Suppport a vsn signature with a git implementation

src/ec_vsn.erl

@@ -0,0 +1,66 @@
+%%% vi:ts=4 sw=4 et
+%%%-------------------------------------------------------------------
+%%% @author Eric Merritt <ericbmerritt@gmail.com>
+%%% @copyright 2014 Erlware, LLC.
+%%% @doc
+%%%  Provides a signature to manage returning semver formatted versions
+%%%  from various version control repositories.
+%%%
+%%%  This interface is a member of the Erlware Commons Library.
+%%% @end
+%%%-------------------------------------------------------------------
+-module(ec_vsn).
+
+%% API
+-export([new/1,
+         vsn/1]).
+
+-export_type([t/0]).
+
+%%%===================================================================
+%%% Types
+%%%===================================================================
+
+-record(t, {callback, data}).
+
+%% This should be opaque, but that kills dialyzer so for now we export it
+%% however you should not rely on the internal representation here
+-type t() :: #t{}.
+
+-ifdef(have_callback_support).
+
+-callback new() -> any().
+-callback vsn(any()) -> {ok, string()} | {error, Reason::any()}.
+
+-else.
+
+%% In the case where R14 or lower is being used to compile the system
+%% we need to export a behaviour info
+-export([behaviour_info/1]).
+-spec behaviour_info(atom()) -> [{atom(), arity()}] | undefined.
+behaviour_info(callbacks) ->
+    [{new, 0},
+     {vsn, 1}];
+behaviour_info(_Other) ->
+    undefined.
+-endif.
+
+%%%===================================================================
+%%% API
+%%%===================================================================
+
+%% @doc create a new dictionary object from the specified module. The
+%% module should implement the dictionary behaviour.
+%%
+%% @param ModuleName The module name.
+-spec new(module()) -> t().
+new(ModuleName) when erlang:is_atom(ModuleName) ->
+    #t{callback = ModuleName, data = ModuleName:new()}.
+
+%% @doc Return the semver or an error depending on what is possible
+%% with this implementation in this directory.
+%%
+%% @param The dictionary object
+-spec vsn(t()) ->  {ok, string()} | {error, Reason::any()}.
+vsn(#t{callback = Mod, data = Data}) ->
+    Mod:vsn(Data).