-module(palin).
-export([
         palin/1,
         nopunct/1,
         palindrome/1,
         client/0,
         server/0
]).

% palindrome problem
%
% palindrome("Madam I\'m Adam.") = true

palindrome(Xs) ->
    palin(nocaps(nopunct(Xs))).

nopunct([]) ->
    [];
nopunct([X|Xs]) ->
    case lists:member(X,".,\ ;:\t\n\'\"") of
	true ->
	    nopunct(Xs);
	false ->
	    [ X | nopunct(Xs) ]
    end.

nocaps([]) ->
    [];
nocaps([X|Xs]) ->
    [ nocap(X) | nocaps(Xs) ].

nocap(X) ->
    case $A =< X andalso X =< $Z of
	true ->
	    X+32;
	false ->
	    X
    end.

% literal palindrome

palin(Xs) ->
    Xs == reverse(Xs).

reverse(Xs) ->
    shunt(Xs,[]).

shunt([],Ys) ->
    Ys;
shunt([X|Xs],Ys) ->
    shunt(Xs,[X|Ys]).

%% -------
%% Client
%% -------

client() ->
    receive
        {send, Pid, Msg} ->
            Pid ! Msg;
        {result, Msg } ->
            io:format("client received: ~p~n", [Msg]),
            client();
        stop ->
            io:format("client stopped!")
    end.


%% -------
%% Server
%% -------
server() ->
    Workers = palin_workers(),
    receive
        {check, Client, Payload} ->
            lb(Workers, Client, Payload),
            server();
        stop -> io:format("stopped ~n")
    end.


lb(Workers, Client, Payload) when is_pid(Client) ->
    Worker = element(rand:uniform(2), Workers),
    Worker ! {Client, Payload}.

palin_workers() ->
    {
      spawn(fun worker1/0),
      spawn(fun worker2/0)
    }.


worker1() ->
    receive
        {Client, Payload} ->
            io:format("response from Sever 1!~n"),
            Client ! response(Payload)
    end.

worker2() ->
    receive
        {Client, Payload} ->
            io:format("response from Sever 2!~n"),
            Client ! response(Payload)
    end.

response(String) ->
    Is = palindrome(String),
    Be = if Is =:= true -> " is ";
            true -> " is not "
         end,
    {result, lists:flatten([$", String, $", Be, "palindrome"])}.


%% ------
%% Usage
%% ------
%% 1> Server = spawn(palin, server, []).
%% 2> Client = spawn(palin, client, []).
%% 3> Server ! {check, Client, "Air an aria"}.
%% 4> Server ! {check, self(), "Air an aria"}.
%% 5> flush().