from __future__ import annotations

import sys
import unittest
from dataclasses import dataclass
from typing import Sequence


@dataclass(frozen=True)
class CliOptions:
    name: str = "world"
    count: int = 1
    verbose: bool = False


class CliError(ValueError):
    """Raised when command-line arguments are invalid."""


def usage(program: str) -> str:
    return (
        f"Usage: {program} [OPTIONS]\n\n"
        "Options:\n"
        "  -n, --name TEXT     Name to greet (default: world)\n"
        "  -c, --count NUMBER  Number of greetings (default: 1)\n"
        "  -v, --verbose       Print extra details\n"
        "  -h, --help          Show this help message\n"
        "      --self-test     Run built-in tests\n"
    )


def parse_args(argv: Sequence[str]) -> CliOptions:
    name = "world"
    count = 1
    verbose = False
    i = 0

    while i < len(argv):
        arg = argv[i]

        if arg in ("-h", "--help"):
            raise SystemExit(0)

        if arg in ("-v", "--verbose"):
            verbose = True
            i += 1
            continue

        if arg in ("-n", "--name", "-c", "--count"):
            if i + 1 >= len(argv):
                raise CliError(f"{arg} requires a value")

            value = argv[i + 1]
            if arg in ("-n", "--name"):
                if not value:
                    raise CliError("name cannot be empty")
                name = value
            else:
                try:
                    count = int(value)
                except ValueError as exc:
                    raise CliError("count must be an integer") from exc
                if count < 1:
                    raise CliError("count must be at least 1")

            i += 2
            continue

        raise CliError(f"unknown argument: {arg}")

    return CliOptions(name=name, count=count, verbose=verbose)


def main(argv: Sequence[str] | None = None) -> int:
    program = sys.argv[0]
    args = list(sys.argv[1:] if argv is None else argv)

    if any(arg in ("-h", "--help") for arg in args):
        print(usage(program))
        return 0

    try:
        options = parse_args(args)
    except CliError as exc:
        print(f"error: {exc}", file=sys.stderr)
        print(usage(program), file=sys.stderr)
        return 2

    # Keep output predictable so the CLI is easy to test and compose.
    if options.verbose:
        print(f"greeting {options.count} time(s) for {options.name!r}")

    for _ in range(options.count):
        print(f"Hello, {options.name}!")

    return 0


class ParseArgsTests(unittest.TestCase):
    def test_defaults(self) -> None:
        self.assertEqual(parse_args([]), CliOptions())

    def test_name_count_and_verbose(self) -> None:
        self.assertEqual(
            parse_args(["--name", "Ada", "--count", "2", "--verbose"]),
            CliOptions(name="Ada", count=2, verbose=True),
        )

    def test_rejects_bad_count(self) -> None:
        with self.assertRaises(CliError):
            parse_args(["--count", "0"])


if __name__ == "__main__":
    if "--self-test" in sys.argv[1:]:
        unittest.main(argv=[sys.argv[0]])
    raise SystemExit(main())