Add a render hook (related to #36)

src/hooks.ml

@@ -2,7 +2,7 @@ module I = Plugin_api.I
 
 let lua_of_toml = Plugin_api.lua_of_toml
 
-let hook_types = ["pre-parse"; "pre-process"; "post-index"; "save"]
+let hook_types = ["pre-parse"; "pre-process"; "post-index"; "render"; "save"]
 
 let hook_should_run settings hook_config hook_type page_file =
   let disabled = Config.find_bool_or ~default:false hook_config ["disabled"] in
@@ -16,6 +16,29 @@ let hook_should_run settings hook_config hook_type page_file =
       hook_type page_file
     in false
 
+let run_render_hook settings soupault_config hook_config file_name lua_code env soup =
+  let open Defaults in
+  let lua_str = I.Value.string in
+  let state = I.mk () in
+   let () =
+    (* Set up the hook environment *)
+    I.register_globals ["page", Plugin_api.lua_of_soup (Plugin_api.Html.SoupNode soup)] state;
+    I.register_globals ["site_index", Plugin_api.lua_of_json (Autoindex.json_of_entries env.site_index)] state;
+    I.register_globals ["target_file", lua_str.embed env.target_file] state;
+    I.register_globals ["target_dir", lua_str.embed env.target_dir] state;
+    I.register_globals ["config", lua_of_toml hook_config] state;
+    I.register_globals ["hook_config", lua_of_toml hook_config] state;
+    I.register_globals ["soupault_config", lua_of_toml soupault_config] state;
+    I.register_globals ["force", I.Value.bool.embed settings.force] state;
+    I.register_globals ["build_dir", lua_str.embed settings.build_dir] state;
+    I.register_globals ["site_dir", lua_str.embed settings.site_dir] state;
+  in
+  let (let*) = Result.bind in
+  let* () = Plugin_api.run_lua file_name state lua_code in
+  let res = I.getglobal state (I.Value.string.embed "page_source") in
+  if I.Value.string.is res then Ok (I.Value.string.project res)
+  else Error "render hook has not assigned a string to the page_source variable"
+
 let run_save_hook settings soupault_config hook_config file_name lua_code env page_source =
   let open Defaults in
   let lua_str = I.Value.string in

src/soupault.ml

@@ -130,7 +130,20 @@ let load_html settings soupault_config hooks page_file =
   (* As of lambdasoup 0.7.2, Soup.parse never fails, only returns empty element trees. *)
   Ok (Soup.parse page_source)
 
-let render_html settings soup =
+let run_render_hook settings config hooks env soup =
+  let hook = Hashtbl.find_opt hooks "render" in
+  match hook with
+  | Some (file_name, source_code, hook_config) ->
+    if not (Hooks.hook_should_run settings hook_config "render" env.page_file)
+    then Ok None
+    else
+      let () = Logs.info @@ fun m -> m "Running the \"render\" hook on page %s" env.page_file in
+      let* page_source = Hooks.run_render_hook
+        settings config hook_config file_name source_code env soup
+      in Ok (Some page_source)
+  | None -> Ok None
+
+let render_html_builtin settings soup =
   let print_html = if settings.pretty_print_html then Soup.pretty_print else Soup.to_string in
   if settings.keep_doctype then
     begin
@@ -175,6 +188,13 @@ let render_html settings soup =
         print_html soup
     end
 
+let render_html settings config hooks env soup =
+  let res = run_render_hook settings config hooks env soup in
+  match res with
+  | Ok (Some page_source) -> Ok page_source
+  | Ok None -> Ok (render_html_builtin settings soup)
+  | Error _ as e -> e
+
 let include_content action selector html content =
   let element = Soup.select_one selector html in
   match element with
@@ -383,7 +403,7 @@ let process_page page_file nav_path index widgets hooks config settings =
   if settings.index_only then Ok index_entry else
   let* () = process_widgets env settings after_index widget_hash config html in
   let* () = mkdir target_dir in
-  let html_str = render_html settings html in
+  let* html_str = render_html settings config hooks env html in
   let* () = save_html settings config hooks env html_str in
   Ok index_entry