refactor(dirvish): extract cj/--wallpaper-program-for helper

`cj/set-wallpaper' had two parallel cond arms hardcoding the X11/Wayland dispatch and the success/failure messages inline.  Lift the program-and-args choice into `cj/--wallpaper-program-for' -- a pcase from a display-server symbol to a (PROGRAM ARG...) list, or nil for unknown environments.  The wrapper now: detect env, ask helper for the command, surface the right message (unknown server / executable missing / success).  Adding a third backend (e.g. xdg-desktop-portal) becomes one pcase clause + one test.

2 files changed, 68 insertions, 14 deletions

diff --git a/modules/dirvish-config.el b/modules/dirvish-config.el
index c01bfafa..3fce616e 100644
--- a/modules/dirvish-config.el
+++ b/modules/dirvish-config.el
@@ -221,26 +221,38 @@ regardless of what file or subdirectory the point is on."
                                      (shell-quote-argument current-dir)))))))
       (message "Could not determine current directory."))))
 
+(defun cj/--wallpaper-program-for (env)
+  "Return the (PROGRAM PRE-FILE-ARG...) list for setting wallpaper under ENV.
+
+ENV is a display-server symbol: `x11' picks feh with --bg-fill, `wayland'
+picks swww with the img subcommand.  Any other value returns nil so the
+caller can surface an \"unknown display server\" error.
+
+Pure helper used by `cj/set-wallpaper'."
+  (pcase env
+    ('x11     '("feh" "--bg-fill"))
+    ('wayland '("swww" "img"))
+    (_ nil)))
+
 (defun cj/set-wallpaper ()
   "Set the image at point as the desktop wallpaper.
 Uses feh on X11, swww on Wayland."
   (interactive)
-  (let ((file (expand-file-name (dired-file-name-at-point))))
+  (let* ((file (expand-file-name (dired-file-name-at-point)))
+         (env (cond ((env-x11-p) 'x11)
+                    ((env-wayland-p) 'wayland)
+                    (t nil)))
+         (cmd (cj/--wallpaper-program-for env)))
     (cond
-     ((env-x11-p)
-      (if (executable-find "feh")
-          (progn
-            (call-process "feh" nil 0 nil "--bg-fill" file)
-            (message "Wallpaper set: %s (feh)" (file-name-nondirectory file)))
-        (message "feh not found")))
-     ((env-wayland-p)
-      (if (executable-find "swww")
-          (progn
-            (call-process "swww" nil 0 nil "img" file)
-            (message "Wallpaper set: %s (swww)" (file-name-nondirectory file)))
-        (message "swww not found")))
+     ((null cmd)
+      (message "Unknown display server (not X11 or Wayland)"))
+     ((not (executable-find (car cmd)))
+      (message "%s not found" (car cmd)))
      (t
-      (message "Unknown display server (not X11 or Wayland)")))))
+      (apply #'call-process (car cmd) nil 0 nil
+             (append (cdr cmd) (list file)))
+      (message "Wallpaper set: %s (%s)"
+               (file-name-nondirectory file) (car cmd))))))
 
 ;;; ---------------------------------- Dirvish ----------------------------------
 
diff --git a/tests/test-dirvish-config-wallpaper-program.el b/tests/test-dirvish-config-wallpaper-program.el
new file mode 100644
index 00000000..556c1310
--- /dev/null
+++ b/tests/test-dirvish-config-wallpaper-program.el
@@ -0,0 +1,42 @@
+;;; test-dirvish-config-wallpaper-program.el --- Tests for the wallpaper command resolver -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; `cj/--wallpaper-program-for' is the pure dispatch behind
+;; `cj/set-wallpaper': given a display-server symbol it returns the
+;; (PROGRAM . PRE-FILE-ARGS) cons that the interactive wrapper passes
+;; to `call-process' alongside the wallpaper file path.  The wrapper
+;; handles environment detection (`env-x11-p' / `env-wayland-p'), the
+;; `executable-find' check, and the user-visible message.
+
+;;; Code:
+
+(require 'ert)
+(require 'package)
+
+(setq package-user-dir (expand-file-name "elpa" user-emacs-directory))
+(package-initialize)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(add-to-list 'load-path (expand-file-name "elpa/dirvish-2.3.0/extensions"
+                                          user-emacs-directory))
+(require 'user-constants)
+(require 'keybindings)
+(require 'dirvish-config)
+
+(ert-deftest test-cj--wallpaper-program-for-x11 ()
+  "Normal: x11 dispatches to feh with --bg-fill."
+  (should (equal (cj/--wallpaper-program-for 'x11)
+                 '("feh" "--bg-fill"))))
+
+(ert-deftest test-cj--wallpaper-program-for-wayland ()
+  "Normal: wayland dispatches to swww with the img subcommand."
+  (should (equal (cj/--wallpaper-program-for 'wayland)
+                 '("swww" "img"))))
+
+(ert-deftest test-cj--wallpaper-program-for-unknown-returns-nil ()
+  "Boundary: an unknown environment returns nil so the wrapper can fall back."
+  (should-not (cj/--wallpaper-program-for 'tty))
+  (should-not (cj/--wallpaper-program-for nil))
+  (should-not (cj/--wallpaper-program-for 'mac)))
+
+(provide 'test-dirvish-config-wallpaper-program)
+;;; test-dirvish-config-wallpaper-program.el ends here