add configuration file, add the ability to disable registrations

src/app.ml

@@ -12,3 +12,36 @@ let data_dir =
   match Project_dirs.data_dir with
   | None -> failwith "can't compute data directory"
   | Some data_dir -> data_dir
+
+let config_dir =
+  match Project_dirs.config_dir with
+  | None -> failwith "can't compute configuration directory"
+  | Some config_dir -> config_dir
+
+let config =
+  let filename = Filename.concat config_dir "config.scfg" in
+  if not @@ Sys.file_exists filename then
+    failwith
+    @@ Format.sprintf "configuration file `%s` does not exist, please create it"
+         filename;
+  Dream.log "config file: %s" filename;
+  match Scfg.Parse.from_file filename with
+  | Error e -> failwith e
+  | Ok config -> config
+
+let open_registration =
+  match Scfg.Query.get_dir "open_registration" config with
+  | None -> true
+  | Some open_registration -> (
+    match Scfg.Query.get_param 0 open_registration with
+    | Error e -> failwith e
+    | Ok "true" -> true
+    | Ok "false" -> false
+    | Ok unknown ->
+      failwith
+      @@ Format.sprintf
+           "invalid value for `open_registration` in configuration file, \
+            expected `true` or `false` but got `%s`"
+           unknown )
+
+let () = Dream.log "open_registration: %s" (Bool.to_string open_registration)