const form = document.querySelector('#contractForm');
const templateSelect = document.querySelector('#template');
const submitButton = document.querySelector('#submitButton');
const downloadButton = document.querySelector('#downloadButton');
const shareButton = document.querySelector('#shareButton');
const message = document.querySelector('#message');
const resultTitle = document.querySelector('#resultTitle');
const connectionStatus = document.querySelector('#connectionStatus');

let currentPdfBlob = null;
let currentPdfFileName = '租屋契約.pdf';

loadTemplates();

form.addEventListener('submit', async (event) => {
  event.preventDefault();
  setBusy(true);
  resetPdf();

  try {
    const formData = new FormData(form);
    const response = await fetch('/api/contracts/pdf', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        template: formData.get('template'),
        monthlyRent: formData.get('monthlyRent'),
        paymentDay: formData.get('paymentDay'),
        deposit: formData.get('deposit'),
      }),
    });

    if (!response.ok) {
      const errorBody = await response.json().catch(() => ({}));
      throw new Error(errorBody.error || 'PDF 產生失敗。');
    }

    currentPdfBlob = await response.blob();
    currentPdfFileName = getFileNameFromDisposition(response.headers.get('Content-Disposition'))
      || buildDefaultFileName(formData.get('template'));

    resultTitle.textContent = 'PDF 已產生';
    message.textContent = currentPdfFileName;
    downloadButton.disabled = false;
    shareButton.disabled = !canShareCurrentPdf();
  } catch (error) {
    resultTitle.textContent = '產生失敗';
    message.textContent = error.message;
  } finally {
    setBusy(false);
  }
});

downloadButton.addEventListener('click', () => {
  if (!currentPdfBlob) {
    return;
  }
  downloadPdf();
});

shareButton.addEventListener('click', async () => {
  if (!currentPdfBlob) {
    return;
  }

  const file = new File([currentPdfBlob], currentPdfFileName, { type: 'application/pdf' });
  if (!navigator.canShare || !navigator.canShare({ files: [file] })) {
    downloadPdf();
    return;
  }

  try {
    await navigator.share({
      title: '租屋契約 PDF',
      files: [file],
    });
  } catch (error) {
    if (error.name !== 'AbortError') {
      message.textContent = '分享失敗，已保留下載按鈕。';
    }
  }
});

async function loadTemplates() {
  try {
    const response = await fetch('/api/templates');
    if (!response.ok) {
      throw new Error('無法讀取範本。');
    }

    const body = await response.json();
    templateSelect.replaceChildren(
      ...body.templates.map((name) => new Option(name, name)),
    );

    if (body.templates.length === 0) {
      templateSelect.append(new Option('templates 資料夾沒有 .doc 範本', ''));
      templateSelect.disabled = true;
      submitButton.disabled = true;
      connectionStatus.textContent = '缺少範本';
      message.textContent = '請先將 .doc 範本放進 templates 資料夾。';
      return;
    }

    connectionStatus.textContent = '可使用';
  } catch (error) {
    templateSelect.append(new Option('讀取失敗', ''));
    templateSelect.disabled = true;
    submitButton.disabled = true;
    connectionStatus.textContent = '離線';
    message.textContent = error.message;
  }
}

function setBusy(isBusy) {
  submitButton.disabled = isBusy || templateSelect.disabled;
  submitButton.textContent = isBusy ? '產生中' : '產生 PDF';
}

function resetPdf() {
  currentPdfBlob = null;
  downloadButton.disabled = true;
  shareButton.disabled = true;
  resultTitle.textContent = '產生中';
  message.textContent = '正在建立 PDF。';
}

function canShareCurrentPdf() {
  if (!currentPdfBlob || !navigator.canShare) {
    return false;
  }
  const file = new File([currentPdfBlob], currentPdfFileName, { type: 'application/pdf' });
  return navigator.canShare({ files: [file] });
}

function downloadPdf() {
  const url = URL.createObjectURL(currentPdfBlob);
  const link = document.createElement('a');
  link.href = url;
  link.download = currentPdfFileName;
  document.body.append(link);
  link.click();
  link.remove();
  URL.revokeObjectURL(url);
}

function getFileNameFromDisposition(disposition) {
  if (!disposition) {
    return '';
  }

  const utf8Match = disposition.match(/filename\*=UTF-8''([^;]+)/i);
  if (utf8Match) {
    return decodeURIComponent(utf8Match[1]);
  }

  const asciiMatch = disposition.match(/filename="([^"]+)"/i);
  return asciiMatch ? asciiMatch[1] : '';
}

function buildDefaultFileName(templateName) {
  const baseName = String(templateName || '租屋契約').replace(/\.[^.]+$/, '');
  return `${baseName}.pdf`;
}