const XLSX = require('xlsx');
const electron = require('@electron/remote');

// --- Supported Extensions ---
const EXTENSIONS = "xls|xlsx|xlsm|xlsb|xml|csv|txt|dif|sylk|slk|prn|ods|fods|htm|html|numbers".split("|");

/**
 * Export current HTML table as a spreadsheet file using Electron API.
 */
async function exportFile() {
  const HTMLOUT = document.getElementById('htmlout');
  const wb = XLSX.utils.table_to_book(HTMLOUT.getElementsByTagName("TABLE")[0]);
  const o = await electron.dialog.showSaveDialog({
    title: 'Save file as',
    filters: [{ name: "Spreadsheets", extensions: EXTENSIONS }]
  });
  XLSX.writeFile(wb, o.filePath);
  electron.dialog.showMessageBox({ message: "Exported data to " + o.filePath, buttons: ["OK"] });
}
document.getElementById('exportBtn').addEventListener('click', exportFile, false);

/**
 * Create a <thead> element for a table from a header row array.
 */
function createTableHead(headerRow) {
  const thead = document.createElement('thead');
  const headRow = document.createElement('tr');
  headerRow.forEach(cell => {
    const th = document.createElement('th');
    th.textContent = cell !== undefined ? cell : '';
    headRow.appendChild(th);
  });
  thead.appendChild(headRow);
  return thead;
}

/**
 * Create a <tbody> element for a table from a 2D data array.
 */
function createTableBody(data) {
  const tbody = document.createElement('tbody');
  for (let i = 1; i < data.length; ++i) {
    const row = data[i];
    const tr = document.createElement('tr');
    row.forEach(cell => {
      const td = document.createElement('td');
      td.textContent = cell !== undefined ? cell : '';
      tr.appendChild(td);
    });
    tbody.appendChild(tr);
  }
  return tbody;
}

/**
 * Wrap a table in a responsive container div.
 */
function createResponsiveDiv(table) {
  const responsiveDiv = document.createElement('div');
  responsiveDiv.className = 'table-responsive';
  responsiveDiv.appendChild(table);
  return responsiveDiv;
}

// --- Main Table Processing ---
/**
 * Render all sheets of a workbook as HTML tables with clickable tabs.
 */
function renderWorkbookToTables(wb) {
  const HTMLOUT = document.getElementById('htmlout');
  const exportBtn = document.getElementById('exportBtn');
  exportBtn.disabled = false;
  HTMLOUT.innerHTML = "";

  // Create tab container
  const tabContainer = document.createElement('div');
  tabContainer.className = 'sheetjs-tab-container';

  // Create content container
  const contentContainer = document.createElement('div');
  contentContainer.className = 'sheetjs-tab-content';

  // Store tables for each sheet
  const tables = [];

  wb.SheetNames.forEach(function(sheetName, idx) {
    // Create tab button
    const tab = document.createElement('button');
    tab.className = 'sheetjs-tab-btn text-small';
    tab.textContent = sheetName;
    tab.setAttribute('data-sheet-idx', idx);
    if(idx === 0) tab.classList.add('active');
    tab.addEventListener('click', function() {
      // Remove active from all tabs
      Array.from(tabContainer.children).forEach(btn => btn.classList.remove('active'));
      tab.classList.add('active');
      // Hide all tables and show the selected one
      tables.forEach((tableDiv, tIdx) => {
        tableDiv.style.display = (tIdx === idx) ? '' : 'none';
      });
    });
    tabContainer.appendChild(tab);

    // Create table for this sheet
    const sheet = wb.Sheets[sheetName];
    const data = XLSX.utils.sheet_to_json(sheet, { header: 1 });
    if (data.length === 0) {
      const emptyDiv = document.createElement('div');
      emptyDiv.textContent = `Sheet '${sheetName}' is empty.`;
      tables.push(emptyDiv);
      contentContainer.appendChild(emptyDiv);
      return;
    }
    const table = document.createElement('table');
    table.className = 'sheetjs-table';
    // Remove caption, handled by tab
    table.appendChild(createTableHead(data[0]));
    table.appendChild(createTableBody(data));
    const responsiveDiv = createResponsiveDiv(table);
    if(idx !== 0) responsiveDiv.style.display = 'none';
    tables.push(responsiveDiv);
    contentContainer.appendChild(responsiveDiv);
  });

  // Only show tabs if more than one sheet
  if (wb.SheetNames.length > 1) {
    HTMLOUT.appendChild(tabContainer);
  }
  HTMLOUT.appendChild(contentContainer);
}

// --- File Import Logic ---
/**
 * Handle file selection dialog and render the selected spreadsheet.
 */
async function handleReadBtn() {
  const o = await electron.dialog.showOpenDialog({
    title: 'Select a file',
    filters: [{ name: "Spreadsheets", extensions: EXTENSIONS }],
    properties: ['openFile']
  });
  if(o.filePaths.length == 0) throw new Error("No file was selected!");
  showSpinner();
  // yield to event loop to render spinner
  await new Promise(resolve => setTimeout(resolve, 200));
  try {
    const filePath = o.filePaths[0];
    const fileName = filePath.split(/[/\\]/).pop();
    renderWorkbookToTables(XLSX.readFile(filePath));
    showLoadedFileUI(fileName);
  } finally {
    hideSpinner();
  }
}

// --- UI Templates and Helpers ---
/**
 * Return HTML for the drag-and-drop area.
 */
function getDropAreaHTML() {
  return `<div id="drop">
    <input type="file" id="readIn" style="display:none">
    <p class="text-muted text-condensed">Drag and drop a file here</p>
    <p class="text-muted text-small">or</p>
    <button type="button" id="readBtn">Click here to select a file</button>
    <div id="fileStatus" class="file-status" style="display: none;"></div>
  </div>`;
}

/**
 * Return HTML for the file-loaded UI.
 */
function getFileLoadedHTML(fileName) {
  return `<div class="file-loaded">
    <span class="file-name text-muted text-small">${fileName}</span>
    <button type="button" id="unloadBtn" class="unload-btn">Unload</button>
  </div>`;
}

/**
 * Update the drop-container's inner HTML.
 */
function updateDropContainer(html) {
  document.getElementById('drop-container').innerHTML = html;
}

/**
 * Restore the original drag-and-drop UI and reset state.
 */
function restoreDropUI() {
  updateDropContainer(getDropAreaHTML());
  // Remove the table/output
  const htmlout = document.getElementById('htmlout');
  if (htmlout) htmlout.innerHTML = '';
  // Reset export button state
  const exportBtn = document.getElementById('exportBtn');
  if (exportBtn) {
    exportBtn.disabled = true;
    exportBtn.classList.add('disabled');
  }
  // Re-attach event listeners after restoring UI
  attachDropListeners();
}

/**
 * Show UI for loaded file and attach unload handler.
 */
function showLoadedFileUI(fileName) {
  updateDropContainer(getFileLoadedHTML(fileName));
  document.getElementById('unloadBtn').addEventListener('click', restoreDropUI);
}

// --- Event Listener Helpers ---
/**
 * Add an event listener to an element if it exists.
 */
function addListener(id, event, handler) {
  const el = document.getElementById(id);
  if (el) el.addEventListener(event, handler, false);
}

/**
 * Attach drag-and-drop and file input listeners to the UI.
 */
function attachDropListeners() {
  addListener('readIn', 'change', (e) => {
    showSpinner();
    // Defer to next tick to ensure spinner renders before heavy work
    setTimeout(() => readFile(e.target.files), 0);
  });
  addListener('readBtn', 'click', handleReadBtn);
  const drop = document.getElementById('drop');
  const dropContainer = document.getElementById('drop-container');
  if (!drop || !dropContainer) return;
  const handleDrag = (e) => {
    e.stopPropagation(); e.preventDefault();
    e.dataTransfer.dropEffect = 'copy';
    dropContainer.classList.add('drag-over');
  };
  const handleDragLeave = (e) => {
    e.stopPropagation(); e.preventDefault();
    dropContainer.classList.remove('drag-over');
  };
  drop.addEventListener('drop', (e) => {
    e.stopPropagation(); e.preventDefault();
    dropContainer.classList.remove('drag-over');
    readFile(e.dataTransfer.files);
  }, false);
  drop.addEventListener('dragenter', handleDrag, false);
  drop.addEventListener('dragover', handleDrag, false);
  drop.addEventListener('dragleave', handleDragLeave, false);
  drop.addEventListener('dragend', handleDragLeave, false);
}

// --- Spinner Helpers ---
function showSpinner() {
  const spinner = document.getElementById('spinner-overlay');
  if (spinner) spinner.style.display = 'flex';
}
function hideSpinner() {
  const spinner = document.getElementById('spinner-overlay');
  if (spinner) spinner.style.display = 'none';
}

// --- File Reader for Drag-and-Drop and Input ---
/**
 * Read file(s) from input or drag-and-drop and render as table.
 */
async function readFile(files) {
  if (!files || files.length === 0) return;
  const f = files[0];
  showSpinner();
  try {
    const data = await f.arrayBuffer();
    renderWorkbookToTables(XLSX.read(data));
    showLoadedFileUI(f.name);
  } finally {
    hideSpinner();
  }
}

// --- Initial Setup ---
attachDropListeners();