Add CommandArgumentParser and integrate argument parsing from cli and menu prompt

examples/simple.py

@@ -8,9 +8,9 @@ setup_logging()
 
 
 # A flaky async step that fails randomly
-async def flaky_step():
+async def flaky_step() -> str:
     await asyncio.sleep(0.2)
-    if random.random() < 0.5:
+    if random.random() < 0.3:
         raise RuntimeError("Random failure!")
     print("Flaky step succeeded!")
     return "ok"

falyx/argparse.py

@@ -0,0 +1,596 @@
+# Falyx CLI Framework — (c) 2025 rtj.dev LLC — MIT Licensed
+from copy import deepcopy
+from dataclasses import dataclass
+from enum import Enum
+from typing import Any, Iterable
+
+from rich.console import Console
+from rich.table import Table
+
+from falyx.exceptions import CommandArgumentError
+from falyx.signals import HelpSignal
+
+
+class ArgumentAction(Enum):
+    """Defines the action to be taken when the argument is encountered."""
+
+    STORE = "store"
+    STORE_TRUE = "store_true"
+    STORE_FALSE = "store_false"
+    APPEND = "append"
+    EXTEND = "extend"
+    COUNT = "count"
+    HELP = "help"
+
+
+@dataclass
+class Argument:
+    """Represents a command-line argument."""
+
+    flags: list[str]
+    dest: str  # Destination name for the argument
+    action: ArgumentAction = (
+        ArgumentAction.STORE
+    )  # Action to be taken when the argument is encountered
+    type: Any = str  # Type of the argument (e.g., str, int, float) or callable
+    default: Any = None  # Default value if the argument is not provided
+    choices: list[str] | None = None  # List of valid choices for the argument
+    required: bool = False  # True if the argument is required
+    help: str = ""  # Help text for the argument
+    nargs: int | str = 1  # int, '?', '*', '+'
+    positional: bool = False  # True if no leading - or -- in flags
+
+
+class CommandArgumentParser:
+    """
+    Custom argument parser for Falyx Commands.
+    It is used to create a command-line interface for Falyx
+    commands, allowing users to specify options and arguments
+    when executing commands.
+    It is not intended to be a full-featured replacement for
+    argparse, but rather a lightweight alternative for specific use
+    cases within the Falyx framework.
+
+    Features:
+    - Customizable argument parsing.
+    - Type coercion for arguments.
+    - Support for positional and keyword arguments.
+    - Support for default values.
+    - Support for boolean flags.
+    - Exception handling for invalid arguments.
+    - Render Help using Rich library.
+    """
+
+    def __init__(self) -> None:
+        """Initialize the CommandArgumentParser."""
+        self.command_description: str = ""
+        self._arguments: list[Argument] = []
+        self._flag_map: dict[str, Argument] = {}
+        self._dest_set: set[str] = set()
+        self._add_help()
+        self.console = Console(color_system="auto")
+
+    def _add_help(self):
+        """Add help argument to the parser."""
+        self.add_argument(
+            "--help",
+            "-h",
+            action=ArgumentAction.HELP,
+            help="Show this help message and exit.",
+            dest="help",
+        )
+
+    def _is_positional(self, flags: tuple[str, ...]) -> bool:
+        """Check if the flags are positional."""
+        positional = False
+        if any(not flag.startswith("-") for flag in flags):
+            positional = True
+
+        if positional and len(flags) > 1:
+            raise CommandArgumentError("Positional arguments cannot have multiple flags")
+        return positional
+
+    def _get_dest_from_flags(
+        self, flags: tuple[str, ...], dest: str | None
+    ) -> str | None:
+        """Convert flags to a destination name."""
+        if dest:
+            if not dest.replace("_", "").isalnum():
+                raise CommandArgumentError(
+                    "dest must be a valid identifier (letters, digits, and underscores only)"
+                )
+            if dest[0].isdigit():
+                raise CommandArgumentError("dest must not start with a digit")
+            return dest
+        dest = None
+        for flag in flags:
+            if flag.startswith("--"):
+                dest = flag.lstrip("-").replace("-", "_").lower()
+                break
+            elif flag.startswith("-"):
+                dest = flag.lstrip("-").replace("-", "_").lower()
+            else:
+                dest = flag.replace("-", "_").lower()
+        assert dest is not None, "dest should not be None"
+        if not dest.replace("_", "").isalnum():
+            raise CommandArgumentError(
+                "dest must be a valid identifier (letters, digits, and underscores only)"
+            )
+        if dest[0].isdigit():
+            raise CommandArgumentError("dest must not start with a digit")
+        return dest
+
+    def _determine_required(
+        self, required: bool, positional: bool, nargs: int | str
+    ) -> bool:
+        """Determine if the argument is required."""
+        if required:
+            return True
+        if positional:
+            if isinstance(nargs, int):
+                return nargs > 0
+            elif isinstance(nargs, str):
+                if nargs in ("+"):
+                    return True
+                elif nargs in ("*", "?"):
+                    return False
+                else:
+                    raise CommandArgumentError(f"Invalid nargs value: {nargs}")
+
+        return required
+
+    def _validate_nargs(self, nargs: int | str) -> int | str:
+        allowed_nargs = ("?", "*", "+")
+        if isinstance(nargs, int):
+            if nargs <= 0:
+                raise CommandArgumentError("nargs must be a positive integer")
+        elif isinstance(nargs, str):
+            if nargs not in allowed_nargs:
+                raise CommandArgumentError(f"Invalid nargs value: {nargs}")
+        else:
+            raise CommandArgumentError(f"nargs must be an int or one of {allowed_nargs}")
+        return nargs
+
+    def _normalize_choices(self, choices: Iterable, expected_type: Any) -> list[Any]:
+        if choices is not None:
+            if isinstance(choices, dict):
+                raise CommandArgumentError("choices cannot be a dict")
+            try:
+                choices = list(choices)
+            except TypeError:
+                raise CommandArgumentError(
+                    "choices must be iterable (like list, tuple, or set)"
+                )
+        else:
+            choices = []
+        for choice in choices:
+            if not isinstance(choice, expected_type):
+                try:
+                    expected_type(choice)
+                except Exception:
+                    raise CommandArgumentError(
+                        f"Invalid choice {choice!r}: not coercible to {expected_type.__name__}"
+                    )
+        return choices
+
+    def _validate_default_type(
+        self, default: Any, expected_type: type, dest: str
+    ) -> None:
+        """Validate the default value type."""
+        if default is not None and not isinstance(default, expected_type):
+            try:
+                expected_type(default)
+            except Exception:
+                raise CommandArgumentError(
+                    f"Default value {default!r} for '{dest}' cannot be coerced to {expected_type.__name__}"
+                )
+
+    def _validate_default_list_type(
+        self, default: list[Any], expected_type: type, dest: str
+    ) -> None:
+        if isinstance(default, list):
+            for item in default:
+                if not isinstance(item, expected_type):
+                    try:
+                        expected_type(item)
+                    except Exception:
+                        raise CommandArgumentError(
+                            f"Default list value {default!r} for '{dest}' cannot be coerced to {expected_type.__name__}"
+                        )
+
+    def _resolve_default(
+        self, action: ArgumentAction, default: Any, nargs: str | int
+    ) -> Any:
+        """Get the default value for the argument."""
+        if default is None:
+            if action == ArgumentAction.STORE_TRUE:
+                return False
+            elif action == ArgumentAction.STORE_FALSE:
+                return True
+            elif action == ArgumentAction.COUNT:
+                return 0
+            elif action in (ArgumentAction.APPEND, ArgumentAction.EXTEND):
+                return []
+            elif nargs in ("+", "*"):
+                return []
+            else:
+                return None
+        return default
+
+    def _validate_flags(self, flags: tuple[str, ...]) -> None:
+        """Validate the flags provided for the argument."""
+        if not flags:
+            raise CommandArgumentError("No flags provided")
+        for flag in flags:
+            if not isinstance(flag, str):
+                raise CommandArgumentError(f"Flag '{flag}' must be a string")
+            if flag.startswith("--") and len(flag) < 3:
+                raise CommandArgumentError(
+                    f"Flag '{flag}' must be at least 3 characters long"
+                )
+            if flag.startswith("-") and not flag.startswith("--") and len(flag) > 2:
+                raise CommandArgumentError(
+                    f"Flag '{flag}' must be a single character or start with '--'"
+                )
+
+    def add_argument(self, *flags, **kwargs):
+        """Add an argument to the parser.
+        Args:
+            name or flags: Either a name or prefixed flags (e.g. 'faylx', '-f', '--falyx').
+            action: The action to be taken when the argument is encountered.
+            nargs: The number of arguments expected.
+            default: The default value if the argument is not provided.
+            type: The type to which the command-line argument should be converted.
+            choices: A container of the allowable values for the argument.
+            required: Whether or not the argument is required.
+            help: A brief description of the argument.
+            dest: The name of the attribute to be added to the object returned by parse_args().
+        """
+        self._validate_flags(flags)
+        positional = self._is_positional(flags)
+        dest = self._get_dest_from_flags(flags, kwargs.get("dest"))
+        if dest in self._dest_set:
+            raise CommandArgumentError(
+                f"Destination '{dest}' is already defined.\n"
+                "Merging multiple arguments into the same dest (e.g. positional + flagged) "
+                "is not supported. Define a unique 'dest' for each argument."
+            )
+        self._dest_set.add(dest)
+        action = kwargs.get("action", ArgumentAction.STORE)
+        if not isinstance(action, ArgumentAction):
+            try:
+                action = ArgumentAction(action)
+            except ValueError:
+                raise CommandArgumentError(
+                    f"Invalid action '{action}' is not a valid ArgumentAction"
+                )
+        flags = list(flags)
+        nargs = self._validate_nargs(kwargs.get("nargs", 1))
+        default = self._resolve_default(action, kwargs.get("default"), nargs)
+        expected_type = kwargs.get("type", str)
+        if (
+            action in (ArgumentAction.STORE, ArgumentAction.APPEND, ArgumentAction.EXTEND)
+            and default is not None
+        ):
+            if isinstance(default, list):
+                self._validate_default_list_type(default, expected_type, dest)
+            else:
+                self._validate_default_type(default, expected_type, dest)
+        choices = self._normalize_choices(kwargs.get("choices"), expected_type)
+        if default is not None and choices and default not in choices:
+            raise CommandArgumentError(
+                f"Default value '{default}' not in allowed choices: {choices}"
+            )
+        required = self._determine_required(
+            kwargs.get("required", False), positional, nargs
+        )
+        argument = Argument(
+            flags=flags,
+            dest=dest,
+            action=action,
+            type=expected_type,
+            default=default,
+            choices=choices,
+            required=required,
+            help=kwargs.get("help", ""),
+            nargs=nargs,
+            positional=positional,
+        )
+        for flag in flags:
+            if flag in self._flag_map:
+                existing = self._flag_map[flag]
+                raise CommandArgumentError(
+                    f"Flag '{flag}' is already used by argument '{existing.dest}'"
+                )
+            self._flag_map[flag] = argument
+        self._arguments.append(argument)
+
+    def get_argument(self, dest: str) -> Argument | None:
+        return next((a for a in self._arguments if a.dest == dest), None)
+
+    def _consume_nargs(
+        self, args: list[str], start: int, spec: Argument
+    ) -> tuple[list[str], int]:
+        values = []
+        i = start
+        if isinstance(spec.nargs, int):
+            # assert i + spec.nargs <= len(
+            #     args
+            # ), "Not enough arguments provided: shouldn't happen"
+            values = args[i : i + spec.nargs]
+            return values, i + spec.nargs
+        elif spec.nargs == "+":
+            if i >= len(args):
+                raise CommandArgumentError(
+                    f"Expected at least one value for '{spec.dest}'"
+                )
+            while i < len(args) and not args[i].startswith("-"):
+                values.append(args[i])
+                i += 1
+            assert values, "Expected at least one value for '+' nargs: shouldn't happen"
+            return values, i
+        elif spec.nargs == "*":
+            while i < len(args) and not args[i].startswith("-"):
+                values.append(args[i])
+                i += 1
+            return values, i
+        elif spec.nargs == "?":
+            if i < len(args) and not args[i].startswith("-"):
+                return [args[i]], i + 1
+            return [], i
+        else:
+            assert False, "Invalid nargs value: shouldn't happen"
+
+    def _consume_all_positional_args(
+        self,
+        args: list[str],
+        result: dict[str, Any],
+        positional_args: list[Argument],
+        consumed_positional_indicies: set[int],
+    ) -> int:
+        remaining_positional_args = [
+            (j, spec)
+            for j, spec in enumerate(positional_args)
+            if j not in consumed_positional_indicies
+        ]
+        i = 0
+
+        for j, spec in remaining_positional_args:
+            # estimate how many args the remaining specs might need
+            is_last = j == len(positional_args) - 1
+            remaining = len(args) - i
+            min_required = 0
+            for next_spec in positional_args[j + 1 :]:
+                if isinstance(next_spec.nargs, int):
+                    min_required += next_spec.nargs
+                elif next_spec.nargs == "+":
+                    min_required += 1
+                elif next_spec.nargs == "?":
+                    min_required += 0
+                elif next_spec.nargs == "*":
+                    min_required += 0
+                else:
+                    assert False, "Invalid nargs value: shouldn't happen"
+
+            slice_args = args[i:] if is_last else args[i : i + (remaining - min_required)]
+            values, new_i = self._consume_nargs(slice_args, 0, spec)
+            i += new_i
+
+            try:
+                typed = [spec.type(v) for v in values]
+            except Exception:
+                raise CommandArgumentError(
+                    f"Invalid value for '{spec.dest}': expected {spec.type.__name__}"
+                )
+
+            if spec.action == ArgumentAction.APPEND:
+                assert result.get(spec.dest) is not None, "dest should not be None"
+                if spec.nargs in (None, 1):
+                    result[spec.dest].append(typed[0])
+                else:
+                    result[spec.dest].append(typed)
+            elif spec.action == ArgumentAction.EXTEND:
+                assert result.get(spec.dest) is not None, "dest should not be None"
+                result[spec.dest].extend(typed)
+            elif spec.nargs in (None, 1, "?"):
+                result[spec.dest] = typed[0] if len(typed) == 1 else typed
+            else:
+                result[spec.dest] = typed
+
+            if spec.nargs not in ("*", "+"):
+                consumed_positional_indicies.add(j)
+
+        if i < len(args):
+            raise CommandArgumentError(f"Unexpected positional argument: {args[i:]}")
+
+        return i
+
+    def parse_args(self, args: list[str] | None = None) -> dict[str, Any]:
+        """Parse Falyx Command arguments."""
+        if args is None:
+            args = []
+
+        result = {arg.dest: deepcopy(arg.default) for arg in self._arguments}
+        positional_args = [arg for arg in self._arguments if arg.positional]
+        consumed_positional_indices: set[int] = set()
+
+        consumed_indices: set[int] = set()
+        i = 0
+        while i < len(args):
+            token = args[i]
+            if token in self._flag_map:
+                spec = self._flag_map[token]
+                action = spec.action
+
+                if action == ArgumentAction.HELP:
+                    self.render_help()
+                    raise HelpSignal()
+                elif action == ArgumentAction.STORE_TRUE:
+                    result[spec.dest] = True
+                    consumed_indices.add(i)
+                    i += 1
+                elif action == ArgumentAction.STORE_FALSE:
+                    result[spec.dest] = False
+                    consumed_indices.add(i)
+                    i += 1
+                elif action == ArgumentAction.COUNT:
+                    result[spec.dest] = result.get(spec.dest, 0) + 1
+                    consumed_indices.add(i)
+                    i += 1
+                elif action == ArgumentAction.APPEND:
+                    assert result.get(spec.dest) is not None, "dest should not be None"
+                    values, new_i = self._consume_nargs(args, i + 1, spec)
+                    try:
+                        typed_values = [spec.type(value) for value in values]
+                    except ValueError:
+                        raise CommandArgumentError(
+                            f"Invalid value for '{spec.dest}': expected {spec.type.__name__}"
+                        )
+                    if spec.nargs in (None, 1):
+                        try:
+                            result[spec.dest].append(spec.type(values[0]))
+                        except ValueError:
+                            raise CommandArgumentError(
+                                f"Invalid value for '{spec.dest}': expected {spec.type.__name__}"
+                            )
+                    else:
+                        result[spec.dest].append(typed_values)
+                    consumed_indices.update(range(i, new_i))
+                    i = new_i
+                elif action == ArgumentAction.EXTEND:
+                    assert result.get(spec.dest) is not None, "dest should not be None"
+                    values, new_i = self._consume_nargs(args, i + 1, spec)
+                    try:
+                        typed_values = [spec.type(value) for value in values]
+                    except ValueError:
+                        raise CommandArgumentError(
+                            f"Invalid value for '{spec.dest}': expected {spec.type.__name__}"
+                        )
+                    result[spec.dest].extend(typed_values)
+                    consumed_indices.update(range(i, new_i))
+                    i = new_i
+                else:
+                    values, new_i = self._consume_nargs(args, i + 1, spec)
+                    try:
+                        typed_values = [spec.type(v) for v in values]
+                    except ValueError:
+                        raise CommandArgumentError(
+                            f"Invalid value for '{spec.dest}': expected {spec.type.__name__}"
+                        )
+                    if (
+                        spec.nargs in (None, 1, "?")
+                        and spec.action != ArgumentAction.APPEND
+                    ):
+                        result[spec.dest] = (
+                            typed_values[0] if len(typed_values) == 1 else typed_values
+                        )
+                    else:
+                        result[spec.dest] = typed_values
+                    consumed_indices.update(range(i, new_i))
+                    i = new_i
+            else:
+                # Get the next flagged argument index if it exists
+                next_flagged_index = -1
+                for index, arg in enumerate(args[i:], start=i):
+                    if arg.startswith("-"):
+                        next_flagged_index = index
+                        break
+                if next_flagged_index == -1:
+                    next_flagged_index = len(args)
+
+                args_consumed = self._consume_all_positional_args(
+                    args[i:next_flagged_index],
+                    result,
+                    positional_args,
+                    consumed_positional_indices,
+                )
+                i += args_consumed
+
+        # Required validation
+        for spec in self._arguments:
+            if spec.dest == "help":
+                continue
+            if spec.required and not result.get(spec.dest):
+                raise CommandArgumentError(f"Missing required argument: {spec.dest}")
+
+            if spec.choices and result.get(spec.dest) not in spec.choices:
+                raise CommandArgumentError(
+                    f"Invalid value for {spec.dest}: must be one of {spec.choices}"
+                )
+
+            if isinstance(spec.nargs, int) and spec.nargs > 1:
+                if not isinstance(result.get(spec.dest), list):
+                    raise CommandArgumentError(
+                        f"Invalid value for {spec.dest}: expected a list"
+                    )
+                if spec.action == ArgumentAction.APPEND:
+                    if not isinstance(result[spec.dest], list):
+                        raise CommandArgumentError(
+                            f"Invalid value for {spec.dest}: expected a list"
+                        )
+                    for group in result[spec.dest]:
+                        if len(group) % spec.nargs != 0:
+                            raise CommandArgumentError(
+                                f"Invalid number of values for {spec.dest}: expected a multiple of {spec.nargs}"
+                            )
+                elif spec.action == ArgumentAction.EXTEND:
+                    if not isinstance(result[spec.dest], list):
+                        raise CommandArgumentError(
+                            f"Invalid value for {spec.dest}: expected a list"
+                        )
+                    if len(result[spec.dest]) % spec.nargs != 0:
+                        raise CommandArgumentError(
+                            f"Invalid number of values for {spec.dest}: expected a multiple of {spec.nargs}"
+                        )
+                elif len(result[spec.dest]) != spec.nargs:
+                    raise CommandArgumentError(
+                        f"Invalid number of values for {spec.dest}: expected {spec.nargs}, got {len(result[spec.dest])}"
+                    )
+
+        result.pop("help", None)
+        return result
+
+    def parse_args_split(self, args: list[str]) -> tuple[tuple[Any, ...], dict[str, Any]]:
+        """
+        Returns:
+            tuple[args, kwargs] - Positional arguments in defined order,
+            followed by keyword argument mapping.
+        """
+        parsed = self.parse_args(args)
+        args_list = []
+        kwargs_dict = {}
+        for arg in self._arguments:
+            if arg.dest == "help":
+                continue
+            if arg.positional:
+                args_list.append(parsed[arg.dest])
+            else:
+                kwargs_dict[arg.dest] = parsed[arg.dest]
+        return tuple(args_list), kwargs_dict
+
+    def render_help(self):
+        table = Table(title=f"{self.command_description} Help")
+        table.add_column("Flags")
+        table.add_column("Help")
+        for arg in self._arguments:
+            if arg.dest == "help":
+                continue
+            flag_str = ", ".join(arg.flags) if not arg.positional else arg.dest
+            table.add_row(flag_str, arg.help or "")
+        table.add_section()
+        arg = self.get_argument("help")
+        flag_str = ", ".join(arg.flags) if not arg.positional else arg.dest
+        table.add_row(flag_str, arg.help or "")
+        self.console.print(table)
+
+    def __str__(self) -> str:
+        positional = sum(arg.positional for arg in self._arguments)
+        required = sum(arg.required for arg in self._arguments)
+        return (
+            f"CommandArgumentParser(args={len(self._arguments)}, "
+            f"flags={len(self._flag_map)}, dests={len(self._dest_set)}, "
+            f"required={required}, positional={positional})"
+        )
+
+    def __repr__(self) -> str:
+        return str(self)

falyx/command.py

@@ -18,6 +18,7 @@ in building robust interactive menus.
 """
 from __future__ import annotations
 
+import shlex
 from functools import cached_property
 from typing import Any, Callable
 
@@ -28,6 +29,7 @@ from rich.tree import Tree
 
 from falyx.action.action import Action, ActionGroup, BaseAction, ChainedAction
 from falyx.action.io_action import BaseIOAction
+from falyx.argparse import CommandArgumentParser
 from falyx.context import ExecutionContext
 from falyx.debug import register_debug_hooks
 from falyx.execution_registry import ExecutionRegistry as er
@@ -35,6 +37,7 @@ from falyx.hook_manager import HookManager, HookType
 from falyx.logger import logger
 from falyx.options_manager import OptionsManager
 from falyx.prompt_utils import confirm_async, should_prompt_user
+from falyx.protocols import ArgParserProtocol
 from falyx.retry import RetryPolicy
 from falyx.retry_utils import enable_retries_recursively
 from falyx.signals import CancelSignal
@@ -121,11 +124,24 @@ class Command(BaseModel):
     logging_hooks: bool = False
     requires_input: bool | None = None
     options_manager: OptionsManager = Field(default_factory=OptionsManager)
+    arg_parser: CommandArgumentParser = Field(default_factory=CommandArgumentParser)
+    custom_parser: ArgParserProtocol | None = None
+    custom_help: Callable[[], str | None] | None = None
 
     _context: ExecutionContext | None = PrivateAttr(default=None)
 
     model_config = ConfigDict(arbitrary_types_allowed=True)
 
+    def parse_args(self, raw_args: list[str] | str) -> tuple[tuple, dict]:
+        if self.custom_parser:
+            if isinstance(raw_args, str):
+                raw_args = shlex.split(raw_args)
+            return self.custom_parser(raw_args)
+
+        if isinstance(raw_args, str):
+            raw_args = shlex.split(raw_args)
+        return self.arg_parser.parse_args_split(raw_args)
+
     @field_validator("action", mode="before")
     @classmethod
     def wrap_callable_as_async(cls, action: Any) -> Any:
@@ -137,6 +153,9 @@ class Command(BaseModel):
 
     def model_post_init(self, _: Any) -> None:
         """Post-initialization to set up the action and hooks."""
+        if isinstance(self.arg_parser, CommandArgumentParser):
+            self.arg_parser.command_description = self.description
+
         if self.retry and isinstance(self.action, Action):
             self.action.enable_retry()
         elif self.retry_policy and isinstance(self.action, Action):
@@ -269,6 +288,18 @@ class Command(BaseModel):
         if self._context:
             self._context.log_summary()
 
+    def show_help(self) -> bool:
+        """Display the help message for the command."""
+        if self.custom_help:
+            output = self.custom_help()
+            if output:
+                console.print(output)
+            return True
+        if isinstance(self.arg_parser, CommandArgumentParser):
+            self.arg_parser.render_help()
+            return True
+        return False
+
     async def preview(self) -> None:
         label = f"[{OneColors.GREEN_b}]Command:[/] '{self.key}' — {self.description}"
 

falyx/exceptions.py

@@ -28,3 +28,7 @@ class CircuitBreakerOpen(FalyxError):
 
 class EmptyChainError(FalyxError):
     """Exception raised when the chain is empty."""
+
+
+class CommandArgumentError(FalyxError):
+    """Exception raised when there is an error in the command argument parser."""

falyx/falyx.py

@@ -23,6 +23,7 @@ from __future__ import annotations
 
 import asyncio
 import logging
+import shlex
 import sys
 from argparse import Namespace
 from difflib import get_close_matches
@@ -34,7 +35,8 @@ from prompt_toolkit import PromptSession
 from prompt_toolkit.completion import WordCompleter
 from prompt_toolkit.formatted_text import AnyFormattedText
 from prompt_toolkit.key_binding import KeyBindings
-from prompt_toolkit.validation import Validator
+from prompt_toolkit.patch_stdout import patch_stdout
+from prompt_toolkit.validation import ValidationError, Validator
 from rich import box
 from rich.console import Console
 from rich.markdown import Markdown
@@ -47,6 +49,7 @@ from falyx.context import ExecutionContext
 from falyx.debug import log_after, log_before, log_error, log_success
 from falyx.exceptions import (
     CommandAlreadyExistsError,
+    CommandArgumentError,
     FalyxError,
     InvalidActionError,
     NotAFalyxError,
@@ -57,19 +60,39 @@ from falyx.logger import logger
 from falyx.options_manager import OptionsManager
 from falyx.parsers import get_arg_parsers
 from falyx.retry import RetryPolicy
-from falyx.signals import BackSignal, CancelSignal, QuitSignal
+from falyx.signals import BackSignal, CancelSignal, HelpSignal, QuitSignal
 from falyx.themes import OneColors, get_nord_theme
 from falyx.utils import CaseInsensitiveDict, _noop, chunks, get_program_invocation
 from falyx.version import __version__
 
 
-class FalyxMode(str, Enum):
+class FalyxMode(Enum):
     MENU = "menu"
     RUN = "run"
     PREVIEW = "preview"
     RUN_ALL = "run-all"
 
 
+class CommandValidator(Validator):
+    """Validator to check if the input is a valid command or toggle key."""
+
+    def __init__(self, falyx: Falyx, error_message: str) -> None:
+        super().__init__()
+        self.falyx = falyx
+        self.error_message = error_message
+
+    def validate(self, document) -> None:
+        text = document.text
+        is_preview, choice, _, __ = self.falyx.get_command(text, from_validate=True)
+        if is_preview:
+            return None
+        if not choice:
+            raise ValidationError(
+                message=self.error_message,
+                cursor_position=document.get_end_of_document_position(),
+            )
+
+
 class Falyx:
     """
     Main menu controller for Falyx CLI applications.
@@ -325,7 +348,7 @@ class Falyx:
             keys.extend(cmd.aliases)
         return WordCompleter(keys, ignore_case=True)
 
-    def _get_validator(self) -> Validator:
+    def _get_validator_error_message(self) -> str:
         """Validator to check if the input is a valid command or toggle key."""
         keys = {self.exit_command.key.upper()}
         keys.update({alias.upper() for alias in self.exit_command.aliases})
@@ -354,18 +377,7 @@ class Falyx:
         if toggle_keys:
             message_lines.append(f"  Toggles: {toggles_str}")
         error_message = " ".join(message_lines)
-
+        return error_message
-        def validator(text):
-            is_preview, choice = self.get_command(text, from_validate=True)
-            if is_preview and choice is None:
-                return True
-            return bool(choice)
-
-        return Validator.from_callable(
-            validator,
-            error_message=error_message,
-            move_cursor_to_end=True,
-        )
 
     def _invalidate_prompt_session_cache(self):
         """Forces the prompt session to be recreated on the next access."""
@@ -428,9 +440,10 @@ class Falyx:
                 multiline=False,
                 completer=self._get_completer(),
                 reserve_space_for_menu=1,
-                validator=self._get_validator(),
+                validator=CommandValidator(self, self._get_validator_error_message()),
                 bottom_toolbar=self._get_bottom_bar_render(),
                 key_bindings=self.key_bindings,
+                validate_while_typing=False,
             )
         return self._prompt_session
 
@@ -694,32 +707,52 @@ class Falyx:
         return False, input_str.strip()
 
     def get_command(
-        self, choice: str, from_validate=False
+        self, raw_choices: str, from_validate=False
-    ) -> tuple[bool, Command | None]:
+    ) -> tuple[bool, Command | None, tuple, dict[str, Any]]:
         """
         Returns the selected command based on user input.
         Supports keys, aliases, and abbreviations.
         """
+        args = ()
+        kwargs: dict[str, Any] = {}
+        choice, *input_args = shlex.split(raw_choices)
         is_preview, choice = self.parse_preview_command(choice)
         if is_preview and not choice and self.help_command:
             is_preview = False
             choice = "?"
         elif is_preview and not choice:
+            # No help command enabled
             if not from_validate:
                 self.console.print(
                     f"[{OneColors.DARK_RED}]❌ You must enter a command for preview mode."
                 )
-            return is_preview, None
+            return is_preview, None, args, kwargs
 
         choice = choice.upper()
         name_map = self._name_map
-
         if choice in name_map:
-            return is_preview, name_map[choice]
+            if not from_validate:
+                logger.info("Command '%s' selected.", choice)
+            if input_args and name_map[choice].arg_parser:
+                try:
+                    args, kwargs = name_map[choice].parse_args(input_args)
+                except CommandArgumentError as error:
+                    if not from_validate:
+                        if not name_map[choice].show_help():
+                            self.console.print(
+                                f"[{OneColors.DARK_RED}]❌ Invalid arguments for '{choice}': {error}"
+                            )
+                    else:
+                        name_map[choice].show_help()
+                        raise ValidationError(
+                            message=str(error), cursor_position=len(raw_choices)
+                        )
+                    return is_preview, None, args, kwargs
+            return is_preview, name_map[choice], args, kwargs
 
         prefix_matches = [cmd for key, cmd in name_map.items() if key.startswith(choice)]
         if len(prefix_matches) == 1:
-            return is_preview, prefix_matches[0]
+            return is_preview, prefix_matches[0], args, kwargs
 
         fuzzy_matches = get_close_matches(choice, list(name_map.keys()), n=3, cutoff=0.7)
         if fuzzy_matches:
@@ -736,7 +769,7 @@ class Falyx:
                 self.console.print(
                     f"[{OneColors.LIGHT_YELLOW}]⚠️ Unknown command '{choice}'[/]"
                 )
-        return is_preview, None
+        return is_preview, None, args, kwargs
 
     def _create_context(self, selected_command: Command) -> ExecutionContext:
         """Creates a context dictionary for the selected command."""
@@ -759,8 +792,9 @@ class Falyx:
 
     async def process_command(self) -> bool:
         """Processes the action of the selected command."""
-        choice = await self.prompt_session.prompt_async()
+        with patch_stdout(raw=True):
-        is_preview, selected_command = self.get_command(choice)
+            choice = await self.prompt_session.prompt_async()
+        is_preview, selected_command, args, kwargs = self.get_command(choice)
         if not selected_command:
             logger.info("Invalid command '%s'.", choice)
             return True
@@ -789,8 +823,8 @@ class Falyx:
         context.start_timer()
         try:
             await self.hooks.trigger(HookType.BEFORE, context)
-
+            print(args, kwargs)
-            result = await selected_command()
+            result = await selected_command(*args, **kwargs)
             context.result = result
             await self.hooks.trigger(HookType.ON_SUCCESS, context)
         except Exception as error:
@@ -803,10 +837,18 @@ class Falyx:
             await self.hooks.trigger(HookType.ON_TEARDOWN, context)
         return True
 
-    async def run_key(self, command_key: str, return_context: bool = False) -> Any:
+    async def run_key(
+        self,
+        command_key: str,
+        return_context: bool = False,
+        args: tuple = (),
+        kwargs: dict[str, Any] | None = None,
+    ) -> Any:
         """Run a command by key without displaying the menu (non-interactive mode)."""
         self.debug_hooks()
-        is_preview, selected_command = self.get_command(command_key)
+        is_preview, selected_command, _, __ = self.get_command(command_key)
+        kwargs = kwargs or {}
+
         self.last_run_command = selected_command
 
         if not selected_command:
@@ -827,7 +869,7 @@ class Falyx:
         context.start_timer()
         try:
             await self.hooks.trigger(HookType.BEFORE, context)
-            result = await selected_command()
+            result = await selected_command(*args, **kwargs)
             context.result = result
 
             await self.hooks.trigger(HookType.ON_SUCCESS, context)
@@ -922,6 +964,8 @@ class Falyx:
                     logger.info("BackSignal received.")
                 except CancelSignal:
                     logger.info("CancelSignal received.")
+                except HelpSignal:
+                    logger.info("HelpSignal received.")
         finally:
             logger.info("Exiting menu: %s", self.get_title())
             if self.exit_message:
@@ -956,7 +1000,7 @@ class Falyx:
 
         if self.cli_args.command == "preview":
             self.mode = FalyxMode.PREVIEW
-            _, command = self.get_command(self.cli_args.name)
+            _, command, args, kwargs = self.get_command(self.cli_args.name)
             if not command:
                 self.console.print(
                     f"[{OneColors.DARK_RED}]❌ Command '{self.cli_args.name}' not found."
@@ -970,7 +1014,7 @@ class Falyx:
 
         if self.cli_args.command == "run":
             self.mode = FalyxMode.RUN
-            is_preview, command = self.get_command(self.cli_args.name)
+            is_preview, command, _, __ = self.get_command(self.cli_args.name)
             if is_preview:
                 if command is None:
                     sys.exit(1)
@@ -981,7 +1025,11 @@ class Falyx:
                 sys.exit(1)
             self._set_retry_policy(command)
             try:
-                await self.run_key(self.cli_args.name)
+                args, kwargs = command.parse_args(self.cli_args.command_args)
+            except HelpSignal:
+                sys.exit(0)
+            try:
+                await self.run_key(self.cli_args.name, args=args, kwargs=kwargs)
             except FalyxError as error:
                 self.console.print(f"[{OneColors.DARK_RED}]❌ Error: {error}[/]")
                 sys.exit(1)

falyx/parsers.py

@@ -2,7 +2,7 @@
 """parsers.py
 This module contains the argument parsers used for the Falyx CLI.
 """
-from argparse import ArgumentParser, Namespace, _SubParsersAction
+from argparse import REMAINDER, ArgumentParser, Namespace, _SubParsersAction
 from dataclasses import asdict, dataclass
 from typing import Any, Sequence
 
@@ -114,6 +114,12 @@ def get_arg_parsers(
         help="Skip confirmation prompts",
     )
 
+    run_group.add_argument(
+        "command_args",
+        nargs=REMAINDER,
+        help="Arguments to pass to the command (if applicable)",
+    )
+
     run_all_parser = subparsers.add_parser(
         "run-all", help="Run all commands with a given tag"
     )

falyx/protocols.py

@@ -2,10 +2,16 @@
 """protocols.py"""
 from __future__ import annotations
 
-from typing import Any, Awaitable, Protocol
+from typing import Any, Awaitable, Protocol, runtime_checkable
 
 from falyx.action.action import BaseAction
 
 
+@runtime_checkable
 class ActionFactoryProtocol(Protocol):
     async def __call__(self, *args: Any, **kwargs: Any) -> Awaitable[BaseAction]: ...
+
+
+@runtime_checkable
+class ArgParserProtocol(Protocol):
+    def __call__(self, args: list[str]) -> tuple[tuple, dict]: ...

falyx/signals.py

@@ -29,3 +29,10 @@ class CancelSignal(FlowSignal):
 
     def __init__(self, message: str = "Cancel signal received."):
         super().__init__(message)
+
+
+class HelpSignal(FlowSignal):
+    """Raised to display help information."""
+
+    def __init__(self, message: str = "Help signal received."):
+        super().__init__(message)

falyx/version.py

@@ -1 +1 @@
-__version__ = "0.1.27"
+__version__ = "0.1.28"

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "falyx"
-version = "0.1.27"
+version = "0.1.28"
 description = "Reliable and introspectable async CLI action framework."
 authors = ["Roland Thomas Jr <roland@rtj.dev>"]
 license = "MIT"

tests/test_command_argument_parser.py

@@ -0,0 +1,678 @@
+import pytest
+
+from falyx.argparse import ArgumentAction, CommandArgumentParser
+from falyx.exceptions import CommandArgumentError
+from falyx.signals import HelpSignal
+
+
+def build_parser_and_parse(args, config):
+    cap = CommandArgumentParser()
+    config(cap)
+    return cap.parse_args(args)
+
+
+def test_none():
+    def config(parser):
+        parser.add_argument("--foo", type=str)
+
+    parsed = build_parser_and_parse(None, config)
+    assert parsed["foo"] is None
+
+
+def test_append_multiple_flags():
+    def config(parser):
+        parser.add_argument("--tag", action=ArgumentAction.APPEND, type=str)
+
+    parsed = build_parser_and_parse(["--tag", "a", "--tag", "b", "--tag", "c"], config)
+    assert parsed["tag"] == ["a", "b", "c"]
+
+
+def test_positional_nargs_plus_and_single():
+    def config(parser):
+        parser.add_argument("files", nargs="+", type=str)
+        parser.add_argument("mode", nargs=1)
+
+    parsed = build_parser_and_parse(["a", "b", "c", "prod"], config)
+    assert parsed["files"] == ["a", "b", "c"]
+    assert parsed["mode"] == "prod"
+
+
+def test_type_validation_failure():
+    def config(parser):
+        parser.add_argument("--count", type=int)
+
+    with pytest.raises(CommandArgumentError):
+        build_parser_and_parse(["--count", "abc"], config)
+
+
+def test_required_field_missing():
+    def config(parser):
+        parser.add_argument("--env", type=str, required=True)
+
+    with pytest.raises(CommandArgumentError):
+        build_parser_and_parse([], config)
+
+
+def test_choices_enforced():
+    def config(parser):
+        parser.add_argument("--mode", choices=["dev", "prod"])
+
+    with pytest.raises(CommandArgumentError):
+        build_parser_and_parse(["--mode", "staging"], config)
+
+
+def test_boolean_flags():
+    def config(parser):
+        parser.add_argument("--debug", action=ArgumentAction.STORE_TRUE)
+        parser.add_argument("--no-debug", action=ArgumentAction.STORE_FALSE)
+
+    parsed = build_parser_and_parse(["--debug", "--no-debug"], config)
+    assert parsed["debug"] is True
+    assert parsed["no_debug"] is False
+    parsed = build_parser_and_parse([], config)
+    print(parsed)
+    assert parsed["debug"] is False
+    assert parsed["no_debug"] is True
+
+
+def test_count_action():
+    def config(parser):
+        parser.add_argument("-v", action=ArgumentAction.COUNT)
+
+    parsed = build_parser_and_parse(["-v", "-v", "-v"], config)
+    assert parsed["v"] == 3
+
+
+def test_nargs_star():
+    def config(parser):
+        parser.add_argument("args", nargs="*", type=str)
+
+    parsed = build_parser_and_parse(["one", "two", "three"], config)
+    assert parsed["args"] == ["one", "two", "three"]
+
+
+def test_flag_and_positional_mix():
+    def config(parser):
+        parser.add_argument("--env", type=str)
+        parser.add_argument("tasks", nargs="+")
+
+    parsed = build_parser_and_parse(["--env", "prod", "build", "test"], config)
+    assert parsed["env"] == "prod"
+    assert parsed["tasks"] == ["build", "test"]
+
+
+def test_duplicate_dest_fails():
+    parser = CommandArgumentParser()
+    parser.add_argument("--foo", dest="shared")
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("bar", dest="shared")
+
+
+def test_add_argument_positional_flag_conflict():
+    parser = CommandArgumentParser()
+
+    # ✅ Single positional argument should work
+    parser.add_argument("faylx")
+
+    # ❌ Multiple positional flags is invalid
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("falyx", "test")
+
+
+def test_add_argument_positional_and_flag_conflict():
+    parser = CommandArgumentParser()
+
+    # ❌ Cannot mix positional and optional in one declaration
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("faylx", "--falyx")
+
+
+def test_add_argument_multiple_optional_flags_same_dest():
+    parser = CommandArgumentParser()
+
+    # ✅ Valid: multiple flags for same dest
+    parser.add_argument("-f", "--falyx")
+    arg = parser._arguments[-1]
+    assert arg.dest == "falyx"
+    assert arg.flags == ["-f", "--falyx"]
+
+
+def test_add_argument_flag_dest_conflict():
+    parser = CommandArgumentParser()
+
+    # First one is fine
+    parser.add_argument("falyx")
+
+    # ❌ Cannot reuse dest name with another flag or positional
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--test", dest="falyx")
+
+
+def test_add_argument_flag_and_positional_conflict_dest_inference():
+    parser = CommandArgumentParser()
+
+    # ❌ "--falyx" and "falyx" result in dest conflict
+    parser.add_argument("--falyx")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("falyx")
+
+
+def test_add_argument_multiple_flags_custom_dest():
+    parser = CommandArgumentParser()
+
+    # ✅ Multiple flags with explicit dest
+    parser.add_argument("-f", "--falyx", "--test", dest="falyx")
+    arg = parser._arguments[-1]
+    assert arg.dest == "falyx"
+    assert arg.flags == ["-f", "--falyx", "--test"]
+
+
+def test_add_argument_multiple_flags_dest():
+    parser = CommandArgumentParser()
+
+    # ✅ Multiple flags with implicit dest first non -flag
+    parser.add_argument("-f", "--falyx", "--test")
+    arg = parser._arguments[-1]
+    assert arg.dest == "falyx"
+    assert arg.flags == ["-f", "--falyx", "--test"]
+
+
+def test_add_argument_single_flag_dest():
+    parser = CommandArgumentParser()
+
+    # ✅ Single flag with explicit dest
+    parser.add_argument("-f")
+    arg = parser._arguments[-1]
+    assert arg.dest == "f"
+    assert arg.flags == ["-f"]
+
+
+def test_add_argument_bad_dest():
+    parser = CommandArgumentParser()
+
+    # ❌ Invalid dest name
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", dest="1falyx")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", dest="falyx%")
+
+
+def test_add_argument_bad_flag():
+    parser = CommandArgumentParser()
+
+    # ❌ Invalid flag name
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--1falyx")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--!falyx")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("_")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument(None)
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument(0)
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("-")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("-asdf")
+
+
+def test_add_argument_duplicate_flags():
+    parser = CommandArgumentParser()
+
+    parser.add_argument("--falyx")
+
+    # ❌ Duplicate flag
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--test", "--falyx")
+
+    # ❌ Duplicate flag
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("falyx")
+
+
+def test_add_argument_no_flags():
+    parser = CommandArgumentParser()
+
+    # ❌ No flags provided
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument()
+
+
+def test_add_argument_default_value():
+    parser = CommandArgumentParser()
+
+    # ✅ Default value provided
+    parser.add_argument("--falyx", default="default_value")
+    arg = parser._arguments[-1]
+    assert arg.dest == "falyx"
+    assert arg.flags == ["--falyx"]
+    assert arg.default == "default_value"
+
+
+def test_add_argument_bad_default():
+    parser = CommandArgumentParser()
+
+    # ❌ Invalid default value
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", type=int, default="1falyx")
+
+
+def test_add_argument_bad_default_list():
+    parser = CommandArgumentParser()
+
+    # ❌ Invalid default value
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", type=int, default=["a", 2, 3])
+
+
+def test_add_argument_bad_action():
+    parser = CommandArgumentParser()
+
+    # ❌ Invalid action
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", action="invalid_action")
+
+    # ❌ Invalid action type
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", action=123)
+
+
+def test_add_argument_default_not_in_choices():
+    parser = CommandArgumentParser()
+
+    # ❌ Default value not in choices
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", choices=["a", "b"], default="c")
+
+
+def test_add_argument_choices():
+    parser = CommandArgumentParser()
+
+    # ✅ Choices provided
+    parser.add_argument("--falyx", choices=["a", "b", "c"])
+    arg = parser._arguments[-1]
+    assert arg.dest == "falyx"
+    assert arg.flags == ["--falyx"]
+    assert arg.choices == ["a", "b", "c"]
+
+    args = parser.parse_args(["--falyx", "a"])
+    assert args["falyx"] == "a"
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["--falyx", "d"])
+
+
+def test_add_argument_choices_invalid():
+    parser = CommandArgumentParser()
+
+    # ❌ Invalid choices
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", choices=["a", "b"], default="c")
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--bad", choices=123)
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--bad3", choices={1: "a", 2: "b"})
+
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--bad4", choices=["a", "b"], type=int)
+
+
+def test_add_argument_bad_nargs():
+    parser = CommandArgumentParser()
+
+    # ❌ Invalid nargs value
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", nargs="invalid")
+
+    # ❌ Invalid nargs type
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", nargs=123)
+
+    # ❌ Invalid nargs type
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("--falyx", nargs=None)
+
+
+def test_add_argument_nargs():
+    parser = CommandArgumentParser()
+    # ✅ Valid nargs value
+    parser.add_argument("--falyx", nargs=2)
+    arg = parser._arguments[-1]
+    assert arg.dest == "falyx"
+    assert arg.flags == ["--falyx"]
+    assert arg.nargs == 2
+
+
+def test_add_argument_valid_nargs():
+    # Valid nargs int, +, * and ?
+    parser = CommandArgumentParser()
+    parser.add_argument("--falyx", nargs="+")
+    arg = parser._arguments[-1]
+    assert arg.nargs == "+"
+
+    parser.add_argument("--test", nargs="*")
+    arg = parser._arguments[-1]
+    assert arg.nargs == "*"
+
+    parser.add_argument("--test2", nargs="?")
+    arg = parser._arguments[-1]
+    assert arg.nargs == "?"
+
+
+def test_get_argument():
+    parser = CommandArgumentParser()
+    parser.add_argument("--falyx", type=str, default="default_value")
+    arg = parser.get_argument("falyx")
+    assert arg.dest == "falyx"
+    assert arg.flags == ["--falyx"]
+    assert arg.default == "default_value"
+
+
+def test_parse_args_nargs():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs="+", type=str)
+    parser.add_argument("mode", nargs=1)
+
+    args = parser.parse_args(["a", "b", "c"])
+
+    assert args["files"] == ["a", "b"]
+    assert args["mode"] == "c"
+
+
+def test_parse_args_nargs_plus():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs="+", type=str)
+
+    args = parser.parse_args(["a", "b", "c"])
+    assert args["files"] == ["a", "b", "c"]
+
+    args = parser.parse_args(["a"])
+    assert args["files"] == ["a"]
+
+
+def test_parse_args_flagged_nargs_plus():
+    parser = CommandArgumentParser()
+    parser.add_argument("--files", nargs="+", type=str)
+
+    args = parser.parse_args(["--files", "a", "b", "c"])
+    assert args["files"] == ["a", "b", "c"]
+
+    args = parser.parse_args(["--files", "a"])
+    print(args)
+    assert args["files"] == ["a"]
+
+    args = parser.parse_args([])
+    assert args["files"] == []
+
+
+def test_parse_args_numbered_nargs():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs=2, type=str)
+
+    args = parser.parse_args(["a", "b"])
+    assert args["files"] == ["a", "b"]
+
+    with pytest.raises(CommandArgumentError):
+        args = parser.parse_args(["a"])
+        print(args)
+
+
+def test_parse_args_nargs_zero():
+    parser = CommandArgumentParser()
+    with pytest.raises(CommandArgumentError):
+        parser.add_argument("files", nargs=0, type=str)
+
+
+def test_parse_args_nargs_more_than_expected():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs=2, type=str)
+
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["a", "b", "c", "d"])
+
+
+def test_parse_args_nargs_one_or_none():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs="?", type=str)
+
+    args = parser.parse_args(["a"])
+    assert args["files"] == "a"
+
+    args = parser.parse_args([])
+    assert args["files"] is None
+
+
+def test_parse_args_nargs_positional():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs="*", type=str)
+
+    args = parser.parse_args(["a", "b", "c"])
+    assert args["files"] == ["a", "b", "c"]
+
+    args = parser.parse_args([])
+    assert args["files"] == []
+
+
+def test_parse_args_nargs_positional_plus():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs="+", type=str)
+
+    args = parser.parse_args(["a", "b", "c"])
+    assert args["files"] == ["a", "b", "c"]
+
+    with pytest.raises(CommandArgumentError):
+        args = parser.parse_args([])
+
+
+def test_parse_args_nargs_multiple_positional():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", nargs="+", type=str)
+    parser.add_argument("mode", nargs=1)
+    parser.add_argument("action", nargs="?")
+    parser.add_argument("target", nargs="*")
+    parser.add_argument("extra", nargs="+")
+
+    args = parser.parse_args(["a", "b", "c", "d", "e"])
+    assert args["files"] == ["a", "b", "c"]
+    assert args["mode"] == "d"
+    assert args["action"] == []
+    assert args["target"] == []
+    assert args["extra"] == ["e"]
+
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args([])
+
+
+def test_parse_args_nargs_invalid_positional_arguments():
+    parser = CommandArgumentParser()
+    parser.add_argument("numbers", nargs="*", type=int)
+    parser.add_argument("mode", nargs=1)
+
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["1", "2", "c", "d"])
+
+
+def test_parse_args_append():
+    parser = CommandArgumentParser()
+    parser.add_argument("--numbers", action=ArgumentAction.APPEND, type=int)
+
+    args = parser.parse_args(["--numbers", "1", "--numbers", "2", "--numbers", "3"])
+    assert args["numbers"] == [1, 2, 3]
+
+    args = parser.parse_args(["--numbers", "1"])
+    assert args["numbers"] == [1]
+
+    args = parser.parse_args([])
+    assert args["numbers"] == []
+
+
+def test_parse_args_nargs_append():
+    parser = CommandArgumentParser()
+    parser.add_argument("numbers", action=ArgumentAction.APPEND, type=int, nargs="*")
+    parser.add_argument("--mode")
+
+    args = parser.parse_args(["1", "2", "3", "--mode", "numbers", "4", "5"])
+    assert args["numbers"] == [[1, 2, 3], [4, 5]]
+
+    args = parser.parse_args(["1"])
+    assert args["numbers"] == [[1]]
+
+    args = parser.parse_args([])
+    assert args["numbers"] == []
+
+
+def test_parse_args_append_flagged_invalid_type():
+    parser = CommandArgumentParser()
+    parser.add_argument("--numbers", action=ArgumentAction.APPEND, type=int)
+
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["--numbers", "a"])
+
+
+def test_append_groups_nargs():
+    cap = CommandArgumentParser()
+    cap.add_argument("--item", action=ArgumentAction.APPEND, type=str, nargs=2)
+
+    parsed = cap.parse_args(["--item", "a", "b", "--item", "c", "d"])
+    assert parsed["item"] == [["a", "b"], ["c", "d"]]
+
+
+def test_extend_flattened():
+    cap = CommandArgumentParser()
+    cap.add_argument("--value", action=ArgumentAction.EXTEND, type=str)
+
+    parsed = cap.parse_args(["--value", "x", "--value", "y"])
+    assert parsed["value"] == ["x", "y"]
+
+
+def test_parse_args_split_order():
+    cap = CommandArgumentParser()
+    cap.add_argument("a")
+    cap.add_argument("--x")
+    cap.add_argument("b", nargs="*")
+    args, kwargs = cap.parse_args_split(["1", "--x", "100", "2"])
+    assert args == ("1", ["2"])
+    assert kwargs == {"x": "100"}
+
+
+def test_help_signal_triggers():
+    parser = CommandArgumentParser()
+    parser.add_argument("--foo")
+    with pytest.raises(HelpSignal):
+        parser.parse_args(["--help"])
+
+
+def test_empty_parser_defaults():
+    parser = CommandArgumentParser()
+    with pytest.raises(HelpSignal):
+        parser.parse_args(["--help"])
+
+
+def test_extend_basic():
+    parser = CommandArgumentParser()
+    parser.add_argument("--tag", action=ArgumentAction.EXTEND, type=str)
+
+    args = parser.parse_args(["--tag", "a", "--tag", "b", "--tag", "c"])
+    assert args["tag"] == ["a", "b", "c"]
+
+
+def test_extend_nargs_2():
+    parser = CommandArgumentParser()
+    parser.add_argument("--pair", action=ArgumentAction.EXTEND, type=str, nargs=2)
+
+    args = parser.parse_args(["--pair", "a", "b", "--pair", "c", "d"])
+    assert args["pair"] == ["a", "b", "c", "d"]
+
+
+def test_extend_nargs_star():
+    parser = CommandArgumentParser()
+    parser.add_argument("--files", action=ArgumentAction.EXTEND, type=str, nargs="*")
+
+    args = parser.parse_args(["--files", "x", "y", "z"])
+    assert args["files"] == ["x", "y", "z"]
+
+    args = parser.parse_args(["--files"])
+    assert args["files"] == []
+
+
+def test_extend_nargs_plus():
+    parser = CommandArgumentParser()
+    parser.add_argument("--inputs", action=ArgumentAction.EXTEND, type=int, nargs="+")
+
+    args = parser.parse_args(["--inputs", "1", "2", "3", "--inputs", "4"])
+    assert args["inputs"] == [1, 2, 3, 4]
+
+
+def test_extend_invalid_type():
+    parser = CommandArgumentParser()
+    parser.add_argument("--nums", action=ArgumentAction.EXTEND, type=int)
+
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["--nums", "a"])
+
+
+def test_greedy_invalid_type():
+    parser = CommandArgumentParser()
+    parser.add_argument("--nums", nargs="*", type=int)
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["--nums", "a"])
+
+
+def test_append_vs_extend_behavior():
+    parser = CommandArgumentParser()
+    parser.add_argument("--x", action=ArgumentAction.APPEND, nargs=2)
+    parser.add_argument("--y", action=ArgumentAction.EXTEND, nargs=2)
+
+    args = parser.parse_args(
+        ["--x", "a", "b", "--x", "c", "d", "--y", "1", "2", "--y", "3", "4"]
+    )
+    assert args["x"] == [["a", "b"], ["c", "d"]]
+    assert args["y"] == ["1", "2", "3", "4"]
+
+
+def test_append_vs_extend_behavior_error():
+    parser = CommandArgumentParser()
+    parser.add_argument("--x", action=ArgumentAction.APPEND, nargs=2)
+    parser.add_argument("--y", action=ArgumentAction.EXTEND, nargs=2)
+
+    # This should raise an error because the last argument is not a valid pair
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["--x", "a", "b", "--x", "c", "d", "--y", "1", "2", "--y", "3"])
+
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args(["--x", "a", "b", "--x", "c", "--y", "1", "--y", "3", "4"])
+
+
+def test_extend_positional():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", action=ArgumentAction.EXTEND, type=str, nargs="*")
+
+    args = parser.parse_args(["a", "b", "c"])
+    assert args["files"] == ["a", "b", "c"]
+
+    args = parser.parse_args([])
+    assert args["files"] == []
+
+
+def test_extend_positional_nargs():
+    parser = CommandArgumentParser()
+    parser.add_argument("files", action=ArgumentAction.EXTEND, type=str, nargs="+")
+
+    args = parser.parse_args(["a", "b", "c"])
+    assert args["files"] == ["a", "b", "c"]
+
+    with pytest.raises(CommandArgumentError):
+        parser.parse_args([])