/* eslint-disable no-control-regex */

// Context: Lean towards breaking out any localizable content into constants so it's
// easier to track content we may need to localize in the future. (i18n)
const UNTITLED_PAGE_NAME = 'Untitled';

/** Tools for exporting files to device. For example, via browser download. */
export const FileExporter = {
  /**
   * Create a download for the user's browser.
   *
   * @param filename
   * @param text
   * @param mimeType like `"text/plain"`, `"text/html"`, `"application/javascript"`, etc. See {@link https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types mdn docs List of MIME types}.
   *
   * @remarks
   * Only accepts data in utf-8 encoding (html files, javascript source, text files, etc).
   *
   * @example
   * const todoMDText = `# Todo items
   * [ ] Item 1
   * [ ] Item 2
   * `
   * FileExporter.exportFile("Todo list.md", todoMDText, "text/plain")
   *
   * @example
   * const stateJsonContent = JSON.stringify({ a: 1, b: 2, c: 3 })
   * FileExporter.exportFile("state.json", jsonContent, "application/json")
   */
  exportFile(filename: string, dataURL: string) {
    const element = document.createElement('a');
    element.setAttribute('href', dataURL);
    const safeFilename = getSafeFileName(filename);
    element.setAttribute('download', safeFilename);

    element.style.display = 'none';
    document.body.appendChild(element);

    element.click();

    document.body.removeChild(element);
  },
  exportPng(pageTitle: string | undefined, dataURL: string) {
    const title = pageTitle?.trim() || UNTITLED_PAGE_NAME;
    FileExporter.exportFile(title + '.png', dataURL);
  },
};

function getSafeFileName(string: string) {
  const replacement = ' ';
  const filenameReservedRegex = /[<>:"/\\|?*\u0000-\u001F]/g;
  const windowsReservedNameRegex = /^(con|prn|aux|nul|com\d|lpt\d)$/i;
  const reControlChars = /[\u0000-\u001F\u0080-\u009F]/g;
  const reTrailingPeriods = /\.+$/;
  const allowedLength = 50;

  function trimRepeated(string: string, target: string) {
    const escapeStringRegexp = target
      .replace(/[|\\{}()[\]^$+*?.]/g, '\\$&')
      .replace(/-/g, '\\x2d');
    const regex = new RegExp(`(?:${escapeStringRegexp}){2,}`, 'g');
    return string.replace(regex, target);
  }

  string = string
    .normalize('NFD')
    .replace(filenameReservedRegex, replacement)
    .replace(reControlChars, replacement)
    .replace(reTrailingPeriods, '');

  string = trimRepeated(string, replacement);
  string = windowsReservedNameRegex.test(string)
    ? string + replacement
    : string;
  const extIndex = string.lastIndexOf('.');
  const filename = string.slice(0, extIndex).trim();
  const extension = string.slice(extIndex);
  string =
    filename.slice(0, Math.max(1, allowedLength - extension.length)) +
    extension;
  return string;
}