLog(b, e) {
    return Math.log(e) / Math.log(b);
  }

  // fallbacks for 'weird' inputs
  function parseCurrOpnd(digitsString) {

    if (digitsString === '.') return 0.0;
    if (isNaN(parseFloat(digitsString))) return 0.0;
    else return parseFloat(digitsString);
  }

  // one callback for all the buttons
  $('.btn').click(function() {
    switch ($(this).text()) {
      case "1":
      case "2":
      case "3":
      case "4":
      case "5":
      case "6":
      case "7":
      case "8":
      case "9":
      case "0":
        {

          // if the user pressed a digit
          // add the symbol to the display array, and show it
          if (current_out.length < 10) {
            current_out.push($(this).text());
            $('.result h2').text(current_out.join(''));
          }
          break;
        }

        // if the user pressed the decimal point
        // add the symbol only if it's the first one, and show it
      case ".":
        {
          if (current_out.indexOf('.') === -1 && current_out.length < 10) {
            current_out.push($(this).text());
            $('.result h2').text(current_out.join(''));
          }
          break;
        }
      case "AC":
        {

          // ALL CLEAR
          current_out = [];
          previous_operand = undefined;
          active_operator = undefined;
          $('.result h2').text('0');
          break;
        }
      case "CE":
        {

          // CLEAR LAST IN : push back a char from display
          current_out.pop();
          var disp = (current_out.length) ? current_out.join('') : '0';
          $('.result h2').text(disp);
          break;
        }

        /* if the user pressed an operator button, the previous pending
        operation is executed and returned, then the active op is set */
      case "x":
        {
          exec_active_oper(parseCurrOpnd(current_out.join('')));
          active_operator = "x";
          break;
        }
      case "+":
        {
          exec_active_oper(parseCurrOpnd(current_out.join('')));
          active_operator = "+";
          break;
        }
      case "-":
        {
          exec_active_oper(parseCurrOpnd(current_out.join('')));
          active_operator = "-";
          break;
        }
      case "/":
        {
          exec_active_oper(parseCurrOpnd(current_out.join('')));
          active_operator = "/";
          break;
        }
      case "%":
        {

          /* % calculates the current display percent of the 
          pending operand*/
          var perc;
          if (previous_operand) {
            if (current_out.length > 0)
              perc = previous_operand * parseCurrOpnd(current_out.join('')) / 100.0;
            else
              perc = 0;
            exec_active_oper(perc);
            active_operator = undefined;
          }
        }
        break;
      case "=":
        {
          exec_active_oper(parseCurrOpnd(current_out.join('')));
          active_operator = undefined;
          break;
        }
    }
  });

  // BUSINESS LOGIC HERE
  function exec_active_oper(curr_opnd) {
    if (active_operator) {
      switch (active_operator) {
        case "x":
          {
            previous_operand *= curr_opnd;
            break;
          }
        case "+":
          {
            previous_operand += curr_opnd;
            break;
          }
        case "-":
          {
            previous_operand -= curr_opnd;
            break;
          }
        case "/":
          {
            previous_operand /= curr_opnd;
            break;
          }
      }
    } else {

      /* if there is not active pending operator, returns the current display
      as the pending operand */
      previous_operand = parseCurrOpnd($('.result h2').text());
    }

    // the calc allows max 10 digits for  rationals
    var rounder;
    if (previous_operand !== 0)
      rounder = Math.floor(getBaseLog(10, /* log10 */
        Math.abs(previous_operand)));
    else
      rounder = 0;
    rounder = Math.pow(10, 10 - rounder);
    var rounded = Math.round(previous_operand * rounder) / rounder;

    // check if output is to big to be displayed.
    // !! No scientific notation.
    if (rounded <= 9999999999 && rounded >= -9999999999) {
      $('.result h2').text(rounded);
    } else {
      $('.result h2').text('err');
      previous_operand = undefined;
    }
    current_out = [];
  }
});