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(
    "|"
  );

const dropContainer = document.getElementById("drop-container");
const dropzone = document.getElementById("drop");
const fileStatus = document.getElementById("fileStatus");
const exportBtn = document.getElementById("exportBtn");
const spinnerOverlay = document.getElementById("spinner-overlay");
const htmlout = document.getElementById("htmlout");

// open external links in default browser
document.addEventListener("click", (e) => {
  if (e.target.tagName === "A" && e.target.href.startsWith("http")) {
    e.preventDefault();
    electron.shell.openExternal(e.target.href);
  }
});

/**
 * Export current HTML table as a spreadsheet file using Electron API.
 */
async function exportFile() {
  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"],
  });
}

exportBtn.addEventListener("click", exportFile, false);

function renderWorkbookToTables(wb) {
  htmlout.innerHTML = "";
  const sheetNames = wb.SheetNames;
  sheetNames.forEach((sheetName) => {
    const sheet = wb.Sheets[sheetName];
    const sheetname = sheetName;
    const table = XLSX.utils.sheet_to_html(sheet);
    htmlout.innerHTML += `<details class="sheetjs-sheet-container">
    <summary class="sheetjs-sheet-name">${sheetname}</summary>
    <div class="sheetjs-tab-content">${table}</div>
  </details>`;
  });
}

// --- 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);
    showExportBtn();
  } finally {
    hideSpinner();
    hideDropUI();
  }
}

// --- UI Templates and Helpers ---

const getLoadedFileUI = (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>`;
};

const hideDropUI = () => {
  if (dropContainer) dropContainer.style.display = "none";
};

const showDropUI = () => {
  if (dropContainer) dropContainer.style.display = "block";
};

const hideLoadedFileUI = () => {
  if (fileStatus) fileStatus.innerHTML = "";
};

const hideOutputUI = () => {
  if (htmlout) htmlout.innerHTML = "";
};

const showLoadedFileUI = (fileName) => {
  const loadedFileUI = getLoadedFileUI(fileName);
  fileStatus.innerHTML = loadedFileUI;
  const unloadBtn = fileStatus.querySelector("#unloadBtn");
  if (unloadBtn) {
    unloadBtn.addEventListener("click", () => {
      hideLoadedFileUI();
      hideExportBtn();
      showDropUI();
      hideOutputUI();
    });
  }
  hideDropUI();
  showExportBtn();
};

const hideExportBtn = () => {
  if (exportBtn) exportBtn.disabled = true;
};

const showExportBtn = () => {
  if (exportBtn) exportBtn.disabled = false;
};

function showSpinner() {
  if (spinnerOverlay) spinnerOverlay.style.display = "flex";
}

function hideSpinner() {
  if (spinnerOverlay) spinnerOverlay.style.display = "none";
}

// --- 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);
  if (!dropzone || !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");
  };
  dropzone.addEventListener(
    "drop",
    (e) => {
      e.stopPropagation();
      e.preventDefault();
      dropContainer.classList.remove("drag-over");
      readFile(e.dataTransfer.files);
    },
    false
  );
  dropzone.addEventListener("dragenter", handleDrag, false);
  dropzone.addEventListener("dragover", handleDrag, false);
  dropzone.addEventListener("dragleave", handleDragLeave, false);
  dropzone.addEventListener("dragend", handleDragLeave, false);
}

// --- 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();