"""Một ca cố định cho mỗi lớp, xung đột xét trên tuần xuất hiện thực tế."""
from itertools import product
import clingo

PROGRAM = r"""
#const k=2.
week(1..4). course(a;b;c). slot(1..k).
standard(a,W) :- week(W).
standard(b,W) :- week(W), W\2 = 1.
standard(c,W) :- week(W), W\2 = 0.
occurs(L,W) :- standard(L,W), not cancelled(L,W).
occurs(L,W) :- extra(L,W), course(L), week(W).
1 { at(L,S) : slot(S) } 1 :- course(L).
:- at(L,S), at(M,S), L < M, occurs(L,W), occurs(M,W).
#show at/2.
"""

def schedules(extra="", slots=2):
    ctl = clingo.Control(["0", "--warn=none", "-c", f"k={slots}"])
    ctl.add("base", [], PROGRAM + extra)
    ctl.ground([("base", [])])
    result = set()
    def collect(model):
        mapping = {str(a.arguments[0]): a.arguments[1].number
                   for a in model.symbols(shown=True)}
        result.add(tuple(mapping[l] for l in ("a", "b", "c")))
    state = ctl.solve(on_model=collect)
    assert state.exhausted and not state.interrupted
    return result

def oracle(weeks, slots):
    return {x for x in product(range(1, slots+1), repeat=3)
            if all(x[i] != x[j] or not (weeks[i] & weeks[j])
                   for i in range(3) for j in range(i+1, 3))}

normal = ({1, 2, 3, 4}, {1, 3}, {2, 4})
changed = ({1, 2, 3, 4}, {1, 2}, {2, 4})
exception = "cancelled(b,3). extra(b,2)."
assert schedules() == oracle(normal, 2) == {(1, 2, 2), (2, 1, 1)}
assert schedules(exception) == oracle(changed, 2) == set()
assert schedules(exception, 3) == oracle(changed, 3)
assert len(schedules(exception, 3)) == 6
print("Lịch thường: 2 phương án.")
print("Chuyển buổi B từ tuần 3 sang tuần 2: vô nghiệm với 2 ca.")
print("Cho 3 ca: 6 phương án.")