import contextlib
import os
import shutil
import sys
import traceback
from itertools import chain
from pathlib import Path
from typing import Generator, Mapping

from build import BuildBackendException, ConfigSettingsType, ProjectBuilder
from build.__main__ import (
    _STYLES,
    _error,
    _handle_build_error,
    _IsolatedEnvBuilder,
    _ProjectBuilder,
)
from build.env import IsolatedEnv
from packaging.requirements import Requirement

from .common import get_hostsitepackages, get_pyversion, get_unisolated_packages


def symlink_unisolated_packages(env: IsolatedEnv) -> None:
    pyversion = get_pyversion()
    site_packages_path = f"lib/{pyversion}/site-packages"
    env_site_packages = Path(env.path) / site_packages_path  # type: ignore[attr-defined]
    sysconfigdata_name = os.environ["SYSCONFIG_NAME"]
    sysconfigdata_path = (
        Path(os.environ["TARGETINSTALLDIR"]) / f"sysconfigdata/{sysconfigdata_name}.py"
    )
    shutil.copy(sysconfigdata_path, env_site_packages)
    host_site_packages = Path(get_hostsitepackages())
    for name in get_unisolated_packages():
        for path in chain(
            host_site_packages.glob(f"{name}*"), host_site_packages.glob(f"_{name}*")
        ):
            (env_site_packages / path.name).unlink(missing_ok=True)
            (env_site_packages / path.name).symlink_to(path)


def remove_unisolated_requirements(requires: set[str]) -> set[str]:
    for reqstr in list(requires):
        req = Requirement(reqstr)
        for avoid_name in get_unisolated_packages():
            if avoid_name in req.name.lower():
                requires.remove(reqstr)
    return requires


@contextlib.contextmanager
def replace_env(build_env: Mapping[str, str]) -> Generator[None, None, None]:
    old_environ = dict(os.environ)
    os.environ.clear()
    os.environ.update(build_env)
    try:
        yield
    finally:
        os.environ.clear()
        os.environ.update(old_environ)


def install_reqs(env: IsolatedEnv, reqs: set[str]) -> None:
    env.install(remove_unisolated_requirements(reqs))
    # Some packages (numcodecs) don't declare cython as a build dependency and
    # only recythonize if it is present. We need them to always recythonize so
    # we always install cython. If the reqs included some cython version already
    # then this won't do anything.
    env.install(["cython", "pythran"])


def _build_in_isolated_env(
    build_env: Mapping[str, str],
    builder: ProjectBuilder,
    outdir: str,
    distribution: str,
    config_settings: ConfigSettingsType,
) -> str:
    # For debugging: The following line disables removal of the isolated venv.
    # It will be left in the /tmp folder and can be inspected or entered as
    # needed.
    # _IsolatedEnvBuilder.__exit__ = lambda *args: None
    with _IsolatedEnvBuilder() as env:
        builder.python_executable = env.executable
        builder.scripts_dir = env.scripts_dir
        # first install the build dependencies
        symlink_unisolated_packages(env)
        install_reqs(env, builder.build_system_requires)
        installed_requires_for_build = False
        try:
            build_reqs = builder.get_requires_for_build(distribution, config_settings)
        except BuildBackendException:
            pass
        else:
            install_reqs(env, build_reqs)
            installed_requires_for_build = True

        with replace_env(build_env):
            if not installed_requires_for_build:
                install_reqs(
                    env, builder.get_requires_for_build(distribution, config_settings)
                )
            return builder.build(distribution, outdir, config_settings)


def parse_backend_flags(backend_flags: str) -> ConfigSettingsType:
    config_settings: dict[str, str | list[str]] = {}
    for arg in backend_flags.split():
        setting, _, value = arg.partition("=")
        if setting not in config_settings:
            config_settings[setting] = value
            continue

        cur_value = config_settings[setting]
        if isinstance(cur_value, str):
            config_settings[setting] = [cur_value, value]
        else:
            cur_value.append(value)
    return config_settings


def build(build_env: Mapping[str, str], backend_flags: str) -> None:
    srcdir = Path.cwd()
    outdir = srcdir / "dist"
    builder = _ProjectBuilder(str(srcdir))
    distribution = "wheel"
    config_settings = parse_backend_flags(backend_flags)
    try:
        with _handle_build_error():
            built = _build_in_isolated_env(
                build_env, builder, str(outdir), distribution, config_settings
            )
            print("{bold}{green}Successfully built {}{reset}".format(built, **_STYLES))
    except Exception as e:  # pragma: no cover
        tb = traceback.format_exc().strip("\n")
        print("\n{dim}{}{reset}\n".format(tb, **_STYLES))
        _error(str(e))
        sys.exit(1)