* mood-line.el: Added evil-mode support

Also laid some ground work for adding other modal editing systems.
Moved the buffer modified segment, but only when some modal-editing
mode is being used. It felt right to give modal-editing the front
of the mode-line.

mood-line.el

@@ -87,6 +87,23 @@
   :group 'mood-line
   :type 'boolean)
 
+(defcustom mood-line-evil-state-alist
+  '((normal . ("<N>" . font-lock-variable-name-face))
+    (insert . ("<I>" . font-lock-string-face))
+    (visual . ("<V>" . font-lock-keyword-face))
+    (replace . ("<R>" . font-lock-type-face))
+    (motion . ("<M>" . font-lock-constant-face))
+    (operator . ("<O>" . font-lock-function-name-face))
+    (emacs . ("<E>" . font-lock-builtin-face)))
+  "Set the string and corresponding face for many `evil-mode' state.
+The `Face' may be either a face symbol or a property list of key-value pairs
+ e.g. (:foreground \"red\")."
+  :group 'mood-line
+  :type '(alist
+          :key-type symbol
+          :value-type
+          (cons (string :tag "Display Text") (choice :tag "Face" face plist))))
+
 (defface mood-line-buffer-name
   '((t (:inherit (mode-line-buffer-id))))
   "Face used for major mode indicator in the mode-line."
@@ -303,6 +320,16 @@
     (unless (string= (mood-line--string-trim process-info) "")
       (concat (mood-line--string-trim process-info) "  "))))
 
+(defun mood-line-segment-evil ()
+  "Display the current evil-mode state."
+  (when evil-state
+    (let ((mode-cons (alist-get evil-state mood-line-evil-state-alist)))
+      (concat (propertize (car mode-cons) 'face (cdr mode-cons)) " "))))
+
+(defun mood-line--modal-editing-p ()
+  "Determine if modal editing is being used."
+  (mood-line-segment-modified)) ; (or) is for future modal additions.
+
 ;;
 ;; Activation function
 ;;
@@ -343,8 +370,14 @@
                           ;; Left
                           (format-mode-line
                            '(" "
-                             (:eval (mood-line-segment-modified))
+                             (:eval (if (mood-line--modal-editing-p)
+                                        (progn
+                                          (mood-line-segment-evil))
+                                      (mood-line-segment-modified)))
                              (:eval (mood-line-segment-buffer-name))
+                             (:eval (if (mood-line--modal-editing-p)
+                                      (concat
+                                       (mood-line-segment-modified) " ")))
                              (:eval (mood-line-segment-anzu))
                              (:eval (mood-line-segment-multiple-cursors))
                              (:eval (mood-line-segment-position))))