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

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


@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, freeze_output, extras=''):
        self.installed_packages = {}
        for line in freeze_output.splitlines():
            line = line.strip()
            if line.startswith('#'):
                continue
            name, version = line.split('==')
            self.installed_packages[name.strip()] = Version(version)

        self.marker_env = {'extra': extras}

        self.missing_requirements = 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 requirement.marker.evaluate(environment=self.marker_env)
        ):
            print_err(f'Ignoring alien requirement:', requirement_str)
            return

        installed = self.installed_packages.get(requirement.name)
        if installed and installed in requirement.specifier:
            print_err(f'Requirement satisfied: {requirement_str}')
            print_err(f'   (installed: {requirement.name} {installed})')
        else:
            self.missing_requirements = True

        together = []
        for specifier in sorted(
            requirement.specifier,
            key=lambda s: (s.operator, s.version),
        ):
            version = canonicalize_version(specifier.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.)',
                )
            if specifier.operator == "!=":
                lower = python3dist(name, '<', version)
                higher = python3dist(name, '>', f'{version}.0')
                together.append(
                    f"({lower} or {higher})"
                )
            else:
                together.append(python3dist(name, specifier.operator, version))
        if len(together) == 0:
            print(python3dist(name))
        elif len(together) == 1:
            print(together[0])
        else:
            print(f"({' and '.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:
        with f:
            pyproject_data = pytoml.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:
        requirements.add("setuptools >= 40.8", source='default build backend')
        requirements.add("wheel", source='default build backend')

        backend_name = 'setuptools.build_meta'

    requirements.check(source='build backend')

    backend_path = buildsystem_data.get('backend-path')
    if backend_path:
        sys.path.insert(0, backend_path)

    return importlib.import_module(backend_name)


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')


def generate_run_requirements(backend, requirements):
    prepare_metadata = getattr(backend, "prepare_metadata_for_build_wheel", None)
    if not prepare_metadata:
        raise ValueError(
            'build backend cannot provide build metadata '
            + '(incl. runtime requirements) before buld'
        )
    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 python3dist(name, op=None, version=None):
    if op is None:
        if version is not None:
            raise AssertionError('op and version go together')
        return f'python3dist({name})'
    else:
        return f'python3dist({name}) {op} {version}'


def generate_requires(
    freeze_output, *, include_runtime=False, toxenv=None, extras='',
):
    requirements = Requirements(freeze_output, extras=extras)

    try:
        backend = get_backend(requirements)
        generate_build_requirements(backend, 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(
        '-t', '--toxenv', metavar='TOXENVS',
        help='generate test tequirements from tox environment '
            + '(not implemented; implies --runtime)',
    )
    parser.add_argument(
        '-x', '--extras', metavar='EXTRAS', default='',
        help='extra for runtime requirements (e.g. -x testing)',
        # XXX: a comma-separated list should be possible here
        #help='comma separated list of "extras" for runtime requirements '
        #    + '(e.g. -x testing,feature-x)',
    )

    args = parser.parse_args(argv)
    if args.toxenv:
        args.runtime = True
        print_err('-t (--toxenv) is not implemented')
        exit(1)
    if args.extras and not args.runtime:
        print_err('-x (--extras) are only useful with -r (--runtime)')
        exit(1)

    freeze_output = subprocess.run(
        [sys.executable, '-I', '-m', 'pip', 'freeze', '--all'],
        encoding='utf-8',
        stdout=subprocess.PIPE,
        check=True,
    ).stdout

    try:
        generate_requires(
            freeze_output,
            include_runtime=args.runtime,
            extras=args.extras,
        )
    except Exception as e:
        # Log the traceback explicitly (it's useful debug info)
        traceback.print_exc()
        exit(1)


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