Add option to set the default reply visibility

This change introduces a new option `mastodon-toot-default-reply-visibility`.
The default is set to "Public". Replies will be defaulted to the value of
this parameter unless the original toot has a more restrictive visiblity.
For example:

with `mastodon-toot--default-reply-visibility` set to "unlisted"

- Original post visibility: public
- Reply default visibility: unlinsted

- Original post visbility: private (only-followers)
- Repy default visibility: private

2 files changed, 26 insertions, 1 deletions

diff --git a/README.org b/README.org
index 85ff179..35ebb99 100644
--- a/README.org
+++ b/README.org
@@ -263,6 +263,9 @@ work without first loading =mastodon.el=:
 - =mastodon-profile--account-sensitive-toggle=: Toggle whether your posts are
   marked as sensitive (nsfw) by default.
 
+- =mastodon-toot--default-reply-visibility=: Set the default visibility for replies.
+  This visibility is used only when the original post has less restrictive visibility.
+
 *** Customization
 
 See =M-x customize-group RET mastodon= to view all customize options.
diff --git a/lisp/mastodon-toot.el b/lisp/mastodon-toot.el
index c18f751..9e8a2cc 100644
--- a/lisp/mastodon-toot.el
+++ b/lisp/mastodon-toot.el
@@ -140,6 +140,16 @@ You need to install company yourself to use this."
   :group 'mastodon-toot
   :type 'integer)
 
+(defcustom mastodon-toot--default-reply-visibility "public"
+  "Default visibility settings when replying.
+If the original toot visibility is different we use the more restricted one."
+  :group 'mastodon-toot
+  :type '(choice
+         (const :tag "public" "public")
+         (const :tag "unlisted" "unlisted")
+         (const :tag "followers only" "private")
+         (const :tag "direct" "direct")))
+
 (defcustom mastodon-toot--enable-custom-instance-emoji nil
   "Whether to enable your instance's custom emoji by default."
   :group 'mastodon-toot
@@ -1348,11 +1358,23 @@ REPLY-TEXT is the text of the toot being replied to."
       'read-only "Edit your message below."
       'toot-post-header t))))
 
+(defun mastodon-toot--most-restrictive-visibility (reply-visibility)
+  "Return REPLY-VISIBILITY or default visibility, whichever is more restrictive.
+The default is given by `mastodon-toot--default-reply-visibility'."
+  (unless (null reply-visibility)
+    (let ((less-restrictive (member (intern mastodon-toot--default-reply-visibility)
+				    mastodon-toot-visibility-list)))
+      (insert (format "%s" reply-visibility))
+      (if (member (intern reply-visibility) less-restrictive)
+	  mastodon-toot--default-reply-visibility reply-visibility))))
+
 (defun mastodon-toot--setup-as-reply (reply-to-user reply-to-id reply-json)
   "If REPLY-TO-USER is provided, inject their handle into the message.
 If REPLY-TO-ID is provided, set `mastodon-toot--reply-to-id'.
 REPLY-JSON is the full JSON of the toot being replied to."
-  (let ((reply-visibility (alist-get 'visibility reply-json))
+  (let ((reply-visibility
+	 (mastodon-toot--most-restrictive-visibility
+	  (alist-get 'visibility reply-json)))
         (reply-cw (alist-get 'spoiler_text reply-json)))
     (when reply-to-user
       (insert (format "%s " reply-to-user))