From fb667d98c6d0b7c133ea5fcfa54fc1f1136772ef Mon Sep 17 00:00:00 2001
From: "Jakob L. Kreuze" <zerodaysfordays@sdf.lonestar.org>
Date: Tue, 23 Jul 2019 17:49:51 -0400
Subject: Implement an Atom feed with support for crossposts.

---
 haunt/haunt.scm              |  2 +-
 haunt/jakob/builder/atom.scm | 83 ++++++++++++++++++++++++++++++++++++++++++++
 haunt/jakob/builder/blog.scm |  3 +-
 3 files changed, 86 insertions(+), 2 deletions(-)
 create mode 100644 haunt/jakob/builder/atom.scm

diff --git a/haunt/haunt.scm b/haunt/haunt.scm
index dcf41b0..8a975ec 100644
--- a/haunt/haunt.scm
+++ b/haunt/haunt.scm
@@ -15,9 +15,9 @@
 ;;; <http://www.gnu.org/licenses/>.
 
 (use-modules (haunt builder assets)
-             (haunt builder atom)
              (haunt post)
              (haunt site)
+             (jakob builder atom)
              (jakob builder blog)
              (jakob builder blogroll)
              (jakob builder htaccess)
diff --git a/haunt/jakob/builder/atom.scm b/haunt/jakob/builder/atom.scm
new file mode 100644
index 0000000..d4f469a
--- /dev/null
+++ b/haunt/jakob/builder/atom.scm
@@ -0,0 +1,83 @@
+;;; Copyright © 2019 Jakob L. Kreuze <zerodaysfordays@sdf.lonestar.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 (jakob builder atom)
+  #:use-module (haunt html)
+  #:use-module (haunt page)
+  #:use-module (haunt post)
+  #:use-module (haunt site)
+  #:use-module (haunt utils)
+  #:use-module (ice-9 match)
+  #:use-module (jakob builder blog)
+  #:use-module (srfi srfi-19)
+  #:use-module (srfi srfi-26)
+  #:use-module (web uri)
+  #:export (atom-feed))
+
+(define* (post->atom-entry site post #:key (blog-prefix ""))
+  "Convert POST into an Atom <entry> XML node."
+  (let ((uri (or (post-ref post 'crosspost)
+                 (post-uri post))))
+    `(entry
+      (title ,(post-ref post 'title))
+      (id ,uri)
+      (author
+       (name ,(post-ref post 'author))
+       ,(let ((email (post-ref post 'email)))
+          (if email `(email ,email) '())))
+      (updated ,(date->string (post-date post) "~4"))
+      (link (@ (href ,uri) (rel "alternate")))
+      (summary (@ (type "html"))
+               ,(sxml->html-string (post-sxml post)))
+      ,@(map (lambda (enclosure)
+               `(link (@ (rel "enclosure")
+                         (title ,(enclosure-title enclosure))
+                         (href ,(enclosure-url enclosure))
+                         (type ,(enclosure-mime-type enclosure))
+                         ,@(map (match-lambda
+                                  ((key . value)
+                                   (list key value)))
+                                (enclosure-extra enclosure)))))
+             (post-ref-all post 'enclosure)))))
+
+(define* (atom-feed #:key
+                    (file-name "feed.xml")
+                    (subtitle "Recent Posts")
+                    (filter posts/reverse-chronological)
+                    (max-entries 20)
+                    (blog-prefix ""))
+  "Minor modification to the 'atom-feed' builder in '(haunt builder atom)' to
+add support for cross-posts. See the docstring in that manual for details on the
+use of this function."
+  (lambda (site posts)
+    (let ((uri (uri->string
+                (build-uri 'http ;; (site-scheme site)
+                           #:host (site-domain site)
+                           #:path (string-append "/" file-name)))))
+      (make-page file-name
+                 `(feed (@ (xmlns "http://www.w3.org/2005/Atom"))
+                        (title ,(site-title site))
+                        (id ,uri)
+                        (subtitle ,subtitle)
+                        (updated ,(date->string (current-date) "~4"))
+                        (link (@ (href ,(string-append (site-domain site)
+                                                       "/" file-name))
+                                 (rel "self")))
+                        (link (@ (href ,(site-domain site))))
+                        ,@(map (cut post->atom-entry site <>
+                                    #:blog-prefix blog-prefix)
+                               (take-up-to max-entries (filter posts))))
+                 (@@ (haunt builder atom) sxml->xml*)))))
diff --git a/haunt/jakob/builder/blog.scm b/haunt/jakob/builder/blog.scm
index b3100fe..93eb519 100644
--- a/haunt/jakob/builder/blog.scm
+++ b/haunt/jakob/builder/blog.scm
@@ -29,7 +29,8 @@
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-19)
   #:use-module (srfi srfi-26)
-  #:export (blog))
+  #:export (post-uri
+            blog))
 
 ;;; Commentary:
 ;;;
-- 
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