-module (module_name).
-behaviour(gen_server).

-include_lib("amqp_client/include/amqp_client.hrl").

-export([start_link/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

%% Internal state
-record(state, {
    connection              :: pid(),           % rabbitMQ connection
    connection_ref          :: reference(),     % connection monitor ref
    channel                 :: pid(),           % rabbitMQ channel
    channel_ref             :: reference(),     % channel monitor ref
    % ---
    rabbitmq_restart_timeout = 5000 :: pos_integer(), % restart timeout
}).

%%==========
start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

init(_Args) ->
    gen_server:cast(self(), connect),
    {ok, #state{rabbitmq_restart_timeout = 5000}}.

%%
%% @doc Handling all messages from RabbitMQ
%% @end
handle_info({#'basic.deliver'{delivery_tag = Tag, routing_key = _Queue}, #amqp_msg{props = #'P_basic'{reply_to = ReplyTo}, payload = Body}} = _Msg, #state{channel = Channel} = State) ->
    amqp_channel:cast(Channel, #'basic.ack'{delivery_tag = Tag}),
    try
        Message = binary_to_term(Body)
        %
        % Message is your payload
        %
    catch
        _:_ ->
            error_logger:error_report("Cannot parse message")
    end,
    {noreply, State};

handle_info({'DOWN', ConnectionRef, process, Connection, Reason}, #state{connection = Connection, connection_ref = ConnectionRef} = State) ->
    error_logger:error_report("AMQP connection error"),
    restart_me(State);

handle_info({'DOWN', ChannelRef, process, Channel, Reason}, #state{channel = Channel, channel_ref = ChannelRef} = State) ->
    error_logger:error_report("AMQP channel error"),
    restart_me(State);

handle_info(_Info, State) ->
    error_logger:error_report("Unsupported info message"),
    {noreply, State}.

handle_cast(connect, State) ->
    % connection parameters
    AMQP_Param = #amqp_params_network{
                    host =          "localhost",
                    username =      <<"username">>,
                    password =      <<"password">>,
                    port =          5672,
                    virtual_host =  <<"vhost">>,
                    heartbeat =     5 %% --- important to keep your connection alive
                },
    % connection...
    case amqp_connection:start(AMQP_Param) of
        {ok, Connection} ->
            % start connection monitor
            ConnectionRef = erlang:monitor(process, Connection),
            case amqp_connection:open_channel(Connection) of
                {ok, Channel} ->
                    % add monitor to catch message when connection is 'DOWN'
                    ChannelRef = erlang:monitor(process, Channel),
                    %
                    %
                    % Here you have to subscribe to queues you want to listen
                    %
                    %
                    {noreply, State#state{
                        connection = Connection,
                        connection_ref = ConnectionRef,
                        channel = Channel,
                        channel_ref = ChannelRef
                    }};
                _Reason2 ->
                    error_logger:error_report("AMQP channel error"),
                    restart_me(State)
            end;
        _Reason1 ->
            error_logger:error_report("AMQP connection error"),
            restart_me(State)
    end;

handle_cast(_Msg, State) ->
    error_logger:error_report("Unsupported cast message"),
    {noreply, State}.

handle_call(_Request, _From, State) ->
    error_logger:error_report("Unsupported call message"),
    {reply, ok, State}.

terminate(_Reason, #state{connection = Connection, channel = Channel} = _State) ->
    if
        is_pid(Channel) -> amqp_channel:close(Channel);
        true -> pass
    end,
    if
        is_pid(Connection) -> amqp_connection:close(Connection);
        true -> pass
    end,
    ok.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

%%
%% This function is called when client lost connection to RabbitMQ
restart_me(#state{rabbitmq_restart_timeout = Wait} = State) ->
    timer:sleep(Wait), % Sleep for rabbitmq_restart_timeout seconds
    {stop, error, State}.