"""Definition of readable_unit function."""


def readable_unit(value: float, unit: str) -> str:
    """Return the given number formatted as a readable string with the specified unit.

    Args:
        value (float): The numeric value to format.
        unit (str): The unit to append to the formatted value.

    Returns:
        str: A string representation of the value with the unit, formatted to two decimal places.
    """
    if not isinstance(value, (int, float)):
        raise ValueError("Value must be a number.")
    if value < 0:
        raise ValueError("Value cannot be negative.")
    if not isinstance(unit, str):
        raise ValueError("Unit must be a string.")
    if unit.strip() == "":
        raise ValueError("Unit cannot be an empty string.")

    # Stop early if value is less than 1
    if value < 1:
        return f"{value:.2f} {unit}"

    # List of (suffix, factor), ordered from largest to smallest
    factors = [
        ("Y", 2**80),
        ("Z", 2**70),
        ("E", 2**60),
        ("P", 2**50),
        ("T", 2**40),
        ("G", 2**30),
        ("M", 2**20),
        ("K", 2**10),
        ("", 1),
    ]

    # Find the largest factor that fits the value
    for suffix, factor in factors:
        if factor <= value:
            value /= factor
            break

    # Build response
    return f"{value:.2f} {suffix}{unit}"