-module(exercise_3_3).

 -compile(export_all).

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

 account(Balance) ->

     receive

 	{withdraw, From, Amount} when Balance < Amount ->

 	    From ! {error, underflow},

 	    account(Balance);

 	{withdraw, From, Amount} ->

 	    account(From ! Balance - Amount);

 	{deposit, From, Amount} ->

 	    account(From ! Balance + Amount);

 	{_, From, _Amount} ->

 	    From ! {error, unknown_request},

 	    account(Balance)

     end.

 make_account(Balance, Password) ->

     Pid = spawn(?MODULE, account, [Balance]),

     fun(Action, P) when Password =:= P ->

 	    fun(Amount) ->

 		    Pid ! {Action, self(), Amount},

 		    receive

 			{error, Why} ->

 			    throw(Why);

 			Result ->

 			    Result

 		    end

 	    end;

        (_Action, _P) ->

 	    fun(_Amount) ->

 		    throw(incorrect_password)

 	    end

     end.

 account_test_() ->

     A = make_account(100, secret_password),

     [?_assertMatch(60, (A(withdraw, secret_password))(40)),

      ?_assertMatch(80, (A(deposit, secret_password))(20)),

      ?_assertMatch(underflow, catch((A(withdraw, secret_password))(100))),

      ?_assertMatch(unknown_request, catch((A(robe, secret_password))(20))),

      ?_assertMatch(incorrect_password, catch((A(withdraw, wrong_password))(20)))].