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+%% -*- erlang-indent-level: 4; indent-tabs-mode: nil; fill-column: 80 -*-
+%%% Copyright 2012 Erlware, LLC. All Rights Reserved.
+%%%
+%%% This file is provided to you under the Apache License,
+%%% Version 2.0 (the "License"); you may not use this file
+%%% except in compliance with the License. You may obtain
+%%% a copy of the License at
+%%%
+%%% http://www.apache.org/licenses/LICENSE-2.0
+%%%
+%%% Unless required by applicable law or agreed to in writing,
+%%% software distributed under the License is distributed on an
+%%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+%%% KIND, either express or implied. See the License for the
+%%% specific language governing permissions and limitations
+%%% under the License.
+%%%-------------------------------------------------------------------
+%%% @author Eric Merritt <[email protected]>
+%%% @copyright 2011 Erlware, LLC.
+%%% @doc
+%%% A module that supports providing state manipulation services to the system.
+%%% @end
+%%%-------------------------------------------------------------------
+-module(rlx_provider).
+
+%% API
+-export([new/2,
+ do/2,
+ impl/1,
+ format_error/1,
+ format_error/2,
+ format/1]).
+
+-export_type([t/0]).
+
+-include_lib("relx/include/relx.hrl").
+
+%%%===================================================================
+%%% Types
+%%%===================================================================
+
+-opaque t() :: {?MODULE, module()}.
+
+
+-ifdef(have_callback_support).
+
+-callback init(rlx_state:t()) -> {ok, rlx_state:t()} | relx:error().
+-callback do(rlx_state:t()) -> {ok, rlx_state:t()} | relx:error().
+-callback format_error(Reason::term()) -> iolist().
+
+-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) ->
+ [{init, 1},
+ {do, 1},
+ {format_error, 1}];
+behaviour_info(_) ->
+ undefined.
+
+-endif.
+
+%%%===================================================================
+%%% API
+%%%===================================================================
+
+%% @doc create a new provider object from the specified module. The
+%% module should implement the provider behaviour.
+%%
+%% @param ModuleName The module name.
+%% @param State0 The current state of the system
+-spec new(module(), rlx_state:t()) ->
+ {t(), {ok, rlx_state:t()}} | relx:error().
+new(ModuleName, State0) when is_atom(ModuleName) ->
+ State1 = ModuleName:init(State0),
+ case code:which(ModuleName) of
+ non_existing ->
+ ?RLX_ERROR({non_existing, ModuleName});
+ _ ->
+ {{?MODULE, ModuleName}, State1}
+ end.
+
+%% @doc Manipulate the state of the system, that new state
+%%
+%% @param Provider the provider object
+%% @param State the current state of the system
+-spec do(Provider::t(), rlx_state:t()) ->
+ {ok, rlx_state:t()} | relx:error().
+do({?MODULE, Mod}, State) ->
+ Mod:do(State).
+
+%%% @doc get the name of the module that implements the provider
+%%% @param Provider the provider object
+-spec impl(Provider::t()) -> module().
+impl({?MODULE, Mod}) ->
+ Mod.
+
+%% @doc format an error produced from a provider.
+-spec format_error(Reason::term()) -> iolist().
+format_error({non_existing, ModuleName}) ->
+ io_lib:format("~p does not exist in the system", [ModuleName]).
+
+%% @doc format an error produced from a provider.
+-spec format_error(t(), Reason::term()) -> iolist().
+format_error({?MODULE, Mod}, Error) ->
+ Mod:format_error(Error).
+
+%% @doc print the provider module name
+%%
+%% @param T - The provider
+%% @return An iolist describing the provider
+-spec format(t()) -> iolist().
+format({?MODULE, Mod}) ->
+ erlang:atom_to_list(Mod).