import base64
import hashlib
import json
import os
import platform
import re
import shutil
import sys
import sysconfig
import warnings

from contextlib import contextmanager
from typing import Any
from typing import Dict
from typing import List
from typing import Optional
from typing import Tuple
from typing import Union

import tomlkit

from clikit.api.io import IO

from poetry.locations import CACHE_DIR
from poetry.poetry import Poetry
from poetry.semver import parse_constraint
from poetry.semver.version import Version
from poetry.utils._compat import CalledProcessError
from poetry.utils._compat import Path
from poetry.utils._compat import decode
from poetry.utils._compat import encode
from poetry.utils._compat import list_to_shell_command
from poetry.utils._compat import subprocess
from poetry.utils.toml_file import TomlFile
from poetry.version.markers import BaseMarker


GET_ENVIRONMENT_INFO = """\
import json
import os
import platform
import sys

if hasattr(sys, "implementation"):
    info = sys.implementation.version
    iver = "{0.major}.{0.minor}.{0.micro}".format(info)
    kind = info.releaselevel
    if kind != "final":
        iver += kind[0] + str(info.serial)

    implementation_name = sys.implementation.name
else:
    iver = "0"
    implementation_name = ""

env = {
    "implementation_name": implementation_name,
    "implementation_version": iver,
    "os_name": os.name,
    "platform_machine": platform.machine(),
    "platform_release": platform.release(),
    "platform_system": platform.system(),
    "platform_version": platform.version(),
    "python_full_version": platform.python_version(),
    "platform_python_implementation": platform.python_implementation(),
    "python_version": platform.python_version()[:3],
    "sys_platform": sys.platform,
    "version_info": tuple(sys.version_info),
}

print(json.dumps(env))
"""


GET_BASE_PREFIX = """\
import sys

if hasattr(sys, "real_prefix"):
    print(sys.real_prefix)
elif hasattr(sys, "base_prefix"):
    print(sys.base_prefix)
else:
    print(sys.prefix)
"""

GET_CONFIG_VAR = """\
import sysconfig

print(sysconfig.get_config_var("{config_var}")),
"""

GET_PYTHON_VERSION = """\
import sys

print('.'.join([str(s) for s in sys.version_info[:3]]))
"""

GET_SYS_PATH = """\
import json
import sys

print(json.dumps(sys.path))
"""

CREATE_VENV_COMMAND = """\
path = {!r}

try:
    from venv import EnvBuilder

    builder = EnvBuilder(with_pip=True)
    builder.create(path)
except ImportError:
    try:
        # We fallback on virtualenv for Python 2.7
        from virtualenv import create_environment

        create_environment(path)
    except ImportError:
        # since virtualenv>20 we have to use cli_run
        from virtualenv import cli_run

        cli_run([path])
"""


class EnvError(Exception):

    pass


class EnvCommandError(EnvError):
    def __init__(self, e, input=None):  # type: (CalledProcessError) -> None
        self.e = e

        message = "Command {} errored with the following return code {}, and output: \n{}".format(
            e.cmd, e.returncode, decode(e.output)
        )
        if input:
            message += "input was : {}".format(input)
        super(EnvCommandError, self).__init__(message)


class NoCompatiblePythonVersionFound(EnvError):
    def __init__(self, expected, given=None):
        if given:
            message = (
                "The specified Python version ({}) "
                "is not supported by the project ({}).\n"
                "Please choose a compatible version "
                "or loosen the python constraint specified "
                "in the pyproject.toml file.".format(given, expected)
            )
        else:
            message = (
                "Poetry was unable to find a compatible version. "
                "If you have one, you can explicitly use it "
                'via the "env use" command.'
            )

        super(NoCompatiblePythonVersionFound, self).__init__(message)


class EnvManager(object):
    """
    Environments manager
    """

    _env = None

    ENVS_FILE = "envs.toml"

    def __init__(self, poetry):  # type: (Poetry) -> None
        self._poetry = poetry

    def activate(self, python, io):  # type: (str, IO) -> Env
        venv_path = self._poetry.config.get("virtualenvs.path")
        if venv_path is None:
            venv_path = Path(CACHE_DIR) / "virtualenvs"
        else:
            venv_path = Path(venv_path)

        cwd = self._poetry.file.parent

        envs_file = TomlFile(venv_path / self.ENVS_FILE)

        try:
            python_version = Version.parse(python)
            python = "python{}".format(python_version.major)
            if python_version.precision > 1:
                python += ".{}".format(python_version.minor)
        except ValueError:
            # Executable in PATH or full executable path
            pass

        try:
            python_version = decode(
                subprocess.check_output(
                    list_to_shell_command(
                        [
                            python,
                            "-c",
                            "\"import sys; print('.'.join([str(s) for s in sys.version_info[:3]]))\"",
                        ]
                    ),
                    shell=True,
                )
            )
        except CalledProcessError as e:
            raise EnvCommandError(e)

        python_version = Version.parse(python_version.strip())
        minor = "{}.{}".format(python_version.major, python_version.minor)
        patch = python_version.text

        create = False
        is_root_venv = self._poetry.config.get("virtualenvs.in-project")
        # If we are required to create the virtual environment in the root folder,
        # create or recreate it if needed
        if is_root_venv:
            create = False
            venv = self._poetry.file.parent / ".venv"
            if venv.exists():
                # We need to check if the patch version is correct
                _venv = VirtualEnv(venv)
                current_patch = ".".join(str(v) for v in _venv.version_info[:3])

                if patch != current_patch:
                    create = True

            self.create_venv(io, executable=python, force=create)

            return self.get(reload=True)

        envs = tomlkit.document()
        base_env_name = self.generate_env_name(self._poetry.package.name, str(cwd))
        if envs_file.exists():
            envs = envs_file.read()
            current_env = envs.get(base_env_name)
            if current_env is not None:
                current_minor = current_env["minor"]
                current_patch = current_env["patch"]

                if current_minor == minor and current_patch != patch:
                    # We need to recreate
                    create = True

        name = "{}-py{}".format(base_env_name, minor)
        venv = venv_path / name

        # Create if needed
        if not venv.exists() or venv.exists() and create:
            in_venv = os.environ.get("VIRTUAL_ENV") is not None
            if in_venv or not venv.exists():
                create = True

            if venv.exists():
                # We need to check if the patch version is correct
                _venv = VirtualEnv(venv)
                current_patch = ".".join(str(v) for v in _venv.version_info[:3])

                if patch != current_patch:
                    create = True

            self.create_venv(io, executable=python, force=create)

        # Activate
        envs[base_env_name] = {"minor": minor, "patch": patch}
        envs_file.write(envs)

        return self.get(reload=True)

    def deactivate(self, io):  # type: (IO) -> None
        venv_path = self._poetry.config.get("virtualenvs.path")
        if venv_path is None:
            venv_path = Path(CACHE_DIR) / "virtualenvs"
        else:
            venv_path = Path(venv_path)

        name = self._poetry.package.name
        name = self.generate_env_name(name, str(self._poetry.file.parent))

        envs_file = TomlFile(venv_path / self.ENVS_FILE)
        if envs_file.exists():
            envs = envs_file.read()
            env = envs.get(name)
            if env is not None:
                io.write_line(
                    "Deactivating virtualenv: <comment>{}</comment>".format(
                        venv_path / (name + "-py{}".format(env["minor"]))
                    )
                )
                del envs[name]

                envs_file.write(envs)

    def get(self, reload=False):  # type: (bool) -> Env
        if self._env is not None and not reload:
            return self._env

        python_minor = ".".join([str(v) for v in sys.version_info[:2]])

        venv_path = self._poetry.config.get("virtualenvs.path")
        if venv_path is None:
            venv_path = Path(CACHE_DIR) / "virtualenvs"
        else:
            venv_path = Path(venv_path)

        cwd = self._poetry.file.parent
        envs_file = TomlFile(venv_path / self.ENVS_FILE)
        env = None
        base_env_name = self.generate_env_name(self._poetry.package.name, str(cwd))
        if envs_file.exists():
            envs = envs_file.read()
            env = envs.get(base_env_name)
            if env:
                python_minor = env["minor"]

        # Check if we are inside a virtualenv or not
        # Conda sets CONDA_PREFIX in its envs, see
        # https://github.com/conda/conda/issues/2764
        env_prefix = os.environ.get("VIRTUAL_ENV", os.environ.get("CONDA_PREFIX"))
        conda_env_name = os.environ.get("CONDA_DEFAULT_ENV")
        # It's probably not a good idea to pollute Conda's global "base" env, since
        # most users have it activated all the time.
        in_venv = env_prefix is not None and conda_env_name != "base"

        if not in_venv or env is not None:
            # Checking if a local virtualenv exists
            if (cwd / ".venv").exists() and (cwd / ".venv").is_dir():
                venv = cwd / ".venv"

                return VirtualEnv(venv)

            create_venv = self._poetry.config.get("virtualenvs.create", True)

            if not create_venv:
                return SystemEnv(Path(sys.prefix))

            venv_path = self._poetry.config.get("virtualenvs.path")
            if venv_path is None:
                venv_path = Path(CACHE_DIR) / "virtualenvs"
            else:
                venv_path = Path(venv_path)

            name = "{}-py{}".format(base_env_name, python_minor.strip())

            venv = venv_path / name

            if not venv.exists():
                return SystemEnv(Path(sys.prefix))

            return VirtualEnv(venv)

        if env_prefix is not None:
            prefix = Path(env_prefix)
            base_prefix = None
        else:
            prefix = Path(sys.prefix)
            base_prefix = self.get_base_prefix()

        return VirtualEnv(prefix, base_prefix)

    def list(self, name=None):  # type: (Optional[str]) -> List[VirtualEnv]
        if name is None:
            name = self._poetry.package.name

        venv_name = self.generate_env_name(name, str(self._poetry.file.parent))

        venv_path = self._poetry.config.get("virtualenvs.path")
        if venv_path is None:
            venv_path = Path(CACHE_DIR) / "virtualenvs"
        else:
            venv_path = Path(venv_path)

        env_list = [
            VirtualEnv(Path(p))
            for p in sorted(venv_path.glob("{}-py*".format(venv_name)))
        ]

        venv = self._poetry.file.parent / ".venv"
        if (
            self._poetry.config.get("virtualenvs.in-project")
            and venv.exists()
            and venv.is_dir()
        ):
            env_list.insert(0, VirtualEnv(venv))
        return env_list

    def remove(self, python):  # type: (str) -> Env
        venv_path = self._poetry.config.get("virtualenvs.path")
        if venv_path is None:
            venv_path = Path(CACHE_DIR) / "virtualenvs"
        else:
            venv_path = Path(venv_path)

        cwd = self._poetry.file.parent
        envs_file = TomlFile(venv_path / self.ENVS_FILE)
        base_env_name = self.generate_env_name(self._poetry.package.name, str(cwd))

        if python.startswith(base_env_name):
            venvs = self.list()
            for venv in venvs:
                if venv.path.name == python:
                    # Exact virtualenv name
                    if not envs_file.exists():
                        self.remove_venv(venv.path)

                        return venv

                    venv_minor = ".".join(str(v) for v in venv.version_info[:2])
                    base_env_name = self.generate_env_name(cwd.name, str(cwd))
                    envs = envs_file.read()

                    current_env = envs.get(base_env_name)
                    if not current_env:
                        self.remove_venv(venv.path)

                        return venv

                    if current_env["minor"] == venv_minor:
                        del envs[base_env_name]
                        envs_file.write(envs)

                    self.remove_venv(venv.path)

                    return venv

            raise ValueError(
                '<warning>Environment "{}" does not exist.</warning>'.format(python)
            )

        try:
            python_version = Version.parse(python)
            python = "python{}".format(python_version.major)
            if python_version.precision > 1:
                python += ".{}".format(python_version.minor)
        except ValueError:
            # Executable in PATH or full executable path
            pass

        try:
            python_version = decode(
                subprocess.check_output(
                    list_to_shell_command(
                        [
                            python,
                            "-c",
                            "\"import sys; print('.'.join([str(s) for s in sys.version_info[:3]]))\"",
                        ]
                    ),
                    shell=True,
                )
            )
        except CalledProcessError as e:
            raise EnvCommandError(e)

        python_version = Version.parse(python_version.strip())
        minor = "{}.{}".format(python_version.major, python_version.minor)

        name = "{}-py{}".format(base_env_name, minor)
        venv = venv_path / name

        if not venv.exists():
            raise ValueError(
                '<warning>Environment "{}" does not exist.</warning>'.format(name)
            )

        if envs_file.exists():
            envs = envs_file.read()
            current_env = envs.get(base_env_name)
            if current_env is not None:
                current_minor = current_env["minor"]

                if current_minor == minor:
                    del envs[base_env_name]
                    envs_file.write(envs)

        self.remove_venv(venv)

        return VirtualEnv(venv)

    def create_venv(
        self, io, name=None, executable=None, force=False
    ):  # type: (IO, Optional[str], Optional[str], bool) -> Env
        if self._env is not None and not force:
            return self._env

        cwd = self._poetry.file.parent
        env = self.get(reload=True)

        if not env.is_sane():
            force = True

        if env.is_venv() and not force:
            # Already inside a virtualenv.
            return env

        create_venv = self._poetry.config.get("virtualenvs.create")
        root_venv = self._poetry.config.get("virtualenvs.in-project")

        venv_path = self._poetry.config.get("virtualenvs.path")
        if root_venv:
            venv_path = cwd / ".venv"
        elif venv_path is None:
            venv_path = Path(CACHE_DIR) / "virtualenvs"
        else:
            venv_path = Path(venv_path)

        if not name:
            name = self._poetry.package.name

        python_patch = ".".join([str(v) for v in sys.version_info[:3]])
        python_minor = ".".join([str(v) for v in sys.version_info[:2]])
        if executable:
            python_patch = decode(
                subprocess.check_output(
                    list_to_shell_command(
                        [
                            executable,
                            "-c",
                            "\"import sys; print('.'.join([str(s) for s in sys.version_info[:3]]))\"",
                        ]
                    ),
                    shell=True,
                ).strip()
            )
            python_minor = ".".join(python_patch.split(".")[:2])

        supported_python = self._poetry.package.python_constraint
        if not supported_python.allows(Version.parse(python_patch)):
            # The currently activated or chosen Python version
            # is not compatible with the Python constraint specified
            # for the project.
            # If an executable has been specified, we stop there
            # and notify the user of the incompatibility.
            # Otherwise, we try to find a compatible Python version.
            if executable:
                raise NoCompatiblePythonVersionFound(
                    self._poetry.package.python_versions, python_patch
                )

            io.write_line(
                "<warning>The currently activated Python version {} "
                "is not supported by the project ({}).\n"
                "Trying to find and use a compatible version.</warning> ".format(
                    python_patch, self._poetry.package.python_versions
                )
            )

            for python_to_try in reversed(
                sorted(
                    self._poetry.package.AVAILABLE_PYTHONS,
                    key=lambda v: (v.startswith("3"), -len(v), v),
                )
            ):
                if len(python_to_try) == 1:
                    if not parse_constraint("^{}.0".format(python_to_try)).allows_any(
                        supported_python
                    ):
                        continue
                elif not supported_python.allows_all(
                    parse_constraint(python_to_try + ".*")
                ):
                    continue

                python = "python" + python_to_try

                if io.is_debug():
                    io.write_line("<debug>Trying {}</debug>".format(python))

                try:
                    python_patch = decode(
                        subprocess.check_output(
                            list_to_shell_command(
                                [
                                    python,
                                    "-c",
                                    "\"import sys; print('.'.join([str(s) for s in sys.version_info[:3]]))\"",
                                ]
                            ),
                            stderr=subprocess.STDOUT,
                            shell=True,
                        ).strip()
                    )
                except CalledProcessError:
                    continue

                if not python_patch:
                    continue

                if supported_python.allows(Version.parse(python_patch)):
                    io.write_line("Using <c1>{}</c1> ({})".format(python, python_patch))
                    executable = python
                    python_minor = ".".join(python_patch.split(".")[:2])
                    break

            if not executable:
                raise NoCompatiblePythonVersionFound(
                    self._poetry.package.python_versions
                )

        if root_venv:
            venv = venv_path
        else:
            name = self.generate_env_name(name, str(cwd))
            name = "{}-py{}".format(name, python_minor.strip())
            venv = venv_path / name

        if not venv.exists():
            if create_venv is False:
                io.write_line(
                    "<fg=black;bg=yellow>"
                    "Skipping virtualenv creation, "
                    "as specified in config file."
                    "</>"
                )

                return SystemEnv(Path(sys.prefix))

            io.write_line(
                "Creating virtualenv <c1>{}</> in {}".format(name, str(venv_path))
            )

            self.build_venv(venv, executable=executable)
        else:
            if force:
                if not env.is_sane():
                    io.write_line(
                        "<warning>The virtual environment found in {} seems to be broken.</warning>".format(
                            env.path
                        )
                    )
                io.write_line(
                    "Recreating virtualenv <c1>{}</> in {}".format(name, str(venv))
                )
                self.remove_venv(venv)
                self.build_venv(venv, executable=executable)
            elif io.is_very_verbose():
                io.write_line("Virtualenv <c1>{}</> already exists.".format(name))

        # venv detection:
        # stdlib venv may symlink sys.executable, so we can't use realpath.
        # but others can symlink *to* the venv Python,
        # so we can't just use sys.executable.
        # So we just check every item in the symlink tree (generally <= 3)
        p = os.path.normcase(sys.executable)
        paths = [p]
        while os.path.islink(p):
            p = os.path.normcase(os.path.join(os.path.dirname(p), os.readlink(p)))
            paths.append(p)

        p_venv = os.path.normcase(str(venv))
        if any(p.startswith(p_venv) for p in paths):
            # Running properly in the virtualenv, don't need to do anything
            return SystemEnv(Path(sys.prefix), self.get_base_prefix())

        return VirtualEnv(venv)

    @classmethod
    def build_venv(
        cls, path, executable=None
    ):  # type: (Union[Path,str], Optional[str]) -> ()
        if executable is not None:
            # Create virtualenv by using an external executable
            try:
                p = subprocess.Popen(
                    list_to_shell_command([executable, "-"]),
                    stdin=subprocess.PIPE,
                    shell=True,
                )
                p.communicate(encode(CREATE_VENV_COMMAND.format(path)))
            except CalledProcessError as e:
                raise EnvCommandError(e)

            return

        try:
            from venv import EnvBuilder

            # use the same defaults as python -m venv
            if os.name == "nt":
                use_symlinks = False
            else:
                use_symlinks = True

            builder = EnvBuilder(with_pip=True, symlinks=use_symlinks)
            builder.create(str(path))
        except ImportError:
            try:
                # We fallback on virtualenv for Python 2.7
                from virtualenv import create_environment

                create_environment(str(path))
            except ImportError:
                # since virtualenv>20 we have to use cli_run
                from virtualenv import cli_run

                cli_run([str(path)])

    @classmethod
    def remove_venv(cls, path):  # type: (Union[Path,str]) -> None
        if isinstance(path, str):
            path = Path(path)
        assert path.is_dir()
        try:
            shutil.rmtree(str(path))
            return
        except OSError as e:
            # Continue only if e.errno == 16
            if e.errno != 16:  # ERRNO 16: Device or resource busy
                raise e

        # Delete all files and folders but the toplevel one. This is because sometimes
        # the venv folder is mounted by the OS, such as in a docker volume. In such
        # cases, an attempt to delete the folder itself will result in an `OSError`.
        # See https://github.com/python-poetry/poetry/pull/2064
        for file_path in path.iterdir():
            if file_path.is_file() or file_path.is_symlink():
                file_path.unlink()
            elif file_path.is_dir():
                shutil.rmtree(str(file_path))

    def get_base_prefix(self):  # type: () -> Path
        if hasattr(sys, "real_prefix"):
            return sys.real_prefix

        if hasattr(sys, "base_prefix"):
            return sys.base_prefix

        return sys.prefix

    @classmethod
    def generate_env_name(cls, name, cwd):  # type: (str, str) -> str
        name = name.lower()
        sanitized_name = re.sub(r'[ $`!*@"\\\r\n\t]', "_", name)[:42]
        h = hashlib.sha256(encode(cwd)).digest()
        h = base64.urlsafe_b64encode(h).decode()[:8]

        return "{}-{}".format(sanitized_name, h)


class Env(object):
    """
    An abstract Python environment.
    """

    def __init__(self, path, base=None):  # type: (Path, Optional[Path]) -> None
        self._is_windows = sys.platform == "win32"

        self._path = path
        bin_dir = "bin" if not self._is_windows else "Scripts"
        self._bin_dir = self._path / bin_dir

        self._base = base or path

        self._marker_env = None
        self._pip_version = None
        self._site_packages = None

    @property
    def path(self):  # type: () -> Path
        return self._path

    @property
    def base(self):  # type: () -> Path
        return self._base

    @property
    def version_info(self):  # type: () -> Tuple[int]
        return tuple(self.marker_env["version_info"])

    @property
    def python_implementation(self):  # type: () -> str
        return self.marker_env["platform_python_implementation"]

    @property
    def python(self):  # type: () -> str
        """
        Path to current python executable
        """
        return self._bin("python")

    @property
    def marker_env(self):
        if self._marker_env is None:
            self._marker_env = self.get_marker_env()

        return self._marker_env

    @property
    def pip(self):  # type: () -> str
        """
        Path to current pip executable
        """
        return self._bin("pip")

    @property
    def platform(self):  # type: () -> str
        return sys.platform

    @property
    def os(self):  # type: () -> str
        return os.name

    @property
    def pip_version(self):
        if self._pip_version is None:
            self._pip_version = self.get_pip_version()

        return self._pip_version

    @property
    def site_packages(self):  # type: () -> Path
        if self._site_packages is None:
            site_packages = []
            dist_packages = []
            for entry in self.sys_path:
                entry = Path(entry)
                if entry.name == "site-packages":
                    site_packages.append(entry)
                elif entry.name == "dist-packages":
                    dist_packages.append(entry)

            if not site_packages and not dist_packages:
                raise RuntimeError("Unable to find the site-packages directory")

            if site_packages:
                self._site_packages = site_packages[0]
            else:
                self._site_packages = dist_packages[0]

        return self._site_packages

    @property
    def sys_path(self):  # type: () -> List[str]
        raise NotImplementedError()

    @classmethod
    def get_base_prefix(cls):  # type: () -> Path
        if hasattr(sys, "real_prefix"):
            return sys.real_prefix

        if hasattr(sys, "base_prefix"):
            return sys.base_prefix

        return sys.prefix

    def get_version_info(self):  # type: () -> Tuple[int]
        raise NotImplementedError()

    def get_python_implementation(self):  # type: () -> str
        raise NotImplementedError()

    def get_marker_env(self):  # type: () -> Dict[str, Any]
        raise NotImplementedError()

    def get_pip_command(self):  # type: () -> List[str]
        raise NotImplementedError()

    def config_var(self, var):  # type: (str) -> Any
        raise NotImplementedError()

    def get_pip_version(self):  # type: () -> Version
        raise NotImplementedError()

    def is_valid_for_marker(self, marker):  # type: (BaseMarker) -> bool
        return marker.validate(self.marker_env)

    def is_sane(self):  # type: () -> bool
        """
        Checks whether the current environment is sane or not.
        """
        return True

    def run(self, bin, *args, **kwargs):
        bin = self._bin(bin)
        cmd = [bin] + list(args)
        return self._run(cmd, **kwargs)

    def run_pip(self, *args, **kwargs):
        pip = self.get_pip_command()
        cmd = pip + list(args)
        return self._run(cmd, **kwargs)

    def _run(self, cmd, **kwargs):
        """
        Run a command inside the Python environment.
        """
        shell = kwargs.get("shell", False)
        call = kwargs.pop("call", False)
        input_ = kwargs.pop("input_", None)

        if shell:
            cmd = list_to_shell_command(cmd)
        try:
            if self._is_windows:
                kwargs["shell"] = True

            if input_:
                output = subprocess.run(
                    cmd,
                    stdout=subprocess.PIPE,
                    stderr=subprocess.STDOUT,
                    input=encode(input_),
                    check=True,
                    **kwargs
                ).stdout
            elif call:
                return subprocess.call(cmd, stderr=subprocess.STDOUT, **kwargs)
            else:
                output = subprocess.check_output(
                    cmd, stderr=subprocess.STDOUT, **kwargs
                )
        except CalledProcessError as e:
            raise EnvCommandError(e, input=input_)

        return decode(output)

    def execute(self, bin, *args, **kwargs):
        bin = self._bin(bin)

        if not self._is_windows:
            args = [bin] + list(args)
            if "env" in kwargs:
                return os.execvpe(bin, args, kwargs["env"])
            else:
                return os.execvp(bin, args)
        else:
            exe = subprocess.Popen([bin] + list(args), **kwargs)
            exe.communicate()
            return exe.returncode

    def is_venv(self):  # type: () -> bool
        raise NotImplementedError()

    def _bin(self, bin):  # type: (str) -> str
        """
        Return path to the given executable.
        """
        bin_path = (self._bin_dir / bin).with_suffix(".exe" if self._is_windows else "")
        if not bin_path.exists():
            # On Windows, some executables can be in the base path
            # This is especially true when installing Python with
            # the official installer, where python.exe will be at
            # the root of the env path.
            # This is an edge case and should not be encountered
            # in normal uses but this happens in the sonnet script
            # that creates a fake virtual environment pointing to
            # a base Python install.
            if self._is_windows:
                bin_path = (self._path / bin).with_suffix(".exe")
                if bin_path.exists():
                    return str(bin_path)

            return bin

        return str(bin_path)

    def __eq__(self, other):  # type: (Env) -> bool
        return other.__class__ == self.__class__ and other.path == self.path

    def __repr__(self):
        return '{}("{}")'.format(self.__class__.__name__, self._path)


class SystemEnv(Env):
    """
    A system (i.e. not a virtualenv) Python environment.
    """

    @property
    def sys_path(self):  # type: () -> List[str]
        return sys.path

    def get_version_info(self):  # type: () -> Tuple[int]
        return sys.version_info

    def get_python_implementation(self):  # type: () -> str
        return platform.python_implementation()

    def get_pip_command(self):  # type: () -> List[str]
        # If we're not in a venv, assume the interpreter we're running on
        # has a pip and use that
        return [sys.executable, "-m", "pip"]

    def get_marker_env(self):  # type: () -> Dict[str, Any]
        if hasattr(sys, "implementation"):
            info = sys.implementation.version
            iver = "{0.major}.{0.minor}.{0.micro}".format(info)
            kind = info.releaselevel
            if kind != "final":
                iver += kind[0] + str(info.serial)

            implementation_name = sys.implementation.name
        else:
            iver = "0"
            implementation_name = ""

        return {
            "implementation_name": implementation_name,
            "implementation_version": iver,
            "os_name": os.name,
            "platform_machine": platform.machine(),
            "platform_release": platform.release(),
            "platform_system": platform.system(),
            "platform_version": platform.version(),
            "python_full_version": platform.python_version(),
            "platform_python_implementation": platform.python_implementation(),
            "python_version": platform.python_version()[:3],
            "sys_platform": sys.platform,
            "version_info": sys.version_info,
        }

    def config_var(self, var):  # type: (str) -> Any
        try:
            return sysconfig.get_config_var(var)
        except IOError as e:
            warnings.warn("{0}".format(e), RuntimeWarning)

            return

    def get_pip_version(self):  # type: () -> Version
        from pip import __version__

        return Version.parse(__version__)

    def is_venv(self):  # type: () -> bool
        return self._path != self._base


class VirtualEnv(Env):
    """
    A virtual Python environment.
    """

    def __init__(self, path, base=None):  # type: (Path, Optional[Path]) -> None
        super(VirtualEnv, self).__init__(path, base)

        # If base is None, it probably means this is
        # a virtualenv created from VIRTUAL_ENV.
        # In this case we need to get sys.base_prefix
        # from inside the virtualenv.
        if base is None:
            self._base = Path(self.run("python", "-", input_=GET_BASE_PREFIX).strip())

    @property
    def sys_path(self):  # type: () -> List[str]
        output = self.run("python", "-", input_=GET_SYS_PATH)

        return json.loads(output)

    def get_version_info(self):  # type: () -> Tuple[int]
        output = self.run("python", "-", input_=GET_PYTHON_VERSION)

        return tuple([int(s) for s in output.strip().split(".")])

    def get_python_implementation(self):  # type: () -> str
        return self.marker_env["platform_python_implementation"]

    def get_pip_command(self):  # type: () -> List[str]
        # We're in a virtualenv that is known to be sane,
        # so assume that we have a functional pip
        return [self._bin("pip")]

    def get_marker_env(self):  # type: () -> Dict[str, Any]
        output = self.run("python", "-", input_=GET_ENVIRONMENT_INFO)

        return json.loads(output)

    def config_var(self, var):  # type: (str) -> Any
        try:
            value = self.run(
                "python", "-", input_=GET_CONFIG_VAR.format(config_var=var)
            ).strip()
        except EnvCommandError as e:
            warnings.warn("{0}".format(e), RuntimeWarning)
            return None

        if value == "None":
            value = None
        elif value == "1":
            value = 1
        elif value == "0":
            value = 0

        return value

    def get_pip_version(self):  # type: () -> Version
        output = self.run_pip("--version").strip()
        m = re.match("pip (.+?)(?: from .+)?$", output)
        if not m:
            return Version.parse("0.0")

        return Version.parse(m.group(1))

    def is_venv(self):  # type: () -> bool
        return True

    def is_sane(self):
        # A virtualenv is considered sane if both "python" and "pip" exist.
        return os.path.exists(self._bin("python")) and os.path.exists(self._bin("pip"))

    def _run(self, cmd, **kwargs):
        with self.temp_environ():
            os.environ["PATH"] = self._updated_path()
            os.environ["VIRTUAL_ENV"] = str(self._path)

            self.unset_env("PYTHONHOME")
            self.unset_env("__PYVENV_LAUNCHER__")

            return super(VirtualEnv, self)._run(cmd, **kwargs)

    def execute(self, bin, *args, **kwargs):
        with self.temp_environ():
            os.environ["PATH"] = self._updated_path()
            os.environ["VIRTUAL_ENV"] = str(self._path)

            self.unset_env("PYTHONHOME")
            self.unset_env("__PYVENV_LAUNCHER__")

            return super(VirtualEnv, self).execute(bin, *args, **kwargs)

    @contextmanager
    def temp_environ(self):
        environ = dict(os.environ)
        try:
            yield
        finally:
            os.environ.clear()
            os.environ.update(environ)

    def unset_env(self, key):
        if key in os.environ:
            del os.environ[key]

    def _updated_path(self):
        return os.pathsep.join([str(self._bin_dir), os.environ["PATH"]])


class NullEnv(SystemEnv):
    def __init__(self, path=None, base=None, execute=False):
        if path is None:
            path = Path(sys.prefix)

        super(NullEnv, self).__init__(path, base=base)

        self._execute = execute
        self.executed = []

    def _run(self, cmd, **kwargs):
        self.executed.append(cmd)

        if self._execute:
            return super(NullEnv, self)._run(cmd, **kwargs)

    def execute(self, bin, *args, **kwargs):
        self.executed.append([bin] + list(args))

        if self._execute:
            return super(NullEnv, self).execute(bin, *args, **kwargs)

    def _bin(self, bin):
        return bin


class MockEnv(NullEnv):
    def __init__(
        self,
        version_info=(3, 7, 0),
        python_implementation="CPython",
        platform="darwin",
        os_name="posix",
        is_venv=False,
        pip_version="19.1",
        sys_path=None,
        config_vars=None,
        **kwargs
    ):
        super(MockEnv, self).__init__(**kwargs)

        self._version_info = version_info
        self._python_implementation = python_implementation
        self._platform = platform
        self._os_name = os_name
        self._is_venv = is_venv
        self._pip_version = Version.parse(pip_version)
        self._sys_path = sys_path
        self._config_vars = config_vars

    @property
    def version_info(self):  # type: () -> Tuple[int]
        return self._version_info

    @property
    def python_implementation(self):  # type: () -> str
        return self._python_implementation

    @property
    def platform(self):  # type: () -> str
        return self._platform

    @property
    def os(self):  # type: () -> str
        return self._os_name

    @property
    def pip_version(self):
        return self._pip_version

    @property
    def sys_path(self):
        if self._sys_path is None:
            return super(MockEnv, self).sys_path

        return self._sys_path

    def is_venv(self):  # type: () -> bool
        return self._is_venv

    def config_var(self, var):  # type: (str) -> Any
        if self._config_vars is None:
            return super().config_var(var)
        else:
            try:
                return self._config_vars[var]
            except KeyError:
                return None
