;;; feedly-to-elfeed.el --- convert feedly OPML to elfeed  -*- lexical-binding: t; -*-

;; Copyright (C) 2019 Michael Herstine

;; Author: Michael Herstine <sp1ff@pobox.com>
;; Maintainer: Michael Herstine <sp1ff@pobox.com>
;; Created: 8 November 2019
;; Keywords: tools, hypermedia

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This package provides a single function: `feedly-to-elfeed'. It
;; takes as input the path to a Feedly OPML export file & returns a
;; string containing Emacs Lisp configuring elfeed with your Feedly
;; tags. Yes, there's `elfeed-load-opml' but it didn't work for my
;; Feedly export.

;;; Code:

(require 'xml)

(defun feedly--outline-to-alist (tags)
  "Convert a list of top-level outline XML nodes to a more convenient alist."
  (let ((feed-alist '())) ;; will be an assoc list: "feed-title" => (xmlUrl (tag-title))
    (while tags
      (let* ((tag (car tags))
	           (tag-title (xml-get-attribute tag 'title))
	           (feeds (xml-get-children tag 'outline)))
        (while feeds
	        (let* ((feed (car feeds))
	               (feed-title (xml-get-attribute feed 'title))
	               (xml-url (xml-get-attribute feed 'xmlUrl))
	               (entry (assoc feed-title feed-alist)))
            (if entry
                ;; `feed-title' is already in `feed-alist', we just
                ;; need to add `tag-title' to the list of tags
                (let ((title (car entry))
                      (url (nth 1 entry))
                      (tags (nth 2 entry)))
                  (unless (member tag-title tags)
                    (setq tags (append tags (list tag-title)))
                    (assoc-delete-all feed-title feed-alist)
                    (setq
                     feed-alist
                     (append
                      feed-alist
                      (list
                       (list feed-title xml-url tags))))))
              ;; This is a new feed-- make a new entry in `feed-alist'.
              (setq
               feed-alist
               (append
                feed-alist
                (list
                 (list feed-title xml-url (list tag-title)))))))
          (setq feeds (cdr feeds))))
      (setq tags (cdr tags)))
    feed-alist))

(defun feedly-to-elfeed--alist-to-org-table (feeds)
  "Convert an association list to an org-mode table.

Produces tab-delimited output-- you'll need to insert it into an org file,
select the text, and do C-|."

  (let ((lines '()))
    (while feeds
      (let* ((feed (car feeds))
             (feed-url (nth 1 feed))
             (tags (nth 2 feed))
             (feed-title (nth 0 feed)))
        (setq
         lines
         (append
          lines
          (list
           (format "%s\t%s\t%s" feed-title (mapconcat 'identity tags " ") feed-url)))))
      (setq feeds (cdr feeds)))
    (format "Title\tTags\tURL\n%s" (mapconcat 'identity lines "\n"))))
  
(defun feedly-to-elfeed (opml-file)
  "Convert Feedly OPML to elfeed configuration."

  (let* ((body (assq 'body (assq 'opml (xml-parse-file opml-file))))
         (tags (xml-get-children body 'outline)))
    ;; `tags' will be the list of "outer" `outline' tags
    (feedly-to-elfeed--alist-to-org-table (feedly--outline-to-alist tags))))

(provide 'feedly-to-elfeed)
;;; feedly-to-elfeed.el ends here