import os
import shutil
import warnings
from typing import List

import torch
from torch.utils.cpp_extension import load


__all__ = ["is_extension_available", "get_extension"]


class Extension(object):
    def __init__(
        self,
        name: str,
        root_dir: str,
        sources: List[str],
        extra_cflags: List[str] = None,
        extra_cuda_cflags: List[str] = None,
    ):
        self.name = name
        self.sources = [f"{root_dir}/{source}" for source in sources]
        self.extra_cflags = extra_cflags
        self.extra_cuda_cflags = extra_cuda_cflags
        self.build_directory = os.path.join(root_dir, "build")
        self._lib = None

    @property
    def lib(self):
        if self._lib is None:
            # We only load the extension when the lib is required
            version_file = os.path.join(self.build_directory, "pytorch_version.txt")
            if os.path.exists(version_file):
                # The extension has already been built: check the torch version for which it was built
                with open(version_file, "r") as f:
                    pytorch_build_version = f.read().rstrip()
                    if pytorch_build_version != torch.__version__:
                        shutil.rmtree(self.build_directory)
                        warnings.warn(
                            f"{self.name} was compiled with pytorch {pytorch_build_version}, but {torch.__version__} is installed: it will be recompiled."
                        )
            os.makedirs(self.build_directory, exist_ok=True)
            self._lib = load(
                name=self.name,
                sources=self.sources,
                extra_cflags=self.extra_cflags,
                extra_cuda_cflags=self.extra_cuda_cflags,
                build_directory=self.build_directory,
            )
            if not os.path.exists(version_file):
                with open(version_file, "w") as f:
                    f.write(torch.__version__)
        return self._lib


_extensions = {}


def register_extension(extension: Extension):
    assert extension.name not in _extensions
    _extensions[extension.name] = extension


def get_extension(extension_type: str):
    """Get an extension

    Args:
        extension_type (`str`):
            The extension type.
    Returns:
        The corresponding extension.
    """
    return _extensions[extension_type]


def is_extension_available(extension_type: str):
    """Check is an extension is available

    Args:
        extension_type (`str`):
            The extension type.
    Returns:
        True if the extension is available.
    """
    return extension_type in _extensions