New mail notifications

features/mail/default.nix

@@ -31,9 +31,26 @@
     # only queries the card reader (no pinentry involved either way), so it's
     # safe to use as a silent presence check: skip the sync entirely when the
     # card isn't there, instead of letting mbsync hit that prompt.
+    #
+    # New mail is detected by counting files under every account's Maildir
+    # "new" subdirectory before and after the sync -- that's where messages
+    # the server hasn't marked seen land, across all three accounts at once,
+    # with no need to touch mu's index. A rise in that count means mail
+    # actually arrived, so only then does it post a desktop notification via
+    # notify-send -- intentionally separate from mu4e's own "mbsync -a" (its
+    # mu4e-get-mail-command), which doesn't go through this script at all.
     mbsyncSafe = pkgs.writeShellScript "mbsync-safe" ''
-      if ${pkgs.gnupg}/bin/gpg --card-status >/dev/null 2>&1; then
-        exec ${pkgs.isync}/bin/mbsync -a
+      if ! ${pkgs.gnupg}/bin/gpg --card-status >/dev/null 2>&1; then
+        exit 0
+      fi
+      before=$(find "$HOME/Maildir" -path '*/new/*' -type f 2>/dev/null | wc -l)
+      ${pkgs.isync}/bin/mbsync -a
+      after=$(find "$HOME/Maildir" -path '*/new/*' -type f 2>/dev/null | wc -l)
+      new=$((after - before))
+      if [ "$new" -gt 0 ]; then
+        label="new message"
+        [ "$new" -ne 1 ] && label="new messages"
+        ${pkgs.libnotify}/bin/notify-send "Mail" "$new $label"
       fi
     '';
   in {