Fix warnings, mainly about missing docstrings

Tekuti gets real confused when a request is sent to
https://tekuti.example.com//admin/new-post claiming that the host field is
missing. From my logs:

    Throw to key `uri-error' with args `("Expected path not starting with
    \"//\" (no host): ~a" ("//admin/new-post"))'.

tekuti.el

@@ -32,7 +32,7 @@
 ;; #+TITLE: SOME TITLE
 ;; #+DATE: <2021-06-03 Thu 22:45>
 ;; #+TAGS: comma,separated
-;; #+COMMENT_STATUS: open
+;; #+COMMENTS: on
 ;; #+COMMENTS_DATE:
 ;; #+STATUS: publish
 
@@ -43,7 +43,11 @@
 
 (require 'org)
 
-(defvar tekuti-host "http://127.0.0.1:8080")
+(defvar tekuti-host "http://127.0.0.1:8080"
+  "The host where tekuti is running.
+This should be the base URL of your blog. Where adding ‘/admin’
+will get you into the admin area of your blog. This shouldn't end
+with a ‘/’.")
 
 (defun tekuti--format-date (&optional date)
   "Format DATE into a date that tekuti understands."
@@ -52,18 +56,8 @@
                         (date-to-time date))
                       t))
 
-(defun tekuti-build-data-from-org ()
-  "Parse the current org buffer to collect the necessary metadata."
-  (let ((defaults `(("TITLE")
-                    ("DATE" ,(tekuti--format-date))
-                    ("TAGS")
-                    ("STATUS")
-                    ("COMMENT_STATUS")
-                    ("COMMENTS-CLOSED-DATE")
-                    ("BODY")))
-        (data (append
-               (mapcar
-                (lambda (pair)
+(defun tekuti--parse-data-keyword (pair)
+  "Ensure that both the key and value in PAIR match what tekuti needs."
   (pcase pair
     (`("DATE" ,date)
      (list "DATE" (tekuti--format-date date)))
@@ -71,29 +65,64 @@
      (list "COMMENTS-CLOSED-DATE"
            (and (not (string-empty-p date))
                 (tekuti--format-date date))))
+    (`("STATUS" ,status)
+     (let ((accepted-values '("publish" "draft" "private")))
+       (if (member status accepted-values)
+           pair
+         (error "Unknown post status: %s; Accepted values are: %s"
+                status accepted-values))))
+    (`("COMMENTS" ,status)
+     (if (string= status "on")
+         pair
+       (error "Unknown value for comments: %s; Can only be ‘on’ or absent"
+              status)))
     (_ pair)))
-                (org-collect-keywords '("TITLE" "TAGS" "STATUS" "COMMENT_STATUS" "DATE" "COMMENTS_DATE")))
+
+(defun tekuti-build-data-from-org ()
+  "Parse the current org buffer to collect the necessary metadata."
+  (let ((defaults `(("TITLE")
+                    ("DATE" ,(tekuti--format-date))
+                    ("TAGS")
+                    ("STATUS")
+                    ("COMMENTS")
+                    ("COMMENTS-CLOSED-DATE")
+                    ("BODY")))
+        (data (append
+               (mapcar
+                #'tekuti--parse-data-keyword
+                (org-collect-keywords '("TITLE" "TAGS" "STATUS" "COMMENTS" "DATE" "COMMENTS_DATE")))
                (list
                 (list "BODY"
                       (with-current-buffer (org-html-export-as-html nil nil nil t)
                         (buffer-substring-no-properties (point-min) (point-max))))))))
+    (seq-remove
+     (lambda (pair) (and (string= "COMMENTS" (car pair))
+                         (null (cdr pair))))
      (mapcar (lambda (item)
                (let ((key (car item)))
                  `(,key ,@(or (alist-get key data nil nil #'string=)
                               (cdr item)))))
-            defaults)))
+             defaults))))
 
 (defun tekuti-form-encode-pair (key value)
+  "Make sure KEY and VALUE are properly form-encoded."
   (concat (url-hexify-string key) "=" (url-hexify-string value)))
 
 (defun tekuti-form-encode-data (data)
+  "Convert DATA from an alist to a form-encoded string."
   (mapconcat
    (lambda (pair)
      (tekuti-form-encode-pair (downcase (car pair)) (cadr pair)))
    data
    "&"))
 
-(defun tekuti--send-finished (status buffer args)
+(defun tekuti--send-finished (status buffer args updatep)
+  "Callback for when the request to tekuti finishes.
+STATUS is the full data structure sent on by ‘url-retrieve’.
+BUFFER is the buffer that was published. ARGS is a list
+containing the data that was collected from the buffer to make
+the request. UPDATEP is a boolean indicating whether a post was
+updated or created."
   (pcase-exhaustive status
     (`(:redirect ,url . ,_)
      (save-excursion
@@ -101,7 +130,7 @@
          (goto-char (point-min))
          (search-forward "\n\n")
          (backward-char)
-         (let ((data (org-collect-keywords '("TITLE" "TAGS" "STATUS" "COMMENT_STATUS" "DATE" "COMMENTS_DATE"))))
+         (let ((data (org-collect-keywords '("TITLE" "TAGS" "STATUS" "COMMENTS" "DATE" "COMMENTS_DATE"))))
            (mapc (lambda (item)
                    (let ((key (car item))
                          (value (cadr item)))
@@ -117,28 +146,34 @@
                                    (car (url-path-and-query
                                          (url-generic-parse-url url))))
                    "\n"))))
-     (message "Created new post: %s" url))
+     (message "%s post: %s" (if updatep "Updated" "Created new") url))
     (`(:error (error http ,code) . ,_)
-     (message "Failed to create post: %d" code))))
+     (message "Failed to %s post: %d" (if updatep "update" "create") code))))
 
 (defun tekuti--get-update-url ()
+  "Try and get the value of the ‘UPDATE_URL’ property in the current buffer."
   (save-excursion
     (goto-char (point-min))
     (car (map-elt (org-collect-keywords '("UPDATE_URL")) "UPDATE_URL"))))
 
 ;;;###autoload
 (defun tekuti-send ()
+  "Export and send the current buffer to tekuti.
+The current buffer should be an ‘org-mode’ buffer that you wish
+to post to your tekuti blog."
   (interactive)
   (let* ((data (tekuti-build-data-from-org))
          (url-request-method "POST")
          (url-request-extra-headers
           `(("Content-Type" . "application/x-www-form-urlencoded")))
-         (url-request-data (tekuti-form-encode-data data)))
-    (url-retrieve (format "%s%s" tekuti-host
-                          (or (tekuti--get-update-url)
+         (url-request-data (tekuti-form-encode-data data))
+         (previous-update-url (tekuti--get-update-url))
+         (updatep (not (null previous-update-url))))
+    (url-retrieve (format "%s%s" (string-trim-right tekuti-host "/")
+                          (or previous-update-url
                               "/admin/new-post"))
                   #'tekuti--send-finished
-                  (list (current-buffer) data))))
+                  (list (current-buffer) data updatep))))
 
 (provide 'tekuti)
 ;;; tekuti.el ends here