Separate erlang config file for reloadable parameters

1 files changed, 57 insertions, 0 deletions

diff --git a/src/plopconfig.erl b/src/plopconfig.erl
new file mode 100644
index 0000000..00b29df
--- /dev/null
+++ b/src/plopconfig.erl
@@ -0,0 +1,57 @@
+%%% Copyright (c) 2017, NORDUnet A/S.
+%%% See LICENSE for licensing information.
+
+-module(plopconfig).
+-export([get_env/1, get_env/2, init_table/0, load_config/0]).
+
+-define(PLOPCONFIG_TABLE, plopconfig).
+
+init_table() ->
+    case ets:info(?PLOPCONFIG_TABLE) of
+	undefined ->
+	    ok;
+	_ ->
+	    ets:delete(?PLOPCONFIG_TABLE)
+    end,
+    ets:new(?PLOPCONFIG_TABLE, [set, public, named_table]),
+    load_config().
+
+keys() ->
+    KeyList = lists:map(fun ({Key, _Value}) -> Key end,
+                        ets:tab2list(?PLOPCONFIG_TABLE)),
+    sets:from_list(KeyList).
+
+load_config() ->
+    {ok, Filename} = application:get_env(plop, plopconfig),
+    {ok, File} = file:consult(Filename),
+    OldKeys = keys(),
+    lists:foreach(
+      fun ({Key, Value}) ->
+              true = ets:insert(?PLOPCONFIG_TABLE, {Key, Value})
+      end, hd(File)),
+    NewKeys = keys(),
+    RemovedKeys = sets:subtract(OldKeys, NewKeys),
+    lists:foreach(fun (Key) ->
+                          ets:delete(?PLOPCONFIG_TABLE, Key)
+                  end, sets:to_list(RemovedKeys)),
+    lager:info("loaded config: new keys ~p old keys ~p removed keys ~p",
+               [sets:to_list(NewKeys),
+                sets:to_list(OldKeys),
+                sets:to_list(RemovedKeys)]),
+    ok.
+
+get_env(Key, DefaultValue) ->
+    case get_env(Key) of
+        {ok, Value} ->
+            Value;
+        _ ->
+            DefaultValue
+    end.
+
+get_env(Key) ->
+    case ets:lookup(?PLOPCONFIG_TABLE, Key) of
+        [{_, Value}] ->
+            {ok, Value};
+        [] ->
+            undefined
+    end.