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

"""
This module provides utility functions for the models package.
"""
# pylint: disable=invalid-name
from collections import UserDict
from collections.abc import MutableMapping
from inspect import signature

import numpy as np
import warnings

from astropy import units as u
from astropy.utils.decorators import deprecated

__doctest_skip__ = ['AliasDict']
__all__ = ['AliasDict', 'poly_map_domain', 'comb', 'ellipse_extent']


deprecation_msg = """
AliasDict is deprecated because it no longer serves a function anywhere
inside astropy.
"""


@deprecated('5.0', deprecation_msg)
class AliasDict(MutableMapping):
    """
    Creates a `dict` like object that wraps an existing `dict` or other
    `MutableMapping`, along with a `dict` of *key aliases* that translate
    between specific keys in this dict to different keys in the underlying
    dict.

    In other words, keys that do not have an associated alias are accessed and
    stored like a normal `dict`.  However, a key that has an alias is accessed
    and stored to the "parent" dict via the alias.

    Parameters
    ----------
    parent : dict-like
        The parent `dict` that aliased keys and accessed from and stored to.

    aliases : dict-like
        Maps keys in this dict to their associated keys in the parent dict.

    Examples
    --------

    >>> parent = {'a': 1, 'b': 2, 'c': 3}
    >>> aliases = {'foo': 'a', 'bar': 'c'}
    >>> alias_dict = AliasDict(parent, aliases)
    >>> alias_dict['foo']
    1
    >>> alias_dict['bar']
    3

    Keys in the original parent dict are not visible if they were not
    aliased:

    >>> alias_dict['b']
    Traceback (most recent call last):
    ...
    KeyError: 'b'

    Likewise, updates to aliased keys are reflected back in the parent dict:

    >>> alias_dict['foo'] = 42
    >>> alias_dict['foo']
    42
    >>> parent['a']
    42

    However, updates/insertions to keys that are *not* aliased are not
    reflected in the parent dict:

    >>> alias_dict['qux'] = 99
    >>> alias_dict['qux']
    99
    >>> 'qux' in parent
    False

    In particular, updates on the `AliasDict` to a key that is equal to
    one of the aliased keys in the parent dict does *not* update the parent
    dict.  For example, ``alias_dict`` aliases ``'foo'`` to ``'a'``.  But
    assigning to a key ``'a'`` on the `AliasDict` does not impact the
    parent:

    >>> alias_dict['a'] = 'nope'
    >>> alias_dict['a']
    'nope'
    >>> parent['a']
    42
    """

    _store_type = dict
    """
    Subclasses may override this to use other mapping types as the underlying
    storage, for example an `OrderedDict`.  However, even in this case
    additional work may be needed to get things like the ordering right.
    """

    def __init__(self, parent, aliases):
        self._parent = parent
        self._store = self._store_type()
        self._aliases = dict(aliases)

    def __getitem__(self, key):
        if key in self._aliases:
            try:
                return self._parent[self._aliases[key]]
            except KeyError:
                raise KeyError(key)

        return self._store[key]

    def __setitem__(self, key, value):
        if key in self._aliases:
            self._parent[self._aliases[key]] = value
        else:
            self._store[key] = value

    def __delitem__(self, key):
        if key in self._aliases:
            try:
                del self._parent[self._aliases[key]]
            except KeyError:
                raise KeyError(key)
        else:
            del self._store[key]

    def __iter__(self):
        """
        First iterates over keys from the parent dict (if the aliased keys are
        present in the parent), followed by any keys in the local store.
        """

        for key, alias in self._aliases.items():
            if alias in self._parent:
                yield key

        for key in self._store:
            yield key

    def __len__(self):
        return len(list(iter(self)))

    def __repr__(self):
        # repr() just like any other dict--this should look transparent
        store_copy = self._store_type()
        for key, alias in self._aliases.items():
            if alias in self._parent:
                store_copy[key] = self._parent[alias]

        store_copy.update(self._store)

        return repr(store_copy)


def make_binary_operator_eval(oper, f, g):
    """
    Given a binary operator (as a callable of two arguments) ``oper`` and
    two callables ``f`` and ``g`` which accept the same arguments,
    returns a *new* function that takes the same arguments as ``f`` and ``g``,
    but passes the outputs of ``f`` and ``g`` in the given ``oper``.

    ``f`` and ``g`` are assumed to return tuples (which may be 1-tuples).  The
    given operator is applied element-wise to tuple outputs).

    Example
    -------

    >>> from operator import add
    >>> def prod(x, y):
    ...     return (x * y,)
    ...
    >>> sum_of_prod = make_binary_operator_eval(add, prod, prod)
    >>> sum_of_prod(3, 5)
    (30,)
    """

    return lambda inputs, params: \
            tuple(oper(x, y) for x, y in zip(f(inputs, params),
                                             g(inputs, params)))


def poly_map_domain(oldx, domain, window):
    """
    Map domain into window by shifting and scaling.

    Parameters
    ----------
    oldx : array
          original coordinates
    domain : list or tuple of length 2
          function domain
    window : list or tuple of length 2
          range into which to map the domain
    """
    domain = np.array(domain, dtype=np.float64)
    window = np.array(window, dtype=np.float64)
    if domain.shape != (2,) or window.shape != (2,):
        raise ValueError('Expected "domain" and window to be a tuple of size 2.')
    scl = (window[1] - window[0]) / (domain[1] - domain[0])
    off = (window[0] * domain[1] - window[1] * domain[0]) / (domain[1] - domain[0])
    return off + scl * oldx


def _validate_domain_window(value):
    if value is not None:
        if np.asanyarray(value).shape != (2, ):
            raise ValueError('domain and window should be tuples of size 2.')
        return tuple(value)
    return value


def comb(N, k):
    """
    The number of combinations of N things taken k at a time.

    Parameters
    ----------
    N : int, array
        Number of things.
    k : int, array
        Number of elements taken.

    """
    if (k > N) or (N < 0) or (k < 0):
        return 0
    val = 1
    for j in range(min(k, N - k)):
        val = (val * (N - j)) / (j + 1)
    return val


def array_repr_oneline(array):
    """
    Represents a multi-dimensional Numpy array flattened onto a single line.
    """
    r = np.array2string(array, separator=', ', suppress_small=True)
    return ' '.join(l.strip() for l in r.splitlines())


def combine_labels(left, right):
    """
    For use with the join operator &: Combine left input/output labels with
    right input/output labels.

    If none of the labels conflict then this just returns a sum of tuples.
    However if *any* of the labels conflict, this appends '0' to the left-hand
    labels and '1' to the right-hand labels so there is no ambiguity).
    """

    if set(left).intersection(right):
        left = tuple(l + '0' for l in left)
        right = tuple(r + '1' for r in right)

    return left + right


def ellipse_extent(a, b, theta):
    """
    Calculates the half size of a box encapsulating a rotated 2D
    ellipse.

    Parameters
    ----------
    a : float or `~astropy.units.Quantity`
        The ellipse semimajor axis.
    b : float or `~astropy.units.Quantity`
        The ellipse semiminor axis.
    theta : float or `~astropy.units.Quantity` ['angle']
        The rotation angle as an angular quantity
        (`~astropy.units.Quantity` or `~astropy.coordinates.Angle`) or
        a value in radians (as a float). The rotation angle increases
        counterclockwise.

    Returns
    -------
    offsets : tuple
        The absolute value of the offset distances from the ellipse center that
        define its bounding box region, ``(dx, dy)``.

    Examples
    --------
    .. plot::
        :include-source:

        import numpy as np
        import matplotlib.pyplot as plt
        from astropy.modeling.models import Ellipse2D
        from astropy.modeling.utils import ellipse_extent, render_model

        amplitude = 1
        x0 = 50
        y0 = 50
        a = 30
        b = 10
        theta = np.pi / 4

        model = Ellipse2D(amplitude, x0, y0, a, b, theta)
        dx, dy = ellipse_extent(a, b, theta)
        limits = [x0 - dx, x0 + dx, y0 - dy, y0 + dy]
        model.bounding_box = limits

        image = render_model(model)

        plt.imshow(image, cmap='binary', interpolation='nearest', alpha=.5,
                  extent = limits)
        plt.show()
    """

    t = np.arctan2(-b * np.tan(theta), a)
    dx = a * np.cos(t) * np.cos(theta) - b * np.sin(t) * np.sin(theta)

    t = np.arctan2(b, a * np.tan(theta))
    dy = b * np.sin(t) * np.cos(theta) + a * np.cos(t) * np.sin(theta)

    if isinstance(dx, u.Quantity) or isinstance(dy, u.Quantity):
        return np.abs(u.Quantity([dx, dy]))
    return np.abs([dx, dy])


def get_inputs_and_params(func):
    """
    Given a callable, determine the input variables and the
    parameters.

    Parameters
    ----------
    func : callable

    Returns
    -------
    inputs, params : tuple
        Each entry is a list of inspect.Parameter objects
    """
    sig = signature(func)

    inputs = []
    params = []
    for param in sig.parameters.values():
        if param.kind in (param.VAR_POSITIONAL, param.VAR_KEYWORD):
            raise ValueError("Signature must not have *args or **kwargs")
        if param.default == param.empty:
            inputs.append(param)
        else:
            params.append(param)

    return inputs, params


def _combine_equivalency_dict(keys, eq1=None, eq2=None):
    # Given two dictionaries that give equivalencies for a set of keys, for
    # example input value names, return a dictionary that includes all the
    # equivalencies
    eq = {}
    for key in keys:
        eq[key] = []
        if eq1 is not None and key in eq1:
            eq[key].extend(eq1[key])
        if eq2 is not None and key in eq2:
            eq[key].extend(eq2[key])
    return eq


def _to_radian(value):
    """ Convert ``value`` to radian. """
    if isinstance(value, u.Quantity):
        return value.to(u.rad)
    return np.deg2rad(value)


def _to_orig_unit(value, raw_unit=None, orig_unit=None):
    """ Convert value with ``raw_unit`` to ``orig_unit``. """
    if raw_unit is not None:
        return (value * raw_unit).to(orig_unit)
    return np.rad2deg(value)


class _ConstraintsDict(UserDict):
    """
    Wrapper around UserDict to allow updating the constraints
    on a Parameter when the dictionary is updated.
    """
    def __init__(self, model, constraint_type):
        self._model = model
        self.constraint_type = constraint_type
        c = {}
        for name in model.param_names:
            param = getattr(model, name)
            c[name] = getattr(param, constraint_type)
        super().__init__(c)

    def __setitem__(self, key, val):
        super().__setitem__(key, val)
        param = getattr(self._model, key)
        setattr(param, self.constraint_type, val)


class _SpecialOperatorsDict(UserDict):
    """
    Wrapper around UserDict to allow for better tracking of the Special
    Operators for CompoundModels. This dictionary is structured so that
    one cannot inadvertently overwrite an existing special operator.

    Parameters
    ----------
    unique_id: int
        the last used unique_id for a SPECIAL OPERATOR
    special_operators: dict
        a dictionary containing the special_operators

    Notes
    -----
    Direct setting of operators (`dict[key] = value`) into the
    dictionary has been deprecated in favor of the `.add(name, value)`
    method, so that unique dictionary keys can be generated and tracked
    consistently.
    """

    def __init__(self, unique_id=0, special_operators={}):
        super().__init__(special_operators)
        self._unique_id = unique_id

    def _set_value(self, key, val):
        if key in self:
            raise ValueError(f'Special operator "{key}" already exists')
        else:
            super().__setitem__(key, val)

    def __setitem__(self, key, val):
        self._set_value(key, val)
        warnings.warn(DeprecationWarning(
            """
            Special operator dictionary assignment has been deprecated.
            Please use `.add` instead, so that you can capture a unique
            key for your operator.
            """
        ))

    def _get_unique_id(self):
        self._unique_id += 1

        return self._unique_id

    def add(self, operator_name, operator):
        """
        Adds a special operator to the dictionary, and then returns the
        unique key that the operator is stored under for later reference.

        Parameters
        ----------
        operator_name: str
            the name for the operator
        operator: function
            the actual operator function which will be used

        Returns
        -------
        the unique operator key for the dictionary
            `(operator_name, unique_id)`
        """
        key = (operator_name, self._get_unique_id())

        self._set_value(key, operator)

        return key