;;; Copyright © 2019 Amin Bandali <bandali@gnu.org>
;;;
;;; 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
;;; <http://www.gnu.org/licenses/>.

(define-module (bandali feeds)
  #:use-module (haunt builder atom)     ; atom-feed
  #:use-module (haunt builder rss)      ; rss-feed
  #:use-module (haunt post)             ; post-*
  #:use-module (ice-9 match)            ; match-lambda
  #:re-export (atom-feed
               rss-feed)
  #:export (atom-feeds-by-tag
            rss-feeds-by-tag))

(define* (atom-feeds-by-tag #:key
                            (prefix "feeds/tags")
                            (filter posts/reverse-chronological)
                            (max-entries 20)
                            (blog-prefix ""))
  "Return a builder procedure that renders an atom feed for every tag
used in a post.  All arguments are optional:

PREFIX: The directory in which to write the feeds
FILTER: The procedure called to manipulate the posts list before rendering
MAX-ENTRIES: The maximum number of posts to render in each feed"
  (lambda (site posts)
    (let ((tag-groups (posts/group-by-tag posts)))
      (map (match-lambda
            ((tag . posts)
             ((atom-feed #:file-name (string-append prefix "/" tag ".atom")
                         #:subtitle (string-append "Tag: " tag)
                         #:filter filter
                         #:max-entries max-entries
                         #:blog-prefix blog-prefix)
              site posts)))
           tag-groups))))

(define* (rss-feeds-by-tag #:key
                           (prefix "feeds/tags")
                           (filter posts/reverse-chronological)
                           (max-entries 20)
                           (blog-prefix ""))
  "Return a builder procedure that renders an rss feed for every tag
used in a post.  All arguments are optional:

PREFIX: The directory in which to write the feeds
FILTER: The procedure called to manipulate the posts list before rendering
MAX-ENTRIES: The maximum number of posts to render in each feed"
  (lambda (site posts)
    (let ((tag-groups (posts/group-by-tag posts)))
      (map (match-lambda
            ((tag . posts)
             ((rss-feed #:file-name (string-append prefix "/" tag ".rss")
                        #:subtitle (string-append "Tag: " tag)
                        #:filter filter
                        #:max-entries max-entries
                        #:blog-prefix blog-prefix)
              site posts)))
           tag-groups))))