import random
from task_scheduler import Task, makespan_exact, makespan_critical_path, _validate


def test_empty():
    assert makespan_exact([]) == 0
    assert makespan_critical_path([]) == 0


def test_single():
    assert makespan_exact([Task("a", 5)]) == 5


def test_chain():
    assert makespan_exact([Task("a", 3), Task("b", 4, {"a"})]) == 7


def test_parallel():
    assert makespan_exact([Task("a", 3), Task("b", 4)]) == 4


def test_diamond():
    tasks = [Task("a", 3), Task("b", 4), Task("c", 2, {"a", "b"})]
    assert makespan_exact(tasks) == 6
    assert makespan_exact(tasks) == makespan_critical_path(tasks)


def test_matches_critical_path_random():
    random.seed(7)
    for trial in range(500):
        n = random.randint(0, 8)
        tids = [f"t{i}" for i in range(n)]
        tasks = []
        for i, tid in enumerate(tids):
            dur = random.randint(1, 6)
            cand = tids[:i]
            preds = set(random.sample(cand, random.randint(0, len(cand))))
            tasks.append(Task(tid, dur, preds))
        a = makespan_exact(tasks)
        b = makespan_critical_path(tasks)
        assert a == b


def test_validation_duplicate():
    try:
        _validate([Task("a", 1), Task("a", 2)])
    except ValueError:
        return
    raise AssertionError("expected ValueError")


def test_validation_unknown_pred():
    try:
        _validate([Task("a", 1, {"z"})])
    except ValueError:
        return
    raise AssertionError("expected ValueError")


def test_validation_self():
    try:
        _validate([Task("a", 1, {"a"})])
    except ValueError:
        return
    raise AssertionError("expected ValueError")


def test_validation_cycle():
    try:
        _validate([Task("a", 1, {"b"}), Task("b", 1, {"a"})])
    except ValueError:
        return
    raise AssertionError("expected ValueError")


def test_zero_duration():
    tasks = [Task("a", 0), Task("b", 2, {"a"})]
    assert makespan_exact(tasks) == 2