?-
    G_People := 200,
    G_Speed := 2,
    G_Ill := 100,

    G_X := 600,
    G_Y := 400,
    G_F := 50,

    array(x, G_People, 100),
    array(y, G_People, 100),
    array(xs, G_People, 100),
    array(ys, G_People, 100),
    array(ill, G_People, 0),
    init_people,
    ill(0) := 1,

    window(title("Pandemia"), size(G_X+2*G_F+20, G_Y+2*G_F+50),
          class(win_func), paint_indirectly).

win_func(init):-
    G_Timer := set_timer(_, 0.1, time_func).

win_func(paint):-
    pen(2, rgb(0,0,0)),
    line(G_F, G_F,
        G_F, G_Y+G_F,
        G_X+G_F, G_Y+G_F,
        G_X+G_F, G_F,
        G_F, G_F),
    for(I, 0, G_People-1),
        color(I, Color),
        pen(4, Color),
        line(x(I), y(I), x(I), y(I)),
    fail.

time_func(end):-
    update_window(_),
    for(I, 0, G_People-1),
        x(I) := x(I) + xs(I),
        y(I) := y(I) + ys(I),
        correct(I),
        ill(I)>0,
            infect(I),
    fail.

infect(I):-
    for(J, 0, G_People-1),
        x(I)=:=x(J),
        y(I)=:=y(J),
        ill(J):=1,
    fail.

color(I, Color):-
    (ill(I)=:=0 ->
        Color := rgb(0,0,0)
    else (ill(I)=:= -1 ->
        Color := rgb(0,255,255)
    else
        Color := rgb(255,0,0)
    )).

correct(I):-
    (x(I)<G_F -> x(I):= x(I) - xs(I), xs(I) := -1*xs(I)), fail.
correct(I):-
    (y(I)<G_F -> y(I):= y(I) - ys(I), ys(I) := -1*ys(I)), fail.
correct(I):-
    (x(I)>G_F+G_X -> x(I):= x(I) - xs(I), xs(I) := -1*xs(I)), fail.
correct(I):-
    (y(I)>G_F+G_Y -> y(I):= y(I) - ys(I), ys(I) := -1*ys(I)).

init_people:-
    for(I, 0, G_People-1),
        x(I) := G_F+random(G_X),
        y(I) := G_F+random(G_Y),
    init_speed(I),
    fail.
init_people.

init_speed(I):-
    xs(I) := random(2*G_Speed)-G_Speed,
    ys(I) := random(2*G_Speed)-G_Speed.