:- module serialize_btree.

:- interface.
:- import_module io.

:- pred main(io::di, io::uo) is cc_multi.

:- implementation.
:- import_module int, string, list.

:- type btree(T) --->
	nil;
	node(btree(T), T, btree(T))
.

:- pragma promise_pure(splitjoin/3). % what even impure? :/
:- pred splitjoin(string, string, list(string)).
:- mode splitjoin(in, in, out) is det.
:- mode splitjoin(in, out, in) is det.

splitjoin(Separator::in, String::in, List::out) :-
	List = split_at_string(Separator, String).
splitjoin(Separator::in, String::out, List::in) :-
	String = join_list(Separator, List).

:- pred serialize(int, btree(string), string).
:- mode serialize(in, in, out) is det.
:- mode serialize(in, out, in) is nondet. % why can't semidet??
serialize(Level, Node, String) :-
(
	Node = nil, String = "nil"
	;
	Node = node(Left, Value, Right),
	serialize(Level + 1, Left, LeftString),
	serialize(Level + 1, Right, RightString),
	Separator = "|" ++ int_to_string(Level) ++ "|",
	splitjoin(Separator, String, [LeftString, Value, RightString])
).

% i pretty much broke all the mercury rules, haven't i?

main(!IO) :-

	Example = node(
		node(
			node(nil, "left.left", nil),
			"left",
			nil
		),
		"root",
		node(
			nil,
			"right",
			nil
		)
	),

	serialize(0, Example, Serialized),
	print(Serialized, !IO), nl(!IO), nl(!IO),

	(serialize(0,GotBack,Serialized)
		-> (Example = GotBack
			-> print("got the tree back!\n", !IO)
			; print("didn't get the tree back O:", !IO)
		)
		; print("couldn't even parse D:", !IO)
	),

true.