diff --git a/src/App.php b/src/App.php
index d76351b97a..815a02f281 100644
--- a/src/App.php
+++ b/src/App.php
@@ -1067,4 +1067,85 @@ class App
 
 		return $sender_email;
 	}
+
+	/**
+	 * Returns the current theme name.
+	 *
+	 * @return string
+	 */
+	public function getCurrentTheme()
+	{
+		if (!$this->current_theme) {
+			$this->computeCurrentTheme();
+		}
+
+		return $this->current_theme;
+	}
+
+	/**
+	 * Computes the current theme name based on the node settings, the user settings and the device type
+	 *
+	 * @throws Exception
+	 */
+	private function computeCurrentTheme()
+	{
+		$system_theme = Config::get('system', 'theme');
+		if (!$system_theme) {
+			throw new Exception(L10n::t('No system theme config value set.'));
+		}
+
+		// Sane default
+		$this->current_theme = $system_theme;
+
+		$allowed_themes = explode(',', Config::get('system', 'allowed_themes', $system_theme));
+
+		$page_theme = null;
+		// Find the theme that belongs to the user whose stuff we are looking at
+		if ($this->profile_uid && ($this->profile_uid != local_user())) {
+			// Allow folks to override user themes and always use their own on their own site.
+			// This works only if the user is on the same server
+			$user = dba::selectFirst('user', ['theme'], ['uid' => $this->profile_uid]);
+			if (DBM::is_result($user) && !PConfig::get(local_user(), 'system', 'always_my_theme')) {
+				$page_theme = $user['theme'];
+			}
+		}
+
+		$user_theme = defaults($_SESSION, 'theme', $system_theme);
+		// Specific mobile theme override
+		if (($this->is_mobile || $this->is_tablet) && defaults($_SESSION, 'show-mobile', true)) {
+			$system_mobile_theme = Config::get('system', 'mobile-theme');
+			$user_mobile_theme = defaults($_SESSION, 'mobile-theme', $system_mobile_theme);
+
+			// --- means same mobile theme as desktop
+			if (!empty($user_mobile_theme) && $user_mobile_theme !== '---') {
+				$user_theme = $user_mobile_theme;
+			}
+		}
+
+		if ($page_theme) {
+			$theme_name = $page_theme;
+		} else {
+			$theme_name = $user_theme;
+		}
+
+		if ($theme_name
+			&& in_array($theme_name, $allowed_themes)
+			&& (file_exists('view/theme/' . $theme_name . '/style.css')
+			|| file_exists('view/theme/' . $theme_name . '/style.php'))
+		) {
+			$this->current_theme = $theme_name;
+		}
+	}
+
+	/**
+	 * @brief Return full URL to theme which is currently in effect.
+	 *
+	 * Provide a sane default if nothing is chosen or the specified theme does not exist.
+	 *
+	 * @return string
+	 */
+	public function getCurrentThemeStylesheetPath()
+	{
+		return Core\Theme::getStylesheetPath($this->getCurrentTheme());
+	}
 }
diff --git a/src/Core/Theme.php b/src/Core/Theme.php
index 16eb7939c5..fe38d09ede 100644
--- a/src/Core/Theme.php
+++ b/src/Core/Theme.php
@@ -180,4 +180,25 @@ class Theme
 		}
 		return '';
 	}
+
+	/**
+	 * @brief Return relative path to theme stylesheet file
+	 *
+	 * Provide a sane default if nothing is chosen or the specified theme does not exist.
+	 *
+	 * @param string $theme Theme name
+	 *
+	 * @return string
+	 */
+	public static function getStylesheetPath($theme)
+	{
+		$a = get_app();
+
+		$opts = (($a->profile_uid) ? '?f=&puid=' . $a->profile_uid : '');
+		if (file_exists('view/theme/' . $theme . '/style.php')) {
+			return 'view/theme/' . $theme . '/style.pcss' . $opts;
+		}
+
+		return 'view/theme/' . $theme . '/style.css';
+	}
 }