from datetime import date

from common_cents.screens.reports import (
    _date_range,
    _month_options,
    _months_in_range,
)


def test_months_in_range_same_month():
    assert _months_in_range("2026-05-01", "2026-05-31") == 1


def test_months_in_range_multi_month():
    assert _months_in_range("2026-01-01", "2026-12-31") == 12


def test_months_in_range_year_crossover():
    assert _months_in_range("2025-11-01", "2026-02-15") == 4


def test_date_range_this_month():
    import calendar

    start, end, label = _date_range("this-month")
    today = date.today()
    last_day = calendar.monthrange(today.year, today.month)[1]
    assert start == today.replace(day=1).isoformat()
    assert end == today.replace(day=last_day).isoformat()
    assert "This Month" in label


def test_date_range_last_month():
    start, end, _label = _date_range("last-month")
    today = date.today()
    end_d = date.fromisoformat(end)
    # last day of previous month
    assert end_d < today.replace(day=1)
    assert date.fromisoformat(start).day == 1
    assert end_d.month == date.fromisoformat(start).month


def test_date_range_ytd():
    start, end, _label = _date_range("ytd")
    today = date.today()
    assert start == date(today.year, 1, 1).isoformat()
    assert end == today.isoformat()


def test_date_range_last_12_months():
    """Trailing 12 months = current month + 11 prior, so spans 12 distinct months."""
    start, end, _label = _date_range("last-12")
    assert _months_in_range(start, end) == 12


def test_date_range_custom_month_bounds():
    """Custom range expands YYYY-MM to first/last day of the chosen months."""
    start, end, label = _date_range("custom", "2026-03", "2026-05")
    assert start == "2026-03-01"
    assert end == "2026-05-31"
    assert "Mar 2026" in label and "May 2026" in label


def test_date_range_custom_single_month():
    start, end, label = _date_range("custom", "2026-02", "2026-02")
    assert start == "2026-02-01"
    assert end == "2026-02-28"
    assert label == "Custom (Feb 2026)"


def test_date_range_custom_swaps_when_inverted():
    start, end, _label = _date_range("custom", "2026-12", "2026-01")
    assert start == "2026-01-01"
    assert end == "2026-12-31"


def test_date_range_custom_falls_back_to_current_month_when_blank():
    start, end, _label = _date_range("custom", "", "")
    today = date.today()
    assert start.startswith(today.strftime("%Y-%m"))
    assert start.endswith("-01")
    assert end.startswith(today.strftime("%Y-%m"))


def test_month_options_descending_and_inclusive():
    opts = _month_options(date(2026, 3, 1), date(2026, 5, 15))
    # latest first, three months, label = abbr month + year, value = YYYY-MM
    assert opts == [
        ("May 2026", "2026-05"),
        ("Apr 2026", "2026-04"),
        ("Mar 2026", "2026-03"),
    ]


def test_month_options_year_crossover():
    opts = _month_options(date(2025, 11, 1), date(2026, 1, 31))
    assert [v for _, v in opts] == ["2026-01", "2025-12", "2025-11"]