%% ---
%%  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(my_bank).

-behaviour(gen_server).
-export([start/0]).
%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
	 terminate/2, code_change/3]).
-compile(export_all).


start() -> gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
stop()  -> gen_server:call(?MODULE, stop).

new_account(Who)      -> gen_server:call(?MODULE, {new, Who}).
deposit(Who, Amount)  -> gen_server:call(?MODULE, {add, Who, Amount}).
withdraw(Who, Amount) -> gen_server:call(?MODULE, {remove, Who, Amount}).



init([]) -> {ok, ets:new(?MODULE,[])}.

handle_call({new,Who}, _From, Tab) ->
    Reply = case ets:lookup(Tab, Who) of
		[]  -> ets:insert(Tab, {Who,0}), 
		       {welcome, Who};
		[_] -> {Who, you_already_are_a_customer}
	    end,
    {reply, Reply, Tab};
handle_call({add,Who,X}, _From, Tab) ->
    Reply = case ets:lookup(Tab, Who) of
		[]  -> not_a_customer;
		[{Who,Balance}] ->
		    NewBalance = Balance + X,
		    ets:insert(Tab, {Who, NewBalance}),
		    {thanks, Who, your_balance_is,  NewBalance}	
	    end,
    {reply, Reply, Tab};
handle_call({remove,Who, X}, _From, Tab) ->
    Reply = case ets:lookup(Tab, Who) of
		[]  -> not_a_customer;
		[{Who,Balance}] when X =< Balance ->
		    NewBalance = Balance - X,
		    ets:insert(Tab, {Who, NewBalance}),
		    {thanks, Who, your_balance_is,  NewBalance};	
		[{Who,Balance}] ->
		    {sorry,Who,you_only_have,Balance,in_the_bank}
	    end,
    {reply, Reply, Tab};
handle_call(stop, _From, Tab) ->
    {stop, normal, stopped, Tab}.

handle_cast(_Msg, State) -> {noreply, State}.
handle_info(_Info, State) -> {noreply, State}.
terminate(_Reason, _State) -> ok.
code_change(_OldVsn, State, Extra) -> {ok, State}.