import os
import random
import unittest
from distutils.util import strtobool

import torch

from packaging import version


global_rng = random.Random()
torch_device = "cuda" if torch.cuda.is_available() else "cpu"
is_torch_higher_equal_than_1_12 = version.parse(version.parse(torch.__version__).base_version) >= version.parse("1.12")

if is_torch_higher_equal_than_1_12:
    torch_device = "mps" if torch.backends.mps.is_available() else torch_device


def parse_flag_from_env(key, default=False):
    try:
        value = os.environ[key]
    except KeyError:
        # KEY isn't set, default to `default`.
        _value = default
    else:
        # KEY is set, convert it to True or False.
        try:
            _value = strtobool(value)
        except ValueError:
            # More values are supported, but let's keep the message simple.
            raise ValueError(f"If set, {key} must be yes or no.")
    return _value


_run_slow_tests = parse_flag_from_env("RUN_SLOW", default=False)


def floats_tensor(shape, scale=1.0, rng=None, name=None):
    """Creates a random float32 tensor"""
    if rng is None:
        rng = global_rng

    total_dims = 1
    for dim in shape:
        total_dims *= dim

    values = []
    for _ in range(total_dims):
        values.append(rng.random() * scale)

    return torch.tensor(data=values, dtype=torch.float).view(shape).contiguous()


def slow(test_case):
    """
    Decorator marking a test as slow.

    Slow tests are skipped by default. Set the RUN_SLOW environment variable to a truthy value to run them.

    """
    return unittest.skipUnless(_run_slow_tests, "test is slow")(test_case)