export function injectPWA() {
  if(!('serviceWorker' in navigator)) return;

  navigator.serviceWorker.addEventListener('message', e => {
    if(e.data?.type === 'SW_UPDATED') {
      localStorage.setItem('sw-version', e.data.version);
      showUpdateBanner(e.data.version);
    }
    if(e.data?.type === 'VERSION') {
      const prev = localStorage.getItem('sw-version');
      if(prev && prev !== e.data.version) showUpdateBanner(e.data.version);
      localStorage.setItem('sw-version', e.data.version);
    }
  });

  navigator.serviceWorker.register('sw.js', { updateViaCache: 'none' }).then(reg => {
    reg.update().catch(() => {});
    const ctrl = navigator.serviceWorker.controller;
    if(ctrl) ctrl.postMessage({ type: 'GET_VERSION' });
  }).catch(() => {});
}

export function showUpdateBanner(version) {
  if(document.getElementById('update-banner')) return;
  const b = document.createElement('div');
  b.id = 'update-banner';
  b.className = 'update-banner';
  b.innerHTML = `
    <span class="update-banner-text">✦ Update verfügbar${version ? ' <span style="opacity:.55;font-size:10px">('+version+')</span>' : ''}</span>
    <button class="update-banner-btn" onclick="window.location.reload()">Neu laden</button>
    <button class="update-banner-close" onclick="document.getElementById('update-banner').remove()">✕</button>
  `;
  document.body.appendChild(b);
}