%Operator definitions
:- op(800, fx, if).
:- op(700, yfx, then).
:- op(200, yfx, and).

:- dynamic forecastDB/2.

% Rule 1
if today(rain) then tomorrow(rain) : 0.5.
if today(dry) then tomorrow(dry) : 0.5.
if today(rain) and rainfall(low) then tomorrow(dry) : 0.6.
if today(rain) and rainfall(low) and temperature(cold) then tomorrow(dry) : 0.7.
if today(dry) and temperature(warm) then tomorrow(rain) : 0.65.
if today(dry) and temperature(warm) and sky(overcast) then tomorrow(rain) : 0.55.

%fact(today(rain), 1.0).
%fact(rainfall(low), 0.8).
%fact(temperature(cold), 0.9).
%fact(sky(overcast), 0.8).

is_true(Prämise, CF) :- fact(Prämise, CF).

min(Number1, Number2, Smaler) :-
	Number1 < Number2,
	Smaler is Number1.
min(Number1, Number2, Smaler) :-
	Number1 > Number2,
	Smaler is Number2.
min(Number1, Number2, Smaler) :-
	Number1 = Number2,
	Smaler is Number1.

composed_fact(Prämise, CF) :-
	is_true(Prämise, CF).

composed_fact(Prämise1 and Prämise2, CF) :-
	composed_fact(Prämise1, CFe1),
	composed_fact(Prämise2, CFe2),
	%is_true(Prämise1, CFe1),
	%is_true(Prämise2, CFe2).
	min(CFe1, CFe2, CF).

calculateTotalCF(CF1, CF2, CFt) :-
	CFt is CF1 + CF2*(1 - CF1).

new_forecast :-
	if X then Forecast : CFr,
	composed_fact(X, CFe),
	CF is CFe * CFr,
	lookup_forecast(Forecast, CF, N),
	assert(forecastDB(Forecast, N)).

lookup_forecast(Forecast, N, NewN) :-
	forecastDB(Forecast, OtherN),
	calculateTotalCF(N, OtherN, NewN),
	retract(forecastDB(Forecast, OtherN)).

lookup_forecast(Forecast, N, NewN) :-
	not(forecastDB(Forecast, _)),
	NewN is N.



% Main clause to process all rules and all cf-values
process:-
	writeln('... processing rules ...'),
	retractall(forecastDB(_, _)),
	%new_forecast(X,Y),
	new_forecast,
	fail;true,
	print_DB.


print_DB :-
	forecastDB(X, Y),
    	write(X),write('\t: '),
    	format('~4f',Y),
    	writeln(''),fail;true.