"""Loading a run's results must not depend on the run being small.

``/detection/runs/{id}/detections`` and its GeoJSON sibling returned every
persisted detection. A regional run holds tens of thousands, so the endpoints
the map and the results table call after every run grew without bound. The
counts stay complete; what is transferred does not.
"""

from __future__ import annotations

import uuid

import pytest

from app.services.detection_service import DetectionService


class _Detection:
    def __init__(self, index: int) -> None:
        self.id = uuid.uuid4()
        self.index = index


def _rows(count: int) -> list[_Detection]:
    return [_Detection(index) for index in range(count)]


def test_a_page_is_returned_with_the_complete_total() -> None:
    page, total, truncated = DetectionService.paginate(_rows(1_000), limit=100, offset=0)

    assert len(page) == 100
    assert total == 1_000
    assert truncated is True


def test_the_offset_walks_the_population() -> None:
    page, total, _ = DetectionService.paginate(_rows(10), limit=3, offset=6)

    assert [row.index for row in page] == [6, 7, 8]
    assert total == 10


def test_an_offset_past_the_end_yields_an_empty_page_not_an_error() -> None:
    page, total, truncated = DetectionService.paginate(_rows(5), limit=10, offset=50)

    assert page == []
    assert total == 5
    assert truncated is True


def test_a_population_inside_one_page_is_not_reported_as_truncated() -> None:
    page, total, truncated = DetectionService.paginate(_rows(7), limit=100, offset=0)

    assert len(page) == 7
    assert total == 7
    assert truncated is False


def test_a_zero_limit_returns_everything_for_callers_that_need_it() -> None:
    page, total, truncated = DetectionService.paginate(_rows(2_500), limit=0, offset=0)

    assert len(page) == 2_500
    assert total == 2_500
    assert truncated is False


def test_a_negative_offset_is_treated_as_the_start() -> None:
    page, _, _ = DetectionService.paginate(_rows(4), limit=2, offset=-5)

    assert [row.index for row in page] == [0, 1]


@pytest.mark.parametrize("limit", [1, 2, 3])
def test_paging_covers_the_population_exactly_once(limit: int) -> None:
    rows = _rows(7)
    seen: list[int] = []
    offset = 0
    while True:
        page, total, _ = DetectionService.paginate(rows, limit=limit, offset=offset)
        if not page:
            break
        seen.extend(row.index for row in page)
        offset += limit

    assert seen == list(range(7))
    assert total == 7