"""The destinations serialiser's contract: it carries suppression through, and
never emits a total that closes a gap left by a suppressed category.

The destination categories sum to the cohort, so an aggregate that happens to
equal the residual names the withheld figure exactly. See
docs/superpowers/specs/2026-08-28-destination-measures-design.md.
"""

from backend.data_loader import _destinations_block, _format_cohort_year


def _row(group, measure, pupils, status, cohort=180, percentage=None, year=202223):
    return {
        "pupil_group": group,
        "destination_measure": measure,
        "pupils": pupils,
        "percentage": percentage,
        "status": status,
        "cohort_pupils": cohort,
        "year": year,
    }


def test_suppressed_category_serialises_as_suppressed_with_null_pupils():
    rows = [
        _row("all", "school_sixth_form", 75, "published", percentage=41.7),
        _row("all", "sixth_form_college", None, "suppressed"),
    ]
    block = _destinations_block(rows)
    cats = {c["category"]: c for c in block["groups"]["all"]["categories"]}
    assert cats["sixth_form_college"]["status"] == "suppressed"
    assert cats["sixth_form_college"]["pupils"] is None
    assert cats["sixth_form_college"]["percentage"] is None


def test_published_category_keeps_its_figures():
    block = _destinations_block([
        _row("all", "school_sixth_form", 75, "published", percentage=41.7),
    ])
    cat = block["groups"]["all"]["categories"][0]
    assert cat["pupils"] == 75
    assert cat["percentage"] == 41.7
    assert cat["status"] == "published"


def test_no_closing_total_is_emitted_for_a_partially_suppressed_group():
    rows = [
        _row("all", "school_sixth_form", 75, "published", percentage=41.7),
        _row("all", "sixth_form_college", None, "suppressed"),
        _row("all", "further_education", 61, "published", percentage=33.9),
        _row("all", "apprenticeship", 8, "published", percentage=4.4),
        _row("all", "employment", 6, "published", percentage=3.3),
        _row("all", "not_sustained", 5, "published", percentage=2.8),
        _row("all", "not_captured", 4, "published", percentage=2.2),
    ]
    block = _destinations_block(rows)
    group = block["groups"]["all"]
    published = sum(c["pupils"] for c in group["categories"] if c["pupils"] is not None)
    residual = group["cohort"] - published
    for value in group["aggregates"].values():
        if value is None or value.get("pupils") is None:
            continue
        assert value["pupils"] != residual, (
            "an aggregate equal to the residual identifies the suppressed cell"
        )


def test_aggregates_are_separated_from_categories():
    rows = [
        _row("all", "school_sixth_form", 75, "published", percentage=41.7),
        _row("all", "agg_sustained_all", 171, "published", percentage=95.0),
    ]
    block = _destinations_block(rows)
    group = block["groups"]["all"]
    assert [c["category"] for c in group["categories"]] == ["school_sixth_form"]
    assert group["aggregates"]["sustained_all"]["pupils"] == 171


def test_only_the_latest_year_is_served():
    rows = [
        _row("all", "school_sixth_form", 60, "published", year=202122),
        _row("all", "school_sixth_form", 75, "published", year=202223),
    ]
    block = _destinations_block(rows)
    assert block["cohort_year"] == "2022/23"
    assert len(block["groups"]["all"]["categories"]) == 1
    assert block["groups"]["all"]["categories"][0]["pupils"] == 75


def test_all_three_pupil_groups_are_carried():
    rows = [
        _row("all", "school_sixth_form", 75, "published"),
        _row("disadvantaged", "school_sixth_form", 17, "published", cohort=62),
        _row("other", "school_sixth_form", 58, "published", cohort=118),
    ]
    block = _destinations_block(rows)
    assert set(block["groups"]) == {"all", "disadvantaged", "other"}
    assert block["groups"]["disadvantaged"]["cohort"] == 62


def test_cohort_year_is_reported_so_the_page_can_date_itself():
    block = _destinations_block([_row("all", "school_sixth_form", 75, "published")])
    assert block["cohort_year"] == "2022/23"


def test_format_cohort_year_handles_the_six_digit_form():
    assert _format_cohort_year(202223) == "2022/23"
    assert _format_cohort_year(None) is None


def test_empty_rows_yield_none_not_an_empty_shell():
    assert _destinations_block([]) is None