# Licensed under a 3-clause BSD style license - see LICENSE.rst

"""
A collection of different unit formats.
"""


# This is pretty atrocious, but it will prevent a circular import for those
# formatters that need access to the units.core module An entry for it should
# exist in sys.modules since astropy.units.core imports this module
import sys
core = sys.modules['astropy.units.core']

from .base import Base  # noqa
from .generic import Generic, Unscaled  # noqa
from .cds import CDS  # noqa
from .console import Console  # noqa
from .fits import Fits  # noqa
from .latex import Latex, LatexInline  # noqa
from .ogip import OGIP  # noqa
from .unicode_format import Unicode  # noqa
from .vounit import VOUnit  # noqa


__all__ = [
    'Base', 'Generic', 'CDS', 'Console', 'Fits', 'Latex', 'LatexInline',
    'OGIP', 'Unicode', 'Unscaled', 'VOUnit', 'get_format']


def _known_formats():
    inout = [name for name, cls in Base.registry.items()
             if cls.parse.__func__ is not Base.parse.__func__]
    out_only = [name for name, cls in Base.registry.items()
                if cls.parse.__func__ is Base.parse.__func__]
    return (f"Valid formatter names are: {inout} for input and output, "
            f"and {out_only} for output only.")


def get_format(format=None):
    """
    Get a formatter by name.

    Parameters
    ----------
    format : str or `astropy.units.format.Base` instance or subclass
        The name of the format, or the format instance or subclass
        itself.

    Returns
    -------
    format : `astropy.units.format.Base` instance
        The requested formatter.
    """
    if format is None:
        return Generic

    if isinstance(format, type) and issubclass(format, Base):
        return format
    elif not (isinstance(format, str) or format is None):
        raise TypeError(
            f"Formatter must a subclass or instance of a subclass of {Base!r} "
            f"or a string giving the name of the formatter. {_known_formats()}.")

    format_lower = format.lower()

    if format_lower in Base.registry:
        return Base.registry[format_lower]

    raise ValueError(f"Unknown format {format!r}.  {_known_formats()}")