-module(bank_server).
-export([start/0, server/1]).
-import(io, [fwrite/1, fwrite/2]).

start() ->
  register(bank_server, spawn(bank_server, server, [[]])).

server(Data) ->
  receive
    {From, {deposit, Who, Amount}} ->
      From ! {bank_server, ok},
      fwrite("Client: ~w, Amount: ~w.~n", [Who, Amount]),
      server(deposit(Who, Amount, Data));
    {From, {ask, Who}} ->
      From ! {bank_server, lookup(Who, Data)},
      fwrite("Client: ~w asks for information.~n", [Who]),
      server(Data);
    {From, {withdraw, Who, Amount}} ->
      case lookup(Who, Data) of
        undefined ->
          From ! {bank_server, no},
          server(Data);
        Balance when Balance > Amount ->
          From ! {bank_server, ok},
          server(deposit(Who, -Amount, Data));
        _ ->
          From ! {bank_server, no},
          server(Data)
      end
  end.

lookup(Who, [{Who, Value}|_]) -> Value;
lookup(Who, [_|T]) -> lookup(Who, T);
lookup(_, _) -> undefined.

deposit(Who, X, [{Who, Balance}|T]) -> 
  [{Who, Balance+X}|T];
deposit(Who, X, [H|T]) ->
  [H|deposit(Who, X, T)];
deposit(Who, X, []) ->
  [{Who, X}].