import polars as pl

from pipeline.utils.postcode_mapping import (
    MAX_REMAP_DISTANCE_M,
    build_postcode_mapping,
)


def test_remap_drops_terminated_postcodes_beyond_distance_cap(tmp_path):
    # One active England postcode at the origin.
    # One terminated postcode 100m away (legitimate adjacent remap -> mapped).
    # One terminated postcode 5km away (gross misattribution -> dropped).
    arcgis = pl.DataFrame(
        {
            "pcds": ["AB1 1AA", "AB1 1AB", "ZZ9 9ZZ"],
            "ctry25cd": ["E92000001", "E92000001", "E92000001"],
            "doterm": [None, "202001", "202001"],
            "east1m": [500000.0, 500100.0, 505000.0],
            "north1m": [200000.0, 200000.0, 200000.0],
        }
    )
    arcgis_path = tmp_path / "arcgis.parquet"
    arcgis.write_parquet(arcgis_path)

    mapping = build_postcode_mapping(arcgis_path)

    # The nearby terminated postcode is remapped onto the active one.
    assert mapping.filter(pl.col("old_postcode") == "AB1 1AB")[
        "new_postcode"
    ].to_list() == ["AB1 1AA"]

    # The far (5km > 1km cap) terminated postcode must NOT appear in the mapping.
    assert "ZZ9 9ZZ" not in mapping["old_postcode"].to_list()
    assert mapping.height == 1


def test_max_remap_distance_constant_is_one_kilometre():
    assert MAX_REMAP_DISTANCE_M == 1000.0