script.js

const currentEl = document.getElementById("current")
const prevEl = document.getElementById("prev")
const keys = document.querySelector('.keys')

// l'etat
let current = '0'
let previous = ''
let operator = null // 'plus' | 'minus' | 'multiply' | 'divide'
let evaluated = false;

// effectuer le calcul
const compute = (vA, vB, op) => {
  const a = Number(vA);
  const b = Number(vB);

  switch (op) {
    case 'plus': return (a + b).toString();
    case 'minus': return (a - b).toString();
    case 'multiply': return (a * b).toString();
    case 'divide': return (b === 0 ? 'Erreur' : (a/b).toString());
    default: return vB
  }
}

// convertir l'affichage
const format = (numStr) => {
  if (numStr === 'Erreur') return numStr;

  const n = Number(numStr);
  if(!isFinite(n)) return 'Erreur'

  let out = n.toString();

  if(out.length > 15) {
    out = n.toExponential()
  }
  return out;
}

// actualiser l'affichage
const setDisplay = () => {
  currentEl.textContent = format(current)

  const operatorMap = {
    plus: '+',
    minus: '-',
    multiply: 'x',
    divide: '÷'
  }

  prevEl.textContent = operator && previous !== '' ? `${format(previous)} ${operatorMap[operator]}` : ''
}

// inserer un chiffre
const inputDigit = (d) => {
  if(evaluated) {
    current = '0';
    evaluated = false;
    return setDisplay();
  }

  if(current === '0') {
    current = String(d);
  } else {
    current += String(d);
  }
  setDisplay()
}

// inserer un point
const inputDot = () => {
  if(evaluated) {
    current = '0.';
    evaluated = false;
    return setDisplay()
  }
  if(!current.includes('.')) {
    current += '.'
  }
  setDisplay();
}

// choisir une opération
const chooseOperator = (op) => {
  if(current == 'Erreur') return
  if(previous !== '' && operator) {
    const result = compute(previous, current, operator);
    current = result;
    previous == result === 'Erreur' ? '' : result;
  } else {
    previous = current;
  }

  operator = op;
  evaluated = false;
  current = '0'
  setDisplay()
}

// tout effacer
const clearAll = () => {
  current = '0';
  previous = '';
  operator = null;
  evaluated = false;
  setDisplay();
}

// effacer un caractere
const backspace = () => {
  if(evaluated) return
  if(current.length <= 1 || (current.length === 2 && current.startsWith('-'))) {
    current = '0'
  } else {
    current = current.slice(0, -1);
  }
  setDisplay();
}

// égale
const equals = () => {
  if(operator && previous !== '' && current !== 'Erreur') {
    current = compute(previous, current, operator);
    previous = '';
    operator = null;
    evaluated = true;
    setDisplay();
  }
}

// pourcentage
const percent = () => {
  if(current == 'Erreur') return;
  current = (Number(current) / 100).toString();
  setDisplay();
}

// ecouter les boutons (clavier)
window.addEventListener('keydown', (e) => {
  const k = e.key
  if(/\d/.test(k)) return inputDigit(k);
  if(k === '.') return inputDot();
  if(k === '+') return chooseOperator('plus');
  if(k === '-') return chooseOperator('minus');
  if(k === '*') return chooseOperator('multiply');
  if(k === '/') return chooseOperator('divide');
  if(k === 'Enter' || k === '=') return equals();
  if(k === 'Backspace') return backspace();
  if(k.toLowerCase() === 'c') return clearAll();
})

// keys events (sur l'interface)
keys.addEventListener('click', (e) => {
  const btn = e.target.closest('button');
  if(!btn) return;

  if(btn.dataset.num !== undefined) return inputDigit(btn.dataset.num)
  if(btn.dataset.dot !== undefined) return inputDot();
  if(btn.dataset.op !== undefined) return chooseOperator(btn.dataset.op);

  const action = btn.dataset.action

  switch (action) {
    case 'clear': return clearAll();
    case 'percent': return percent();
    case 'backspace': return backspace();
    case 'equals': return equals();
    default: return;
  }
})