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# This file defines functions for generating an Atom feed.
{ depot, lib, ... }:
with depot.nix.yants;
let
inherit (builtins) map readFile replaceStrings;
inherit (lib) concatStrings concatStringsSep removeSuffix;
inherit (depot.third_party) runCommandNoCC;
# 'link' describes a related link to a feed, or feed element.
#
# https://validator.w3.org/feed/docs/atom.html#link
link = struct "link" {
rel = string;
href = string;
};
# 'entry' describes a feed entry, for example a single post on a
# blog. Some optional fields have been omitted.
#
# https://validator.w3.org/feed/docs/atom.html#requiredEntryElements
entry = struct "entry" {
# Identifies the entry using a universally unique and permanent URI.
id = string;
# Contains a human readable title for the entry. This value should
# not be blank.
title = string;
# Content of the entry. This element is technically optional, but
# only if an alternate link is provided. In practice it should
# always be present in the feeds generated by this code.
content = string;
# Indicates the last time the entry was modified in a significant
# way (in seconds since epoch).
updated = int;
# Names authors of the entry. Recommended element.
authors = option (list string);
# Related web pages, such as the web location of a blog post.
links = option (list link);
# Conveys a short summary, abstract, or excerpt of the entry.
summary = option string;
# Contains the time of the initial creation or first availability
# of the entry.
published = option int;
# Conveys information about rights, e.g. copyrights, held in and
# over the entry.
rights = option string;
};
# 'feed' describes the metadata of the Atom feed itself.
#
# Some optional fields have been omitted.
#
# https://validator.w3.org/feed/docs/atom.html#requiredFeedElements
feed = struct "feed" {
# Identifies the feed using a universally unique and permanent URI.
id = string;
# Contains a human readable title for the feed.
title = string;
# Indicates the last time the feed was modified in a significant
# way (in seconds since epoch). Recommended element.
updated = int;
# Entries contained within the feed.
entries = list entry;
# Names authors of the feed. Recommended element.
authors = option (list string);
# Related web locations. Recommended element.
links = option (list link);
# Conveys information about rights, e.g. copyrights, held in and
# over the feed.
rights = option string;
# Contains a human-readable description or subtitle for the feed.
subtitle = option string;
};
# Feed generation functions:
renderEpoch = epoch: removeSuffix "\n" (readFile (runCommandNoCC "date-${toString epoch}" {} ''
date --date='@${toString epoch}' --utc --iso-8601='seconds' > $out
''));
escape = replaceStrings [ "<" ">" "&" "'" ] [ "<" ">" "&" "'" ];
elem = name: content: ''<${name}>${escape content}</${name}>'';
renderLink = defun [ link string ] (l: ''
<link href="${escape l.href}" rel="${escape l.rel}" />
'');
# Technically the author element can also contain 'uri' and 'email'
# fields, but they are not used for the purpose of this feed and are
# omitted.
renderAuthor = author: ''<author><name>${escape author}</name></author>'';
renderEntry = defun [ entry string ] (e: ''
<entry>
${elem "title" e.title}
${elem "id" e.id}
${elem "updated" (renderEpoch e.updated)}
<content type="html">${escape e.content}</content>
${concatStrings (map renderAuthor (e.authors or []))}
${if e ? subtitle then elem "subtitle" e.subtitle else ""}
${if e ? rights then elem "rights" e.rights else ""}
${concatStrings (map renderLink (e.links or []))}
</entry>
'');
renderFeed = defun [ feed string ] (f: ''
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
${elem "id" f.id}
${elem "title" f.title}
${elem "updated" (renderEpoch f.updated)}
${concatStringsSep "\n" (map renderAuthor (f.authors or []))}
${if f ? subtitle then elem "subtitle" f.subtitle else ""}
${if f ? rights then elem "rights" f.rights else ""}
${concatStrings (map renderLink (f.links or []))}
${concatStrings (map renderEntry f.entries)}
</feed>
'');
in {
inherit entry feed renderFeed renderEpoch;
}
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