Link fcitx and emacs's input method

init.el

@@ -491,6 +491,88 @@ directory. Otherwise, run `find-file' on that file."
 ;; mozc
 (require 'mozc nil t)
 (setq default-input-method "japanese-mozc")
+(defun my/-cmdline-for-pid (pid)
+  "Return the command line arguments passed to PID.
+PID can be a string or a number."
+  (butlast (string-split
+            (with-temp-buffer
+              (insert-file-contents-literally
+               (format "/proc/%s/cmdline" pid))
+              (buffer-substring-no-properties (point-min)
+                                              (point-max)))
+            "\0")))
+(defun my/-current-eww-config-dir ()
+  "Return the configuration directory for a currently running eww process."
+  ;; This probably only works on Linux
+  (catch 'found
+    (dolist (subdir (directory-files "/proc"))
+      (when (string-match-p (rx bos (+ num) eos) subdir)
+        (ignore-error permission-denied
+          (let* ((attrs (file-attributes (format "/proc/%s/exe" subdir)))
+                 (type (file-attribute-type attrs)))
+            (when (and (stringp type)
+                       (string-match-p (rx (or bos "/") "eww") type))
+              (cl-maplist (lambda (tail)
+                            (when (equal (car tail) "-c")
+                              (throw 'found (cl-second tail))))
+                          (my/-cmdline-for-pid subdir)))))))))
+(defun my/-set-eww-fcitx-state (enabled)
+  "Set the fcitx state for eww to ENABLED."
+  (let ((args (list "update" (format "fcitx5-state=%s" (if enabled 2 1))))
+        (cfg-dir (my/-current-eww-config-dir)))
+    (when cfg-dir
+      (setq args (nconc (list "-c" cfg-dir) args)))
+    (apply 'call-process "eww" nil 0 nil args)))
+(defun my/global-toggle-mozc (&optional no-eww)
+  "Toggle mozc for all buffers.
+With NO-EWW, don't update eww's state."
+  (interactive)
+  (let ((default-input-method "japanese-mozc"))
+    (toggle-input-method nil t)
+    (let ((activate (or (bound-and-true-p evil-input-method)
+                        current-input-method)))
+      (dolist (buffer (buffer-list))
+        (with-current-buffer buffer
+          (if activate
+              (activate-input-method activate)
+            (deactivate-input-method)
+            (mozc-mode -1)
+            (when (boundp 'evil-input-method)
+              (setq-local evil-input-method nil)))))
+      (unless no-eww
+        (my/-set-eww-fcitx-state activate)))
+    (force-mode-line-update t)))
+(keymap-global-set "C-\\" #'my/global-toggle-mozc)
+(defun my/mozc-active-in-buffer-p (&optional buffer)
+  "Return non-nil if mozc is active in BUFFER."
+  (unless buffer (setq buffer (current-buffer)))
+  (with-current-buffer buffer
+    (or (equal (or (bound-and-true-p evil-input-method) current-input-method)
+               "japanese-mozc")
+        (bound-and-true-p mozc-mode))))
+(defun my/-fcitx-enabled-p ()
+  "Return non-nil if fcitx is enabled."
+  (ignore-errors
+    (= 2 (dbus-call-method :session "org.fcitx.Fcitx5" "/controller"
+                           "org.fcitx.Fcitx.Controller1" "State"))))
+(defun my/-set-fcitx-enabled (enabled)
+  "If ENABLED is non-nil, enabled fcitx, otherwise disabled it."
+  (dbus-call-method :session "org.fcitx.Fcitx5" "/controller"
+                    "org.fcitx.Fcitx.Controller1"
+                    (if enabled "Activate" "Deactivate")))
+(defun my/-normalize-mozc-state ()
+  "Normalize the mozc state between Emacs and fcitx."
+  (if (cl-some 'frame-focus-state (frame-list))
+      (progn
+        (when (my/-fcitx-enabled-p)
+          (my/-set-fcitx-enabled nil)
+          (when (not (my/mozc-active-in-buffer-p))
+            (my/global-toggle-mozc t))))
+    (when (cl-some 'my/mozc-active-in-buffer-p (buffer-list))
+      (my/global-toggle-mozc t)
+      (my/-set-fcitx-enabled t)
+      (my/-set-eww-fcitx-state t))))
+(add-function :after after-focus-change-function #'my/-normalize-mozc-state)
 
 ;; migemo
 (use-package migemo