from pathlib import Path
import sys

import pytest


SCRIPTS = Path(__file__).resolve().parents[1] / "scripts"
sys.path.insert(0, str(SCRIPTS))

from flow_network import FlowNetwork  # noqa: E402


def test_returns_all_upstream_reaches_without_including_target():
    network = FlowNetwork(
        [
            ("headwater-a", "confluence"),
            ("headwater-b", "confluence"),
            ("confluence", "emerson"),
        ]
    )

    assert network.upstream_reaches("emerson") == {
        "headwater-a",
        "headwater-b",
        "confluence",
    }


def test_rejects_cycle_in_directed_flow_network():
    with pytest.raises(ValueError, match="cycle"):
        FlowNetwork(
            [
                ("reach-a", "reach-b"),
                ("reach-b", "reach-a"),
            ]
        )