"""A PEP 517 interface to setuptools

Previously, when a user or a command line tool (let's call it a "frontend")
needed to make a request of setuptools to take a certain action, for
example, generating a list of installation requirements, the frontend would
would call "setup.py egg_info" or "setup.py bdist_wheel" on the command line.

PEP 517 defines a different method of interfacing with setuptools. Rather
than calling "setup.py" directly, the frontend should:

  1. Set the current directory to the directory with a setup.py file
  2. Import this module into a safe python interpreter (one in which
     setuptools can potentially set global variables or crash hard).
  3. Call one of the functions defined in PEP 517.

What each function does is defined in PEP 517. However, here is a "casual"
definition of the functions (this definition should not be relied on for
bug reports or API stability):

  - `build_wheel`: build a wheel in the folder and return the basename
  - `get_requires_for_build_wheel`: get the `setup_requires` to build
  - `prepare_metadata_for_build_wheel`: get the `install_requires`
  - `build_sdist`: build an sdist in the folder and return the basename
  - `get_requires_for_build_sdist`: get the `setup_requires` to build

Again, this is not a formal definition! Just a "taste" of the module.
"""

import os
import sys
import tokenize
import shutil
import contextlib

import setuptools
import distutils


class SetupRequirementsError(BaseException):
    def __init__(self, specifiers):
        self.specifiers = specifiers


class Distribution(setuptools.dist.Distribution):
    def fetch_build_eggs(self, specifiers):
        raise SetupRequirementsError(specifiers)

    @classmethod
    @contextlib.contextmanager
    def patch(cls):
        """
        Replace
        distutils.dist.Distribution with this class
        for the duration of this context.
        """
        orig = distutils.core.Distribution
        distutils.core.Distribution = cls
        try:
            yield
        finally:
            distutils.core.Distribution = orig


def _to_str(s):
    """
    Convert a filename to a string (on Python 2, explicitly
    a byte string, not Unicode) as distutils checks for the
    exact type str.
    """
    if sys.version_info[0] == 2 and not isinstance(s, str):
        # Assume it's Unicode, as that's what the PEP says
        # should be provided.
        return s.encode(sys.getfilesystemencoding())
    return s


def _run_setup(setup_script='setup.py'):
    # Note that we can reuse our build directory between calls
    # Correctness comes first, then optimization later
    __file__ = setup_script
    __name__ = '__main__'
    f = getattr(tokenize, 'open', open)(__file__)
    code = f.read().replace('\\r\\n', '\\n')
    f.close()
    exec(compile(code, __file__, 'exec'), locals())


def _fix_config(config_settings):
    config_settings = config_settings or {}
    config_settings.setdefault('--global-option', [])
    return config_settings


def _get_build_requires(config_settings, requirements):
    config_settings = _fix_config(config_settings)

    sys.argv = sys.argv[:1] + ['egg_info'] + \
        config_settings["--global-option"]
    try:
        with Distribution.patch():
            _run_setup()
    except SetupRequirementsError as e:
        requirements += e.specifiers

    return requirements


def _get_immediate_subdirectories(a_dir):
    return [name for name in os.listdir(a_dir)
            if os.path.isdir(os.path.join(a_dir, name))]


def get_requires_for_build_wheel(config_settings=None):
    config_settings = _fix_config(config_settings)
    return _get_build_requires(config_settings, requirements=['wheel'])


def get_requires_for_build_sdist(config_settings=None):
    config_settings = _fix_config(config_settings)
    return _get_build_requires(config_settings, requirements=[])


def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):
    sys.argv = sys.argv[:1] + ['dist_info', '--egg-base', _to_str(metadata_directory)]
    _run_setup()

    dist_info_directory = metadata_directory
    while True:
        dist_infos = [f for f in os.listdir(dist_info_directory)
                      if f.endswith('.dist-info')]

        if len(dist_infos) == 0 and \
                len(_get_immediate_subdirectories(dist_info_directory)) == 1:
            dist_info_directory = os.path.join(
                dist_info_directory, os.listdir(dist_info_directory)[0])
            continue

        assert len(dist_infos) == 1
        break

    # PEP 517 requires that the .dist-info directory be placed in the
    # metadata_directory. To comply, we MUST copy the directory to the root
    if dist_info_directory != metadata_directory:
        shutil.move(
            os.path.join(dist_info_directory, dist_infos[0]),
            metadata_directory)
        shutil.rmtree(dist_info_directory, ignore_errors=True)

    return dist_infos[0]


def _file_with_extension(directory, extension):
    matching = (
        f for f in os.listdir(directory)
        if f.endswith(extension)
    )
    file, = matching
    return file


def build_wheel(wheel_directory, config_settings=None,
                metadata_directory=None):
    config_settings = _fix_config(config_settings)
    wheel_directory = os.path.abspath(wheel_directory)
    sys.argv = sys.argv[:1] + ['bdist_wheel'] + \
        config_settings["--global-option"]
    _run_setup()
    if wheel_directory != 'dist':
        shutil.rmtree(wheel_directory)
        shutil.copytree('dist', wheel_directory)

    return _file_with_extension(wheel_directory, '.whl')


def build_sdist(sdist_directory, config_settings=None):
    config_settings = _fix_config(config_settings)
    sdist_directory = os.path.abspath(sdist_directory)
    sys.argv = sys.argv[:1] + ['sdist', '--formats', 'gztar'] + \
        config_settings["--global-option"] + \
        ["--dist-dir", sdist_directory]
    _run_setup()

    return _file_with_extension(sdist_directory, '.tar.gz')
