calculator.js

let display;
let previous = null;
let operator = null;
let operatorClicked = false;
let isFoot = false;
let isInch = false;

/**
 * Calculates the operation and updates the display.
 */
function performOperation() {
  if (!previous || !operator) return; // Ignore if no operation
  let result;
  const current = parseNumber(feetToInchDecimal(display.value));
  const prev = parseNumber(previous);

  switch (operator) {
    case '+':
      result = prev + current;
      break;
    case '-':
      result = prev - current;
      break;
    case '*':
      result = prev * current;
      break;
    case '/':
      if (current === 0) {
        display.value = "Error";
        return;
      }
      result = prev / current;
      break;
    default:
      return;
  }

  display.value = InchDecimalToFeet(result);
  previous = null;
  operator = null;
}

/**
 * Parses the display value into a number (float or int).
 * @param {String} num 
 */
function parseNumber(num) {
  return num.includes('.') ? parseFloat(num) : parseInt(num);
}

/**
 * Captures the previous value and the clicked operator
 * so that an operation can be performed.
 */
function clickOperator(event) {
  if (display.value === "") return; // Ignore if no input
  operator = event.target.value;
  previous = feetToInchDecimal(display.value);
  operatorClicked = true;
}

/**
 * Captures a number click and updates the display value.
 * @param {Event} event 
 */
function clickNumber(event) {
  const val = event.target.value;

  if (operatorClicked) {
    display.value = val;
    operatorClicked = false;
  } else {
    if (val === "'" && !isFoot) {
      isFoot = true;
    } else if (val === '"' && !isInch) {
      isInch = true;
    } else if (val === '.' && display.value.includes('.')) {
      return; // Prevent multiple decimal points
    }
    display.value = display.value === "0" ? val : display.value + val;
  }
}

/**
 * Resets the display value and state.
 */
function clear() {
  display.value = 0;
  previous = null;
  operator = null;
  operatorClicked = false;
  isFoot = false;
  isInch = false;
}

/**
 * Converts feet and inches to decimal inches.
 */
function feetToInchDecimal(display) {
  if (isFoot || isInch) {
    const feetIndex = display.indexOf("'");
    const inchIndex = display.indexOf('"');
    let footToInch = 0;
    let inches = 0;

    if (feetIndex !== -1) {
      footToInch = parseFloat(display.substring(0, feetIndex)) * 12 || 0;
    }
    if (inchIndex !== -1) {
      inches = parseFloat(display.substring(feetIndex + 1, inchIndex)) || 0;
    }

    return (footToInch + inches).toString();
  }
  return display;
}

/**
 * Converts decimal inches to feet and inches.
 */
function InchDecimalToFeet(results) {
  if (isFoot || isInch) {
    const feet = Math.floor(results / 12);
    const inches = Math.round(results % 12);
    return `${feet}'${inches}"`;
  }
  return results;
}

// Add event listener for when the DOM is loaded
document.addEventListener('DOMContentLoaded', () => {
  display = document.getElementById('display');

  // Number buttons
  const nums = document.querySelectorAll('.number');
  for (const num of nums) {
    num.addEventListener('click', clickNumber);
  }

  // Decimal, foot, and inch buttons
  const decimalPoint = document.querySelector('.decimal');
  decimalPoint.addEventListener('click', clickNumber);

  const foot = document.querySelector('.foot');
  foot.addEventListener('click', clickNumber);

  const inch = document.querySelector('.inch');
  inch.addEventListener('click', clickNumber);

  // Clear button
  const clearButton = document.querySelector('.all-clear');
  clearButton.addEventListener('click', clear);

  // Operator buttons
  const operators = document.querySelectorAll('.operator');
  for (const operator of operators) {
    operator.addEventListener('click', clickOperator);
  }

  // Equal sign
  const equal = document.querySelector('.equal-sign');
  equal.addEventListener('click', performOperation);
});