#!/usr/bin/env python3
# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.

import errno
import logging
import os
import shutil
from collections import OrderedDict
from typing import (
    IO,
    Any,
    Callable,
    Dict,
    List,
    MutableMapping,
    Optional,
    Union,
)

__all__ = ["PathManager", "get_cache_dir"]


def get_cache_dir(cache_dir: Optional[str] = None) -> str:
    """
    Returns a default directory to cache static files
    (usually downloaded from Internet), if None is provided.
    Args:
        cache_dir (None or str): if not None, will be returned as is.
            If None, returns the default cache directory as:
        1) $FVCORE_CACHE, if set
        2) otherwise ~/.torch/fvcore_cache
    """
    if cache_dir is None:
        cache_dir = os.path.expanduser(
            os.getenv("FVCORE_CACHE", "~/.torch/fvcore_cache")
        )
    return cache_dir


class PathHandler:
    """
    PathHandler is a base class that defines common I/O functionality for a URI
    protocol. It routes I/O for a generic URI which may look like "protocol://*"
    or a canonical filepath "/foo/bar/baz".
    """

    _strict_kwargs_check = True

    def _check_kwargs(self, kwargs: Dict[str, Any]) -> None:
        """
        Checks if the given arguments are empty. Throws a ValueError if strict
        kwargs checking is enabled and args are non-empty. If strict kwargs
        checking is disabled, only a warning is logged.
        Args:
            kwargs (Dict[str, Any])
        """
        if self._strict_kwargs_check:
            if len(kwargs) > 0:
                raise ValueError("Unused arguments: {}".format(kwargs))
        else:
            logger = logging.getLogger(__name__)
            for k, v in kwargs.items():
                logger.warning(
                    "[PathManager] {}={} argument ignored".format(k, v)
                )

    def _get_supported_prefixes(self) -> List[str]:
        """
        Returns:
            List[str]: the list of URI prefixes this PathHandler can support
        """
        raise NotImplementedError()

    def _get_local_path(self, path: str, **kwargs: Any) -> str:
        """
        Get a filepath which is compatible with native Python I/O such as `open`
        and `os.path`.
        If URI points to a remote resource, this function may download and cache
        the resource to local disk. In this case, this function is meant to be
        used with read-only resources.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            local_path (str): a file path which exists on the local file system
        """
        raise NotImplementedError()

    def _open(
            self, path: str, mode: str = "r", buffering: int = -1, **kwargs: Any
    ) -> Union[IO[str], IO[bytes]]:
        """
        Open a stream to a URI, similar to the built-in `open`.
        Args:
            path (str): A URI supported by this PathHandler
            mode (str): Specifies the mode in which the file is opened. It defaults
                to 'r'.
            buffering (int): An optional integer used to set the buffering policy.
                Pass 0 to switch buffering off and an integer >= 1 to indicate the
                size in bytes of a fixed-size chunk buffer. When no buffering
                argument is given, the default buffering policy depends on the
                underlying I/O implementation.
        Returns:
            file: a file-like object.
        """
        raise NotImplementedError()

    def _copy(
            self,
            src_path: str,
            dst_path: str,
            overwrite: bool = False,
            **kwargs: Any,
    ) -> bool:
        """
        Copies a source path to a destination path.
        Args:
            src_path (str): A URI supported by this PathHandler
            dst_path (str): A URI supported by this PathHandler
            overwrite (bool): Bool flag for forcing overwrite of existing file
        Returns:
            status (bool): True on success
        """
        raise NotImplementedError()

    def _exists(self, path: str, **kwargs: Any) -> bool:
        """
        Checks if there is a resource at the given URI.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            bool: true if the path exists
        """
        raise NotImplementedError()

    def _isfile(self, path: str, **kwargs: Any) -> bool:
        """
        Checks if the resource at the given URI is a file.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            bool: true if the path is a file
        """
        raise NotImplementedError()

    def _isdir(self, path: str, **kwargs: Any) -> bool:
        """
        Checks if the resource at the given URI is a directory.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            bool: true if the path is a directory
        """
        raise NotImplementedError()

    def _ls(self, path: str, **kwargs: Any) -> List[str]:
        """
        List the contents of the directory at the provided URI.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            List[str]: list of contents in given path
        """
        raise NotImplementedError()

    def _mkdirs(self, path: str, **kwargs: Any) -> None:
        """
        Recursive directory creation function. Like mkdir(), but makes all
        intermediate-level directories needed to contain the leaf directory.
        Similar to the native `os.makedirs`.
        Args:
            path (str): A URI supported by this PathHandler
        """
        raise NotImplementedError()

    def _rm(self, path: str, **kwargs: Any) -> None:
        """
        Remove the file (not directory) at the provided URI.
        Args:
            path (str): A URI supported by this PathHandler
        """
        raise NotImplementedError()


class NativePathHandler(PathHandler):
    """
    Handles paths that can be accessed using Python native system calls. This
    handler uses `open()` and `os.*` calls on the given path.
    """

    def _get_local_path(self, path: str, **kwargs: Any) -> str:
        self._check_kwargs(kwargs)
        return path

    def _open(
            self,
            path: str,
            mode: str = "r",
            buffering: int = -1,
            encoding: Optional[str] = None,
            errors: Optional[str] = None,
            newline: Optional[str] = None,
            closefd: bool = True,
            opener: Optional[Callable] = None,
            **kwargs: Any,
    ) -> Union[IO[str], IO[bytes]]:
        """
        Open a path.
        Args:
            path (str): A URI supported by this PathHandler
            mode (str): Specifies the mode in which the file is opened. It defaults
                to 'r'.
            buffering (int): An optional integer used to set the buffering policy.
                Pass 0 to switch buffering off and an integer >= 1 to indicate the
                size in bytes of a fixed-size chunk buffer. When no buffering
                argument is given, the default buffering policy works as follows:
                    * Binary files are buffered in fixed-size chunks; the size of
                    the buffer is chosen using a heuristic trying to determine the
                    underlying device’s “block size” and falling back on
                    io.DEFAULT_BUFFER_SIZE. On many systems, the buffer will
                    typically be 4096 or 8192 bytes long.
            encoding (Optional[str]): the name of the encoding used to decode or
                encode the file. This should only be used in text mode.
            errors (Optional[str]): an optional string that specifies how encoding
                and decoding errors are to be handled. This cannot be used in binary
                mode.
            newline (Optional[str]): controls how universal newlines mode works
                (it only applies to text mode). It can be None, '', '\n', '\r',
                and '\r\n'.
            closefd (bool): If closefd is False and a file descriptor rather than
                a filename was given, the underlying file descriptor will be kept
                open when the file is closed. If a filename is given closefd must
                be True (the default) otherwise an error will be raised.
            opener (Optional[Callable]): A custom opener can be used by passing
                a callable as opener. The underlying file descriptor for the file
                object is then obtained by calling opener with (file, flags).
                opener must return an open file descriptor (passing os.open as opener
                results in functionality similar to passing None).
            See https://docs.python.org/3/library/functions.html#open for details.
        Returns:
            file: a file-like object.
        """
        self._check_kwargs(kwargs)
        return open(  # type: ignore
            path,
            mode,
            buffering=buffering,
            encoding=encoding,
            errors=errors,
            newline=newline,
            closefd=closefd,
            opener=opener,
        )

    def _copy(
            self,
            src_path: str,
            dst_path: str,
            overwrite: bool = False,
            **kwargs: Any,
    ) -> bool:
        """
        Copies a source path to a destination path.
        Args:
            src_path (str): A URI supported by this PathHandler
            dst_path (str): A URI supported by this PathHandler
            overwrite (bool): Bool flag for forcing overwrite of existing file
        Returns:
            status (bool): True on success
        """
        self._check_kwargs(kwargs)

        if os.path.exists(dst_path) and not overwrite:
            logger = logging.getLogger(__name__)
            logger.error("Destination file {} already exists.".format(dst_path))
            return False

        try:
            shutil.copyfile(src_path, dst_path)
            return True
        except Exception as e:
            logger = logging.getLogger(__name__)
            logger.error("Error in file copy - {}".format(str(e)))
            return False

    def _exists(self, path: str, **kwargs: Any) -> bool:
        self._check_kwargs(kwargs)
        return os.path.exists(path)

    def _isfile(self, path: str, **kwargs: Any) -> bool:
        self._check_kwargs(kwargs)
        return os.path.isfile(path)

    def _isdir(self, path: str, **kwargs: Any) -> bool:
        self._check_kwargs(kwargs)
        return os.path.isdir(path)

    def _ls(self, path: str, **kwargs: Any) -> List[str]:
        self._check_kwargs(kwargs)
        return os.listdir(path)

    def _mkdirs(self, path: str, **kwargs: Any) -> None:
        self._check_kwargs(kwargs)
        try:
            os.makedirs(path, exist_ok=True)
        except OSError as e:
            # EEXIST it can still happen if multiple processes are creating the dir
            if e.errno != errno.EEXIST:
                raise

    def _rm(self, path: str, **kwargs: Any) -> None:
        self._check_kwargs(kwargs)
        os.remove(path)


class PathManager:
    """
    A class for users to open generic paths or translate generic paths to file names.
    """

    _PATH_HANDLERS: MutableMapping[str, PathHandler] = OrderedDict()
    _NATIVE_PATH_HANDLER = NativePathHandler()

    @staticmethod
    def __get_path_handler(path: str) -> PathHandler:
        """
        Finds a PathHandler that supports the given path. Falls back to the native
        PathHandler if no other handler is found.
        Args:
            path (str): URI path to resource
        Returns:
            handler (PathHandler)
        """
        for p in PathManager._PATH_HANDLERS.keys():
            if path.startswith(p):
                return PathManager._PATH_HANDLERS[p]
        return PathManager._NATIVE_PATH_HANDLER

    @staticmethod
    def open(
            path: str, mode: str = "r", buffering: int = -1, **kwargs: Any
    ) -> Union[IO[str], IO[bytes]]:
        """
        Open a stream to a URI, similar to the built-in `open`.
        Args:
            path (str): A URI supported by this PathHandler
            mode (str): Specifies the mode in which the file is opened. It defaults
                to 'r'.
            buffering (int): An optional integer used to set the buffering policy.
                Pass 0 to switch buffering off and an integer >= 1 to indicate the
                size in bytes of a fixed-size chunk buffer. When no buffering
                argument is given, the default buffering policy depends on the
                underlying I/O implementation.
        Returns:
            file: a file-like object.
        """
        return PathManager.__get_path_handler(path)._open(  # type: ignore
            path, mode, buffering=buffering, **kwargs
        )

    @staticmethod
    def copy(
            src_path: str, dst_path: str, overwrite: bool = False, **kwargs: Any
    ) -> bool:
        """
        Copies a source path to a destination path.
        Args:
            src_path (str): A URI supported by this PathHandler
            dst_path (str): A URI supported by this PathHandler
            overwrite (bool): Bool flag for forcing overwrite of existing file
        Returns:
            status (bool): True on success
        """

        # Copying across handlers is not supported.
        assert PathManager.__get_path_handler(  # type: ignore
            src_path
        ) == PathManager.__get_path_handler(dst_path)
        return PathManager.__get_path_handler(src_path)._copy(
            src_path, dst_path, overwrite, **kwargs
        )

    @staticmethod
    def get_local_path(path: str, **kwargs: Any) -> str:
        """
        Get a filepath which is compatible with native Python I/O such as `open`
        and `os.path`.
        If URI points to a remote resource, this function may download and cache
        the resource to local disk.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            local_path (str): a file path which exists on the local file system
        """
        return PathManager.__get_path_handler(  # type: ignore
            path
        )._get_local_path(path, **kwargs)

    @staticmethod
    def exists(path: str, **kwargs: Any) -> bool:
        """
        Checks if there is a resource at the given URI.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            bool: true if the path exists
        """
        return PathManager.__get_path_handler(path)._exists(  # type: ignore
            path, **kwargs
        )

    @staticmethod
    def isfile(path: str, **kwargs: Any) -> bool:
        """
        Checks if there the resource at the given URI is a file.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            bool: true if the path is a file
        """
        return PathManager.__get_path_handler(path)._isfile(  # type: ignore
            path, **kwargs
        )

    @staticmethod
    def isdir(path: str, **kwargs: Any) -> bool:
        """
        Checks if the resource at the given URI is a directory.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            bool: true if the path is a directory
        """
        return PathManager.__get_path_handler(path)._isdir(  # type: ignore
            path, **kwargs
        )

    @staticmethod
    def ls(path: str, **kwargs: Any) -> List[str]:
        """
        List the contents of the directory at the provided URI.
        Args:
            path (str): A URI supported by this PathHandler
        Returns:
            List[str]: list of contents in given path
        """
        return PathManager.__get_path_handler(path)._ls(  # type: ignore
            path, **kwargs
        )

    @staticmethod
    def mkdirs(path: str, **kwargs: Any) -> None:
        """
        Recursive directory creation function. Like mkdir(), but makes all
        intermediate-level directories needed to contain the leaf directory.
        Similar to the native `os.makedirs`.
        Args:
            path (str): A URI supported by this PathHandler
        """
        return PathManager.__get_path_handler(path)._mkdirs(  # type: ignore
            path, **kwargs
        )

    @staticmethod
    def rm(path: str, **kwargs: Any) -> None:
        """
        Remove the file (not directory) at the provided URI.
        Args:
            path (str): A URI supported by this PathHandler
        """
        return PathManager.__get_path_handler(path)._rm(  # type: ignore
            path, **kwargs
        )

    @staticmethod
    def register_handler(handler: PathHandler) -> None:
        """
        Register a path handler associated with `handler._get_supported_prefixes`
        URI prefixes.
        Args:
            handler (PathHandler)
        """
        assert isinstance(handler, PathHandler), handler
        for prefix in handler._get_supported_prefixes():
            assert prefix not in PathManager._PATH_HANDLERS
            PathManager._PATH_HANDLERS[prefix] = handler

        # Sort path handlers in reverse order so longer prefixes take priority,
        # eg: http://foo/bar before http://foo
        PathManager._PATH_HANDLERS = OrderedDict(
            sorted(
                PathManager._PATH_HANDLERS.items(),
                key=lambda t: t[0],
                reverse=True,
            )
        )

    @staticmethod
    def set_strict_kwargs_checking(enable: bool) -> None:
        """
        Toggles strict kwargs checking. If enabled, a ValueError is thrown if any
        unused parameters are passed to a PathHandler function. If disabled, only
        a warning is given.
        With a centralized file API, there's a tradeoff of convenience and
        correctness delegating arguments to the proper I/O layers. An underlying
        `PathHandler` may support custom arguments which should not be statically
        exposed on the `PathManager` function. For example, a custom `HTTPURLHandler`
        may want to expose a `cache_timeout` argument for `open()` which specifies
        how old a locally cached resource can be before it's refetched from the
        remote server. This argument would not make sense for a `NativePathHandler`.
        If strict kwargs checking is disabled, `cache_timeout` can be passed to
        `PathManager.open` which will forward the arguments to the underlying
        handler. By default, checking is enabled since it is innately unsafe:
        multiple `PathHandler`s could reuse arguments with different semantic
        meanings or types.
        Args:
            enable (bool)
        """
        PathManager._NATIVE_PATH_HANDLER._strict_kwargs_check = enable
        for handler in PathManager._PATH_HANDLERS.values():
            handler._strict_kwargs_check = enable