# Copyright © 2016-2020 Scott Stevenson <scott@stevenson.io>
#
# Permission to use, copy, modify, and/or distribute this software for
# any purpose with or without fee is hereby granted, provided that the
# above copyright notice and this permission notice appear in all
# copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
# WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
# AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
# DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
# PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
# TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
# PERFORMANCE OF THIS SOFTWARE.

"""XDG Base Directory Specification variables.

xdg_cache_home(), xdg_config_home(), and xdg_data_home() return
pathlib.Path objects containing the value of the environment variable
named XDG_CACHE_HOME, XDG_CONFIG_HOME, and XDG_DATA_HOME respectively,
or the default defined in the specification if the environment variable
is unset or empty.

xdg_config_dirs() and xdg_data_dirs() return a list of pathlib.Path
objects containing the value, split on colons, of the environment
variable named XDG_CONFIG_DIRS and XDG_DATA_DIRS respectively, or the
default defined in the specification if the environment variable is
unset or empty.

xdg_runtime_dir() returns a pathlib.Path object containing the value of
the XDG_RUNTIME_DIR environment variable, or None if the environment
variable is not set.

"""

# pylint: disable=fixme

import os
from pathlib import Path
from typing import List, Optional

__all__ = [
    "xdg_cache_home",
    "xdg_config_dirs",
    "xdg_config_home",
    "xdg_data_dirs",
    "xdg_data_home",
    "xdg_runtime_dir",
    "XDG_CACHE_HOME",
    "XDG_CONFIG_DIRS",
    "XDG_CONFIG_HOME",
    "XDG_DATA_DIRS",
    "XDG_DATA_HOME",
    "XDG_RUNTIME_DIR",
]


def _home_dir() -> Path:
    """Return a Path corresponding to the user's home directory."""
    return Path(os.path.expandvars("$HOME"))


def _path_from_env(variable: str, default: Path) -> Path:
    """Read an environment variable as a path.

    The environment variable with the specified name is read, and its
    value returned as a path. If the environment variable is not set, or
    set to the empty string, the default value is returned.

    Parameters
    ----------
    variable : str
        Name of the environment variable.
    default : Path
        Default value.

    Returns
    -------
    Path
        Value from environment or default.

    """
    # TODO(srstevenson): Use assignment expression in Python 3.8.
    value = os.environ.get(variable)
    if value:
        return Path(value)
    return default


def _paths_from_env(variable: str, default: List[Path]) -> List[Path]:
    """Read an environment variable as a list of paths.

    The environment variable with the specified name is read, and its
    value split on colons and returned as a list of paths. If the
    environment variable is not set, or set to the empty string, the
    default value is returned.

    Parameters
    ----------
    variable : str
        Name of the environment variable.
    default : List[Path]
        Default value.

    Returns
    -------
    List[Path]
        Value from environment or default.

    """
    # TODO(srstevenson): Use assignment expression in Python 3.8.
    value = os.environ.get(variable)
    if value:
        return [Path(path) for path in value.split(":")]
    return default


def xdg_cache_home() -> Path:
    """Return a Path corresponding to XDG_CACHE_HOME."""
    return _path_from_env("XDG_CACHE_HOME", _home_dir() / ".cache")


def xdg_config_dirs() -> List[Path]:
    """Return a list of Paths corresponding to XDG_CONFIG_DIRS."""
    return _paths_from_env("XDG_CONFIG_DIRS", [Path("/etc/xdg")])


def xdg_config_home() -> Path:
    """Return a Path corresponding to XDG_CONFIG_HOME."""
    return _path_from_env("XDG_CONFIG_HOME", _home_dir() / ".config")


def xdg_data_dirs() -> List[Path]:
    """Return a list of Paths corresponding to XDG_DATA_DIRS."""
    return _paths_from_env(
        "XDG_DATA_DIRS",
        [Path(path) for path in "/usr/local/share/:/usr/share/".split(":")],
    )


def xdg_data_home() -> Path:
    """Return a Path corresponding to XDG_DATA_HOME."""
    return _path_from_env("XDG_DATA_HOME", _home_dir() / ".local" / "share")


def xdg_runtime_dir() -> Optional[Path]:
    """Return a Path corresponding to XDG_RUNTIME_DIR.

    If the XDG_RUNTIME_DIR environment variable is not set, None will be
    returned as per the specification.

    """
    try:
        return Path(os.environ["XDG_RUNTIME_DIR"])
    except KeyError:
        return None


# The following variables are deprecated, but remain for backward compatibility.
XDG_CACHE_HOME = xdg_cache_home()
XDG_CONFIG_DIRS = xdg_config_dirs()
XDG_CONFIG_HOME = xdg_config_home()
XDG_DATA_DIRS = xdg_data_dirs()
XDG_DATA_HOME = xdg_data_home()
XDG_RUNTIME_DIR = xdg_runtime_dir()