From c967aa9d7c59832805829e2ec7ced13f29a267b1 Mon Sep 17 00:00:00 2001
From: xvw <xavier.vdw@gmail.com>
Date: Sun, 11 Aug 2024 21:06:50 +0200
Subject: [PATCH 1/4] Some refactoring on test, extracting Chain

---
 test/gem/chain_test.ml | 55 +++++++++++++++---------------------------
 test/gem/util.ml       | 17 +++++++++++++
 test/gem/util.mli      | 11 +++++++++
 3 files changed, 48 insertions(+), 35 deletions(-)

diff --git a/test/gem/chain_test.ml b/test/gem/chain_test.ml
index 0da0f23..7088db9 100644
--- a/test/gem/chain_test.ml
+++ b/test/gem/chain_test.ml
@@ -1,40 +1,24 @@
 open Gem.Model
-
-let make_member ident url =
-  let open Yocaml.Data in
-  ( ident,
-    record
-      [ ("id", string ident); ("main_link", record [ ("url", string url) ]) ] )
-
-let m1 = make_member "m1" "https://xvw.lol"
-let m2 = make_member "m2" "https://wvx.lol"
-let m3 = make_member "m3" "https://xxx.lol"
-let m4 = make_member "m4" "https://vvv.lol"
-
-let make l =
-  let chain, members = List.split l in
-  Yocaml.Data.Validation.list_of Member.validate (Yocaml.Data.list members)
-  |> Result.map (fun members -> (chain, members))
+open Util
 
 let from_list list =
-  make list
-  |> Result.map (fun (chain, members) ->
-         Chain.init ~chain ~members
-         |> Chain.fold
-              (fun acc ~pred ~curr ~succ ->
-                Format.asprintf "%s\n%s [< %s | %s >]" acc (Member.id curr)
-                  (Member.id pred) (Member.id succ))
-              "")
+  make_chain list
+  |> Result.map
+       (Chain.fold
+          (fun acc ~pred ~curr ~succ ->
+            Format.asprintf "%s\n%s [< %s | %s >]" acc (Member.id curr)
+              (Member.id pred) (Member.id succ))
+          "")
 
 let%expect_test "Test with a regular chain" =
-  let ctx = from_list [ m1; m2; m3; m4 ] in
+  let ctx = from_list [ member_1; member_2; member_3; member_4 ] in
   Util.print_validated_value Format.pp_print_string ctx;
   [%expect
     {|
-    m1 [< m4 | m2 >]
-    m2 [< m1 | m3 >]
-    m3 [< m2 | m4 >]
-    m4 [< m3 | m1 >]
+    member-1 [< member-4 | member-2 >]
+    member-2 [< member-1 | member-3 >]
+    member-3 [< member-2 | member-4 >]
+    member-4 [< member-3 | member-1 >]
     |}]
 
 let%expect_test "Test with an empty chain" =
@@ -43,14 +27,15 @@ let%expect_test "Test with an empty chain" =
   [%expect {| |}]
 
 let%expect_test "Test with an 1-element chain" =
-  let ctx = from_list [ m1 ] in
+  let ctx = from_list [ member_1 ] in
   Util.print_validated_value Format.pp_print_string ctx;
-  [%expect {| m1 [< m1 | m1 >] |}]
+  [%expect {| member-1 [< member-1 | member-1 >] |}]
 
 let%expect_test "Test with an 2-element chain" =
-  let ctx = from_list [ m1; m2 ] in
+  let ctx = from_list [ member_1; member_2 ] in
   Util.print_validated_value Format.pp_print_string ctx;
-  [%expect {|
-    m1 [< m2 | m2 >]
-    m2 [< m1 | m1 >]
+  [%expect
+    {|
+    member-1 [< member-2 | member-2 >]
+    member-2 [< member-1 | member-1 >]
     |}]
diff --git a/test/gem/util.ml b/test/gem/util.ml
index 736cb3b..ed0395e 100644
--- a/test/gem/util.ml
+++ b/test/gem/util.ml
@@ -29,3 +29,20 @@ let print_validated_value pp_ok x =
   @@ Format.asprintf "%a"
        (Format.pp_print_result ~ok:pp_ok ~error:pp_value_error)
        x
+
+let make_member ident url =
+  let open Yocaml.Data in
+  ( ident,
+    record
+      [ ("id", string ident); ("main_link", record [ ("url", string url) ]) ] )
+
+let make_chain l =
+  let chain, members = List.split l in
+  Yocaml.Data.Validation.list_of Gem.Model.Member.validate
+    (Yocaml.Data.list members)
+  |> Result.map (fun members -> Gem.Model.Chain.init ~chain ~members)
+
+let member_1 = make_member "member-1" "https://xvw.lol"
+let member_2 = make_member "member-2" "https://wvx.lol"
+let member_3 = make_member "member-3" "https://xxx.lol"
+let member_4 = make_member "member-4" "https://vvv.lol"
diff --git a/test/gem/util.mli b/test/gem/util.mli
index a6b2d68..3fc11ec 100644
--- a/test/gem/util.mli
+++ b/test/gem/util.mli
@@ -6,3 +6,14 @@ val print_validated_value :
   unit
 (** Print a validated value (for expect-test). Mostly a readable value (but
     not-so exhaustive) *)
+
+val make_member : string -> string -> string * Yocaml.Data.t
+
+val make_chain :
+  (string * Yocaml.Data.t) list ->
+  Gem.Model.Chain.t Yocaml.Data.Validation.validated_value
+
+val member_1 : string * Yocaml.Data.t
+val member_2 : string * Yocaml.Data.t
+val member_3 : string * Yocaml.Data.t
+val member_4 : string * Yocaml.Data.t

From cc92c93d7b22fbeef8d21cadca9fa9aa2fb634df Mon Sep 17 00:00:00 2001
From: xvw <xavier.vdw@gmail.com>
Date: Sun, 11 Aug 2024 21:18:31 +0200
Subject: [PATCH 2/4] Add Article Model (and Validation/Normalization)

---
 lib/model/article.ml     | 47 ++++++++++++++++++++++++++
 lib/model/article.mli    | 14 ++++++++
 test/gem/article_test.ml | 72 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 133 insertions(+)
 create mode 100644 lib/model/article.ml
 create mode 100644 lib/model/article.mli
 create mode 100644 test/gem/article_test.ml

diff --git a/lib/model/article.ml b/lib/model/article.ml
new file mode 100644
index 0000000..413af8c
--- /dev/null
+++ b/lib/model/article.ml
@@ -0,0 +1,47 @@
+type t = {
+  title : string;
+  synopsis : string option;
+  date : Yocaml.Archetype.Datetime.t;
+  tags : string list;
+  authors : string list;
+  url : Url.t;
+}
+
+let entity_name = "Article"
+let neutral = Yocaml.Metadata.required entity_name
+
+let validate =
+  let open Yocaml.Data.Validation in
+  record (fun fl ->
+      let+ title = required fl "title" string
+      and+ synopsis = optional fl "synopsis" string
+      and+ date = required fl "date" Yocaml.Archetype.Datetime.validate
+      and+ url = required fl "url" Url.validate
+      and+ tags =
+        optional_or fl ~default:[] "tags" @@ list_of Yocaml.Slug.validate
+      and+ authors =
+        required fl "authors"
+        @@ ((string $ fun x -> [ x ]) / list_of Yocaml.Slug.validate)
+      in
+      { title; synopsis; date; tags; authors; url })
+
+let authors_in_chain chain { authors; _ } =
+  chain
+  |> Chain.to_list
+  |> List.exists (fun (x, _) ->
+         List.exists (String.equal @@ Member.id x) authors)
+
+let normalize { title; synopsis; date; tags; authors; url } =
+  let open Yocaml.Data in
+  [
+    ("title", string title);
+    ("synopsis", option string synopsis);
+    ("date", Yocaml.Archetype.Datetime.normalize date);
+    ("tags", list_of string tags);
+    ("authors", list_of string authors);
+    ("url", Url.normalize url);
+  ]
+
+let pp ppf article =
+  Format.fprintf ppf "%a" Yocaml.Data.pp
+    (article |> normalize |> Yocaml.Data.record)
diff --git a/lib/model/article.mli b/lib/model/article.mli
new file mode 100644
index 0000000..d2749b0
--- /dev/null
+++ b/lib/model/article.mli
@@ -0,0 +1,14 @@
+(** Describes an external Article. *)
+
+type t
+(** The type describing an article. *)
+
+val authors_in_chain : Chain.t -> t -> bool
+(** Ensure that authors are present in chain. *)
+
+val pp : Format.formatter -> t -> unit
+
+(** {1 Dealing as metadata} *)
+
+include Yocaml.Required.DATA_READABLE with type t := t
+include Yocaml.Required.DATA_INJECTABLE with type t := t
diff --git a/test/gem/article_test.ml b/test/gem/article_test.ml
new file mode 100644
index 0000000..6732872
--- /dev/null
+++ b/test/gem/article_test.ml
@@ -0,0 +1,72 @@
+open Yocaml
+open Gem.Model
+open Util
+
+let%expect_test "Validate a minimal article" =
+  let article =
+    let open Data in
+    record
+      [
+        ("title", string "An Article");
+        ("date", string "2024-08-11");
+        ("authors", string "xvw");
+        ("url", string "https://xvw.lol/a.html");
+      ]
+  in
+  print_validated_value Article.pp (Article.validate article);
+  [%expect
+    {|
+    {"title": "An Article", "synopsis": null, "date":
+     {"year": 2024, "month": 8, "day": 11, "hour": 0, "min": 0, "sec": 0,
+     "has_time": false, "day_of_week": 6, "repr":
+      {"month": "aug", "datetime": "2024-08-11 00:00:00", "date": "2024-08-11",
+      "time": "00:00:00", "day_of_week": "sun"}},
+    "tags": [], "authors": ["xvw"], "url":
+     {"url": "https://xvw.lol/a.html", "scheme": "https", "url_without_scheme":
+      "xvw.lol/a.html"}}
+    |}]
+
+let%expect_test "Validate a full article" =
+  let article =
+    let open Data in
+    record
+      [
+        ("title", string "An Article");
+        ("date", string "2024-08-11");
+        ("authors", list_of string [ "xvw"; "grim" ]);
+        ("synopsis", string "A synopsis");
+        ("url", string "https://xvw.lol/a.html");
+        ("tags", list_of string [ "a"; "b"; "c-d" ]);
+      ]
+  in
+  print_validated_value Article.pp (Article.validate article);
+  [%expect
+    {|
+    {"title": "An Article", "synopsis": "A synopsis", "date":
+     {"year": 2024, "month": 8, "day": 11, "hour": 0, "min": 0, "sec": 0,
+     "has_time": false, "day_of_week": 6, "repr":
+      {"month": "aug", "datetime": "2024-08-11 00:00:00", "date": "2024-08-11",
+      "time": "00:00:00", "day_of_week": "sun"}},
+    "tags": ["a", "b", "c-d"], "authors": ["xvw", "grim"], "url":
+     {"url": "https://xvw.lol/a.html", "scheme": "https", "url_without_scheme":
+      "xvw.lol/a.html"}}
+    |}]
+
+let%expect_test "Validate an invalid article" =
+  let article =
+    let open Data in
+    record
+      [
+        ("title", string "An Article");
+        ("authors", list_of string [ "xvw"; "grim" ]);
+        ("synopsis", string "A synopsis");
+        ("tags", list_of string [ "a"; "b"; "c-d" ]);
+      ]
+  in
+  print_validated_value Article.pp (Article.validate article);
+  [%expect
+    {|
+    <error-invalid-record missing field: date
+    missing field: url> for {"title": "An Article", "authors": ["xvw", "grim"],
+                            "synopsis": "A synopsis", "tags": ["a", "b", "c-d"]}
+    |}]

From 955ec8d1b411ceeb5b6bb532c0f670477380a188 Mon Sep 17 00:00:00 2001
From: xvw <xavier.vdw@gmail.com>
Date: Mon, 12 Aug 2024 03:36:02 +0200
Subject: [PATCH 3/4] Add a federated blog

---
 data/articles/guarded-methods.yml |  13 ++++
 data/articles/import-modules.yml  |  10 +++
 data/articles/merlin-destruct.yml |   8 +++
 data/blog.md                      |   9 +++
 lib/action/all.ml                 |   1 +
 lib/action/articles.ml            |  17 +++++
 lib/action/articles.mli           |   3 +
 lib/model/article.ml              |  25 ++++---
 lib/model/article.mli             |   1 +
 lib/model/articles.ml             |  40 ++++++++++++
 lib/model/articles.mli            |  10 +++
 lib/model/link.ml                 |  17 ++---
 lib/resolver.ml                   |   3 +
 lib/sigs.mli                      |   3 +
 static/css/style.css              | 105 ++++++++++++++++++++++++++++--
 static/templates/blog.html        |  30 +++++++++
 static/templates/index.html       |   2 +-
 static/templates/layout.html      |   3 +
 test/gem/article_test.ml          |  28 ++++----
 19 files changed, 294 insertions(+), 34 deletions(-)
 create mode 100644 data/articles/guarded-methods.yml
 create mode 100644 data/articles/import-modules.yml
 create mode 100644 data/articles/merlin-destruct.yml
 create mode 100644 data/blog.md
 create mode 100644 lib/action/articles.ml
 create mode 100644 lib/action/articles.mli
 create mode 100644 lib/model/articles.ml
 create mode 100644 lib/model/articles.mli
 create mode 100644 static/templates/blog.html

diff --git a/data/articles/guarded-methods.yml b/data/articles/guarded-methods.yml
new file mode 100644
index 0000000..6778f2f
--- /dev/null
+++ b/data/articles/guarded-methods.yml
@@ -0,0 +1,13 @@
+title: Guarded methods using equality witnesses
+synopsis: Guarded methods allow constraints to be attached to the receiver
+  (self) only for certain methods, so that these methods can only
+  be called if the receiver satisfies these constraints (these guards).
+  OCaml does not syntactically allow this type of method to be defined
+  directly. In this note, we'll look at how to encode them using a
+  type equality witness.
+date: 2022-05-29
+authors: [xvw]
+link:
+  url: https://xvw.lol/pages/oop-refl.html
+  lang: fra
+tags: [ocaml, oop, refl, gadt]
diff --git a/data/articles/import-modules.yml b/data/articles/import-modules.yml
new file mode 100644
index 0000000..5bcbf8b
--- /dev/null
+++ b/data/articles/import-modules.yml
@@ -0,0 +1,10 @@
+title: OCaml, modules and import schemes
+synopsis: In this article, we're going to look at how generalised openings
+  can be used to reproduce a common practice in other languages,
+  which I call, somewhat pompously, import strategies,
+date: 2023-10-31
+authors: [xvw]
+link:
+  url: https://xvw.lol/pages/modules-import.html
+  lang: fra
+tags: [ocaml, module]
diff --git a/data/articles/merlin-destruct.yml b/data/articles/merlin-destruct.yml
new file mode 100644
index 0000000..ac82899
--- /dev/null
+++ b/data/articles/merlin-destruct.yml
@@ -0,0 +1,8 @@
+title: Effective ML Through Merlin's Destruct Command
+synopsis: This article presents the use of the destruct command in Merlin
+  and OCaml-lsp to generate missing patterns, or to specify patterns in
+  pattern matching.
+date: 2024-05-29
+authors: [xvw]
+link: https://tarides.com/blog/2024-05-29-effective-ml-through-merlin-s-destruct-command/
+tags: [ocaml, lsp, ide, emacs, vscode, vim, merlin]
diff --git a/data/blog.md b/data/blog.md
new file mode 100644
index 0000000..b095f79
--- /dev/null
+++ b/data/blog.md
@@ -0,0 +1,9 @@
+---
+page_title: Blog
+description: A federated blog of Webring's member
+---
+
+The **Federated Blog** allows [webring members](/) to showcase federated
+articles on this page from _time to time_. The list of articles is not
+calculated automatically (via RSS/Atom feeds) but is the result of **a manual
+addition**.
diff --git a/lib/action/all.ml b/lib/action/all.ml
index 0c3ddcd..193cad5 100644
--- a/lib/action/all.ml
+++ b/lib/action/all.ml
@@ -13,6 +13,7 @@ let run (module R : Sigs.RESOLVER) () =
   >>= Fonts.run (module R)
   >>= Css.run (module R)
   >>= Images.run (module R)
+  >>= Articles.run (module R) chain
   >>= Opml.run (module R) chain
   >>= Chain.run (module R) chain
   >>= Index.run (module R) chain
diff --git a/lib/action/articles.ml b/lib/action/articles.ml
new file mode 100644
index 0000000..7b30c6c
--- /dev/null
+++ b/lib/action/articles.ml
@@ -0,0 +1,17 @@
+let run (module R : Sigs.RESOLVER) chain =
+  Yocaml.Action.write_static_file R.Target.blog
+    (let open Yocaml.Task in
+     R.track_common_dependencies
+     >>> Yocaml.Pipeline.track_file R.Source.articles
+     >>> Yocaml_yaml.Pipeline.read_file_with_metadata
+           (module Model.Page)
+           R.Source.blog
+     >>> first @@ Model.Articles.index chain R.Source.articles
+     >>> Yocaml_omd.content_to_html ()
+     >>> Yocaml_jingoo.Pipeline.as_template
+           (module Model.Articles)
+           (R.Source.template "blog.html")
+     >>> Yocaml_jingoo.Pipeline.as_template
+           (module Model.Articles)
+           (R.Source.template "layout.html")
+     >>> drop_first ())
diff --git a/lib/action/articles.mli b/lib/action/articles.mli
new file mode 100644
index 0000000..365335a
--- /dev/null
+++ b/lib/action/articles.mli
@@ -0,0 +1,3 @@
+(** An action that builds the webring blog. *)
+
+val run : (module Sigs.RESOLVER) -> Model.Chain.t -> Yocaml.Action.t
diff --git a/lib/model/article.ml b/lib/model/article.ml
index 413af8c..e796bda 100644
--- a/lib/model/article.ml
+++ b/lib/model/article.ml
@@ -1,10 +1,12 @@
+open Model_util
+
 type t = {
   title : string;
   synopsis : string option;
   date : Yocaml.Archetype.Datetime.t;
   tags : string list;
   authors : string list;
-  url : Url.t;
+  link : Link.t;
 }
 
 let entity_name = "Article"
@@ -16,32 +18,37 @@ let validate =
       let+ title = required fl "title" string
       and+ synopsis = optional fl "synopsis" string
       and+ date = required fl "date" Yocaml.Archetype.Datetime.validate
-      and+ url = required fl "url" Url.validate
+      and+ link = required fl "link" Link.validate
       and+ tags =
         optional_or fl ~default:[] "tags" @@ list_of Yocaml.Slug.validate
       and+ authors =
         required fl "authors"
         @@ ((string $ fun x -> [ x ]) / list_of Yocaml.Slug.validate)
       in
-      { title; synopsis; date; tags; authors; url })
+      { title; synopsis; date; tags; authors; link })
 
 let authors_in_chain chain { authors; _ } =
-  chain
-  |> Chain.to_list
-  |> List.exists (fun (x, _) ->
-         List.exists (String.equal @@ Member.id x) authors)
+  let chain = Chain.to_list chain in
+  List.for_all
+    (fun author ->
+      chain |> List.exists (fun (x, _) -> String.equal author (Member.id x)))
+    authors
 
-let normalize { title; synopsis; date; tags; authors; url } =
+let normalize { title; synopsis; date; tags; authors; link } =
   let open Yocaml.Data in
   [
     ("title", string title);
+    ("has_synopsis", has_opt synopsis);
     ("synopsis", option string synopsis);
     ("date", Yocaml.Archetype.Datetime.normalize date);
     ("tags", list_of string tags);
+    ("has_tags", has_list tags);
     ("authors", list_of string authors);
-    ("url", Url.normalize url);
+    ("link", Link.normalize link);
   ]
 
 let pp ppf article =
   Format.fprintf ppf "%a" Yocaml.Data.pp
     (article |> normalize |> Yocaml.Data.record)
+
+let sort a b = Yocaml.Archetype.Datetime.compare a.date b.date
diff --git a/lib/model/article.mli b/lib/model/article.mli
index d2749b0..2296bb5 100644
--- a/lib/model/article.mli
+++ b/lib/model/article.mli
@@ -7,6 +7,7 @@ val authors_in_chain : Chain.t -> t -> bool
 (** Ensure that authors are present in chain. *)
 
 val pp : Format.formatter -> t -> unit
+val sort : t -> t -> int
 
 (** {1 Dealing as metadata} *)
 
diff --git a/lib/model/articles.ml b/lib/model/articles.ml
new file mode 100644
index 0000000..8c25e07
--- /dev/null
+++ b/lib/model/articles.ml
@@ -0,0 +1,40 @@
+open Model_util
+
+type t = { page : Page.t; articles : Article.t list }
+
+let from_page = Yocaml.Task.lift (fun (page, articles) -> { page; articles })
+
+let fetch ?limit chain path =
+  Yocaml.Task.from_effect (fun () ->
+      let open Yocaml.Eff in
+      let* files =
+        read_directory ~on:`Source ~only:`Files
+          ~where:(Yocaml.Path.has_extension "yml")
+          path
+      in
+
+      let+ articles =
+        List.traverse
+          (fun file ->
+            Yocaml_yaml.Eff.read_file_as_metadata
+              (module Article)
+              ~on:`Source file)
+          files
+      in
+      limit
+      |> Option.fold ~none:articles ~some:(fun limit ->
+             articles |> Stdlib.List.filteri (fun i _ -> i > limit))
+      |> Stdlib.List.sort (fun a b -> Article.sort b a)
+      |> Stdlib.List.filter (Article.authors_in_chain chain))
+
+let index ?limit chain path =
+  let open Yocaml.Task in
+  lift (fun x -> (x, ())) >>> second (fetch ?limit chain path) >>> from_page
+
+let normalize { page; articles } =
+  let open Yocaml.Data in
+  Page.normalize page
+  @ [
+      ("articles", list_of (fun x -> record (Article.normalize x)) articles);
+      ("has_articles", has_list articles);
+    ]
diff --git a/lib/model/articles.mli b/lib/model/articles.mli
new file mode 100644
index 0000000..f0e5e7a
--- /dev/null
+++ b/lib/model/articles.mli
@@ -0,0 +1,10 @@
+(** Describes a federation page of external articles published by ring members. *)
+
+type t
+(** The type describing the federation. *)
+
+val index : ?limit:int -> Chain.t -> Yocaml.Path.t -> (Page.t, t) Yocaml.Task.t
+
+(** {1 Dealing as metadata} *)
+
+include Yocaml.Required.DATA_INJECTABLE with type t := t
diff --git a/lib/model/link.ml b/lib/model/link.ml
index db4ed1a..ce31313 100644
--- a/lib/model/link.ml
+++ b/lib/model/link.ml
@@ -4,14 +4,15 @@ type t = string * Lang.t * Url.t
 
 let validate =
   let open Yocaml.Data.Validation in
-  record (fun fields ->
-      let* url = required fields "url" Url.validate in
-      let+ lang = optional_or fields "lang" ~default:Lang.Eng Lang.validate
-      and+ title =
-        optional_or fields ~default:(Url.url url) "title"
-          (string & minimal_length 1)
-      in
-      (title, lang, url))
+  (Url.validate $ fun url -> (Url.url url, Lang.Eng, url))
+  / record (fun fields ->
+        let* url = required fields "url" Url.validate in
+        let+ lang = optional_or fields "lang" ~default:Lang.Eng Lang.validate
+        and+ title =
+          optional_or fields ~default:(Url.url url) "title"
+            (string & minimal_length 1)
+        in
+        (title, lang, url))
 
 let normalize_underlying_link (title, lang, url) =
   let open Yocaml.Data in
diff --git a/lib/resolver.ml b/lib/resolver.ml
index ef619c2..b898602 100644
--- a/lib/resolver.ml
+++ b/lib/resolver.ml
@@ -12,10 +12,12 @@ module Make (R : Sigs.RESOLVABLE) = struct
     let templates = Path.(static / "templates")
     let template file = Path.(templates / file)
     let members = Path.(data / "members")
+    let articles = Path.(data / "articles")
     let chain = Path.(data / "chain.yml")
     let common_deps = [ binary; chain ]
     let cname = Path.(static / "CNAME")
     let index = Path.(data / "index.md")
+    let blog = Path.(data / "blog.md")
     let static_images = Path.(static / "images")
     let avatars = Path.(data / "avatars")
   end
@@ -32,6 +34,7 @@ module Make (R : Sigs.RESOLVABLE) = struct
     let images = Path.(R.target / "images")
     let avatars = Path.(images / "avatars")
     let member ~id = Path.(members / id / "index.html")
+    let blog = Path.(R.target / "blog.html")
 
     let member_redirection ~id pred_or_succ =
       let target = Path.(members / id) in
diff --git a/lib/sigs.mli b/lib/sigs.mli
index 8440746..3b64142 100644
--- a/lib/sigs.mli
+++ b/lib/sigs.mli
@@ -41,8 +41,10 @@ module type RESOLVER = sig
     val fonts : Yocaml.Path.t
     val templates : Yocaml.Path.t
     val members : Yocaml.Path.t
+    val articles : Yocaml.Path.t
     val chain : Yocaml.Path.t
     val index : Yocaml.Path.t
+    val blog : Yocaml.Path.t
     val avatars : Yocaml.Path.t
 
     val template : Yocaml.Path.fragment -> Yocaml.Path.t
@@ -74,5 +76,6 @@ module type RESOLVER = sig
     val member_redirection : id:string -> [ `Pred | `Succ ] -> Yocaml.Path.t
     val member : id:string -> Yocaml.Path.t
     val avatars : Yocaml.Path.t
+    val blog : Yocaml.Path.t
   end
 end
diff --git a/static/css/style.css b/static/css/style.css
index 510634a..0834891 100644
--- a/static/css/style.css
+++ b/static/css/style.css
@@ -74,6 +74,27 @@ footer p {
     padding: 32px 12px;
 }
 
+header > .container {
+    display: flex;
+    flex-direction: row;
+}
+
+header > .container > h1 {
+    flex: 1;
+}
+
+.button,
+header > .container nav > a {
+    font-family: "Inter";
+    text-decoration: none;
+    background-color: var(--main-contrast-dark-color);
+    padding: 4px 12px;
+}
+
+header > .container nav > a {
+    font-size: 80%;
+}
+
 .members {
     display: grid;
     grid-template-columns: repeat(3, 1fr);
@@ -82,7 +103,7 @@ footer p {
 }
 
 .members > div {
-    border-left: 8px solid var(--main-contrast-light-color);
+    border-left: 6px solid var(--main-contrast-light-color);
     background-color: var(--main-contrast-dark-color);
     padding: 8px;
     font-family: "Inter";
@@ -122,7 +143,7 @@ footer p {
     font-size: 80%;
 }
 
-.no-members {
+.no-elts {
     color: var(--main-contrast-light-color);
     border-left: 8px solid var(--main-contrast-dark-color);
     padding: 32px;
@@ -165,7 +186,7 @@ footer p {
 .member .link-list > div {
     background-color: var(--main-contrast-dark-color);
     padding: 4px 12px;
-    border-left: 4px solid var(--main-contrast-light-color);
+    font-size: 80%;
 }
 
 .member nav > div > a,
@@ -190,13 +211,84 @@ footer p {
     text-align: right;
 }
 
+section.articles {
+    margin-top: 64px;
+    font-size: 90%;
+    padding-bottom: 32px;
+}
+
+section.articles article {
+    border-bottom: 4px solid var(--main-contrast-dark-color);
+    padding-bottom: 32px;
+    margin-bottom: 32px;
+}
+
+section.articles article:last-child {
+    border-bottom-color: transparent;
+}
+
+section.articles .lang > span {
+    margin-bottom: 12px;
+    background-color: var(--main-contrast-dark-color);
+    padding: 4px 12px;
+    display: inline-block;
+    color: var(--main-contrast-light-color);
+    font-family: "Inter";
+    text-transform: uppercase;
+}
+
+section.articles .date span {
+    color: var(--main-contrast-light-color);
+    font-weight: 700;
+    font-family: "Inter";
+}
+
+section.articles .date a {
+    margin-left: 4px;
+}
+
+section.articles h2 {
+    margin-bottom: 12px;
+}
+
+section.articles h2 > a {
+    text-decoration: none;
+    color: var(--main-light-color);
+    font-weight: 300;
+}
+
+section.articles p {
+    padding: 12px 0;
+    font-weight: 200;
+}
+
+section.articles ul.tags {
+    padding: 0;
+}
+
+section.articles ul.tags > li:first-child {
+    padding-left: 0;
+}
+section.articles ul.tags > li {
+    list-style: none;
+    display: inline-block;
+    padding: 4px;
+    font-weight: 300;
+    font-family: "Inter";
+}
+
+section.articles ul.tags > li::before {
+    content: "#";
+    color: var(--main-contrast-light-color);
+}
+
 @media all and (max-width: 1024px) {
     .members {
         grid-template-columns: repeat(2, 1fr);
     }
 }
 
-@media all and (orientation: portrait), @media all and (max-width: 800px) {
+@media all and (orientation: portrait), @media all and (max-width: 820px) {
     body {
         font-size: 1.5rem;
         line-height: 1.8;
@@ -209,6 +301,7 @@ footer p {
 
     header h1 {
         line-height: 4rem;
+        margin-bottom: 32px;
     }
 
     .member {
@@ -222,4 +315,8 @@ footer p {
     .member img {
         margin: 32px auto;
     }
+
+    header > .container {
+        flex-direction: column;
+    }
 }
diff --git a/static/templates/blog.html b/static/templates/blog.html
new file mode 100644
index 0000000..e68a88f
--- /dev/null
+++ b/static/templates/blog.html
@@ -0,0 +1,30 @@
+{%- autoescape false -%} {{ yocaml_body }} {%- endautoescape -%} {%- if
+has_articles -%}
+<section class="articles">
+  {%- for article in articles -%}
+  <article>
+    <div class="info">
+      <div class="lang"><span>{{ article.link.lang }}</span></div>
+      <h2><a href="{{ article.link.url.url }}">{{ article.title }}</a></h2>
+      <div class="date">
+        published on <span>{{ article.date.repr.date }}</span> by {% for author
+        in article.authors -%}
+        <a class="button" href="/u/{{ author  }}">{{ author }}</a>
+        {%- endfor -%}
+      </div>
+    </div>
+    {%- if article.has_synopsis -%}
+    <p>{{ article.synopsis }}</p>
+    {%- endif -%} {%- if article.has_tags -%}
+    <ul class="tags">
+      {%- for tag in article.tags -%}
+      <li>{{ tag }}</li>
+      {%- endfor -%}
+    </ul>
+    {%- endif -%}
+  </article>
+  {%- endfor -%}
+</section>
+{%- else -%}
+<section class="no-elts">There are no federated articles</section>
+{%- endif -%}
diff --git a/static/templates/index.html b/static/templates/index.html
index ab1974f..6af0d06 100644
--- a/static/templates/index.html
+++ b/static/templates/index.html
@@ -31,5 +31,5 @@ <h2><a href="/u/{{ m.id }}">{{ m.display_name }}</a></h2>
   {%- endfor -%}
 </section>
 {%- else -%}
-<section class="no-members">The ring is empty</section>
+<section class="no-elts">The ring is empty</section>
 {%- endif -%}
diff --git a/static/templates/layout.html b/static/templates/layout.html
index 8c33fd8..1f42f17 100644
--- a/static/templates/layout.html
+++ b/static/templates/layout.html
@@ -21,6 +21,9 @@ <h1 class="logo">
           <span class="sub-path">{{ sub_path }}</span>
           {%- endif -%}
         </h1>
+        <div>
+          <nav><a href="/blog.html">Federated blog</a></nav>
+        </div>
       </div>
     </header>
     <main>
diff --git a/test/gem/article_test.ml b/test/gem/article_test.ml
index 6732872..8c061e0 100644
--- a/test/gem/article_test.ml
+++ b/test/gem/article_test.ml
@@ -10,20 +10,21 @@ let%expect_test "Validate a minimal article" =
         ("title", string "An Article");
         ("date", string "2024-08-11");
         ("authors", string "xvw");
-        ("url", string "https://xvw.lol/a.html");
+        ("link", record [ ("url", string "https://xvw.lol/a.html") ]);
       ]
   in
   print_validated_value Article.pp (Article.validate article);
   [%expect
     {|
-    {"title": "An Article", "synopsis": null, "date":
+    {"title": "An Article", "has_synopsis": false, "synopsis": null, "date":
      {"year": 2024, "month": 8, "day": 11, "hour": 0, "min": 0, "sec": 0,
      "has_time": false, "day_of_week": 6, "repr":
       {"month": "aug", "datetime": "2024-08-11 00:00:00", "date": "2024-08-11",
       "time": "00:00:00", "day_of_week": "sun"}},
-    "tags": [], "authors": ["xvw"], "url":
-     {"url": "https://xvw.lol/a.html", "scheme": "https", "url_without_scheme":
-      "xvw.lol/a.html"}}
+    "tags": [], "has_tags": false, "authors": ["xvw"], "link":
+     {"title": "xvw.lol/a.html", "lang": "eng", "url":
+      {"url": "https://xvw.lol/a.html", "scheme": "https", "url_without_scheme":
+       "xvw.lol/a.html"}}}
     |}]
 
 let%expect_test "Validate a full article" =
@@ -35,21 +36,24 @@ let%expect_test "Validate a full article" =
         ("date", string "2024-08-11");
         ("authors", list_of string [ "xvw"; "grim" ]);
         ("synopsis", string "A synopsis");
-        ("url", string "https://xvw.lol/a.html");
+        ("link", record [ ("url", string "https://xvw.lol/a.html") ]);
         ("tags", list_of string [ "a"; "b"; "c-d" ]);
       ]
   in
   print_validated_value Article.pp (Article.validate article);
   [%expect
     {|
-    {"title": "An Article", "synopsis": "A synopsis", "date":
+    {"title": "An Article", "has_synopsis": true, "synopsis": "A synopsis",
+    "date":
      {"year": 2024, "month": 8, "day": 11, "hour": 0, "min": 0, "sec": 0,
      "has_time": false, "day_of_week": 6, "repr":
       {"month": "aug", "datetime": "2024-08-11 00:00:00", "date": "2024-08-11",
       "time": "00:00:00", "day_of_week": "sun"}},
-    "tags": ["a", "b", "c-d"], "authors": ["xvw", "grim"], "url":
-     {"url": "https://xvw.lol/a.html", "scheme": "https", "url_without_scheme":
-      "xvw.lol/a.html"}}
+    "tags": ["a", "b", "c-d"], "has_tags": true, "authors": ["xvw", "grim"],
+    "link":
+     {"title": "xvw.lol/a.html", "lang": "eng", "url":
+      {"url": "https://xvw.lol/a.html", "scheme": "https", "url_without_scheme":
+       "xvw.lol/a.html"}}}
     |}]
 
 let%expect_test "Validate an invalid article" =
@@ -67,6 +71,6 @@ let%expect_test "Validate an invalid article" =
   [%expect
     {|
     <error-invalid-record missing field: date
-    missing field: url> for {"title": "An Article", "authors": ["xvw", "grim"],
-                            "synopsis": "A synopsis", "tags": ["a", "b", "c-d"]}
+    missing field: link> for {"title": "An Article", "authors": ["xvw", "grim"],
+                             "synopsis": "A synopsis", "tags": ["a", "b", "c-d"]}
     |}]

From 579fbdd24ec87588af6913d5df833d0f908b8526 Mon Sep 17 00:00:00 2001
From: xvw <xavier.vdw@gmail.com>
Date: Mon, 12 Aug 2024 05:00:04 +0200
Subject: [PATCH 4/4] Add Atom Suppport for the federated blog

---
 data/blog.md                 |  2 +-
 lib/action/all.ml            |  1 +
 lib/action/atom.ml           |  6 ++++++
 lib/action/atom.mli          |  3 +++
 lib/model/article.ml         | 12 ++++++++++++
 lib/model/article.mli        |  1 +
 lib/model/articles.ml        | 13 +++++++++++++
 lib/model/articles.mli       |  1 +
 lib/model/chain.ml           | 13 +++++++++++++
 lib/model/chain.mli          |  2 ++
 lib/model/member.ml          |  5 +++++
 lib/model/member.mli         |  2 ++
 lib/resolver.ml              |  1 +
 lib/sigs.mli                 |  1 +
 static/css/style.css         |  5 +++++
 static/templates/layout.html |  4 ++++
 16 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100644 lib/action/atom.ml
 create mode 100644 lib/action/atom.mli

diff --git a/data/blog.md b/data/blog.md
index b095f79..2b1d5b5 100644
--- a/data/blog.md
+++ b/data/blog.md
@@ -6,4 +6,4 @@ description: A federated blog of Webring's member
 The **Federated Blog** allows [webring members](/) to showcase federated
 articles on this page from _time to time_. The list of articles is not
 calculated automatically (via RSS/Atom feeds) but is the result of **a manual
-addition**.
+addition**. You can retrieve the [ATOM feed from the federated blog](/atom.xml).
diff --git a/lib/action/all.ml b/lib/action/all.ml
index 193cad5..17824f9 100644
--- a/lib/action/all.ml
+++ b/lib/action/all.ml
@@ -14,6 +14,7 @@ let run (module R : Sigs.RESOLVER) () =
   >>= Css.run (module R)
   >>= Images.run (module R)
   >>= Articles.run (module R) chain
+  >>= Atom.run (module R) chain
   >>= Opml.run (module R) chain
   >>= Chain.run (module R) chain
   >>= Index.run (module R) chain
diff --git a/lib/action/atom.ml b/lib/action/atom.ml
new file mode 100644
index 0000000..ffbf3a2
--- /dev/null
+++ b/lib/action/atom.ml
@@ -0,0 +1,6 @@
+let run (module R : Sigs.RESOLVER) chain =
+  Yocaml.Action.write_static_file R.Target.atom
+    (let open Yocaml.Task in
+     R.track_common_dependencies
+     >>> Yocaml.Pipeline.track_file R.Source.articles
+     >>> Model.Articles.atom chain R.Source.articles)
diff --git a/lib/action/atom.mli b/lib/action/atom.mli
new file mode 100644
index 0000000..28b510b
--- /dev/null
+++ b/lib/action/atom.mli
@@ -0,0 +1,3 @@
+(** An action that builds the Atom file of the federated blog. *)
+
+val run : (module Sigs.RESOLVER) -> Model.Chain.t -> Yocaml.Action.t
diff --git a/lib/model/article.ml b/lib/model/article.ml
index e796bda..68f688c 100644
--- a/lib/model/article.ml
+++ b/lib/model/article.ml
@@ -52,3 +52,15 @@ let pp ppf article =
     (article |> normalize |> Yocaml.Data.record)
 
 let sort a b = Yocaml.Archetype.Datetime.compare a.date b.date
+
+let to_atom chain { title; synopsis; date; tags; authors; link } =
+  let open Yocaml_syndication in
+  let title = title in
+  let authors = List.map (Chain.as_author chain) authors in
+  let updated = Datetime.make date in
+  let categories = List.map Category.make tags in
+  let url = link |> Link.url |> Url.to_string in
+  let summary = synopsis |> Option.map Atom.text in
+  let links = [ Atom.alternate url ~title ] in
+  Atom.entry ~authors ~updated ~categories ?summary ~links
+    ~title:(Atom.text title) ~id:url ()
diff --git a/lib/model/article.mli b/lib/model/article.mli
index 2296bb5..2752718 100644
--- a/lib/model/article.mli
+++ b/lib/model/article.mli
@@ -8,6 +8,7 @@ val authors_in_chain : Chain.t -> t -> bool
 
 val pp : Format.formatter -> t -> unit
 val sort : t -> t -> int
+val to_atom : Chain.t -> t -> Yocaml_syndication.Atom.entry
 
 (** {1 Dealing as metadata} *)
 
diff --git a/lib/model/articles.ml b/lib/model/articles.ml
index 8c25e07..bb2fe70 100644
--- a/lib/model/articles.ml
+++ b/lib/model/articles.ml
@@ -38,3 +38,16 @@ let normalize { page; articles } =
       ("articles", list_of (fun x -> record (Article.normalize x)) articles);
       ("has_articles", has_list articles);
     ]
+
+let atom chain path =
+  let open Yocaml_syndication in
+  let open Yocaml.Task in
+  let id = "https://ring.muhokama.fun/atom.xml" in
+  let title = Atom.text "ring.muhokama.fun" in
+  let subtitle = Atom.text "federated blog of Muhokama webring" in
+  let links = [ Atom.self id; Atom.link "https://ring.muhokama.fun" ] in
+  let updated = Atom.updated_from_entries () in
+  let authors = Chain.to_authors chain in
+  fetch chain path
+  >>> Atom.from ~updated ~title ~subtitle ~id ~links ~authors
+        (Article.to_atom chain)
diff --git a/lib/model/articles.mli b/lib/model/articles.mli
index f0e5e7a..e882191 100644
--- a/lib/model/articles.mli
+++ b/lib/model/articles.mli
@@ -4,6 +4,7 @@ type t
 (** The type describing the federation. *)
 
 val index : ?limit:int -> Chain.t -> Yocaml.Path.t -> (Page.t, t) Yocaml.Task.t
+val atom : Chain.t -> Yocaml.Path.t -> (unit, string) Yocaml.Task.t
 
 (** {1 Dealing as metadata} *)
 
diff --git a/lib/model/chain.ml b/lib/model/chain.ml
index 9d1c12a..6300cf3 100644
--- a/lib/model/chain.ml
+++ b/lib/model/chain.ml
@@ -69,5 +69,18 @@ let normalize_elt { pred; curr; succ } =
     @ [ ("pred", string @@ Member.id pred); ("succ", string @@ Member.id succ) ]
     )
 
+let unknow_author = Yocaml_syndication.Person.make "Unknown author"
 let normalize = Yocaml.Data.list_of normalize_elt
 let is_empty = List.is_empty
+
+let to_authors chain =
+  match List.map (fun { curr; _ } -> Member.as_author curr) chain with
+  | [] -> (* Should never happen *) Yocaml.Nel.singleton unknow_author
+  | x :: xs -> Yocaml.Nel.(x :: xs)
+
+let as_author chain id =
+  chain
+  |> List.find_map (fun { curr; _ } ->
+         if String.equal (Member.id curr) id then Some curr else None)
+  |> Option.fold ~none:unknow_author (* Should never happen *)
+       ~some:Member.as_author
diff --git a/lib/model/chain.mli b/lib/model/chain.mli
index f42de83..72161ca 100644
--- a/lib/model/chain.mli
+++ b/lib/model/chain.mli
@@ -31,6 +31,8 @@ val to_list : t -> (Member.t * (Member.t * Member.t)) list
 val to_opml : (t, string) Yocaml.Task.t
 (** [to_opml] An arrow that lift a chain into an OPML file. *)
 
+val as_author : t -> string -> Yocaml_syndication.Person.t
+val to_authors : t -> Yocaml_syndication.Person.t Yocaml.Nel.t
 val is_empty : t -> bool
 val normalize : t -> Yocaml.Data.t
 
diff --git a/lib/model/member.ml b/lib/model/member.ml
index bfcc925..bba766c 100644
--- a/lib/model/member.ml
+++ b/lib/model/member.ml
@@ -146,3 +146,8 @@ let to_outline member =
            feed_to_outline title description feed)
   in
   main_feed @ additional_feeds
+
+let as_author m =
+  Yocaml_syndication.Person.make
+    ~uri:(m.main_link |> Link.url |> Url.url)
+    (display_name m)
diff --git a/lib/model/member.mli b/lib/model/member.mli
index 9db3d48..070a6af 100644
--- a/lib/model/member.mli
+++ b/lib/model/member.mli
@@ -31,6 +31,8 @@ val to_string : t -> string
 val equal : t -> t -> bool
 (** Equality between members. *)
 
+val as_author : t -> Yocaml_syndication.Person.t
+
 (** {1 Dealing as metadata} *)
 
 include Yocaml.Required.DATA_READABLE with type t := t
diff --git a/lib/resolver.ml b/lib/resolver.ml
index b898602..88c75bb 100644
--- a/lib/resolver.ml
+++ b/lib/resolver.ml
@@ -26,6 +26,7 @@ module Make (R : Sigs.RESOLVABLE) = struct
     let root = R.target
     let cache = Path.(R.target / "cache")
     let opml = Path.(R.target / "opml")
+    let atom = Path.(R.target / "atom.xml")
     let ring_opml = Path.(opml / "ring.opml")
     let members = Path.(R.target / "u")
     let css = Path.(R.target / "css")
diff --git a/lib/sigs.mli b/lib/sigs.mli
index 3b64142..1583ea5 100644
--- a/lib/sigs.mli
+++ b/lib/sigs.mli
@@ -69,6 +69,7 @@ module type RESOLVER = sig
     val css : Yocaml.Path.t
     val fonts : Yocaml.Path.t
     val opml : Yocaml.Path.t
+    val atom : Yocaml.Path.t
     val ring_opml : Yocaml.Path.t
     val index : Yocaml.Path.t
     val images : Yocaml.Path.t
diff --git a/static/css/style.css b/static/css/style.css
index 0834891..a0cd010 100644
--- a/static/css/style.css
+++ b/static/css/style.css
@@ -282,6 +282,11 @@ section.articles ul.tags > li::before {
     color: var(--main-contrast-light-color);
 }
 
+footer nav {
+    margin-top: 32px;
+    font-size: 80%;
+}
+
 @media all and (max-width: 1024px) {
     .members {
         grid-template-columns: repeat(2, 1fr);
diff --git a/static/templates/layout.html b/static/templates/layout.html
index 1f42f17..220a60a 100644
--- a/static/templates/layout.html
+++ b/static/templates/layout.html
@@ -39,6 +39,10 @@ <h1 class="logo">
           <a href="https://github.com/muhokama/ring">free software</a> proudly
           propulsed by <a href="https://gitlab.com/funkywork/yocaml">YOCaml</a>
         </p>
+        <nav>
+          <a class="button" href="/opml/ring.opml">OPML</a>
+          <a class="button" href="/atom.xml">ATOM</a>
+        </nav>
       </div>
     </footer>
   </body>