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# Source code for betty.machine_name

    """
    Define portable machine names.
    """

    from __future__ import annotations

    import re
    from typing import TypeAlias, TypeGuard, Self, Any

    from betty.assertion import assert_str, AssertionChain
    from betty.error import UserFacingError
    from betty.locale.localizable import _

    MachineName: TypeAlias = str
    """
    A machine name is a string that meets these criteria:
    - At most 250 characters long.
    - Lowercase letters, numbers, and hyphens (-).

    See :py:func:`betty.machine_name.validate_machine_name`.
    """

    _MACHINE_NAME_PATTERN = re.compile(r"^[a-z0-9\-]{1,250}$")

    def validate_machine_name(alleged_machine_name: str) -> TypeGuard[MachineName]:
        """
        Validate that a string is a machine name.
        """
        return _MACHINE_NAME_PATTERN.fullmatch(alleged_machine_name) is not None

    class InvalidMachineName(UserFacingError, ValueError):
        """
        Raised when something is not a valid machine name.
        """

        @classmethod
        def new(cls, value: str) -> Self:
            """
            Create a new instance.
            """
            return cls(
                _(
                    '"{value}" is not a valid machine name: only lowercase letters, digits, and hyphens (-) are allowed.'
                ).format(value=value)
            )

    def assert_machine_name() -> AssertionChain[Any, MachineName]:
        """
        Assert that a string is a machine name.
        """

        def _assert(value: Any) -> MachineName:
            if not validate_machine_name(value):
                raise InvalidMachineName.new(value)
            return value

        return assert_str() | _assert

    _MACHINIFY_DISALLOWED_CHARACTER_PATTERN = re.compile(r"[^a-z0-9\-]")
    _MACHINIFY_HYPHEN_PATTERN = re.compile(r"-{2,}")

    def machinify(source: str) -> MachineName | None:
        """
        Attempt to convert a source string into a valid machine name.
        """
        return (
            _MACHINIFY_HYPHEN_PATTERN.sub(
                "-", _MACHINIFY_DISALLOWED_CHARACTER_PATTERN.sub("-", source.lower())
            ).strip("-")[:250]
            or None
        )