# Copyright The PyTorch Lightning team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import time
from unittest.mock import patch

import pytest

import pytorch_lightning.utilities.xla_device as xla_utils
from pytorch_lightning.utilities import _XLA_AVAILABLE
from tests.helpers.runif import RunIf
from tests.helpers.utils import pl_multi_process_test


@pytest.mark.skipif(_XLA_AVAILABLE, reason="test requires torch_xla to be absent")
def test_tpu_device_absence():
    """Check tpu_device_exists returns None when torch_xla is not available"""
    assert xla_utils.XLADeviceUtils.tpu_device_exists() is None


@RunIf(tpu=True)
@pl_multi_process_test
def test_tpu_device_presence():
    """Check tpu_device_exists returns True when TPU is available"""
    assert xla_utils.XLADeviceUtils.tpu_device_exists() is True


@patch('pytorch_lightning.utilities.xla_device.TPU_CHECK_TIMEOUT', 10)
def test_result_returns_within_timeout_seconds():
    """Check that pl_multi_process returns within 10 seconds"""
    start = time.time()
    result = xla_utils.pl_multi_process(time.sleep)(xla_utils.TPU_CHECK_TIMEOUT * 1.25)
    end = time.time()
    elapsed_time = int(end - start)
    assert elapsed_time <= xla_utils.TPU_CHECK_TIMEOUT
    assert result is False