[elpa] externals/ef-themes 274ca3863d 5/5: Add ef-themes-toggle cmd and ef-themes-toggle var

[ELPA Syncer]

branch: externals/ef-themes
commit 274ca3863d682d0431aa037a638f72aaf4647317
Author: Protesilaos Stavrou <info@protesilaos.com>
Commit: Protesilaos Stavrou <info@protesilaos.com>

    Add ef-themes-toggle cmd and ef-themes-toggle var
---
 README.org   | 31 ++++++++++++++++++++++++++++---
 ef-themes.el | 28 ++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/README.org b/README.org
index 142c2b7bfc..8ee6ec8c05 100644
--- a/README.org
+++ b/README.org
@@ -124,8 +124,13 @@ Everything is in place to set up the package.
 #+begin_src emacs-lisp
 (require 'ef-themes)
 
-;; Make customisations BEFORE loading a theme (any change needs a theme
-;; re-load to take effect).
+;; If you like two specific themes and want to switch between them, you
+;; can specify them in `ef-themes-to-toggle' and then invoke the command
+;; `ef-themes-toggle':
+(setq ef-themes-to-toggle '(ef-summer ef-winter))
+
+;; Make customisations that affect Emacs faces BEFORE loading a theme
+;; (any change needs a theme re-load to take effect).
 
 (setq ef-themes-headings ; read the manual's entry of the doc string
       '((0 . (variable-pitch light 1.9))
@@ -154,6 +159,7 @@ Everything is in place to set up the package.
 
 ;; We also provide these commands, but do not assign them to any key:
 ;;
+;; - `ef-themes-toggle'
 ;; - `ef-themes-select'
 ;; - `ef-themes-load-random'
 ;; - `ef-themes-preview-colors'
@@ -312,7 +318,8 @@ as =init.el=.
 #+vindex: ef-themes-post-load-hook
 The commands mentioned herein call ~ef-themes-post-load-hook~ at the
 end.  This is for advanced users who want to trigger some code after an
-Ef theme is loaded ([[#h:5b74bd9e-e7f2-46b3-af2e-7c45b2e69245][Use colors from 
the active Ef theme]]).
+Ef theme is loaded ([[#h:5b74bd9e-e7f2-46b3-af2e-7c45b2e69245][Use colors from 
the active Ef theme]]).  The same goes
+for ~ef-themes-toggle~ ([[#h:a58b8e21-0f8f-4763-9b47-185bf7e10043][Toggle 
between two Ef themes]]).
 
 #+findex: ef-themes-select
 The themes can also be loaded interactively 
([[#h:75d74aea-d17f-497f-a3b8-f0bf4c372de0][Loading a theme]]).  The
@@ -370,6 +377,24 @@ light/dark theme and then loads an appropriate Ef theme at 
random:
   (ef-themes-load-random 'light))
 #+end_src
 
+* Toggle between two Ef themes
+:PROPERTIES:
+:CUSTOM_ID: h:a58b8e21-0f8f-4763-9b47-185bf7e10043
+:END:
+
+[ Part of {{{development-version}}}. ]
+
+#+vindex: ef-themes-to-toggle
+#+findex: ef-themes-toggle
+The user option ~ef-themes-to-toggle~ expects two symbols that name
+items in the Ef themes collection.  The variable ~ef-themes-collection~
+includes a list with all relevant symbols.  The user can then switch
+between the two specified themes by invoking the ~ef-themes-toggle~
+command.
+
+This is in addition to the other ways of loading a theme, either with
+minibuffer completion or at random 
([[#h:58345e8c-2bec-459c-872c-a85a29e9fe97][Commands to load an Ef theme]]).
+
 * Preview theme colors
 :PROPERTIES:
 :CUSTOM_ID: h:8dd67bf5-879e-46e5-b277-5bac141f53d1
diff --git a/ef-themes.el b/ef-themes.el
index 3f9174f22d..cf079ed1db 100644
--- a/ef-themes.el
+++ b/ef-themes.el
@@ -76,6 +76,13 @@ This is used by the commands `ef-themes-select' and
   :type 'hook
   :group 'ef-themes)
 
+(defcustom ef-themes-to-toggle nil
+  "Specify two `ef-themes' for `ef-themes-toggle' command.
+The variable `ef-themes-collection' contains the symbols of all
+themes that form part of this collection."
+  :type '(repeat symbol) ; FIXME 2022-08-19: Replace `symbol' with specific 
choices.  How?
+  :group 'ef-themes)
+
 (defconst ef-themes-weights
   '( thin ultralight extralight light semilight regular medium
      semibold bold heavy extrabold ultrabold)
@@ -299,6 +306,27 @@ When called from Lisp, THEME is a symbol."
   (interactive (list (intern (ef-themes--select-prompt))))
   (ef-themes--load-theme theme))
 
+(defun ef-themes--toggle-theme-p ()
+  "Return non-nil if `ef-themes-to-toggle' are valid."
+  (mapc (lambda (theme)
+          (if (memq theme ef-themes-collection)
+              theme
+            (user-error "`%s' is not part of `ef-themes-collection'" theme)))
+        ef-themes-to-toggle))
+
+;;;###autoload
+(defun ef-themes-toggle ()
+  "Toggle between the two `ef-themes-to-toggle'."
+  (interactive)
+  (when-let ((themes (ef-themes--toggle-theme-p))
+             (one (car themes))
+             (two (cadr themes)))
+    (unless (eq (length themes) 2)
+      (user-error "Can only toggle between two themes"))
+    (if (eq (car custom-enabled-themes) one)
+        (ef-themes--load-theme two)
+      (ef-themes--load-theme one))))
+
 (defun ef-themes--minus-current (&optional variant)
   "Return list of Ef themes minus the current one.
 VARIANT is either `light' or `dark', which stand for