"""
Recommendation ITU-R BT.601-7
=============================

Define the *Recommendation ITU-R BT.601-7* opto-electrical transfer function
(OETF) and its inverse.

-   :func:`colour.models.oetf_BT601`
-   :func:`colour.models.oetf_inverse_BT601`

References
----------
-   :cite:`InternationalTelecommunicationUnion2011f` : International
    Telecommunication Union. (2011). Recommendation ITU-R BT.601-7 - Studio
    encoding parameters of digital television for standard 4:3 and wide-screen
    16:9 aspect ratios.
    http://www.itu.int/dms_pubrec/itu-r/rec/bt/\
R-REC-BT.601-7-201103-I!!PDF-E.pdf
"""

from __future__ import annotations

import numpy as np

from colour.algebra import spow
from colour.hints import (  # noqa: TC001
    Domain1,
    Range1,
)
from colour.utilities import as_float, domain_range_scale, from_range_1, to_domain_1

__author__ = "Colour Developers"
__copyright__ = "Copyright 2013 Colour Developers"
__license__ = "BSD-3-Clause - https://opensource.org/licenses/BSD-3-Clause"
__maintainer__ = "Colour Developers"
__email__ = "colour-developers@colour-science.org"
__status__ = "Production"

__all__ = [
    "oetf_BT601",
    "oetf_inverse_BT601",
]


def oetf_BT601(L: Domain1) -> Range1:
    """
    Apply the *Recommendation ITU-R BT.601-7* opto-electronic transfer
    function (OETF).

    Parameters
    ----------
    L
        *Luminance* :math:`L` of the image.

    Returns
    -------
    :class:`numpy.ndarray`
        Electrical signal :math:`E`.

    Notes
    -----
    +------------+-----------------------+---------------+
    | **Domain** | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``L``      | 1                     | 1             |
    +------------+-----------------------+---------------+

    +------------+-----------------------+---------------+
    | **Range**  | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``E``      | 1                     | 1             |
    +------------+-----------------------+---------------+

    References
    ----------
    :cite:`InternationalTelecommunicationUnion2011f`

    Examples
    --------
    >>> oetf_BT601(0.18)  # doctest: +ELLIPSIS
    0.4090077...
    """

    L = to_domain_1(L)

    E = np.where(L < 0.018, L * 4.5, 1.099 * spow(L, 0.45) - 0.099)

    return as_float(from_range_1(E))


def oetf_inverse_BT601(E: Domain1) -> Range1:
    """
    Apply the *Recommendation ITU-R BT.601-7* inverse opto-electronic
    transfer function (OETF).

    Parameters
    ----------
    E
        Electrical signal :math:`E`.

    Returns
    -------
    :class:`numpy.ndarray`
        *Luminance* :math:`L` of the image.

    Notes
    -----
    +------------+-----------------------+---------------+
    | **Domain** | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``E``      | 1                     | 1             |
    +------------+-----------------------+---------------+

    +------------+-----------------------+---------------+
    | **Range**  | **Scale - Reference** | **Scale - 1** |
    +============+=======================+===============+
    | ``L``      | 1                     | 1             |
    +------------+-----------------------+---------------+

    References
    ----------
    :cite:`InternationalTelecommunicationUnion2011f`

    Examples
    --------
    >>> oetf_inverse_BT601(0.409007728864150)  # doctest: +ELLIPSIS
    0.1...
    """

    E = to_domain_1(E)

    with domain_range_scale("ignore"):
        L = np.where(
            oetf_BT601(0.018) > E,
            E / 4.5,
            spow((E + 0.099) / 1.099, 1 / 0.45),
        )

    return as_float(from_range_1(L))
