(feature): update `org-roam-insert` behaviour on region-selection (#148)

`org-roam-insert` now uses active region to pre-populate insert completion, and as the link description

fixes #127

org-roam.el

@@ -300,11 +300,18 @@ If not provided, derive the title from the file name."
 
 If PREFIX, downcase the title before insertion."
   (interactive "P")
-  (let* ((completions (mapcar (lambda (file)
+  (let* ((region (and (region-active-p)
+                      ;; following may lose active region, so save it
+                      (cons (region-beginning) (region-end))))
+         (region-text (when region
+                        (buffer-substring-no-properties
+                         (car region) (cdr region))))
+         (completions (mapcar (lambda (file)
                                 (list (org-roam--get-title-or-slug file)
                                       file))
                               (org-roam--find-all-files)))
-         (title (completing-read "File: " completions))
+         (title (completing-read "File: " completions nil nil region-text))
+         (region-or-title (or region-text title))
          (absolute-file-path (or (cadr (assoc title completions))
                                  (org-roam--make-new-file-path (org-roam--get-new-id title) t)))
          (current-file-path (-> (or (buffer-base-buffer)
@@ -314,12 +321,15 @@ If PREFIX, downcase the title before insertion."
                                 (file-name-directory))))
     (unless (file-exists-p absolute-file-path)
       (org-roam--make-file absolute-file-path title))
+    (when region ;; Remove previously selected text.
+      (goto-char (car region))
+      (delete-char (- (cdr region) (car region))))
     (insert (format "[[%s][%s]]"
                     (concat "file:" (file-relative-name absolute-file-path
                                                         current-file-path))
                     (format org-roam-link-title-format (if prefix
-                                                           (downcase title)
-                                                         title))))))
+                                                           (downcase region-or-title)
+                                                         region-or-title))))))
 
 ;;; Finding org-roam files
 (defun org-roam-find-file ()