%% ---
%%  Excerpted from "Programming Erlang",
%%  published by The Pragmatic Bookshelf.
%%  Copyrights apply to this code. It may not be used to create training material,
%%  courses, books, articles, and the like. Contact us if you are in doubt.
%%  We make no guarantees that this code is fit for any purpose.
%%  Visit http://www.pragmaticprogrammer.com/titles/jaerlang for more book information.
%%---
-module(server).
-export([start/2, rpc/2, swap_code/2]).

start(Name, Mod) ->
    register(Name, spawn(fun() -> loop(Name,Mod,Mod:init()) end)).

swap_code(Name, Mod) -> rpc(Name, {swap_code, Mod}).

rpc(Name, Request) ->
    Name ! {self(), Request},
    receive
        {Name, crash} -> exit(rpc);
        {Name, ok, Response} -> Response
    end.

loop(Name, Mod, OldState) ->
    receive
        {From, {swap_code, NewCallbackMod}} ->
            From ! {Name, ok, ack},
            loop(Name, NewCallbackMod, OldState);
        {From, Request} ->
            try Mod:handle(From, Request, OldState) of
                {Response, NewState} ->
                    From ! {Name, ok, Response},
                    loop(Name, Mod, NewState)
            catch
                _: Why ->
                    log_the_error(Name, Request, Why),
                    From ! {Name, crash},
                    loop(Name, Mod, OldState)
            end
    end.

log_the_error(Name, Request, Why) ->
    io:format("Server ~p request ~p ~n"
              "caused exception ~p~n",
              [Name, Request, Why]).