"""Checks for the statistics, using tiny hand-made data with known answers."""

import sys
from pathlib import Path

import pytest

sys.path.insert(0, str(Path(__file__).resolve().parent.parent))

import itemstats  # noqa: E402

QUIZ = {
    "title": "tiny",
    "items": [
        {"id": "I1", "stem": "", "options": {"A": "", "B": ""}, "key": "A"},
        {"id": "I2", "stem": "", "options": {"A": "", "B": ""}, "key": "A"},
        {"id": "I3", "stem": "", "options": {"A": "", "B": ""}, "key": "B"},
    ],
}


def learners(rows):
    return [{"learner_id": f"L{n}", "I1": a, "I2": b, "I3": c} for n, (a, b, c) in enumerate(rows)]


def test_difficulty_is_share_correct():
    stats = itemstats.analyze(QUIZ, learners([("A", "A", "B"), ("A", "B", "A"), ("B", "B", "A"), ("A", "A", "A")]))
    assert stats.items[0].difficulty == pytest.approx(0.75)
    assert stats.items[1].difficulty == pytest.approx(0.50)
    assert stats.items[2].difficulty == pytest.approx(0.25)


def test_pearson_known_values():
    assert itemstats.pearson([1, 2, 3], [2, 4, 6]) == pytest.approx(1.0)
    assert itemstats.pearson([1, 2, 3], [3, 2, 1]) == pytest.approx(-1.0)
    assert itemstats.pearson([1, 1, 1], [1, 2, 3]) is None


def test_kr20_perfectly_consistent_test():
    # Every learner either gets everything right or everything wrong.
    matrix = [[1, 1, 1], [1, 1, 1], [0, 0, 0], [0, 0, 0]]
    assert itemstats.kr20(matrix) == pytest.approx(1.0)


def test_miskeyed_item_gets_flagged():
    # Strong learners (right on I1 and I2) all pick A on I3, but the key says B.
    rows = [("A", "A", "A")] * 6 + [("B", "B", "B")] * 6
    stats = itemstats.analyze(QUIZ, learners(rows))
    flags = " ".join(stats.items[2].flags)
    assert "negative discrimination" in flags
    assert "option A attracts stronger learners" in flags


def test_easy_item_gets_flagged():
    rows = [("A", "A", "B")] * 19 + [("A", "B", "A")]
    stats = itemstats.analyze(QUIZ, learners(rows))
    assert any("very easy" in f for f in stats.items[0].flags)