"""Change detection must answer the question the operator actually asked.

Every other analysis in the workbench is bounded by the drawn selection.
Change detection was not: it compared two datasets in full, loaded every
feature of both into Python, and — with ``include_unchanged`` defaulting to
true — returned a FeatureCollection containing both datasets entire. For a
regional building layer that is the wrong answer to "what changed here" and a
response no browser should be asked to hold.
"""

from __future__ import annotations

import pytest
from shapely.geometry import box

from app.core.errors import AppError
from app.services.change_detection_service import ChangeDetectionService


def _feature(feature_id: str, geometry):
    return {"feature_id": feature_id, "properties": {}, "geometry": geometry}


INSIDE = box(0.0, 0.0, 1.0, 1.0)
OUTSIDE = box(50.0, 50.0, 51.0, 51.0)
SELECTION = box(-1.0, -1.0, 2.0, 2.0)


def test_features_outside_the_selection_are_not_compared() -> None:
    kept = ChangeDetectionService.restrict_to_selection(
        [_feature("in", INSIDE), _feature("out", OUTSIDE)],
        SELECTION,
    )

    assert [item["feature_id"] for item in kept] == ["in"]


def test_a_feature_crossing_the_selection_edge_is_kept_and_flagged() -> None:
    crossing = box(1.5, 1.5, 3.0, 3.0)

    kept = ChangeDetectionService.restrict_to_selection(
        [_feature("crossing", crossing)],
        SELECTION,
    )

    assert len(kept) == 1
    assert kept[0]["partially_covered"] is True
    # The geometry is not clipped: a change class describes a whole object, and
    # comparing a clipped 2020 footprint with an unclipped 2024 one would
    # invent change at the selection edge.
    assert kept[0]["geometry"].equals(crossing)


def test_a_feature_wholly_inside_is_not_flagged() -> None:
    kept = ChangeDetectionService.restrict_to_selection([_feature("in", INSIDE)], SELECTION)

    assert kept[0]["partially_covered"] is False


def test_no_selection_leaves_the_population_untouched() -> None:
    features = [_feature("in", INSIDE), _feature("out", OUTSIDE)]

    assert ChangeDetectionService.restrict_to_selection(features, None) == features


def test_an_empty_intersection_is_an_explicit_error_not_a_silent_zero() -> None:
    with pytest.raises(AppError) as exc_info:
        ChangeDetectionService.restrict_to_selection([_feature("out", OUTSIDE)], SELECTION, label="Source")

    assert exc_info.value.code == "CHANGE_DETECTION_SELECTION_EMPTY"
    assert "Source" in exc_info.value.message


def test_the_preview_is_capped_while_the_counts_stay_complete() -> None:
    features = [
        {
            "change_type": "added" if index % 2 else "removed",
            "geometry": box(index, 0, index + 1, 1),
            "source_feature_id": None,
            "target_feature_id": f"t{index}",
            "iou": None,
            "properties": {},
        }
        for index in range(250)
    ]

    preview, truncated = ChangeDetectionService.limit_preview(features, limit=100)

    assert len(preview) == 100
    assert truncated is True


def test_a_short_result_is_not_reported_as_truncated() -> None:
    features = [
        {
            "change_type": "added",
            "geometry": box(0, 0, 1, 1),
            "source_feature_id": None,
            "target_feature_id": "t",
            "iou": None,
            "properties": {},
        }
    ]

    preview, truncated = ChangeDetectionService.limit_preview(features, limit=100)

    assert len(preview) == 1
    assert truncated is False


def test_the_preview_prefers_changes_over_unchanged_features() -> None:
    """A cap must not spend its budget on the least interesting class."""

    features = [
        {"change_type": "unchanged", "geometry": box(index, 0, index + 1, 1), "source_feature_id": f"s{index}",
         "target_feature_id": f"t{index}", "iou": 1.0, "properties": {}}
        for index in range(100)
    ] + [
        {"change_type": "added", "geometry": box(0, 5, 1, 6), "source_feature_id": None,
         "target_feature_id": "new", "iou": None, "properties": {}},
        {"change_type": "modified", "geometry": box(0, 7, 1, 8), "source_feature_id": "s",
         "target_feature_id": "t", "iou": 0.6, "properties": {}},
    ]

    preview, truncated = ChangeDetectionService.limit_preview(features, limit=3)

    assert truncated is True
    assert sorted(item["change_type"] for item in preview[:2]) == ["added", "modified"]