import os
from unittest import mock

import pytest
import torch

import pytorch_lightning.utilities.seed as seed_utils


@mock.patch.dict(os.environ, {}, clear=True)
def test_seed_stays_same_with_multiple_seed_everything_calls():
    """Ensure that after the initial seed everything, the seed stays the same for the same run."""
    with pytest.warns(UserWarning, match="No seed found"):
        seed_utils.seed_everything()
    initial_seed = os.environ.get("PL_GLOBAL_SEED")

    with pytest.warns(None) as record:
        seed_utils.seed_everything()
    assert not record  # does not warn
    seed = os.environ.get("PL_GLOBAL_SEED")

    assert initial_seed == seed


@mock.patch.dict(os.environ, {"PL_GLOBAL_SEED": "2020"}, clear=True)
def test_correct_seed_with_environment_variable():
    """Ensure that the PL_GLOBAL_SEED environment is read."""
    assert seed_utils.seed_everything() == 2020


@mock.patch.dict(os.environ, {"PL_GLOBAL_SEED": "invalid"}, clear=True)
@mock.patch.object(seed_utils, attribute="_select_seed_randomly", new=lambda *_: 123)
def test_invalid_seed():
    """Ensure that we still fix the seed even if an invalid seed is given."""
    with pytest.warns(UserWarning, match="Invalid seed found"):
        seed = seed_utils.seed_everything()
    assert seed == 123


@mock.patch.dict(os.environ, {}, clear=True)
@mock.patch.object(seed_utils, attribute="_select_seed_randomly", new=lambda *_: 123)
@pytest.mark.parametrize("seed", (10e9, -10e9))
def test_out_of_bounds_seed(seed):
    """Ensure that we still fix the seed even if an out-of-bounds seed is given."""
    with pytest.warns(UserWarning, match="is not in bounds"):
        actual = seed_utils.seed_everything(seed)
    assert actual == 123


def test_reset_seed_no_op():
    """Test that the reset_seed function is a no-op when seed_everything() was not used."""
    assert "PL_GLOBAL_SEED" not in os.environ
    seed_before = torch.initial_seed()
    seed_utils.reset_seed()
    assert torch.initial_seed() == seed_before
    assert "PL_GLOBAL_SEED" not in os.environ


def test_reset_seed_everything():
    """Test that we can reset the seed to the initial value set by seed_everything()"""
    assert "PL_GLOBAL_SEED" not in os.environ
    seed_utils.seed_everything(123)
    assert os.environ["PL_GLOBAL_SEED"] == "123"
    before = torch.rand(1)
    seed_utils.reset_seed()
    after = torch.rand(1)
    assert torch.allclose(before, after)