;; (assert (string= (tags-sort-tags-string "zee bee   cee") "bee cee zee") t "Tags not sorted.")
(defun tagging-sort-tags-string (string)
  "Return an alphabetically-sorted list of words in this string."
  (save-match-data
    (mapconcat 'identity
               (sort (mapcar 'downcase
                             (split-string string))
                     'string<)
               " ")))

(defun tagging-sort-tags ()
  "Find the first line beginning with Tags: tag tag tag and sort the tags alphabetically."
  (interactive)
  (goto-char (point-min))
  (when (re-search-forward "^Tags: \\(.+\\)" nil t)
    (replace-match (tagging-sort-tags-string (match-string 1)) t t nil 1)))

;; (assert (string-match (tags-make-emacs-search-regexp '("bee")) "bee cee"))
;; (assert (string-match (tags-make-emacs-search-regexp '("cee")) "bee cee"))
;; (assert (string-match (tags-make-emacs-search-regexp '("cee" "bee")) "bee cee"))
;; (assert (null (string-match (tags-make-emacs-search-regexp '("zee" "cee")) "bee cee")))
;; (assert (null (string-match (tags-make-emacs-search-regexp '("cee" "b")) "bee cee")))

(defun tagging-make-emacs-search-regexp (tags)
  "Convert TAGS to a regular expression."
  (concat
   "\\b"
   (mapconcat 'downcase
             (sort tags 'string<)
             "\\b+\\(.+\\b\\)*")
   "\\b"))

;;(tagging-grep-directory '("book") "~/howm")
;;(tagging-make-grep-search-regexp '("paper"))
(defun tagging-grep-directory (tags directory)
  "Return a list files matching TAGS in DIRECTORY."
  (when (stringp tags) (setq tags (split-string tags)))
  (setq tags (sort tags 'string<))
  (split-string
   (shell-command-to-string
      (concat "~/bin/find-tag.pl "
              directory
              " "
              (mapconcat 'shell-quote-argument tags " ")))
   "\n"
   t))

;; (assert (equal (tagging-tag-cloud-from-list '("a" "b" "a")) '(("a" . 2) ("b" . 1))))
(defun tagging-tag-cloud-from-list (tags)
  "Create a tagcloud with elements (tag-name . count) from TAGS.
TAGS is a list of tag strings."
  (let (result
        lookup)
    (while tags
      (setq lookup (assoc (downcase (car tags)) result))
      (if lookup
          (setcdr lookup (1+ (cdr lookup)))
        (setq result (cons (cons (car tags) 1) result)))
      (setq tags (cdr tags)))
    (sort result (lambda (a b) (< (cdr b) (cdr a))))))

;;(tagging-get-tagcloud-from-files (howm-files-in-directory howm-directory))                                                              
(defun tagging-get-tagcloud-from-files (files)
  "Return the tagcloud for this set of FILES."
  (let (tags)
    (while files
      (let ((tag-string
             (shell-command-to-string
              (concat
               "grep Tags: "
               (shell-quote-argument (car files))))))
        (when (and tag-string
                   (string-match "^Tags:\\(.+\\)" tag-string))
          (setq tags (append (split-string (match-string 1 tag-string)) tags))))
      (setq files (cdr files)))
    (tagging-tag-cloud-from-list tags)))