const display = document.getElementById('display');
const buttons = document.querySelectorAll('#buttons button');
const historyList = document.getElementById('history-list');
const historyBtn = document.getElementById('history');

let expression = '';

buttons.forEach(button => {
  button.addEventListener('click', () => {
    if (button.id === 'clear') {
      expression = '';
      display.value = '';
    } else if (button.id === 'equals') {
      try {
        const result = eval(expression);
        display.value = result;
        sendToBackend(expression, result);
        expression = result.toString();
      } catch (e) {
        display.value = 'Error';
        expression = '';
      }
    } else {
      expression += button.textContent;
      display.value = expression;
    }
  });
});

historyBtn.addEventListener('click', () => {
  fetch('http://aliscloudwork.tech/history')  // Kubernetes DNS for backend service
    .then(res => res.json())
    .then(data => {
      historyList.innerHTML = '';
      data.forEach(item => {
        const li = document.createElement('li');
        li.textContent = `${item.expression} = ${item.result}`;
        historyList.appendChild(li);
      });
    })
    .catch(err => alert('Failed to load history'));
});

function sendToBackend(expr, res) {
  fetch('http://aliscloudwork.tech/save', {
    method: 'POST',
    headers: {'Content-Type': 'application/json'},
    body: JSON.stringify({expression: expr, result: res})
  }).catch(err => console.log('Failed to save:', err));
}