from datetime import date

from app.fitness.charts import linear_regression, week_start


def test_week_start_monday():
    assert week_start(date(2026, 6, 13)) == date(2026, 6, 8)


def test_linear_regression_increasing():
    points = [(0.0, 1.0), (1.0, 2.0), (2.0, 3.0)]
    fit = linear_regression(points)
    assert fit is not None
    assert abs(fit["slope"] - 1.0) < 1e-9
    assert abs(fit["intercept"] - 1.0) < 1e-9


def test_linear_regression_requires_two_points():
    assert linear_regression([(0.0, 5.0)]) is None
    assert linear_regression([]) is None