# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
# The idea for this module (but no code) was borrowed from the
# quantities (http://pythonhosted.org/quantities/) package.
"""Helper functions for Quantity.

In particular, this implements the logic that determines scaling and result
units for a given ufunc, given input units.
"""

from fractions import Fraction

import numpy as np

from . import UFUNC_HELPERS, UNSUPPORTED_UFUNCS
from astropy.units.core import (
    UnitsError, UnitConversionError, UnitTypeError,
    dimensionless_unscaled, get_current_unit_registry)


def _d(unit):
    if unit is None:
        return dimensionless_unscaled
    else:
        return unit


def get_converter(from_unit, to_unit):
    """Like Unit._get_converter, except returns None if no scaling is needed,
    i.e., if the inferred scale is unity."""
    try:
        scale = from_unit._to(to_unit)
    except UnitsError:
        return from_unit._apply_equivalencies(
                from_unit, to_unit, get_current_unit_registry().equivalencies)
    except AttributeError:
        raise UnitTypeError("Unit '{0}' cannot be converted to '{1}'"
                            .format(from_unit, to_unit))
    if scale == 1.:
        return None
    else:
        return lambda val: scale * val


def get_converters_and_unit(f, unit1, unit2):
    converters = [None, None]
    # By default, we try adjusting unit2 to unit1, so that the result will
    # be unit1 as well. But if there is no second unit, we have to try
    # adjusting unit1 (to dimensionless, see below).
    if unit2 is None:
        if unit1 is None:
            # No units for any input -- e.g., np.add(a1, a2, out=q)
            return converters, dimensionless_unscaled
        changeable = 0
        # swap units.
        unit2 = unit1
        unit1 = None
    elif unit2 is unit1:
        # ensure identical units is fast ("==" is slow, so avoid that).
        return converters, unit1
    else:
        changeable = 1

    # Try to get a converter from unit2 to unit1.
    if unit1 is None:
        try:
            converters[changeable] = get_converter(unit2,
                                                   dimensionless_unscaled)
        except UnitsError:
            # special case: would be OK if unitless number is zero, inf, nan
            converters[1-changeable] = False
            return converters, unit2
        else:
            return converters, dimensionless_unscaled
    else:
        try:
            converters[changeable] = get_converter(unit2, unit1)
        except UnitsError:
            raise UnitConversionError(
                "Can only apply '{0}' function to quantities "
                "with compatible dimensions"
                .format(f.__name__))

        return converters, unit1


# SINGLE ARGUMENT UFUNC HELPERS
#
# The functions below take a single argument, which is the quantity upon which
# the ufunc is being used. The output of the helper function should be two
# values: a list with a single converter to be used to scale the input before
# it is being passed to the ufunc (or None if no conversion is needed), and
# the unit the output will be in.

def helper_onearg_test(f, unit):
    return ([None], None)


def helper_invariant(f, unit):
    return ([None], _d(unit))


def helper_square(f, unit):
    return ([None], unit ** 2 if unit is not None else dimensionless_unscaled)


def helper_reciprocal(f, unit):
    return ([None], unit ** -1 if unit is not None else dimensionless_unscaled)


one_half = 0.5  # faster than Fraction(1, 2)
one_third = Fraction(1, 3)


def helper_sqrt(f, unit):
    return ([None], unit ** one_half if unit is not None
            else dimensionless_unscaled)


def helper_cbrt(f, unit):
    return ([None], (unit ** one_third if unit is not None
                     else dimensionless_unscaled))


def helper_modf(f, unit):
    if unit is None:
        return [None], (dimensionless_unscaled, dimensionless_unscaled)

    try:
        return ([get_converter(unit, dimensionless_unscaled)],
                (dimensionless_unscaled, dimensionless_unscaled))
    except UnitsError:
        raise UnitTypeError("Can only apply '{0}' function to "
                            "dimensionless quantities"
                            .format(f.__name__))


def helper__ones_like(f, unit):
    return [None], dimensionless_unscaled


def helper_dimensionless_to_dimensionless(f, unit):
    if unit is None:
        return [None], dimensionless_unscaled

    try:
        return ([get_converter(unit, dimensionless_unscaled)],
                dimensionless_unscaled)
    except UnitsError:
        raise UnitTypeError("Can only apply '{0}' function to "
                            "dimensionless quantities"
                            .format(f.__name__))


def helper_dimensionless_to_radian(f, unit):
    from astropy.units.si import radian
    if unit is None:
        return [None], radian

    try:
        return [get_converter(unit, dimensionless_unscaled)], radian
    except UnitsError:
        raise UnitTypeError("Can only apply '{0}' function to "
                            "dimensionless quantities"
                            .format(f.__name__))


def helper_degree_to_radian(f, unit):
    from astropy.units.si import degree, radian
    try:
        return [get_converter(unit, degree)], radian
    except UnitsError:
        raise UnitTypeError("Can only apply '{0}' function to "
                            "quantities with angle units"
                            .format(f.__name__))


def helper_radian_to_degree(f, unit):
    from astropy.units.si import degree, radian
    try:
        return [get_converter(unit, radian)], degree
    except UnitsError:
        raise UnitTypeError("Can only apply '{0}' function to "
                            "quantities with angle units"
                            .format(f.__name__))


def helper_radian_to_dimensionless(f, unit):
    from astropy.units.si import radian
    try:
        return [get_converter(unit, radian)], dimensionless_unscaled
    except UnitsError:
        raise UnitTypeError("Can only apply '{0}' function to "
                            "quantities with angle units"
                            .format(f.__name__))


def helper_frexp(f, unit):
    if not unit.is_unity():
        raise UnitTypeError("Can only apply '{0}' function to "
                            "unscaled dimensionless quantities"
                            .format(f.__name__))
    return [None], (None, None)


# TWO ARGUMENT UFUNC HELPERS
#
# The functions below take a two arguments. The output of the helper function
# should be two values: a tuple of two converters to be used to scale the
# inputs before being passed to the ufunc (None if no conversion is needed),
# and the unit the output will be in.

def helper_multiplication(f, unit1, unit2):
    return [None, None], _d(unit1) * _d(unit2)


def helper_division(f, unit1, unit2):
    return [None, None], _d(unit1) / _d(unit2)


def helper_power(f, unit1, unit2):
    # TODO: find a better way to do this, currently need to signal that one
    # still needs to raise power of unit1 in main code
    if unit2 is None:
        return [None, None], False

    try:
        return [None, get_converter(unit2, dimensionless_unscaled)], False
    except UnitsError:
        raise UnitTypeError("Can only raise something to a "
                            "dimensionless quantity")


def helper_ldexp(f, unit1, unit2):
    if unit2 is not None:
        raise TypeError("Cannot use ldexp with a quantity "
                        "as second argument.")
    else:
        return [None, None], _d(unit1)


def helper_copysign(f, unit1, unit2):
    # if first arg is not a quantity, just return plain array
    if unit1 is None:
        return [None, None], None
    else:
        return [None, None], unit1


def helper_heaviside(f, unit1, unit2):
    try:
        converter2 = (get_converter(unit2, dimensionless_unscaled)
                      if unit2 is not None else None)
    except UnitsError:
        raise UnitTypeError("Can only apply 'heaviside' function with a "
                            "dimensionless second argument.")
    return ([None, converter2], dimensionless_unscaled)


def helper_two_arg_dimensionless(f, unit1, unit2):
    try:
        converter1 = (get_converter(unit1, dimensionless_unscaled)
                      if unit1 is not None else None)
        converter2 = (get_converter(unit2, dimensionless_unscaled)
                      if unit2 is not None else None)
    except UnitsError:
        raise UnitTypeError("Can only apply '{0}' function to "
                            "dimensionless quantities"
                            .format(f.__name__))
    return ([converter1, converter2], dimensionless_unscaled)


# This used to be a separate function that just called get_converters_and_unit.
# Using it directly saves a few us; keeping the clearer name.
helper_twoarg_invariant = get_converters_and_unit


def helper_twoarg_comparison(f, unit1, unit2):
    converters, _ = get_converters_and_unit(f, unit1, unit2)
    return converters, None


def helper_twoarg_invtrig(f, unit1, unit2):
    from astropy.units.si import radian
    converters, _ = get_converters_and_unit(f, unit1, unit2)
    return converters, radian


def helper_twoarg_floor_divide(f, unit1, unit2):
    converters, _ = get_converters_and_unit(f, unit1, unit2)
    return converters, dimensionless_unscaled


def helper_divmod(f, unit1, unit2):
    converters, result_unit = get_converters_and_unit(f, unit1, unit2)
    return converters, (dimensionless_unscaled, result_unit)


# list of ufuncs:
# http://docs.scipy.org/doc/numpy/reference/ufuncs.html#available-ufuncs

UNSUPPORTED_UFUNCS |= {
    np.bitwise_and, np.bitwise_or, np.bitwise_xor, np.invert, np.left_shift,
    np.right_shift, np.logical_and, np.logical_or, np.logical_xor,
    np.logical_not}
for name in 'isnat', 'gcd', 'lcm':
    # isnat was introduced in numpy 1.14, gcd+lcm in 1.15
    ufunc = getattr(np, name, None)
    if isinstance(ufunc, np.ufunc):
        UNSUPPORTED_UFUNCS |= {ufunc}

# SINGLE ARGUMENT UFUNCS

# ufuncs that return a boolean and do not care about the unit
onearg_test_ufuncs = (np.isfinite, np.isinf, np.isnan, np.sign, np.signbit)
for ufunc in onearg_test_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_onearg_test

# ufuncs that return a value with the same unit as the input
invariant_ufuncs = (np.absolute, np.fabs, np.conj, np.conjugate, np.negative,
                    np.spacing, np.rint, np.floor, np.ceil, np.trunc,
                    np.positive)
for ufunc in invariant_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_invariant

# ufuncs that require dimensionless input and and give dimensionless output
dimensionless_to_dimensionless_ufuncs = (np.exp, np.expm1, np.exp2, np.log,
                                         np.log10, np.log2, np.log1p)
# As found out in gh-7058, some numpy 1.13 conda installations also provide
# np.erf, even though upstream doesn't have it.  We include it if present.
if isinstance(getattr(np.core.umath, 'erf', None), np.ufunc):
    dimensionless_to_dimensionless_ufuncs += (np.core.umath.erf,)
for ufunc in dimensionless_to_dimensionless_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_dimensionless_to_dimensionless

# ufuncs that require dimensionless input and give output in radians
dimensionless_to_radian_ufuncs = (np.arccos, np.arcsin, np.arctan, np.arccosh,
                                  np.arcsinh, np.arctanh)
for ufunc in dimensionless_to_radian_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_dimensionless_to_radian

# ufuncs that require input in degrees and give output in radians
degree_to_radian_ufuncs = (np.radians, np.deg2rad)
for ufunc in degree_to_radian_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_degree_to_radian

# ufuncs that require input in radians and give output in degrees
radian_to_degree_ufuncs = (np.degrees, np.rad2deg)
for ufunc in radian_to_degree_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_radian_to_degree

# ufuncs that require input in radians and give dimensionless output
radian_to_dimensionless_ufuncs = (np.cos, np.sin, np.tan, np.cosh, np.sinh,
                                  np.tanh)
for ufunc in radian_to_dimensionless_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_radian_to_dimensionless

# ufuncs handled as special cases
UFUNC_HELPERS[np.sqrt] = helper_sqrt
UFUNC_HELPERS[np.square] = helper_square
UFUNC_HELPERS[np.reciprocal] = helper_reciprocal
UFUNC_HELPERS[np.cbrt] = helper_cbrt
UFUNC_HELPERS[np.core.umath._ones_like] = helper__ones_like
UFUNC_HELPERS[np.modf] = helper_modf
UFUNC_HELPERS[np.frexp] = helper_frexp


# TWO ARGUMENT UFUNCS

# two argument ufuncs that require dimensionless input and and give
# dimensionless output
two_arg_dimensionless_ufuncs = (np.logaddexp, np.logaddexp2)
for ufunc in two_arg_dimensionless_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_two_arg_dimensionless

# two argument ufuncs that return a value with the same unit as the input
twoarg_invariant_ufuncs = (np.add, np.subtract, np.hypot, np.maximum,
                           np.minimum, np.fmin, np.fmax, np.nextafter,
                           np.remainder, np.mod, np.fmod)
for ufunc in twoarg_invariant_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_twoarg_invariant

# two argument ufuncs that need compatible inputs and return a boolean
twoarg_comparison_ufuncs = (np.greater, np.greater_equal, np.less,
                            np.less_equal, np.not_equal, np.equal)
for ufunc in twoarg_comparison_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_twoarg_comparison

# two argument ufuncs that do inverse trigonometry
twoarg_invtrig_ufuncs = (np.arctan2,)
# another private function in numpy; use getattr in case it disappears
if isinstance(getattr(np.core.umath, '_arg', None), np.ufunc):
    twoarg_invtrig_ufuncs += (np.core.umath._arg,)
for ufunc in twoarg_invtrig_ufuncs:
    UFUNC_HELPERS[ufunc] = helper_twoarg_invtrig

# ufuncs handled as special cases
UFUNC_HELPERS[np.multiply] = helper_multiplication
if isinstance(getattr(np, 'matmul', None), np.ufunc):
    UFUNC_HELPERS[np.matmul] = helper_multiplication
UFUNC_HELPERS[np.divide] = helper_division
UFUNC_HELPERS[np.true_divide] = helper_division
UFUNC_HELPERS[np.power] = helper_power
UFUNC_HELPERS[np.ldexp] = helper_ldexp
UFUNC_HELPERS[np.copysign] = helper_copysign
UFUNC_HELPERS[np.floor_divide] = helper_twoarg_floor_divide
UFUNC_HELPERS[np.heaviside] = helper_heaviside
UFUNC_HELPERS[np.float_power] = helper_power
UFUNC_HELPERS[np.divmod] = helper_divmod