Mini Shell

"""Alias generators for converting between different capitalization conventions."""
import re

__all__ = ('to_pascal', 'to_camel', 'to_snake')


def to_pascal(snake: str) -> str:
    """Convert a snake_case string to PascalCase.

    Args:
        snake: The string to convert.

    Returns:
        The PascalCase string.
    """
    camel = snake.title()
    return re.sub('([0-9A-Za-z])_(?=[0-9A-Z])', lambda m: m.group(1), camel)


def to_camel(snake: str) -> str:
    """Convert a snake_case string to camelCase.

    Args:
        snake: The string to convert.

    Returns:
        The converted camelCase string.
    """
    camel = to_pascal(snake)
    return re.sub('(^_*[A-Z])', lambda m: m.group(1).lower(), camel)


def to_snake(camel: str) -> str:
    """Convert a PascalCase or camelCase string to snake_case.

    Args:
        camel: The string to convert.

    Returns:
        The converted string in snake_case.
    """
    # Handle the sequence of uppercase letters followed by a lowercase letter
    snake = re.sub(r'([A-Z]+)([A-Z][a-z])', lambda m: f'{m.group(1)}_{m.group(2)}', camel)
    # Insert an underscore between a lowercase letter and an uppercase letter
    snake = re.sub(r'([a-z])([A-Z])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
    # Insert an underscore between a digit and an uppercase letter
    snake = re.sub(r'([0-9])([A-Z])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
    # Insert an underscore between a lowercase letter and a digit
    snake = re.sub(r'([a-z])([0-9])', lambda m: f'{m.group(1)}_{m.group(2)}', snake)
    return snake.lower()