ahbeng/NUSMods

import Bowser from 'bowser';
import browsersList from 'browserslist-config-nusmods';

export type Platform = 'mobile' | 'desktop' | 'tablet';
export type VersionMap = Record<string, any>; // Too fiddly to type properly

function parseBrowser(browser: string): { platform?: Platform; browser: string } {
  // Split desktop and mobile Safari because we support different versions of each
  if (browser === 'ios_saf') return { platform: 'mobile', browser: 'safari' };
  if (browser === 'safari') return { platform: 'desktop', browser: 'safari' };

  // Samsung internet browser has a different name under bowser
  if (browser === 'samsung') return { platform: 'mobile', browser: 'samsung_internet' };

  return { browser };
}

function parseVersion(version: string): number {
  const versions = version.split(/-/g).map((versionStr) => parseFloat(versionStr));
  return Math.min(...versions);
}

function convertToCheckTree(versionMap: VersionMap): Bowser.Parser.checkTree {
  const checkTree: Bowser.Parser.checkTree = {};

  Object.keys(versionMap).forEach((key) => {
    if (typeof versionMap[key] === 'number') {
      checkTree[key] = `>=${versionMap[key]}`;
    } else {
      checkTree[key] = convertToCheckTree(versionMap[key]);
    }
  });

  return checkTree;
}

function setMinVersion(versionMap: VersionMap, key: string, version: number) {
  const currentVersion = versionMap[key];
  if (currentVersion == null || version < currentVersion) {
    // eslint-disable-next-line no-param-reassign
    versionMap[key] = version;
  }
}

export function browserlistToBowser(browserlist: string[]): Bowser.Parser.checkTree {
  const minVersions: VersionMap = {
    desktop: {},
    mobile: {},
    tablet: {},
  };

  browserlist.forEach((browserlistItem) => {
    const [browserName, versions] = browserlistItem.split(/\s+/g);

    const { browser, platform } = parseBrowser(browserName);
    const minVersion = parseVersion(versions);

    if (platform != null) {
      setMinVersion(minVersions[platform], browser, minVersion);

      // Bowser treats tablet and phones OS separate, but we don't want that distinction
      if (platform === 'mobile') setMinVersion(minVersions.tablet, browser, minVersion);
      if (platform === 'tablet') setMinVersion(minVersions.mobile, browser, minVersion);
    } else {
      setMinVersion(minVersions, browser, minVersion);
    }
  });

  return convertToCheckTree(minVersions);
}

const checkTree = browserlistToBowser(browsersList);
const parser = Bowser.getParser(window.navigator.userAgent);

export const isIOS = parser.is('ios');
export const isAndroidChrome = parser.satisfies({ mobile: { chrome: '>1' } });
export const isBrowserSupported = () => {
  if (parser.satisfies(checkTree)) {
    return true;
  }

  if (isIOS) {
    const os = parser.getOS();
    const minVersion = parseFloat(checkTree.mobile.safari.slice(2));
    if (os.version != null && parseFloat(os.version) >= minVersion) {
      return true;
    }
  }

  return false;
};