Generate Atom feeds for the website

* org-conf.el (durand-sitemap-custom-string-alist)
(durand-org-publish-sitemap): Add links to the atom files.

(durand-org-post-process): Call `durand-org-generate-atom-feed' in
this function.

(durand-org-atom-titles-alist): Associate titles and feed files with
the project name.

(durand-org-atom-preamble, durand-org-atom-entry-template)
(durand-org-atom-postamble): The generated Atom file is controlled by
these template variables.

(durand-org-atom-format-time): The zone of the time should be in a
specific format that no time format string provides.  So I write this
function to provide this formatting.

(durand-org-generate-atom-feed): Apply the templates to generate the
Atom feed files.

1 files changed, 194 insertions, 26 deletions

diff --git a/org-conf.el b/org-conf.el
index 68d4de7..bf1d50d 100644
--- a/org-conf.el
+++ b/org-conf.el
@@ -709,14 +709,17 @@ href='https://jsdurand.xyz/favicon.ico'/>")
 
 (setq durand-sitemap-custom-string-alist
       (list
-       (cons "About coding"
+       (list "About coding"
              "This is my coding blog.  It contains my coding experiments, or \
-one might think of them as development diaries.")
-       (cons "My life"
+one might think of them as development diaries."
+             "code-atom.xml")
+       (list "My life"
              "This is my casual blog.  It contains articles about my plain \
-life.")
-       (cons "Mathematics"
-             "My Mathematics-related articles are put here.")))
+life."
+             "life-atom.xml")
+       (list "Mathematics"
+             "My Mathematics-related articles are put here."
+             "math-atom.xml")))
 
 ;;;;;; Custom sitemap function
 
@@ -729,17 +732,19 @@ project.  Use such functions as `org-list-to-org' or
 `org-list-to-subtree' to transform it."
   (format "#+TITLE: %s\n#+AUTHOR: JSDurand\n%s#+DATE: <%s>\n\n%s\n\n\
 #+ATTR_HTML: :border nil :rules nil :frame nil\n\
-%s"
+%s\n\n\
+[[https://jsdurand.xyz/%s][Web feed]]"
           title
           "#+HTML_LINK_UP: index.html"
           (format-time-string "%F %a %R")
-          (cdr (assoc title durand-sitemap-custom-string-alist #'string=))
+          (cadr (assoc title durand-sitemap-custom-string-alist #'string=))
           ;; generate a table
           (org-list-to-generic
            rep
            '(:ustart "|---|"
              :uend "|---|"
-             :isep "|---|"))))
+             :isep "|---|"))
+          (caddr (assoc title durand-sitemap-custom-string-alist #'string=))))
 
 ;;;;;; Custom sitemap format
 
@@ -812,7 +817,9 @@ are present."
 (defun durand-org-post-process (project)
   "Generate a proper index page and Atom feeds.
 Also shorten the date strings in the sitemap files, and store the
-completion information in an attribute."
+completion information in an attribute.
+
+The feeds are generated by the function `durand-org-generate-atom-feed'."
   (let* ((project-plist (cdr (assoc project org-publish-project-alist #'string=)))
          (components (durand-org-publish-plist-get
                       :components project-plist))
@@ -831,7 +838,7 @@ completion information in an attribute."
      ;; depth-first recursion
      (components
       (setq contents (apply #'append
-                      (delete nil (mapcar #'durand-org-post-process components))))
+                            (delete nil (mapcar #'durand-org-post-process components))))
       ;; We only want some items
       (setq contents
             (durand-take
@@ -875,9 +882,7 @@ completion information in an attribute."
              (insert "</td>\n</tr>\n"))
            contents)
           (insert "</tbody>\n</table>")
-          (setq contents (buffer-substring-no-properties
-                          (point-min) (point-max))))
-        (write-region contents nil index-file))))
+          (write-region nil nil index-file)))))
      ((and publish-sitemap-file
            (stringp publish-sitemap-file)
            (file-exists-p publish-sitemap-file))
@@ -943,21 +948,184 @@ completion information in an attribute."
             (setq
              temp
              (cons
-              (cons temp-time
-                    (progn
-                      (re-search-forward regexp)
-                      (setq pos (point))
-                      (search-forward "</t")
-                      (buffer-substring-no-properties
-                       pos (match-beginning 0))))
+              (cons
+               temp-time
+               (progn
+                 (re-search-forward regexp)
+                 (setq pos (point))
+                 (search-forward "</t")
+                 (buffer-substring-no-properties
+                  pos (match-beginning 0))))
               temp)))
+          (durand-org-generate-atom-feed
+           project
+           (expand-file-name (concat project "-atom.xml")
+                             publishing-dir)
+           (mapcar
+            (lambda (cell)
+              (let* ((orig-string (cdr cell))
+                     (temp 0)
+                     (title
+                      (progn
+                        (string-match ">" orig-string)
+                        (setq temp (match-end 0))
+                        (substring
+                         orig-string
+                         temp
+                         (progn
+                           (string-match "</a>" orig-string temp)
+                           (match-beginning 0)))))
+                     (file-name
+                      (progn
+                        (string-match "href=\"" orig-string)
+                        (setq temp (match-end 0))
+                        (substring
+                         orig-string
+                         temp
+                         (progn
+                           (string-match "\">" orig-string temp)
+                           (match-beginning 0)))))
+                     (content
+                      (with-temp-buffer
+                        (insert-file-contents
+                         (expand-file-name file-name publishing-dir))
+                        (goto-char (point-min))
+                        (search-forward "<div id=\"content\">" nil t)
+                        (search-forward "<p>" nil t)
+                        (buffer-substring-no-properties
+                         (1+ (point))
+                         (progn
+                           (search-forward "</p>" nil t)
+                           (match-beginning 0)))))
+                     ;; escape html
+                     (content
+                      (replace-regexp-in-string
+                       ">" "&gt;"
+                       (replace-regexp-in-string
+                        "<" "&lt;"
+                        (replace-regexp-in-string
+                         "&" "&amp;" content)))))
+                (list
+                 title
+                 (durand-org-atom-format-time
+                  (file-attribute-modification-time
+                   (file-attributes
+                    (expand-file-name file-name publishing-dir))))
+                 (concat "https://jsdurand.xyz/" file-name)
+                 (concat "https://jsdurand.xyz/" file-name)
+                 (durand-org-atom-format-time (car cell))
+                 content)))
+            (reverse temp)))
           (reverse temp)))))))
 
 ;;;;; Atom feed
 
-;; The Atom feeds are generated in this function.
+;;;;;; Fixed pre-amble, template, and post-amble.
+
+(defvar durand-org-atom-titles-alist nil
+  "An assocuation list of Atom feed titles with the project name.")
+
+(setq durand-org-atom-titles-alist
+      (list
+       (list "code" "JSDurand's codes" "https://jsdurand.xyz/code-atom.xml")
+       (list "math" "Math articles of JSDurand"
+             "https://jsdurand.xyz/math-atom.xml")
+       (list "life" "JSDurand's life"
+             "https://jsdurand.xyz/life-atom.xml")))
+
+(defvar durand-org-atom-preamble nil
+  "The preamble of an Atom feed.")
+
+(setq durand-org-atom-preamble
+      "<?xml version=\"1.0\" encoding=\"utf-8\" ?>
+<feed xmlns=\"http://www.w3.org/2005/Atom\">
+<id>https://jsdurand.xyz/atom.xml</id>
+<title>%s</title>
+<author>
+<name>JSDurand</name>
+<uri> https://jsdurand.xyz </uri>
+<email>mmemmew@gmail.com</email>
+</author>
+<link rel=\"self\" type=\"applicatoin/atom+xml\" href=\"%s\"/>
+<rights>Copyright (c) 2021, JSDurand</rights>
+<updated>%s</updated>
+<generator uri=\"https://www.gnu.org/software/emacs/\" version=\"28.0.50\">\
+Emacs</generator>\n")
+
+(defvar durand-org-atom-entry-template nil
+  "The template for an Atom entry.
+It HAS to be formatted with 6 arguments in the following order:
+
+TITLE: the title.  Note this does not have a subtitle.
+
+UPDATED-TIME: the newest updated time.
+
+ID: I think I will use the URL as the ID directly.
+
+LINK: Link to this entry.
+
+PUBLISHED-TIME: the time this is published.
+
+CONTENT: a short content.
+")
+
+(setq durand-org-atom-entry-template
+      "<entry>
+<title type=\"text\">%s</title>
+<updated>%s</updated>
+<id>%s</id>
+<link rel=\"self\" type=\"text/html\" href=\"%s\"/>
+<published>%s</published>
+<content type=\"html\">
+%s
+</content>
+</entry>")
+
+(defvar durand-org-atom-postamble nil
+  "The post-amble of an Atom feed.")
+
+(setq durand-org-atom-postamble
+      "</feed>")
+
+;;;;;; Format time easily
+
+(defun durand-org-atom-format-time (time)
+  "Format TIME in an acceptable way."
+  (concat
+   (format-time-string
+    "%FT%T" time)
+   (format "%s%02d:%02d"
+           (cond ((> (car (current-time-zone)) 0) "+")
+                 ("-"))
+           (/ (car (current-time-zone)) 3600)
+           (% (car (current-time-zone)) 3600))))
+
+;;;;;; The Atom feeds are generated in this function.
+
+(defun durand-org-generate-atom-feed (project file-name entries)
+  "Generate an Atom feed for ENTRIES and save in FILE-NAME.
+PROJECT is the name of the subproject.
+
+ENTRIES is a list of entries.
+
+An entry is a list of the form (TITLE UPTIME ID LINK PUBTIME CONTENT).
+See the documentation string for `durand-org-atom-entry-template' for more."
+  (with-temp-buffer
+    (insert (apply #'format
+                   durand-org-atom-preamble
+                   (append
+                    (cdr
+                     (assoc project durand-org-atom-titles-alist
+                            #'string=))
+                    (list (durand-org-atom-format-time nil))))
+            "\n")
+    (mapc
+     (lambda (entry)
+       (insert (apply #'format durand-org-atom-entry-template
+                      entry)
+               "\n"))
+     entries)
+    (insert durand-org-atom-postamble)
+    (write-region nil nil file-name)))
+
 
-(defun durand-org-generate-atom-feed (project)
-  "Generate an Atom feed for PROJECT."
-  ;; TODO 
-  )