1 files changed, 76 insertions, 0 deletions
diff --git a/comm/mail/modules/UIDensity.jsm b/comm/mail/modules/UIDensity.jsm
new file mode 100644
index 0000000000..be94ed1408
--- /dev/null
+++ b/comm/mail/modules/UIDensity.jsm
@@ -0,0 +1,76 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const EXPORTED_SYMBOLS = ["UIDensity"];
+
+const { XPCOMUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/XPCOMUtils.sys.mjs"
+);
+
+var registeredWindows = new Set();
+
+function updateWindow(win) {
+  switch (UIDensity.prefValue) {
+    case UIDensity.MODE_COMPACT:
+      win.document.documentElement.setAttribute("uidensity", "compact");
+      break;
+    case UIDensity.MODE_TOUCH:
+      win.document.documentElement.setAttribute("uidensity", "touch");
+      break;
+    default:
+      win.document.documentElement.removeAttribute("uidensity");
+      break;
+  }
+
+  if (win.TabsInTitlebar !== undefined) {
+    win.TabsInTitlebar.update();
+  }
+
+  win.dispatchEvent(
+    new win.CustomEvent("uidensitychange", { detail: UIDensity.prefValue })
+  );
+}
+
+function updateAllWindows() {
+  for (let win of registeredWindows) {
+    updateWindow(win);
+  }
+}
+
+var UIDensity = {
+  MODE_COMPACT: 0,
+  MODE_NORMAL: 1,
+  MODE_TOUCH: 2,
+
+  prefName: "mail.uidensity",
+
+  /**
+   * Set the UI density.
+   *
+   * @param {integer} mode - One of the MODE constants.
+   */
+  setMode(mode) {
+    Services.prefs.setIntPref(this.prefName, mode);
+  },
+
+  /**
+   * Register a window to be updated if the mode ever changes. The current
+   * value is applied to the window. Deregistration is automatic.
+   *
+   * @param {Window} win
+   */
+  registerWindow(win) {
+    registeredWindows.add(win);
+    win.addEventListener("unload", () => registeredWindows.delete(win));
+    updateWindow(win);
+  },
+};
+
+XPCOMUtils.defineLazyPreferenceGetter(
+  UIDensity,
+  "prefValue",
+  UIDensity.prefName,
+  null,
+  updateAllWindows
+);