Add startup hook

src/hooks.ml

@@ -22,6 +22,7 @@ let lua_of_json = Plugin_api.lua_of_json
 (* Auxilliary functions *)
 
 let hook_types = [
+  "startup";
   "pre-parse";
   "pre-process";
   "post-index";
@@ -337,6 +338,43 @@ let run_post_save_hook soupault_state hook_config file_name lua_code env =
   let () = soupault_state.global_data := (Plugin_api.extract_global_data lua_state) in
   Ok ()
 
+(** These two hooks are executed only once rather than for every page:
+    before the first page is processed and after the last page is processed. *)
+
+(* pre-parse hook runs just after the page source is loaded from a file or received from a preprocessor
+   and before it's parsed into an HTML element tree.
+
+   It only has access to the page source, not an element tree.
+   It is free to modify the [page_source] variable that contains the page source.
+ *)
+
+let run_startup_hook soupault_state hooks =
+  let open Defaults in
+  let hook = Hashtbl.find_opt hooks "startup" in
+  match hook with
+  | None -> Ok ()
+  | Some (file_name, source_code, hook_config) ->
+    let lua_str = I.Value.string in
+    let lua_state = I.mk () in
+    let settings = soupault_state.soupault_settings in
+    let () =
+      (* Set up the hook environment *)
+      I.register_globals [
+        "config", lua_of_toml hook_config;
+        "hook_config", lua_of_toml hook_config;
+        "soupault_config", lua_of_toml soupault_state.soupault_config;
+        "force", I.Value.bool.embed settings.force;
+        "site_dir", lua_str.embed settings.site_dir;
+        "soupault_pass", I.Value.int.embed soupault_state.soupault_pass;
+        "global_data", lua_of_json !(soupault_state.global_data);
+      ] lua_state
+    in
+    let (let*) = Result.bind in
+    let () = Logs.info @@ fun m -> m "Running the startup hook" in
+    let* () = Plugin_api.run_lua lua_state file_name source_code in
+    let () = soupault_state.global_data := (Plugin_api.extract_global_data lua_state) in
+    Ok()
+
 let run_post_build_hook soupault_state site_index hooks =
   let open Defaults in
   let hook = Hashtbl.find_opt hooks "post-build" in

src/soupault.ml

@@ -967,6 +967,7 @@ let main cli_options =
       then Logs.info @@ fun m -> m "Running with build profiles: %s" (String.concat ", " settings.build_profiles)
     in
     let* () = make_build_dir settings.build_dir in
+    let* () = Hooks.run_startup_hook state hooks in
     let (page_files, index_files, asset_files) = Site_dir.get_site_files settings in
     (* If settings.process_pages_first is set, extract those pages and move them to the head of the list.
        For an empty list it would return the original list, but it would require traversing that list twice,