from __future__ import annotations

import contextlib
import functools
import os
import sys
from collections.abc import Generator
from collections.abc import Sequence

import pre_commit.constants as C
from pre_commit import lang_base
from pre_commit.envcontext import envcontext
from pre_commit.envcontext import PatchesT
from pre_commit.envcontext import UNSET
from pre_commit.envcontext import Var
from pre_commit.parse_shebang import find_executable
from pre_commit.prefix import Prefix
from pre_commit.util import CalledProcessError
from pre_commit.util import cmd_output
from pre_commit.util import cmd_output_b
from pre_commit.util import win_exe

ENVIRONMENT_DIR = 'py_env'
run_hook = lang_base.basic_run_hook


@functools.cache
def _version_info(exe: str) -> str:
    prog = 'import sys;print(".".join(str(p) for p in sys.version_info))'
    try:
        return cmd_output(exe, '-S', '-c', prog)[1].strip()
    except CalledProcessError:
        return f'<<error retrieving version from {exe}>>'


def _read_pyvenv_cfg(filename: str) -> dict[str, str]:
    ret = {}
    with open(filename, encoding='UTF-8') as f:
        for line in f:
            try:
                k, v = line.split('=')
            except ValueError:  # blank line / comment / etc.
                continue
            else:
                ret[k.strip()] = v.strip()
    return ret


def bin_dir(venv: str) -> str:
    """On windows there's a different directory for the virtualenv"""
    bin_part = 'Scripts' if sys.platform == 'win32' else 'bin'
    return os.path.join(venv, bin_part)


def get_env_patch(venv: str) -> PatchesT:
    return (
        ('PIP_DISABLE_PIP_VERSION_CHECK', '1'),
        ('PYTHONHOME', UNSET),
        ('VIRTUAL_ENV', venv),
        ('PATH', (bin_dir(venv), os.pathsep, Var('PATH'))),
    )


def _find_by_py_launcher(
        version: str,
) -> str | None:  # pragma: no cover (windows only)
    if version.startswith('python'):
        num = version.removeprefix('python')
        cmd = ('py', f'-{num}', '-c', 'import sys; print(sys.executable)')
        env = dict(os.environ, PYTHONIOENCODING='UTF-8')
        try:
            return cmd_output(*cmd, env=env)[1].strip()
        except CalledProcessError:
            pass
    return None


def _impl_exe_name() -> str:
    if sys.implementation.name == 'cpython':  # pragma: cpython cover
        return 'python'
    else:  # pragma: cpython no cover
        return sys.implementation.name  # pypy mostly


def _find_by_sys_executable() -> str | None:
    def _norm(path: str) -> str | None:
        _, exe = os.path.split(path.lower())
        exe, _, _ = exe.partition('.exe')
        if exe not in {'python', 'pythonw'} and find_executable(exe):
            return exe
        return None

    # On linux, I see these common sys.executables:
    #
    # system `python`: /usr/bin/python -> python2.7
    # system `python2`: /usr/bin/python2 -> python2.7
    # virtualenv v: v/bin/python (will not return from this loop)
    # virtualenv v -ppython2: v/bin/python -> python2
    # virtualenv v -ppython2.7: v/bin/python -> python2.7
    # virtualenv v -ppypy: v/bin/python -> v/bin/pypy
    for path in (sys.executable, os.path.realpath(sys.executable)):
        exe = _norm(path)
        if exe:
            return exe
    return None


@functools.lru_cache(maxsize=1)
def get_default_version() -> str:  # pragma: no cover (platform dependent)
    v_major = f'{sys.version_info[0]}'
    v_minor = f'{sys.version_info[0]}.{sys.version_info[1]}'

    # attempt the likely implementation exe
    for potential in (v_minor, v_major):
        exe = f'{_impl_exe_name()}{potential}'
        if find_executable(exe):
            return exe

    # next try `sys.executable` (or the realpath)
    maybe_exe = _find_by_sys_executable()
    if maybe_exe:
        return maybe_exe

    # maybe on windows we can find it via py launcher?
    if sys.platform == 'win32':  # pragma: win32 cover
        exe = f'python{v_minor}'
        if _find_by_py_launcher(exe):
            return exe

    # We tried!
    return C.DEFAULT


def _sys_executable_matches(version: str) -> bool:
    if version == 'python':
        return True
    elif not version.startswith('python'):
        return False

    try:
        info = tuple(int(p) for p in version.removeprefix('python').split('.'))
    except ValueError:
        return False

    return sys.version_info[:len(info)] == info


def norm_version(version: str) -> str | None:
    if version == C.DEFAULT:  # use virtualenv's default
        return None
    elif _sys_executable_matches(version):  # virtualenv defaults to our exe
        return None

    if sys.platform == 'win32':  # pragma: no cover (windows)
        version_exec = _find_by_py_launcher(version)
        if version_exec:
            return version_exec

        # Try looking up by name
        version_exec = find_executable(version)
        if version_exec and version_exec != version:
            return version_exec

    # Otherwise assume it is a path
    return os.path.expanduser(version)


@contextlib.contextmanager
def in_env(prefix: Prefix, version: str) -> Generator[None]:
    envdir = lang_base.environment_dir(prefix, ENVIRONMENT_DIR, version)
    with envcontext(get_env_patch(envdir)):
        yield


def health_check(prefix: Prefix, version: str) -> str | None:
    envdir = lang_base.environment_dir(prefix, ENVIRONMENT_DIR, version)
    pyvenv_cfg = os.path.join(envdir, 'pyvenv.cfg')

    # created with "old" virtualenv
    if not os.path.exists(pyvenv_cfg):
        return 'pyvenv.cfg does not exist (old virtualenv?)'

    exe_name = win_exe('python')
    py_exe = prefix.path(bin_dir(envdir), exe_name)
    cfg = _read_pyvenv_cfg(pyvenv_cfg)

    if 'version_info' not in cfg:
        return "created virtualenv's pyvenv.cfg is missing `version_info`"

    # always use uncached lookup here in case we replaced an unhealthy env
    virtualenv_version = _version_info.__wrapped__(py_exe)
    if virtualenv_version != cfg['version_info']:
        return (
            f'virtualenv python version did not match created version:\n'
            f'- actual version: {virtualenv_version}\n'
            f'- expected version: {cfg["version_info"]}\n'
        )

    # made with an older version of virtualenv? skip `base-executable` check
    if 'base-executable' not in cfg:
        return None

    base_exe_version = _version_info(cfg['base-executable'])
    if base_exe_version != cfg['version_info']:
        return (
            f'base executable python version does not match created version:\n'
            f'- base-executable version: {base_exe_version}\n'
            f'- expected version: {cfg["version_info"]}\n'
        )
    else:
        return None


def install_environment(
        prefix: Prefix,
        version: str,
        additional_dependencies: Sequence[str],
) -> None:
    envdir = lang_base.environment_dir(prefix, ENVIRONMENT_DIR, version)
    venv_cmd = [sys.executable, '-mvirtualenv', envdir]
    python = norm_version(version)
    if python is not None:
        venv_cmd.extend(('-p', python))
    install_cmd = ('python', '-mpip', 'install', '.', *additional_dependencies)

    cmd_output_b(*venv_cmd, cwd='/')
    with in_env(prefix, version):
        lang_base.setup_cmd(prefix, install_cmd)