from datetime import date, datetime, time, timezone

import availability as av

BERLIN = "Europe/Berlin"
NINE_TO_FIVE = {d: (time(9, 0), time(17, 0)) for d in range(7)}


def _far_past():
    # "far enough in the past" relative to the 2026 test dates below, not
    # literally far past -- max_advance_days is finite, so "now" has to be
    # within max_advance_days of the date under test.
    return datetime(2026, 1, 1, tzinfo=timezone.utc)


def _far_future_notice():
    return {"min_notice_minutes": 0, "max_advance_days": 365 * 10}


def test_normal_day_matches_hand_computed_slots():
    # 2026-07-06 is a Monday in Berlin summer time (CEST, UTC+2).
    day = date(2026, 7, 6)
    slots = av.generate_slots(
        {0: (time(9, 0), time(12, 0))}, duration_minutes=60,
        date_from=day, date_to=day, tz_name=BERLIN, now=_far_past(),
        **_far_future_notice())
    assert slots == [
        datetime(2026, 7, 6, 7, 0, tzinfo=timezone.utc),
        datetime(2026, 7, 6, 8, 0, tzinfo=timezone.utc),
        datetime(2026, 7, 6, 9, 0, tzinfo=timezone.utc),
    ]


def test_dst_spring_forward_shifts_utc_offset_but_keeps_slot_count():
    # Berlin DST 2026 starts 2026-03-29 (clocks 02:00 -> 03:00 CET->CEST).
    before = date(2026, 3, 28)   # CET, UTC+1
    on_day = date(2026, 3, 29)   # transition day; business hours all CEST
    after = date(2026, 3, 30)    # CEST, UTC+2

    def slots_for(day):
        return av.generate_slots(
            NINE_TO_FIVE, duration_minutes=60, date_from=day, date_to=day,
            tz_name=BERLIN, now=_far_past(), **_far_future_notice())

    before_slots = slots_for(before)
    on_day_slots = slots_for(on_day)
    after_slots = slots_for(after)

    assert len(before_slots) == len(on_day_slots) == len(after_slots) == 8
    assert before_slots[0] == datetime(2026, 3, 28, 8, 0, tzinfo=timezone.utc)
    # one hour earlier in UTC once CEST (UTC+2) kicks in
    assert on_day_slots[0] == datetime(2026, 3, 29, 7, 0, tzinfo=timezone.utc)
    assert after_slots[0] == datetime(2026, 3, 30, 7, 0, tzinfo=timezone.utc)


def test_dst_fall_back_shifts_utc_offset_but_keeps_slot_count():
    # Berlin DST 2026 ends 2026-10-25 (clocks 03:00 -> 02:00 CEST->CET).
    before = date(2026, 10, 24)  # CEST, UTC+2
    after = date(2026, 10, 26)   # CET, UTC+1

    def slots_for(day):
        return av.generate_slots(
            NINE_TO_FIVE, duration_minutes=60, date_from=day, date_to=day,
            tz_name=BERLIN, now=_far_past(), **_far_future_notice())

    before_slots = slots_for(before)
    after_slots = slots_for(after)
    assert len(before_slots) == len(after_slots) == 8
    assert before_slots[0] == datetime(2026, 10, 24, 7, 0, tzinfo=timezone.utc)
    assert after_slots[0] == datetime(2026, 10, 26, 8, 0, tzinfo=timezone.utc)


def test_min_notice_excludes_near_term_slots():
    day = date(2026, 7, 6)
    now = datetime(2026, 7, 6, 6, 30, tzinfo=timezone.utc)  # 08:30 local
    slots = av.generate_slots(
        {0: (time(9, 0), time(12, 0))}, duration_minutes=60,
        date_from=day, date_to=day, tz_name=BERLIN, now=now,
        min_notice_minutes=60, max_advance_days=365)
    # 07:00 UTC (09:00 local) is only 30min out -- excluded by 60min notice.
    assert slots == [
        datetime(2026, 7, 6, 8, 0, tzinfo=timezone.utc),
        datetime(2026, 7, 6, 9, 0, tzinfo=timezone.utc),
    ]


def test_max_advance_excludes_far_future_slots():
    day = date(2026, 7, 6)
    now = datetime(2026, 7, 5, 0, 0, tzinfo=timezone.utc)
    slots = av.generate_slots(
        {0: (time(9, 0), time(12, 0))}, duration_minutes=60,
        date_from=day, date_to=day, tz_name=BERLIN, now=now,
        min_notice_minutes=0, max_advance_days=1)
    assert slots == []


def test_buffer_excludes_slots_too_close_to_an_existing_booking():
    day = date(2026, 7, 6)
    # existing booking 09:00-10:00 local (07:00-08:00 UTC)
    busy = [(datetime(2026, 7, 6, 7, 0, tzinfo=timezone.utc),
              datetime(2026, 7, 6, 8, 0, tzinfo=timezone.utc))]
    slots = av.generate_slots(
        {0: (time(9, 0), time(12, 0))}, duration_minutes=60,
        date_from=day, date_to=day, tz_name=BERLIN, now=_far_past(),
        min_notice_minutes=0, max_advance_days=365, buffer_minutes=30,
        busy=busy)
    # 08:00 UTC (10:00 local) slot starts only 30min after the busy booking
    # ends at 08:00 -- exactly at the buffer boundary, so still blocked;
    # 09:00 UTC (11:00 local) is clear.
    assert slots == [datetime(2026, 7, 6, 9, 0, tzinfo=timezone.utc)]


def test_no_hours_configured_for_weekday_yields_no_slots():
    day = date(2026, 7, 6)  # Monday, but hours only configured for Tuesday
    slots = av.generate_slots(
        {1: (time(9, 0), time(12, 0))}, duration_minutes=60,
        date_from=day, date_to=day, tz_name=BERLIN, now=_far_past(),
        **_far_future_notice())
    assert slots == []