import distutils.util  # FIXME: For change_root.
import logging
import os
import sys
import sysconfig
import typing

from pip._internal.exceptions import InvalidSchemeCombination, UserInstallationInvalid
from pip._internal.models.scheme import SCHEME_KEYS, Scheme
from pip._internal.utils.virtualenv import running_under_virtualenv

from .base import get_major_minor_version

logger = logging.getLogger(__name__)


# Notes on _infer_* functions.
# Unfortunately ``_get_default_scheme()`` is private, so there's no way to
# ask things like "what is the '_prefix' scheme on this platform". These
# functions try to answer that with some heuristics while accounting for ad-hoc
# platforms not covered by CPython's default sysconfig implementation. If the
# ad-hoc implementation does not fully implement sysconfig, we'll fall back to
# a POSIX scheme.

_AVAILABLE_SCHEMES = set(sysconfig.get_scheme_names())


def _infer_prefix():
    # type: () -> str
    """Try to find a prefix scheme for the current platform.

    This tries:

    * Implementation + OS, used by PyPy on Windows (``pypy_nt``).
    * Implementation without OS, used by PyPy on POSIX (``pypy``).
    * OS + "prefix", used by CPython on POSIX (``posix_prefix``).
    * Just the OS name, used by CPython on Windows (``nt``).

    If none of the above works, fall back to ``posix_prefix``.
    """
    implementation_suffixed = f"{sys.implementation.name}_{os.name}"
    if implementation_suffixed in _AVAILABLE_SCHEMES:
        return implementation_suffixed
    if sys.implementation.name in _AVAILABLE_SCHEMES:
        return sys.implementation.name
    suffixed = f"{os.name}_prefix"
    if suffixed in _AVAILABLE_SCHEMES:
        return suffixed
    if os.name in _AVAILABLE_SCHEMES:  # On Windows, prefx is just called "nt".
        return os.name
    return "posix_prefix"


def _infer_user():
    # type: () -> str
    """Try to find a user scheme for the current platform."""
    suffixed = f"{os.name}_user"
    if suffixed in _AVAILABLE_SCHEMES:
        return suffixed
    if "posix_user" not in _AVAILABLE_SCHEMES:  # User scheme unavailable.
        raise UserInstallationInvalid()
    return "posix_user"


def _infer_home():
    # type: () -> str
    """Try to find a home for the current platform."""
    suffixed = f"{os.name}_home"
    if suffixed in _AVAILABLE_SCHEMES:
        return suffixed
    return "posix_home"


# Update these keys if the user sets a custom home.
_HOME_KEYS = [
    "installed_base",
    "base",
    "installed_platbase",
    "platbase",
    "prefix",
    "exec_prefix",
]
if sysconfig.get_config_var("userbase") is not None:
    _HOME_KEYS.append("userbase")


def get_scheme(
    dist_name,  # type: str
    user=False,  # type: bool
    home=None,  # type: typing.Optional[str]
    root=None,  # type: typing.Optional[str]
    isolated=False,  # type: bool
    prefix=None,  # type: typing.Optional[str]
):
    # type: (...) -> Scheme
    """
    Get the "scheme" corresponding to the input parameters.

    :param dist_name: the name of the package to retrieve the scheme for, used
        in the headers scheme path
    :param user: indicates to use the "user" scheme
    :param home: indicates to use the "home" scheme
    :param root: root under which other directories are re-based
    :param isolated: ignored, but kept for distutils compatibility (where
        this controls whether the user-site pydistutils.cfg is honored)
    :param prefix: indicates to use the "prefix" scheme and provides the
        base directory for the same
    """
    if user and prefix:
        raise InvalidSchemeCombination("--user", "--prefix")
    if home and prefix:
        raise InvalidSchemeCombination("--home", "--prefix")

    if home is not None:
        scheme_name = _infer_home()
    elif user:
        scheme_name = _infer_user()
    else:
        scheme_name = _infer_prefix()

    if home is not None:
        variables = {k: home for k in _HOME_KEYS}
    elif prefix is not None:
        variables = {k: prefix for k in _HOME_KEYS}
    else:
        variables = {}

    paths = sysconfig.get_paths(scheme=scheme_name, vars=variables)

    # Logic here is very arbitrary, we're doing it for compatibility, don't ask.
    # 1. Pip historically uses a special header path in virtual environments.
    # 2. If the distribution name is not known, distutils uses 'UNKNOWN'. We
    #    only do the same when not running in a virtual environment because
    #    pip's historical header path logic (see point 1) did not do this.
    if running_under_virtualenv():
        if user:
            base = variables.get("userbase", sys.prefix)
        else:
            base = variables.get("base", sys.prefix)
        python_xy = f"python{get_major_minor_version()}"
        paths["include"] = os.path.join(base, "include", "site", python_xy)
    elif not dist_name:
        dist_name = "UNKNOWN"

    scheme = Scheme(
        platlib=paths["platlib"],
        purelib=paths["purelib"],
        headers=os.path.join(paths["include"], dist_name),
        scripts=paths["scripts"],
        data=paths["data"],
    )
    if root is not None:
        for key in SCHEME_KEYS:
            value = distutils.util.change_root(root, getattr(scheme, key))
            setattr(scheme, key, value)
    return scheme


def get_bin_prefix():
    # type: () -> str
    # Forcing to use /usr/local/bin for standard macOS framework installs.
    if sys.platform[:6] == "darwin" and sys.prefix[:16] == "/System/Library/":
        return "/usr/local/bin"
    return sysconfig.get_paths()["scripts"]


def get_purelib():
    # type: () -> str
    return sysconfig.get_paths()["purelib"]


def get_platlib():
    # type: () -> str
    return sysconfig.get_paths()["platlib"]


def get_prefixed_libs(prefix):
    # type: (str) -> typing.Tuple[str, str]
    paths = sysconfig.get_paths(vars={"base": prefix, "platbase": prefix})
    return (paths["purelib"], paths["platlib"])
