simple-cli.py

import sys
from inspect import signature, Signature, Parameter, BoundArguments, cleandoc
from argparse import ArgumentParser, RawTextHelpFormatter
from typing import TypeVar, Callable


F = TypeVar("F", bound=Callable[..., None])


class Commands:
    def __init__(self) -> None:
        self.parser = ArgumentParser(formatter_class=RawTextHelpFormatter)
        self.subparsers = self.parser.add_subparsers()
        self.parser.add_argument(
            "--debug", action="store_true", dest="_debug", default=False
        )

    def add(self, func: F) -> F:
        sig = signature(func)

        parser = self.subparsers.add_parser(
            name=func.__name__.replace("_", "-"),
            help=cleandoc(func.__doc__),
        )
        parser.set_defaults(_func=func)
        parser.set_defaults(_sig=sig)

        for i, param in enumerate(sig.parameters.values()):
            name = param.name
            flag = f"--{name.replace('_', '-')}"
            if param.kind == Parameter.VAR_POSITIONAL:
                parser.add_argument(name if i == 0 else flag, nargs="*", default=[])
            elif param.kind not in (
                Parameter.POSITIONAL_OR_KEYWORD,
                Parameter.KEYWORD_ONLY,
            ):
                raise TypeError(f"Unsupported parameter type {param.kind.description}")
            elif param.default is not Parameter.empty:
                if isinstance(param.default, bool):
                    parser.add_argument(
                        flag,
                        action=f"store_{str(not param.default).lower()}",
                        default=param.default,
                    )
                else:
                    parser.add_argument(flag, nargs="?", default=param.default)
            else:
                parser.add_argument(flag, nargs="?")

    def __call__(self):
        self.run(*sys.argv[1:])

    def run(self, *args: str) -> None:
        namespace = self.parser.parse_args(args)

        if not (hasattr(namespace, "_func") and hasattr(namespace, "_sig")):
            self.parser.print_help()
            return

        debug: bool = namespace._debug
        func: Callable[..., None] = namespace._func
        sig: Signature = namespace._sig

        bound = BoundArguments(sig, namespace.__dict__)

        try:
            func(*bound.args, **bound.kwargs)
        except Exception as error:
            if debug:
                raise
            print(error)
            print("Use --debug to see the a full traceback")