from goodnews.briefs import _select_diverse


def row(id, source, category):
    # _select_diverse only reads these three keys; plain dicts support [] access.
    return {"id": id, "source_name": source, "default_category": category}


def test_prefers_distinct_sources_best_first():
    rows = [
        row(1, "A", "science"),
        row(2, "A", "science"),   # same source as #1 — should be skipped while others remain
        row(3, "B", "science"),
        row(4, "C", "environment"),
    ]
    selected = _select_diverse(rows, limit=3)
    ids = [r["id"] for r in selected]
    assert ids == [1, 3, 4]  # one per source, ranked order preserved


def test_backfills_when_sources_exhausted():
    rows = [row(1, "A", "science"), row(2, "A", "science"), row(3, "A", "science")]
    selected = _select_diverse(rows, limit=2)
    assert len(selected) == 2  # repeats source A only because no others exist


def test_injects_second_category_without_shrinking():
    rows = [
        row(1, "A", "science"),
        row(2, "B", "science"),
        row(3, "C", "science"),
        row(4, "D", "environment"),  # the only other category, lowest ranked
    ]
    selected = _select_diverse(rows, limit=3)
    cats = {r["default_category"] for r in selected}
    assert len(selected) == 3
    assert len(cats) >= 2  # environment swapped in for diversity
    assert any(r["default_category"] == "environment" for r in selected)


def test_keeps_single_category_when_no_alternative_exists():
    rows = [row(1, "A", "science"), row(2, "B", "science"), row(3, "C", "science")]
    selected = _select_diverse(rows, limit=3)
    assert len(selected) == 3
    assert {r["default_category"] for r in selected} == {"science"}


def test_never_returns_more_than_limit():
    rows = [row(i, f"S{i}", "science") for i in range(10)]
    assert len(_select_diverse(rows, limit=5)) == 5