"""
Behavioral based tests for offsets and date_range.

This file is adapted from https://github.com/pandas-dev/pandas/pull/18761 -
which was more ambitious but less idiomatic in its use of Hypothesis.

You may wish to consult the previous version for inspiration on further
tests, or when trying to pin down the bugs exposed by the tests below.
"""
import warnings

from hypothesis import assume, given, strategies as st
from hypothesis.errors import Flaky
from hypothesis.extra.dateutil import timezones as dateutil_timezones
from hypothesis.extra.pytz import timezones as pytz_timezones
import pytest
import pytz

import pandas as pd
from pandas import Timestamp

from pandas.tseries.offsets import (
    BMonthBegin,
    BMonthEnd,
    BQuarterBegin,
    BQuarterEnd,
    BYearBegin,
    BYearEnd,
    MonthBegin,
    MonthEnd,
    QuarterBegin,
    QuarterEnd,
    YearBegin,
    YearEnd,
)

# ----------------------------------------------------------------
# Helpers for generating random data

with warnings.catch_warnings():
    warnings.simplefilter("ignore")
    min_dt = Timestamp(1900, 1, 1).to_pydatetime()
    max_dt = Timestamp(1900, 1, 1).to_pydatetime()

gen_date_range = st.builds(
    pd.date_range,
    start=st.datetimes(
        # TODO: Choose the min/max values more systematically
        min_value=Timestamp(1900, 1, 1).to_pydatetime(),
        max_value=Timestamp(2100, 1, 1).to_pydatetime(),
    ),
    periods=st.integers(min_value=2, max_value=100),
    freq=st.sampled_from("Y Q M D H T s ms us ns".split()),
    tz=st.one_of(st.none(), dateutil_timezones(), pytz_timezones()),
)

gen_random_datetime = st.datetimes(
    min_value=min_dt,
    max_value=max_dt,
    timezones=st.one_of(st.none(), dateutil_timezones(), pytz_timezones()),
)

# The strategy for each type is registered in conftest.py, as they don't carry
# enough runtime information (e.g. type hints) to infer how to build them.
gen_yqm_offset = st.one_of(
    *map(
        st.from_type,
        [
            MonthBegin,
            MonthEnd,
            BMonthBegin,
            BMonthEnd,
            QuarterBegin,
            QuarterEnd,
            BQuarterBegin,
            BQuarterEnd,
            YearBegin,
            YearEnd,
            BYearBegin,
            BYearEnd,
        ],
    )
)


# ----------------------------------------------------------------
# Offset-specific behaviour tests


@pytest.mark.arm_slow
@given(gen_random_datetime, gen_yqm_offset)
def test_on_offset_implementations(dt, offset):
    assume(not offset.normalize)
    # check that the class-specific implementations of is_on_offset match
    # the general case definition:
    #   (dt + offset) - offset == dt
    try:
        compare = (dt + offset) - offset
    except pytz.NonExistentTimeError:
        # dt + offset does not exist, assume(False) to indicate
        #  to hypothesis that this is not a valid test case
        assume(False)

    assert offset.is_on_offset(dt) == (compare == dt)


@pytest.mark.xfail(strict=False, raises=Flaky, reason="unreliable test timings")
@given(gen_yqm_offset)
def test_shift_across_dst(offset):
    # GH#18319 check that 1) timezone is correctly normalized and
    # 2) that hour is not incorrectly changed by this normalization
    assume(not offset.normalize)

    # Note that dti includes a transition across DST boundary
    dti = pd.date_range(
        start="2017-10-30 12:00:00", end="2017-11-06", freq="D", tz="US/Eastern"
    )
    assert (dti.hour == 12).all()  # we haven't screwed up yet

    res = dti + offset
    assert (res.hour == 12).all()