import os
import sys
import importlib.metadata
import argparse
import functools
import traceback
import contextlib
from io import StringIO
import json
import subprocess
import re
import tempfile
import email.parser
import pathlib

print_err = functools.partial(print, file=sys.stderr)

# Some valid Python version specifiers are not supported.
# Whitelist characters we can handle.
VERSION_RE = re.compile('[a-zA-Z0-9.-]+')


class EndPass(Exception):
    """End current pass of generating requirements"""


try:
    from packaging.requirements import Requirement, InvalidRequirement
    from packaging.utils import canonicalize_name
except ImportError as e:
    print_err('Import error:', e)
    # already echoed by the %pyproject_buildrequires macro
    sys.exit(0)

# uses packaging, needs to be imported after packaging is verified to be present
from pyproject_convert import convert


@contextlib.contextmanager
def hook_call():
    captured_out = StringIO()
    with contextlib.redirect_stdout(captured_out):
        yield
    for line in captured_out.getvalue().splitlines():
        print_err('HOOK STDOUT:', line)


class Requirements:
    """Requirement printer"""
    def __init__(self, get_installed_version, extras=None,
                 generate_extras=False, python3_pkgversion='3'):
        self.get_installed_version = get_installed_version
        self.extras = set()

        if extras:
            for extra in extras:
                self.add_extras(*extra.split(','))

        self.missing_requirements = False

        self.generate_extras = generate_extras
        self.python3_pkgversion = python3_pkgversion

    def add_extras(self, *extras):
        self.extras |= set(e.strip() for e in extras)

    @property
    def marker_envs(self):
        if self.extras:
            return [{'extra': e} for e in sorted(self.extras)]
        return [{'extra': ''}]

    def evaluate_all_environamnets(self, requirement):
        for marker_env in self.marker_envs:
            if requirement.marker.evaluate(environment=marker_env):
                return True
        return False

    def add(self, requirement_str, *, source=None):
        """Output a Python-style requirement string as RPM dep"""
        print_err(f'Handling {requirement_str} from {source}')

        try:
            requirement = Requirement(requirement_str)
        except InvalidRequirement as e:
            print_err(
                f'WARNING: Skipping invalid requirement: {requirement_str}\n'
                + f'    {e}',
            )
            return

        name = canonicalize_name(requirement.name)
        if (requirement.marker is not None and
                not self.evaluate_all_environamnets(requirement)):
            print_err(f'Ignoring alien requirement:', requirement_str)
            return

        try:
            # TODO: check if requirements with extras are satisfied
            installed = self.get_installed_version(requirement.name)
        except importlib.metadata.PackageNotFoundError:
            print_err(f'Requirement not satisfied: {requirement_str}')
            installed = None
        if installed and installed in requirement.specifier:
            print_err(f'Requirement satisfied: {requirement_str}')
            print_err(f'   (installed: {requirement.name} {installed})')
            if requirement.extras:
                print_err(f'   (extras are currently not checked)')
        else:
            self.missing_requirements = True

        if self.generate_extras:
            extra_names = [f'{name}[{extra.lower()}]' for extra in sorted(requirement.extras)]
        else:
            extra_names = []

        for name in [name] + extra_names:
            together = []
            for specifier in sorted(
                requirement.specifier,
                key=lambda s: (s.operator, s.version),
            ):
                if not VERSION_RE.fullmatch(str(specifier.version)):
                    raise ValueError(
                        f'Unknown character in version: {specifier.version}. '
                        + '(This is probably a bug in pyproject-rpm-macros.)',
                    )
                together.append(convert(python3dist(name, python3_pkgversion=self.python3_pkgversion),
                                        specifier.operator, specifier.version))
            if len(together) == 0:
                print(python3dist(name,
                                  python3_pkgversion=self.python3_pkgversion))
            elif len(together) == 1:
                print(together[0])
            else:
                print(f"({' with '.join(together)})")

    def check(self, *, source=None):
        """End current pass if any unsatisfied dependencies were output"""
        if self.missing_requirements:
            print_err(f'Exiting dependency generation pass: {source}')
            raise EndPass(source)

    def extend(self, requirement_strs, *, source=None):
        """add() several requirements"""
        for req_str in requirement_strs:
            self.add(req_str, source=source)


def get_backend(requirements):
    try:
        f = open('pyproject.toml')
    except FileNotFoundError:
        pyproject_data = {}
    else:
        try:
            # lazy import toml here, not needed without pyproject.toml
            import toml
        except ImportError as e:
            print_err('Import error:', e)
            # already echoed by the %pyproject_buildrequires macro
            sys.exit(0)
        with f:
            pyproject_data = toml.load(f)

    buildsystem_data = pyproject_data.get('build-system', {})
    requirements.extend(
        buildsystem_data.get('requires', ()),
        source='build-system.requires',
    )

    backend_name = buildsystem_data.get('build-backend')
    if not backend_name:
        # https://www.python.org/dev/peps/pep-0517/:
        # If the pyproject.toml file is absent, or the build-backend key is
        # missing, the source tree is not using this specification, and tools
        # should revert to the legacy behaviour of running setup.py
        # (either directly, or by implicitly invoking the [following] backend).
        backend_name = 'setuptools.build_meta:__legacy__'

        # Note: For projects without pyproject.toml, this was already echoed
        # by the %pyproject_buildrequires macro, but this also handles cases
        # with pyproject.toml without a specified build backend.
        # If the default requirements change, also change them in the macro!
        requirements.add('setuptools >= 40.8', source='default build backend')
        requirements.add('wheel', source='default build backend')

    requirements.check(source='build backend')

    backend_path = buildsystem_data.get('backend-path')
    if backend_path:
        # PEP 517 example shows the path as a list, but some projects don't follow that
        if isinstance(backend_path, str):
            backend_path = [backend_path]
        sys.path = backend_path + sys.path

    module_name, _, object_name = backend_name.partition(":")
    backend_module = importlib.import_module(module_name)

    if object_name:
        return getattr(backend_module, object_name)

    return backend_module


def generate_build_requirements(backend, requirements):
    get_requires = getattr(backend, 'get_requires_for_build_wheel', None)
    if get_requires:
        with hook_call():
            new_reqs = get_requires()
        requirements.extend(new_reqs, source='get_requires_for_build_wheel')
        requirements.check(source='get_requires_for_build_wheel')


def generate_run_requirements(backend, requirements):
    hook_name = 'prepare_metadata_for_build_wheel'
    prepare_metadata = getattr(backend, hook_name, None)
    if not prepare_metadata:
        raise ValueError(
            'build backend cannot provide build metadata '
            + '(incl. runtime requirements) before build'
        )
    with hook_call():
        dir_basename = prepare_metadata('.')
    with open(dir_basename + '/METADATA') as f:
        message = email.parser.Parser().parse(f, headersonly=True)
    for key in 'Requires', 'Requires-Dist':
        requires = message.get_all(key, ())
        requirements.extend(requires, source=f'wheel metadata: {key}')


def parse_requirements_lines(lines, path=None):
    packages = []
    for line in lines:
        line, _, comment = line.partition('#')
        if comment.startswith('egg='):
            # not a real comment
            # e.g. git+https://github.com/monty/spam.git@master#egg=spam&...
            egg, *_ = comment.strip().partition(' ')
            egg, *_ = egg.strip().partition('&')
            line = egg[4:]
        line = line.strip()
        if line.startswith('-r'):
            recursed_path = line[2:].strip()
            if path:
                recursed_path = path.parent / recursed_path
            with open(recursed_path) as f:
                packages.extend(parse_requirements_lines(f.read().splitlines(), recursed_path))
        elif line.startswith('-'):
            print_err(
                f'WARNING: Skipping dependency line: {line}\n'
                + f'    tox deps options other than -r are not supported (yet).',
            )
        elif line:
            packages.append(line)
    return packages


def generate_tox_requirements(toxenv, requirements):
    toxenv = ','.join(toxenv)
    requirements.add('tox-current-env >= 0.0.6', source='tox itself')
    requirements.check(source='tox itself')
    with tempfile.NamedTemporaryFile('r') as deps, \
        tempfile.NamedTemporaryFile('r') as extras, \
            tempfile.NamedTemporaryFile('r') as provision:
        r = subprocess.run(
            [sys.executable, '-m', 'tox',
             '--print-deps-to', deps.name,
             '--print-extras-to', extras.name,
             '--no-provision', provision.name,
             '-qre', toxenv],
            check=False,
            encoding='utf-8',
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
        )
        if r.stdout:
            print_err(r.stdout, end='')

        provision_content = provision.read()
        if provision_content and r.returncode != 0:
            provision_requires = json.loads(provision_content)
            if 'minversion' in provision_requires:
                requirements.add(f'tox >= {provision_requires["minversion"]}',
                                 source='tox provision (minversion)')
            if 'requires' in provision_requires:
                requirements.extend(provision_requires["requires"],
                                    source='tox provision (requires)')
            requirements.check(source='tox provision')  # this terminates the script
            raise RuntimeError(
                'Dependencies requested by tox provisioning appear installed, '
                'but tox disagreed.')
        else:
            r.check_returncode()

        deplines = deps.read().splitlines()
        packages = parse_requirements_lines(deplines)
        requirements.add_extras(*extras.read().splitlines())
        requirements.extend(packages,
                            source=f'tox --print-deps-only: {toxenv}')


def python3dist(name, op=None, version=None, python3_pkgversion="3"):
    prefix = f"python{python3_pkgversion}dist"

    if op is None:
        if version is not None:
            raise AssertionError('op and version go together')
        return f'{prefix}({name})'
    else:
        return f'{prefix}({name}) {op} {version}'


def generate_requires(
    *, include_runtime=False, toxenv=None, extras=None,
    get_installed_version=importlib.metadata.version,  # for dep injection
    generate_extras=False, python3_pkgversion="3", requirement_files=None, use_build_system=True
):
    """Generate the BuildRequires for the project in the current directory

    This is the main Python entry point.
    """
    requirements = Requirements(
        get_installed_version, extras=extras or [],
        generate_extras=generate_extras,
        python3_pkgversion=python3_pkgversion
    )

    try:
        if (include_runtime or toxenv) and not use_build_system:
            raise ValueError('-N option cannot be used in combination with -r, -e, -t, -x options')
        if requirement_files:
            for req_file in requirement_files:
                lines = req_file.read().splitlines()
                packages = parse_requirements_lines(lines, pathlib.Path(req_file.name))
                requirements.extend(packages,
                                    source=f'requirements file {req_file.name}')
            requirements.check(source='all requirement files')
        if use_build_system:
            backend = get_backend(requirements)
            generate_build_requirements(backend, requirements)
        if toxenv:
            include_runtime = True
            generate_tox_requirements(toxenv, requirements)
        if include_runtime:
            generate_run_requirements(backend, requirements)
    except EndPass:
        return


def main(argv):
    parser = argparse.ArgumentParser(
        description='Generate BuildRequires for a Python project.'
    )
    parser.add_argument(
        '-r', '--runtime', action='store_true',
        help='Generate run-time requirements',
    )
    parser.add_argument(
        '-e', '--toxenv', metavar='TOXENVS', action='append',
        help=('specify tox environments (comma separated and/or repeated)'
              '(implies --tox)'),
    )
    parser.add_argument(
        '-t', '--tox', action='store_true',
        help=('generate test tequirements from tox environment '
              '(implies --runtime)'),
    )
    parser.add_argument(
        '-x', '--extras', metavar='EXTRAS', action='append',
        help='comma separated list of "extras" for runtime requirements '
             '(e.g. -x testing,feature-x) (implies --runtime, can be repeated)',
    )
    parser.add_argument(
        '--generate-extras', action='store_true',
        help='Generate build requirements on Python Extras',
    )
    parser.add_argument(
        '-p', '--python3_pkgversion', metavar='PYTHON3_PKGVERSION',
        default="3", help=('Python version for pythonXdist()'
                           'or pythonX.Ydist() requirements'),
    )
    parser.add_argument(
        '-N', '--no-use-build-system', dest='use_build_system',
        action='store_false', help='Use -N to indicate that project does not use any build system',
    )
    parser.add_argument(
       'requirement_files', nargs='*', type=argparse.FileType('r'),
        help=('Add buildrequires from file'),
    )

    args = parser.parse_args(argv)

    if args.toxenv:
        args.tox = True

    if args.tox:
        args.runtime = True
        if not args.toxenv:
            _default = f'py{sys.version_info.major}{sys.version_info.minor}'
            args.toxenv = [os.getenv('RPM_TOXENV', _default)]

    if args.extras:
        args.runtime = True

    try:
        generate_requires(
            include_runtime=args.runtime,
            toxenv=args.toxenv,
            extras=args.extras,
            generate_extras=args.generate_extras,
            python3_pkgversion=args.python3_pkgversion,
            requirement_files=args.requirement_files,
            use_build_system=args.use_build_system,
        )
    except Exception:
        # Log the traceback explicitly (it's useful debug info)
        traceback.print_exc()
        exit(1)


if __name__ == '__main__':
    main(sys.argv[1:])