Merge pull request #3615 from matrix-org/travis/base-theme

Add a function to get the "base" theme for a theme

src/theme.js

@@ -60,6 +60,22 @@ function getCustomTheme(themeName) {
  return customTheme;
 }
 
+/**
+ * Gets the underlying theme name for the given theme. This is usually the theme or
+ * CSS resource that the theme relies upon to load.
+ * @param {string} theme The theme name to get the base of.
+ * @returns {string} The base theme (typically "light" or "dark").
+ */
+export function getBaseTheme(theme) {
+ if (!theme) return "light";
+ if (theme.startsWith("custom-")) {
+ const customTheme = getCustomTheme(theme.substr(7));
+ return customTheme.is_dark ? "dark-custom" : "light-custom";
+ }
+
+ return theme; // it's probably a base theme
+}
+
 /**
  * Called whenever someone changes the theme
  *