from __future__ import annotations

import os
from collections import namedtuple
from typing import Any
from typing import List
from typing import Optional

from pip._internal.exceptions import InstallationError
from pip._internal.exceptions import InvalidPyProjectBuildRequires
from pip._internal.exceptions import MissingPyProjectBuildRequires
from pip._vendor import tomli
from pip._vendor.packaging.requirements import InvalidRequirement
from pip._vendor.packaging.requirements import Requirement


def _is_list_of_str(obj: Any) -> bool:
    return isinstance(obj, list) and all(isinstance(item, str) for item in obj)


def make_pyproject_path(unpacked_source_directory: str) -> str:
    return os.path.join(unpacked_source_directory, 'pyproject.toml')


BuildSystemDetails = namedtuple(
    'BuildSystemDetails', ['requires', 'backend', 'check', 'backend_path'],
)


def load_pyproject_toml(
    use_pep517: bool | None, pyproject_toml: str, setup_py: str, req_name: str,
) -> BuildSystemDetails | None:
    """Load the pyproject.toml file.

    Parameters:
        use_pep517 - Has the user requested PEP 517 processing? None
                     means the user hasn't explicitly specified.
        pyproject_toml - Location of the project's pyproject.toml file
        setup_py - Location of the project's setup.py file
        req_name - The name of the requirement we're processing (for
                   error reporting)

    Returns:
        None if we should use the legacy code path, otherwise a tuple
        (
            requirements from pyproject.toml,
            name of PEP 517 backend,
            requirements we should check are installed after setting
                up the build environment
            directory paths to import the backend from (backend-path),
                relative to the project root.
        )
    """
    has_pyproject = os.path.isfile(pyproject_toml)
    has_setup = os.path.isfile(setup_py)

    if not has_pyproject and not has_setup:
        raise InstallationError(
            f'{req_name} does not appear to be a Python project: '
            f"neither 'setup.py' nor 'pyproject.toml' found.",
        )

    if has_pyproject:
        with open(pyproject_toml, encoding='utf-8') as f:
            pp_toml = tomli.loads(f.read())
        build_system = pp_toml.get('build-system')
    else:
        build_system = None

    # The following cases must use PEP 517
    # We check for use_pep517 being non-None and falsey because that means
    # the user explicitly requested --no-use-pep517.  The value 0 as
    # opposed to False can occur when the value is provided via an
    # environment variable or config file option (due to the quirk of
    # strtobool() returning an integer in pip's configuration code).
    if has_pyproject and not has_setup:
        if use_pep517 is not None and not use_pep517:
            raise InstallationError(
                'Disabling PEP 517 processing is invalid: '
                'project does not have a setup.py',
            )
        use_pep517 = True
    elif build_system and 'build-backend' in build_system:
        if use_pep517 is not None and not use_pep517:
            raise InstallationError(
                'Disabling PEP 517 processing is invalid: '
                'project specifies a build backend of {} '
                'in pyproject.toml'.format(build_system['build-backend']),
            )
        use_pep517 = True

    # If we haven't worked out whether to use PEP 517 yet,
    # and the user hasn't explicitly stated a preference,
    # we do so if the project has a pyproject.toml file.
    elif use_pep517 is None:
        use_pep517 = has_pyproject

    # At this point, we know whether we're going to use PEP 517.
    assert use_pep517 is not None

    # If we're using the legacy code path, there is nothing further
    # for us to do here.
    if not use_pep517:
        return None

    if build_system is None:
        # Either the user has a pyproject.toml with no build-system
        # section, or the user has no pyproject.toml, but has opted in
        # explicitly via --use-pep517.
        # In the absence of any explicit backend specification, we
        # assume the setuptools backend that most closely emulates the
        # traditional direct setup.py execution, and require wheel and
        # a version of setuptools that supports that backend.

        build_system = {
            'requires': ['setuptools>=40.8.0', 'wheel'],
            'build-backend': 'setuptools.build_meta:__legacy__',
        }

    # If we're using PEP 517, we have build system information (either
    # from pyproject.toml, or defaulted by the code above).
    # Note that at this point, we do not know if the user has actually
    # specified a backend, though.
    assert build_system is not None

    # Ensure that the build-system section in pyproject.toml conforms
    # to PEP 518.

    # Specifying the build-system table but not the requires key is invalid
    if 'requires' not in build_system:
        raise MissingPyProjectBuildRequires(package=req_name)

    # Error out if requires is not a list of strings
    requires = build_system['requires']
    if not _is_list_of_str(requires):
        raise InvalidPyProjectBuildRequires(
            package=req_name,
            reason='It is not a list of strings.',
        )

    # Each requirement must be valid as per PEP 508
    for requirement in requires:
        try:
            Requirement(requirement)
        except InvalidRequirement as error:
            raise InvalidPyProjectBuildRequires(
                package=req_name,
                reason=f'It contains an invalid requirement: {requirement!r}',
            ) from error

    backend = build_system.get('build-backend')
    backend_path = build_system.get('backend-path', [])
    check: list[str] = []
    if backend is None:
        # If the user didn't specify a backend, we assume they want to use
        # the setuptools backend. But we can't be sure they have included
        # a version of setuptools which supplies the backend, or wheel
        # (which is needed by the backend) in their requirements. So we
        # make a note to check that those requirements are present once
        # we have set up the environment.
        # This is quite a lot of work to check for a very specific case. But
        # the problem is, that case is potentially quite common - projects that
        # adopted PEP 518 early for the ability to specify requirements to
        # execute setup.py, but never considered needing to mention the build
        # tools themselves. The original PEP 518 code had a similar check (but
        # implemented in a different way).
        backend = 'setuptools.build_meta:__legacy__'
        check = ['setuptools>=40.8.0', 'wheel']

    return BuildSystemDetails(requires, backend, check, backend_path)