content: // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
  // for details. All rights reserved. Use of this source code is governed by a
  // BSD-style license that can be found in the LICENSE file.
  
  part of html_common;
  
  /**
   * Utils for device detection.
   */
  class Device {
    static bool _isOpera;
    static bool _isIE;
    static bool _isFirefox;
    static bool _isWebKit;
    static String _cachedCssPrefix;
    static String _cachedPropertyPrefix;
  
    /**
     * Gets the browser's user agent. Using this function allows tests to inject
     * the user agent.
   * Returns the user agent.
     */
    static String get userAgent => window.navigator.userAgent;
  
    /**
     * Determines if the current device is running Opera.
     */
    static bool get isOpera {
      if (_isOpera == null) {
        _isOpera = userAgent.contains("Opera", 0);
      }
      return _isOpera;
    }
  
    /**
     * Determines if the current device is running Internet Explorer.
     */
    static bool get isIE {
      if (_isIE == null) {
        _isIE = !isOpera && userAgent.contains("Trident/", 0);
      }
      return _isIE;
    }
  
    /**
     * Determines if the current device is running Firefox.
     */
    static bool get isFirefox {
      if (_isFirefox == null) {
        _isFirefox = userAgent.contains("Firefox", 0);
      }
      return _isFirefox;
    }
  
    /**
     * Determines if the current device is running WebKit.
     */
    static bool get isWebKit {
      if (_isWebKit == null) {
        _isWebKit = !isOpera && userAgent.contains("WebKit", 0);
      }
      return _isWebKit;
    }
  
    /**
     * Gets the CSS property prefix for the current platform.
     */
    static String get cssPrefix {
      if (_cachedCssPrefix == null) {
        if (isFirefox) {
          _cachedCssPrefix = '-moz-';
        } else if (isIE) {
          _cachedCssPrefix = '-ms-';
        } else if (isOpera) {
          _cachedCssPrefix = '-o-';
        } else {
          _cachedCssPrefix = '-webkit-';
        }
      }
      return _cachedCssPrefix;
    }
  
    /**
     * Prefix as used for JS property names.
     */
    static String get propertyPrefix {
      if (_cachedPropertyPrefix == null) {
        if (isFirefox) {
          _cachedPropertyPrefix = 'moz';
        } else if (isIE) {
          _cachedPropertyPrefix = 'ms';
        } else if (isOpera) {
          _cachedPropertyPrefix = 'o';
        } else {
          _cachedPropertyPrefix = 'webkit';
        }
      }
      return _cachedPropertyPrefix;
    }
  
    /**
     * Checks to see if the event class is supported by the current platform.
     */
    static bool isEventTypeSupported(String eventType) {
      // Browsers throw for unsupported event names.
      try {
        var e = new Event.eventType(eventType, '');
        return e is Event;
      } catch (_) { }
      return false;
    }
  }
  