"""Classes for spectral bases and functions for evaluation."""

from abc import ABC, abstractmethod
from math import factorial

import mpmath
import numpy as np

from desc.backend import fori_loop, gammaln, jit, jnp, sign
from desc.io import IOAble
from desc.utils import flatten_list

__all__ = [
    "PowerSeries",
    "FourierSeries",
    "DoubleFourierSeries",
    "ZernikePolynomial",
    "ChebyshevDoubleFourierBasis",
    "FourierZernikeBasis",
]


class Basis(IOAble, ABC):
    """Basis is an abstract base class for spectral basis sets."""

    _io_attrs_ = [
        "_L",
        "_M",
        "_N",
        "_NFP",
        "_modes",
        "_sym",
        "_spectral_indexing",
    ]

    def __init__(self):
        self._enforce_symmetry()
        self._sort_modes()
        self._create_idx()

    def _set_up(self):
        """Do things after loading or changing resolution."""
        # Also recreates any attributes not in _io_attrs on load from input file.
        # See IOAble class docstring for more info.
        self._enforce_symmetry()
        self._sort_modes()
        self._create_idx()

    def _enforce_symmetry(self):
        """Enforce stellarator symmetry."""
        assert self.sym in [
            "sin",
            "sine",
            "cos",
            "cosine",
            "even",
            "cos(t)",
            False,
            None,
        ], f"Unknown symmetry type {self.sym}"
        if self.sym in ["cos", "cosine"]:  # cos(m*t-n*z) symmetry
            self._modes = self.modes[sign(self.modes[:, 1]) == sign(self.modes[:, 2])]
        elif self.sym in ["sin", "sine"]:  # sin(m*t-n*z) symmetry
            self._modes = self.modes[sign(self.modes[:, 1]) != sign(self.modes[:, 2])]
        elif self.sym == "even":  # even powers of rho
            self._modes = self.modes[self.modes[:, 0] % 2 == 0]
        elif self.sym == "cos(t)":  # cos(m*t) terms only
            self._modes = self.modes[sign(self.modes[:, 1]) >= 0]
        elif self.sym is None:
            self._sym = False

    def _sort_modes(self):
        """Sorts modes for use with FFT."""
        sort_idx = np.lexsort((self.modes[:, 1], self.modes[:, 0], self.modes[:, 2]))
        self._modes = self.modes[sort_idx]

    def _create_idx(self):
        """Create index for use with self.get_idx()."""
        self._idx = {}
        for idx, (L, M, N) in enumerate(self.modes):
            if L not in self._idx:
                self._idx[L] = {}
            if M not in self._idx[L]:
                self._idx[L][M] = {}
            self._idx[L][M][N] = idx

    def get_idx(self, L=0, M=0, N=0, error=True):
        """Get the index of the ``'modes'`` array corresponding to given mode numbers.

        Parameters
        ----------
        L : int
            Radial mode number.
        M : int
            Poloidal mode number.
        N : int
            Toroidal mode number.
        error : bool
            whether to raise exception if mode is not in basis, or return empty array

        Returns
        -------
        idx : ndarray of int
            Index of given mode numbers.

        """
        try:
            return self._idx[L][M][N]
        except KeyError as e:
            if error:
                raise ValueError(
                    "mode ({}, {}, {}) is not in basis {}".format(L, M, N, str(self))
                ) from e
            else:
                return np.array([]).astype(int)

    @abstractmethod
    def _get_modes(self):
        """ndarray: Mode numbers for the basis."""

    @abstractmethod
    def evaluate(
        self, nodes, derivatives=np.array([0, 0, 0]), modes=None, unique=False
    ):
        """Evaluate basis functions at specified nodes.

        Parameters
        ----------
        nodes : ndarray of float, size(num_nodes,3)
            node coordinates, in (rho,theta,zeta)
        derivatives : ndarray of int, shape(3,)
            order of derivatives to compute in (rho,theta,zeta)
        modes : ndarray of in, shape(num_modes,3), optional
            basis modes to evaluate (if None, full basis is used)
        unique : bool, optional
            whether to workload by only calculating for unique values of nodes, modes
            can be faster, but doesn't work with jit or autodiff

        Returns
        -------
        y : ndarray, shape(num_nodes,num_modes)
            basis functions evaluated at nodes

        """

    @abstractmethod
    def change_resolution(self):
        """Change resolution of the basis to the given resolutions."""

    @property
    def L(self):
        """int: Maximum radial resolution."""
        return self.__dict__.setdefault("_L", 0)

    @L.setter
    def L(self, L):
        assert int(L) == L, "Basis Resolution must be an integer!"
        self._L = int(L)

    @property
    def M(self):
        """int:  Maximum poloidal resolution."""
        return self.__dict__.setdefault("_M", 0)

    @M.setter
    def M(self, M):
        assert int(M) == M, "Basis Resolution must be an integer!"
        self._M = int(M)

    @property
    def N(self):
        """int: Maximum toroidal resolution."""
        return self.__dict__.setdefault("_N", 0)

    @N.setter
    def N(self, N):
        assert int(N) == N, "Basis Resolution must be an integer!"
        self._N = int(N)

    @property
    def NFP(self):
        """int: Number of field periods."""
        return self.__dict__.setdefault("_NFP", 1)

    @property
    def sym(self):
        """str: {``'cos'``, ``'sin'``, ``False``} Type of symmetry."""
        return self.__dict__.setdefault("_sym", False)

    @property
    def modes(self):
        """ndarray: Mode numbers [l,m,n]."""
        return self.__dict__.setdefault("_modes", np.array([]).reshape((0, 3)))

    @modes.setter
    def modes(self, modes):
        self._modes = modes

    @property
    def num_modes(self):
        """int: Total number of modes in the spectral basis."""
        return self.modes.shape[0]

    @property
    def spectral_indexing(self):
        """str: Type of indexing used for the spectral basis."""
        return self.__dict__.setdefault("_spectral_indexing", "linear")

    def __repr__(self):
        """Get the string form of the object."""
        return (
            type(self).__name__
            + " at "
            + str(hex(id(self)))
            + " (L={}, M={}, N={}, NFP={}, sym={}, spectral_indexing={})".format(
                self.L, self.M, self.N, self.NFP, self.sym, self.spectral_indexing
            )
        )


class PowerSeries(Basis):
    """1D basis set for flux surface quantities.

    Power series in the radial coordinate.

    Parameters
    ----------
    L : int
        Maximum radial resolution.
    sym : {"even", False}
        Type of symmetry. "even" has only even powers of rho, for an analytic profile
        on the disc. False uses the full (odd + even) powers.

    """

    def __init__(self, L, sym="even"):
        self.L = L
        self.M = 0
        self.N = 0
        self._NFP = 1
        self._sym = sym
        self._spectral_indexing = "linear"

        self._modes = self._get_modes(L=self.L)

        super().__init__()

    def _get_modes(self, L=0):
        """Get mode numbers for power series.

        Parameters
        ----------
        L : int
            Maximum radial resolution.

        Returns
        -------
        modes : ndarray of int, shape(num_modes,3)
            Array of mode numbers [l,m,n].
            Each row is one basis function with modes (l,m,n).

        """
        l = np.arange(L + 1).reshape((-1, 1))
        z = np.zeros((L + 1, 2))
        return np.hstack([l, z])

    def evaluate(
        self, nodes, derivatives=np.array([0, 0, 0]), modes=None, unique=False
    ):
        """Evaluate basis functions at specified nodes.

        Parameters
        ----------
        nodes : ndarray of float, size(num_nodes,3)
            Node coordinates, in (rho,theta,zeta).
        derivatives : ndarray of int, shape(num_derivatives,3)
            Order of derivatives to compute in (rho,theta,zeta).
        modes : ndarray of in, shape(num_modes,3), optional
            Basis modes to evaluate (if None, full basis is used)
        unique : bool, optional
            whether to workload by only calculating for unique values of nodes, modes
            can be faster, but doesn't work with jit or autodiff

        Returns
        -------
        y : ndarray, shape(num_nodes,num_modes)
            basis functions evaluated at nodes

        """
        if modes is None:
            modes = self.modes
        if (derivatives[1] != 0) or (derivatives[2] != 0):
            return jnp.zeros((nodes.shape[0], modes.shape[0]))
        if not len(modes):
            return np.array([]).reshape((len(nodes), 0))

        r, t, z = nodes.T
        l, m, n = modes.T

        if unique:
            _, ridx, routidx = np.unique(
                r, return_index=True, return_inverse=True, axis=0
            )
            _, lidx, loutidx = np.unique(
                l, return_index=True, return_inverse=True, axis=0
            )
            r = r[ridx]
            l = l[lidx]

        radial = powers(r, l, dr=derivatives[0])
        if unique:
            radial = radial[routidx][:, loutidx]

        return radial

    def change_resolution(self, L):
        """Change resolution of the basis to the given resolution.

        Parameters
        ----------
        L : int
            Maximum radial resolution.

        """
        if L != self.L:
            self.L = L
            self._modes = self._get_modes(self.L)
            self._set_up()


class FourierSeries(Basis):
    """1D basis set for use with the magnetic axis.

    Fourier series in the toroidal coordinate.

    Parameters
    ----------
    N : int
        Maximum toroidal resolution.
    NFP : int
        number of field periods
    sym : {``'cos'``, ``'sin'``, False}
        * ``'cos'`` for cos(m*t-n*z) symmetry
        * ``'sin'`` for sin(m*t-n*z) symmetry
        * ``False`` for no symmetry (Default)

    """

    def __init__(self, N, NFP=1, sym=False):
        self.L = 0
        self.M = 0
        self.N = N
        self._NFP = NFP
        self._sym = sym
        self._spectral_indexing = "linear"

        self._modes = self._get_modes(N=self.N)

        super().__init__()

    def _get_modes(self, N=0):
        """Get mode numbers for Fourier series.

        Parameters
        ----------
        N : int
            Maximum toroidal resolution.

        Returns
        -------
        modes : ndarray of int, shape(num_modes,3)
            Array of mode numbers [l,m,n].
            Each row is one basis function with modes (l,m,n).

        """
        dim_tor = 2 * N + 1
        n = np.arange(dim_tor).reshape((-1, 1)) - N
        z = np.zeros((dim_tor, 2))
        return np.hstack([z, n])

    def evaluate(
        self, nodes, derivatives=np.array([0, 0, 0]), modes=None, unique=False
    ):
        """Evaluate basis functions at specified nodes.

        Parameters
        ----------
        nodes : ndarray of float, size(num_nodes,3)
            Node coordinates, in (rho,theta,zeta).
        derivatives : ndarray of int, shape(num_derivatives,3)
            Order of derivatives to compute in (rho,theta,zeta).
        modes : ndarray of in, shape(num_modes,3), optional
            Basis modes to evaluate (if None, full basis is used).
        unique : bool, optional
            Whether to workload by only calculating for unique values of nodes, modes
            can be faster, but doesn't work with jit or autodiff.

        Returns
        -------
        y : ndarray, shape(num_nodes,num_modes)
            Basis functions evaluated at nodes.

        """
        if modes is None:
            modes = self.modes
        if (derivatives[0] != 0) or (derivatives[1] != 0):
            return jnp.zeros((nodes.shape[0], modes.shape[0]))
        if not len(modes):
            return np.array([]).reshape((len(nodes), 0))

        r, t, z = nodes.T
        l, m, n = modes.T

        if unique:
            _, zidx, zoutidx = np.unique(
                z, return_index=True, return_inverse=True, axis=0
            )
            _, nidx, noutidx = np.unique(
                n, return_index=True, return_inverse=True, axis=0
            )
            z = z[zidx]
            n = n[nidx]

        toroidal = fourier(z[:, np.newaxis], n, self.NFP, derivatives[2])
        if unique:
            toroidal = toroidal[zoutidx][:, noutidx]

        return toroidal

    def change_resolution(self, N, NFP=None, sym=None):
        """Change resolution of the basis to the given resolutions.

        Parameters
        ----------
        N : int
            Maximum toroidal resolution.
        NFP : int
            Number of field periods.
        sym : bool
            Whether to enforce stellarator symmetry.

        """
        self._NFP = NFP if NFP is not None else self.NFP
        if N != self.N:
            self.N = N
            self._sym = sym if sym is not None else self.sym
            self._modes = self._get_modes(self.N)
            self._set_up()


class DoubleFourierSeries(Basis):
    """2D basis set for use on a single flux surface.

    Fourier series in both the poloidal and toroidal coordinates.

    Parameters
    ----------
    M : int
        Maximum poloidal resolution.
    N : int
        Maximum toroidal resolution.
    NFP : int
        Number of field periods.
    sym : {``'cos'``, ``'sin'``, ``False``}
        * ``'cos'`` for cos(m*t-n*z) symmetry
        * ``'sin'`` for sin(m*t-n*z) symmetry
        * ``False`` for no symmetry (Default)

    """

    def __init__(self, M, N, NFP=1, sym=False):
        self.L = 0
        self.M = M
        self.N = N
        self._NFP = NFP
        self._sym = sym
        self._spectral_indexing = "linear"

        self._modes = self._get_modes(M=self.M, N=self.N)

        super().__init__()

    def _get_modes(self, M=0, N=0):
        """Get mode numbers for double Fourier series.

        Parameters
        ----------
        M : int
            Maximum poloidal resolution.
        N : int
            Maximum toroidal resolution.

        Returns
        -------
        modes : ndarray of int, shape(num_modes,3)
            Array of mode numbers [l,m,n].
            Each row is one basis function with modes (l,m,n).

        """
        dim_pol = 2 * M + 1
        dim_tor = 2 * N + 1
        m = np.arange(dim_pol) - M
        n = np.arange(dim_tor) - N
        mm, nn = np.meshgrid(m, n)
        mm = mm.reshape((-1, 1), order="F")
        nn = nn.reshape((-1, 1), order="F")
        z = np.zeros_like(mm)
        y = np.hstack([z, mm, nn])
        return y

    def evaluate(
        self, nodes, derivatives=np.array([0, 0, 0]), modes=None, unique=False
    ):
        """Evaluate basis functions at specified nodes.

        Parameters
        ----------
        nodes : ndarray of float, size(num_nodes,3)
            Node coordinates, in (rho,theta,zeta).
        derivatives : ndarray of int, shape(num_derivatives,3)
            Order of derivatives to compute in (rho,theta,zeta).
        modes : ndarray of in, shape(num_modes,3), optional
            Basis modes to evaluate (if None, full basis is used).
        unique : bool, optional
            Whether to workload by only calculating for unique values of nodes, modes
            can be faster, but doesn't work with jit or autodiff.

        Returns
        -------
        y : ndarray, shape(num_nodes,num_modes)
            Basis functions evaluated at nodes.

        """
        if modes is None:
            modes = self.modes
        if derivatives[0] != 0:
            return jnp.zeros((nodes.shape[0], modes.shape[0]))
        if not len(modes):
            return np.array([]).reshape((len(nodes), 0))

        r, t, z = nodes.T
        l, m, n = modes.T

        if unique:
            _, tidx, toutidx = np.unique(
                t, return_index=True, return_inverse=True, axis=0
            )
            _, zidx, zoutidx = np.unique(
                z, return_index=True, return_inverse=True, axis=0
            )
            _, midx, moutidx = np.unique(
                m, return_index=True, return_inverse=True, axis=0
            )
            _, nidx, noutidx = np.unique(
                n, return_index=True, return_inverse=True, axis=0
            )
            t = t[tidx]
            z = z[zidx]
            m = m[midx]
            n = n[nidx]

        poloidal = fourier(t[:, np.newaxis], m, 1, derivatives[1])
        toroidal = fourier(z[:, np.newaxis], n, self.NFP, derivatives[2])
        if unique:
            poloidal = poloidal[toutidx][:, moutidx]
            toroidal = toroidal[zoutidx][:, noutidx]

        return poloidal * toroidal

    def change_resolution(self, M, N, NFP=None, sym=None):
        """Change resolution of the basis to the given resolutions.

        Parameters
        ----------
        M : int
            Maximum poloidal resolution.
        N : int
            Maximum toroidal resolution.
        NFP : int
            Number of field periods.
        sym : bool
            Whether to enforce stellarator symmetry.

        Returns
        -------
        None

        """
        self._NFP = NFP if NFP is not None else self.NFP
        if M != self.M or N != self.N or sym != self.sym:
            self.M = M
            self.N = N
            self._sym = sym if sym is not None else self.sym
            self._modes = self._get_modes(self.M, self.N)
            self._set_up()


class ZernikePolynomial(Basis):
    """2D basis set for analytic functions in a unit disc.

    Parameters
    ----------
    L : int
        Maximum radial resolution. Use L=-1 for default based on M.
    M : int
        Maximum poloidal resolution.
    sym : {``'cos'``, ``'sin'``, ``False``}
        * ``'cos'`` for cos(m*t-n*z) symmetry
        * ``'sin'`` for sin(m*t-n*z) symmetry
        * ``False`` for no symmetry (Default)
    spectral_indexing : {``'ansi'``, ``'fringe'``}
        Indexing method, default value = ``'ansi'``

        For L=0, all methods are equivalent and give a "chevron" shaped
        basis (only the outer edge of the zernike pyramid of width M).
        For L>0, the indexing scheme defines order of the basis functions:

        ``'ansi'``: ANSI indexing fills in the pyramid with triangles of
        decreasing size, ending in a triangle shape. For L == M,
        the traditional ANSI pyramid indexing is recovered. For L>M, adds rows
        to the bottom of the pyramid, increasing L while keeping M constant,
        giving a "house" shape.

        ``'fringe'``: Fringe indexing fills in the pyramid with chevrons of
        decreasing size, ending in a diamond shape for L=2*M where
        the traditional fringe/U of Arizona indexing is recovered.
        For L > 2*M, adds chevrons to the bottom, making a hexagonal diamond.

    """

    def __init__(self, L, M, sym=False, spectral_indexing="ansi"):
        self.L = L
        self.M = M
        self.N = 0
        self._NFP = 1
        self._sym = sym
        self._spectral_indexing = spectral_indexing

        self._modes = self._get_modes(
            L=self.L, M=self.M, spectral_indexing=self.spectral_indexing
        )

        super().__init__()

    def _get_modes(self, L=-1, M=0, spectral_indexing="ansi"):
        """Get mode numbers for Fourier-Zernike basis functions.

        Parameters
        ----------
        L : int
            Maximum radial resolution.
        M : int
            Maximum poloidal resolution.
        spectral_indexing : {``'ansi'``, ``'fringe'``}
            Indexing method, default value = ``'ansi'``

            For L=0, all methods are equivalent and give a "chevron" shaped
            basis (only the outer edge of the zernike pyramid of width M).
            For L>0, the indexing scheme defines order of the basis functions:

            ``'ansi'``: ANSI indexing fills in the pyramid with triangles of
            decreasing size, ending in a triangle shape. For L == M,
            the traditional ANSI pyramid indexing is recovered. For L>M, adds rows
            to the bottom of the pyramid, increasing L while keeping M constant,
            giving a "house" shape.

            ``'fringe'``: Fringe indexing fills in the pyramid with chevrons of
            decreasing size, ending in a diamond shape for L=2*M where
            the traditional fringe/U of Arizona indexing is recovered.
            For L > 2*M, adds chevrons to the bottom, making a hexagonal diamond.

        Returns
        -------
        modes : ndarray of int, shape(num_modes,3)
            Array of mode numbers [l,m,n].
            Each row is one basis function with modes (l,m,n).

        """
        assert spectral_indexing in [
            "ansi",
            "fringe",
        ], "Unknown spectral_indexing: {}".format(spectral_indexing)
        default_L = {"ansi": M, "fringe": 2 * M}
        L = L if L >= 0 else default_L.get(spectral_indexing, M)
        self.L = L

        if spectral_indexing == "ansi":
            pol_posm = [
                [(m + d, m) for m in range(0, M + 1) if m + d < M + 1]
                for d in range(0, L + 1, 2)
            ]
            if L > M:
                pol_posm += [
                    (l, m)
                    for l in range(M + 1, L + 1)
                    for m in range(0, M + 1)
                    if (l - m) % 2 == 0
                ]

        elif spectral_indexing == "fringe":
            pol_posm = [
                [(m + d // 2, m - d // 2) for m in range(0, M + 1) if m - d // 2 >= 0]
                for d in range(0, L + 1, 2)
            ]
            if L > 2 * M:
                pol_posm += [
                    [(l - m, m) for m in range(0, M + 1)]
                    for l in range(2 * M, L + 1, 2)
                ]

        pol = [
            [(l, m), (l, -m)] if m != 0 else [(l, m)] for l, m in flatten_list(pol_posm)
        ]
        pol = np.array(flatten_list(pol))
        num_pol = len(pol)
        tor = np.zeros((num_pol, 1))

        return np.hstack([pol, tor])

    def evaluate(
        self, nodes, derivatives=np.array([0, 0, 0]), modes=None, unique=False
    ):
        """Evaluate basis functions at specified nodes.

        Parameters
        ----------
        nodes : ndarray of float, size(num_nodes,3)
            Node coordinates, in (rho,theta,zeta).
        derivatives : ndarray of int, shape(num_derivatives,3)
            Order of derivatives to compute in (rho,theta,zeta).
        modes : ndarray of int, shape(num_modes,3), optional
            Basis modes to evaluate (if None, full basis is used).
        unique : bool, optional
            Whether to workload by only calculating for unique values of nodes, modes
            can be faster, but doesn't work with jit or autodiff.

        Returns
        -------
        y : ndarray, shape(num_nodes,num_modes)
            Basis functions evaluated at nodes.

        """
        if modes is None:
            modes = self.modes
        if derivatives[2] != 0:
            return jnp.zeros((nodes.shape[0], modes.shape[0]))
        if not len(modes):
            return np.array([]).reshape((len(nodes), 0))

        r, t, z = nodes.T
        l, m, n = modes.T
        lm = modes[:, :2]

        if unique:
            _, ridx, routidx = np.unique(
                r, return_index=True, return_inverse=True, axis=0
            )
            _, tidx, toutidx = np.unique(
                t, return_index=True, return_inverse=True, axis=0
            )
            _, lmidx, lmoutidx = np.unique(
                lm, return_index=True, return_inverse=True, axis=0
            )
            _, midx, moutidx = np.unique(
                m, return_index=True, return_inverse=True, axis=0
            )
            r = r[ridx]
            t = t[tidx]
            lm = lm[lmidx]
            m = m[midx]

        # some logic here to use the fastest method, assuming that you're not using
        # "unique" within jit/AD since that doesn't work
        if unique and (np.max(modes[:, 0]) <= 24):
            radial_fun = zernike_radial_poly
        else:
            radial_fun = zernike_radial

        radial = radial_fun(r[:, np.newaxis], lm[:, 0], lm[:, 1], dr=derivatives[0])
        poloidal = fourier(t[:, np.newaxis], m, 1, derivatives[1])

        if unique:
            radial = radial[routidx][:, lmoutidx]
            poloidal = poloidal[toutidx][:, moutidx]

        return radial * poloidal

    def change_resolution(self, L, M, sym=None):
        """Change resolution of the basis to the given resolutions.

        Parameters
        ----------
        L : int
            Maximum radial resolution.
        M : int
            Maximum poloidal resolution.
        sym : bool
            Whether to enforce stellarator symmetry.

        Returns
        -------
        None

        """
        if L != self.L or M != self.M or sym != self.sym:
            self.L = L
            self.M = M
            self._sym = sym if sym is not None else self.sym
            self._modes = self._get_modes(
                self.L, self.M, spectral_indexing=self.spectral_indexing
            )
            self._set_up()


class ChebyshevDoubleFourierBasis(Basis):
    """3D basis: tensor product of Chebyshev poynomials and two Fourier series.

    Fourier series in both the poloidal and toroidal coordinates.

    Parameters
    ----------
    L : int
        Maximum radial resolution.
    M : int
        Maximum poloidal resolution.
    N : int
        Maximum toroidal resolution.
    NFP : int
        Number of field periods.
    sym : {``'cos'``, ``'sin'``, ``False``}
        * ``'cos'`` for cos(m*t-n*z) symmetry
        * ``'sin'`` for sin(m*t-n*z) symmetry
        * ``False`` for no symmetry (Default)

    """

    def __init__(self, L, M, N, NFP=1, sym=False):
        self.L = L
        self.M = M
        self.N = N
        self._NFP = NFP
        self._sym = sym
        self._spectral_indexing = "linear"

        self._modes = self._get_modes(L=self.L, M=self.M, N=self.N)

        super().__init__()

    def _get_modes(self, L=0, M=0, N=0):
        """Get mode numbers for Chebyshev-Fourier series.

        Parameters
        ----------
        L : int
            Maximum radial resoltuion.
        M : int
            Maximum poloidal resolution.
        N : int
            Maximum toroidal resolution.

        Returns
        -------
        modes : ndarray of int, shape(num_modes,3)
            Array of mode numbers [l,m,n].
            Each row is one basis function with modes (l,m,n).

        """
        dim_pol = 2 * M + 1
        dim_tor = 2 * N + 1
        l = np.arange(L + 1)
        m = np.arange(dim_pol) - M
        n = np.arange(dim_tor) - N
        ll, mm, nn = np.meshgrid(l, m, n)
        ll = ll.reshape((-1, 1), order="F")
        mm = mm.reshape((-1, 1), order="F")
        nn = nn.reshape((-1, 1), order="F")
        y = np.hstack([ll, mm, nn])
        return y

    def evaluate(
        self, nodes, derivatives=np.array([0, 0, 0]), modes=None, unique=False
    ):
        """Evaluate basis functions at specified nodes.

        Parameters
        ----------
        nodes : ndarray of float, size(num_nodes,3)
            Node coordinates, in (rho,theta,zeta).
        derivatives : ndarray of int, shape(num_derivatives,3)
            Order of derivatives to compute in (rho,theta,zeta).
        modes : ndarray of in, shape(num_modes,3), optional
            Basis modes to evaluate (if None, full basis is used).
        unique : bool, optional
            whether to workload by only calculating for unique values of nodes, modes
            can be faster, but doesn't work with jit or autodiff

        Returns
        -------
        y : ndarray, shape(num_nodes,num_modes)
            Basis functions evaluated at nodes.

        """
        if modes is None:
            modes = self.modes
        if not len(modes):
            return np.array([]).reshape((len(nodes), 0))

        r, t, z = nodes.T
        l, m, n = modes.T

        radial = chebyshev(r[:, np.newaxis], l, dr=derivatives[0])
        poloidal = fourier(t[:, np.newaxis], m, 1, derivatives[1])
        toroidal = fourier(z[:, np.newaxis], n, self.NFP, derivatives[2])

        return radial * poloidal * toroidal

    def change_resolution(self, L, M, N, NFP=None, sym=None):
        """Change resolution of the basis to the given resolutions.

        Parameters
        ----------
        L : int
            Maximum radial resolution.
        M : int
            Maximum poloidal resolution.
        N : int
            Maximum toroidal resolution.
        NFP : int
            Number of field periods.
        sym : bool
            Whether to enforce stellarator symmetry.

        Returns
        -------
        None

        """
        self._NFP = NFP if NFP is not None else self.NFP
        if L != self.L or M != self.M or N != self.N or sym != self.sym:
            self._L = L
            self._M = M
            self._N = N
            self._sym = sym if sym is not None else self.sym
            self._modes = self._get_modes(self.L, self.M, self.N)
            self._set_up()


class FourierZernikeBasis(Basis):
    """3D basis set for analytic functions in a toroidal volume.

    Zernike polynomials in the radial & poloidal coordinates, and a Fourier
    series in the toroidal coordinate.

    Parameters
    ----------
    L : int
        Maximum radial resolution. Use L=-1 for default based on M.
    M : int
        Maximum poloidal resolution.
    N : int
        Maximum toroidal resolution.
    NFP : int
        Number of field periods.
    sym : {``'cos'``, ``'sin'``, ``False``}
        * ``'cos'`` for cos(m*t-n*z) symmetry
        * ``'sin'`` for sin(m*t-n*z) symmetry
        * ``False`` for no symmetry (Default)
    spectral_indexing : {``'ansi'``, ``'fringe'``}
        Indexing method, default value = ``'ansi'``

        For L=0, all methods are equivalent and give a "chevron" shaped
        basis (only the outer edge of the zernike pyramid of width M).
        For L>0, the indexing scheme defines order of the basis functions:

        ``'ansi'``: ANSI indexing fills in the pyramid with triangles of
        decreasing size, ending in a triangle shape. For L == M,
        the traditional ANSI pyramid indexing is recovered. For L>M, adds rows
        to the bottom of the pyramid, increasing L while keeping M constant,
        giving a "house" shape.

        ``'fringe'``: Fringe indexing fills in the pyramid with chevrons of
        decreasing size, ending in a diamond shape for L=2*M where
        the traditional fringe/U of Arizona indexing is recovered.
        For L > 2*M, adds chevrons to the bottom, making a hexagonal diamond.

    """

    def __init__(self, L, M, N, NFP=1, sym=False, spectral_indexing="ansi"):
        self.L = L
        self.M = M
        self.N = N
        self._NFP = NFP
        self._sym = sym
        self._spectral_indexing = spectral_indexing

        self._modes = self._get_modes(
            L=self.L, M=self.M, N=self.N, spectral_indexing=self.spectral_indexing
        )

        super().__init__()

    def _get_modes(self, L=-1, M=0, N=0, spectral_indexing="ansi"):
        """Get mode numbers for Fourier-Zernike basis functions.

        Parameters
        ----------
        L : int
            Maximum radial resolution.
        M : int
            Maximum poloidal resolution.
        N : int
            Maximum toroidal resolution.
        spectral_indexing : {``'ansi'``, ``'fringe'``}
            Indexing method, default value = ``'ansi'``

            For L=0, all methods are equivalent and give a "chevron" shaped
            basis (only the outer edge of the zernike pyramid of width M).
            For L>0, the indexing scheme defines order of the basis functions:

            ``'ansi'``: ANSI indexing fills in the pyramid with triangles of
            decreasing size, ending in a triangle shape. For L == M,
            the traditional ANSI pyramid indexing is recovered. For L>M, adds rows
            to the bottom of the pyramid, increasing L while keeping M constant,
            giving a "house" shape.

            ``'fringe'``: Fringe indexing fills in the pyramid with chevrons of
            decreasing size, ending in a diamond shape for L=2*M where
            the traditional fringe/U of Arizona indexing is recovered.
            For L > 2*M, adds chevrons to the bottom, making a hexagonal diamond.

        Returns
        -------
        modes : ndarray of int, shape(num_modes,3)
            Array of mode numbers [l,m,n].
            Each row is one basis function with modes (l,m,n).

        """
        assert spectral_indexing in [
            "ansi",
            "fringe",
        ], "Unknown spectral_indexing: {}".format(spectral_indexing)
        default_L = {"ansi": M, "fringe": 2 * M}
        L = L if L >= 0 else default_L.get(spectral_indexing, M)
        self.L = L

        if spectral_indexing == "ansi":
            pol_posm = [
                [(m + d, m) for m in range(0, M + 1) if m + d < M + 1]
                for d in range(0, L + 1, 2)
            ]
            if L > M:
                pol_posm += [
                    (l, m)
                    for l in range(M + 1, L + 1)
                    for m in range(0, M + 1)
                    if (l - m) % 2 == 0
                ]

        elif spectral_indexing == "fringe":
            pol_posm = [
                [(m + d // 2, m - d // 2) for m in range(0, M + 1) if m - d // 2 >= 0]
                for d in range(0, L + 1, 2)
            ]
            if L > 2 * M:
                pol_posm += [
                    [(l - m, m) for m in range(0, M + 1)]
                    for l in range(2 * M, L + 1, 2)
                ]

        pol = [
            [(l, m), (l, -m)] if m != 0 else [(l, m)] for l, m in flatten_list(pol_posm)
        ]
        pol = np.array(flatten_list(pol))
        num_pol = len(pol)

        pol = np.tile(pol, (2 * N + 1, 1))
        tor = np.atleast_2d(
            np.tile(np.arange(-N, N + 1), (num_pol, 1)).flatten(order="f")
        ).T
        return np.unique(np.hstack([pol, tor]), axis=0)

    def evaluate(
        self, nodes, derivatives=np.array([0, 0, 0]), modes=None, unique=False
    ):
        """Evaluate basis functions at specified nodes.

        Parameters
        ----------
        nodes : ndarray of float, size(num_nodes,3)
            Node coordinates, in (rho,theta,zeta).
        derivatives : ndarray of int, shape(num_derivatives,3)
            Order of derivatives to compute in (rho,theta,zeta).
        modes : ndarray of int, shape(num_modes,3), optional
            Basis modes to evaluate (if None, full basis is used).
        unique : bool, optional
            Whether to workload by only calculating for unique values of nodes, modes
            can be faster, but doesn't work with jit or autodiff.

        Returns
        -------
        y : ndarray, shape(num_nodes,num_modes)
            Basis functions evaluated at nodes.

        """
        if modes is None:
            modes = self.modes
        if not len(modes):
            return np.array([]).reshape((len(nodes), 0))

        # TODO: avoid duplicate calculations when mixing derivatives
        r, t, z = nodes.T
        l, m, n = modes.T
        lm = modes[:, :2]

        if unique:
            _, ridx, routidx = np.unique(
                r, return_index=True, return_inverse=True, axis=0
            )
            _, tidx, toutidx = np.unique(
                t, return_index=True, return_inverse=True, axis=0
            )
            _, zidx, zoutidx = np.unique(
                z, return_index=True, return_inverse=True, axis=0
            )
            _, lmidx, lmoutidx = np.unique(
                lm, return_index=True, return_inverse=True, axis=0
            )
            _, midx, moutidx = np.unique(
                m, return_index=True, return_inverse=True, axis=0
            )
            _, nidx, noutidx = np.unique(
                n, return_index=True, return_inverse=True, axis=0
            )
            r = r[ridx]
            t = t[tidx]
            z = z[zidx]
            lm = lm[lmidx]
            m = m[midx]
            n = n[nidx]

        # some logic here to use the fastest method, assuming that you're not using
        # "unique" within jit/AD since that doesn't work
        if unique and (np.max(modes[:, 0]) <= 24):
            radial_fun = zernike_radial_poly
        else:
            radial_fun = zernike_radial

        radial = radial_fun(r[:, np.newaxis], lm[:, 0], lm[:, 1], dr=derivatives[0])
        poloidal = fourier(t[:, np.newaxis], m, dt=derivatives[1])
        toroidal = fourier(z[:, np.newaxis], n, NFP=self.NFP, dt=derivatives[2])
        if unique:
            radial = radial[routidx][:, lmoutidx]
            poloidal = poloidal[toutidx][:, moutidx]
            toroidal = toroidal[zoutidx][:, noutidx]

        return radial * poloidal * toroidal

    def change_resolution(self, L, M, N, NFP=None, sym=None):
        """Change resolution of the basis to the given resolutions.

        Parameters
        ----------
        L : int
            Maximum radial resolution.
        M : int
            Maximum poloidal resolution.
        N : int
            Maximum toroidal resolution.
        NFP : int
            Number of field periods.
        sym : bool
            Whether to enforce stellarator symmetry.

        Returns
        -------
        None

        """
        self._NFP = NFP if NFP is not None else self.NFP
        if L != self.L or M != self.M or N != self.N or sym != self.sym:
            self.L = L
            self.M = M
            self.N = N
            self._sym = sym if sym is not None else self.sym
            self._modes = self._get_modes(
                self.L, self.M, self.N, spectral_indexing=self.spectral_indexing
            )
            self._set_up()


def polyder_vec(p, m):
    """Vectorized version of polyder.

    For differentiating multiple polynomials of the same degree

    Parameters
    ----------
    p : ndarray, shape(N,M)
        polynomial coefficients. Each row is 1 polynomial, in descending powers of x,
        each column is a power of x
    m : int >=0
        order of derivative

    Returns
    -------
    der : ndarray, shape(N,M)
        polynomial coefficients for derivative in descending order

    """
    factorial = np.math.factorial
    m = np.asarray(m, dtype=int)  # order of derivative
    p = np.atleast_2d(p)
    order = p.shape[1] - 1

    D = np.arange(order, -1, -1)
    num = np.array([factorial(i) for i in D], dtype=object)
    den = np.array([factorial(max(i - m, 0)) for i in D], dtype=object)
    D = (num // den).astype(p.dtype)

    p = np.roll(D * p, m, axis=1)
    idx = np.arange(p.shape[1])
    p = np.where(idx < m, 0, p)

    return p


def polyval_vec(p, x, prec=None):
    """Evaluate a polynomial at specific values.

    Vectorized for evaluating multiple polynomials of the same degree.

    Parameters
    ----------
    p : ndarray, shape(N,M)
        Array of coefficient for N polynomials of order M.
        Each row is one polynomial, given in descending powers of x.
    x : ndarray, shape(K,)
        A number, or 1d array of numbers at
        which to evaluate p. If greater than 1d it is flattened.
    prec : int, optional
        precision to use, in number of decimal places. Default is
        double precision (~16 decimals) which should be enough for
        most cases with L <= 24

    Returns
    -------
    y : ndarray, shape(N,K)
        polynomials evaluated at x.
        Each row corresponds to a polynomial, each column to a value of x

    """
    p = np.atleast_2d(p)
    x = np.atleast_1d(x).flatten()
    # for modest to large arrays, faster to find unique values and
    # only evaluate those. Have to cast to float because np.unique
    # can't handle object types like python native int
    unq_x, xidx = np.unique(x, return_inverse=True)
    _, pidx, outidx = np.unique(
        p.astype(float), return_index=True, return_inverse=True, axis=0
    )
    unq_p = p[pidx]

    if prec is not None and prec > 18:
        # TODO: possibly multithread this bit
        mpmath.mp.dps = prec
        y = np.array([np.asarray(mpmath.polyval(list(pi), unq_x)) for pi in unq_p])
    else:
        npoly = unq_p.shape[0]  # number of polynomials
        order = unq_p.shape[1]  # order of polynomials
        nx = len(unq_x)  # number of coordinates
        y = np.zeros((npoly, nx))

        for k in range(order):
            y = y * unq_x + np.atleast_2d(unq_p[:, k]).T

    return y[outidx][:, xidx].astype(float)


def zernike_radial_coeffs(l, m, exact=True):
    """Polynomial coefficients for radial part of zernike basis.

    Parameters
    ----------
    l : ndarray of int, shape(K,)
        radial mode number(s)
    m : ndarray of int, shape(K,)
        azimuthal mode number(s)
    exact : bool
        whether to return exact coefficients with `object` dtype
        or return integer or floating point approximation

    Returns
    -------
    coeffs : ndarray


    Notes
    -----
    Integer representation is exact up to l~54, so leaving `exact` arg as False
    can speed up evaluation with no loss in accuracy
    """
    l = np.atleast_1d(l).astype(int)
    m = np.atleast_1d(np.abs(m)).astype(int)
    lm = np.vstack([l, m]).T
    # for modest to large arrays, faster to find unique values and
    # only evaluate those
    lms, idx = np.unique(lm, return_inverse=True, axis=0)

    npoly = len(lms)
    lmax = np.max(lms[:, 0])
    coeffs = np.zeros((npoly, lmax + 1), dtype=object)
    lm_even = ((lms[:, 0] - lms[:, 1]) % 2 == 0)[:, np.newaxis]
    for ii in range(npoly):
        ll = lms[ii, 0]
        mm = lms[ii, 1]
        for s in range(mm, ll + 1, 2):
            coeffs[ii, s] = (
                (-1) ** ((ll - s) // 2)
                * factorial((ll + s) // 2)
                // (
                    factorial((ll - s) // 2)
                    * factorial((s + mm) // 2)
                    * factorial((s - mm) // 2)
                )
            )
    c = np.fliplr(np.where(lm_even, coeffs, 0))
    if not exact:
        try:
            c = c.astype(int)
        except OverflowError:
            c = c.astype(float)
    c = c[idx]
    return c


def zernike_radial_poly(r, l, m, dr=0):
    """Radial part of zernike polynomials.

    Evaluates basis functions using numpy to
    exactly compute the polynomial coefficients
    and Horner's method for low resolution,
    or extended precision arithmetic for high resolution.
    Faster for low resolution, but not differentiable.

    Parameters
    ----------
    r : ndarray, shape(N,)
        radial coordinates to evaluate basis
    l : ndarray of int, shape(K,)
        radial mode number(s)
    m : ndarray of int, shape(K,)
        azimuthal mode number(s)
    dr : int
        order of derivative (Default = 0)

    Returns
    -------
    y : ndarray, shape(N,K)
        basis function(s) evaluated at specified points

    """
    coeffs = zernike_radial_coeffs(l, m)
    lmax = np.max(l)
    coeffs = polyder_vec(coeffs, dr)
    # this should give accuracy of ~1e-10 in the eval'd polynomials
    prec = int(0.4 * lmax + 8.4)
    return polyval_vec(coeffs, r, prec=prec).T


def zernike_radial(r, l, m, dr=0):
    """Radial part of zernike polynomials.

    Evaluates basis functions using JAX and a stable
    evaluation scheme based on jacobi polynomials and
    binomial coefficients. Generally faster for L>24
    and differentiable, but slower for low resolution.

    Parameters
    ----------
    r : ndarray, shape(N,)
        radial coordinates to evaluate basis
    l : ndarray of int, shape(K,)
        radial mode number(s)
    m : ndarray of int, shape(K,)
        azimuthal mode number(s)
    dr : int
        order of derivative (Default = 0)

    Returns
    -------
    y : ndarray, shape(N,K)
        basis function(s) evaluated at specified points

    """
    m = jnp.abs(m)
    alpha = m
    beta = 0
    n = (l - m) // 2
    s = (-1) ** n
    jacobi_arg = 1 - 2 * r**2
    if dr == 0:
        out = r**m * _jacobi(n, alpha, beta, jacobi_arg, 0)
    elif dr == 1:
        f = _jacobi(n, alpha, beta, jacobi_arg, 0)
        df = _jacobi(n, alpha, beta, jacobi_arg, 1)
        out = m * r ** jnp.maximum(m - 1, 0) * f - 4 * r ** (m + 1) * df
    elif dr == 2:
        f = _jacobi(n, alpha, beta, jacobi_arg, 0)
        df = _jacobi(n, alpha, beta, jacobi_arg, 1)
        d2f = _jacobi(n, alpha, beta, jacobi_arg, 2)
        out = (
            (m - 1) * m * r ** jnp.maximum(m - 2, 0) * f
            - 4 * (2 * m + 1) * r**m * df
            + 16 * r ** (m + 2) * d2f
        )
    elif dr == 3:
        f = _jacobi(n, alpha, beta, jacobi_arg, 0)
        df = _jacobi(n, alpha, beta, jacobi_arg, 1)
        d2f = _jacobi(n, alpha, beta, jacobi_arg, 2)
        d3f = _jacobi(n, alpha, beta, jacobi_arg, 3)
        out = (
            (m - 2) * (m - 1) * m * r ** jnp.maximum(m - 3, 0) * f
            - 12 * m**2 * r ** jnp.maximum(m - 1, 0) * df
            + 48 * (m + 1) * r ** (m + 1) * d2f
            - 64 * r ** (m + 3) * d3f
        )
    elif dr == 4:
        f = _jacobi(n, alpha, beta, jacobi_arg, 0)
        df = _jacobi(n, alpha, beta, jacobi_arg, 1)
        d2f = _jacobi(n, alpha, beta, jacobi_arg, 2)
        d3f = _jacobi(n, alpha, beta, jacobi_arg, 3)
        d4f = _jacobi(n, alpha, beta, jacobi_arg, 4)
        out = (
            (m - 3) * (m - 2) * (m - 1) * m * r ** jnp.maximum(m - 4, 0) * f
            - 8 * m * (2 * m**2 - 3 * m + 1) * r ** jnp.maximum(m - 2, 0) * df
            + 48 * (2 * m**2 + 2 * m + 1) * r**m * d2f
            - 128 * (2 * m + 3) * r ** (m + 2) * d3f
            + 256 * r ** (m + 4) * d4f
        )
    else:
        raise NotImplementedError(
            "Analytic radial derivatives of Zernike polynomials for order>4 "
            + "have not been implemented."
        )
    return s * jnp.where((l - m) % 2 == 0, out, 0)


def power_coeffs(l):
    """Power series coefficients.

    Parameters
    ----------
    l : ndarray of int, shape(K,)
        radial mode number(s)

    Returns
    -------
    coeffs : ndarray, shape(l+1,)

    """
    l = np.atleast_1d(l).astype(int)
    npoly = len(l)  # number of polynomials
    order = np.max(l)  # order of polynomials
    coeffs = np.zeros((npoly, order + 1))
    coeffs[range(npoly), l] = 1
    return coeffs


def powers(rho, l, dr=0):
    """Power series.

    Parameters
    ----------
    rho : ndarray, shape(N,)
        radial coordinates to evaluate basis
    l : ndarray of int, shape(K,)
        radial mode number(s)
    dr : int
        order of derivative (Default = 0)

    Returns
    -------
    y : ndarray, shape(N,K)
        basis function(s) evaluated at specified points

    """
    coeffs = power_coeffs(l)
    coeffs = polyder_vec(np.fliplr(coeffs), dr)
    return polyval_vec(coeffs, rho).T


def chebyshev(r, l, dr=0):
    """Shifted Chebyshev polynomial.

    Parameters
    ----------
    rho : ndarray, shape(N,)
        radial coordinates to evaluate basis
    l : ndarray of int, shape(K,)
        radial mode number(s)
    dr : int
        order of derivative (Default = 0)

    Returns
    -------
    y : ndarray, shape(N,K)
        basis function(s) evaluated at specified points

    """
    x = 2 * r - 1  # shift
    x, l, dr = map(jnp.asarray, (x, l, dr))
    if dr == 0:
        return jnp.cos(l * jnp.arccos(x))
    else:
        # dy/dr = dy/dx * dx/dr = dy/dx * 2
        raise NotImplementedError(
            "Analytic radial derivatives of Chebyshev polynomials "
            + "have not been implemented."
        )


@jit
def fourier(theta, m, NFP=1, dt=0):
    """Fourier series.

    Parameters
    ----------
    theta : ndarray, shape(N,)
        poloidal/toroidal coordinates to evaluate basis
    m : ndarray of int, shape(K,)
        poloidal/toroidal mode number(s)
    NFP : int
        number of field periods (Default = 1)
    dt : int
        order of derivative (Default = 0)

    Returns
    -------
    y : ndarray, shape(N,K)
        basis function(s) evaluated at specified points

    """
    theta, m, NFP, dt = map(jnp.asarray, (theta, m, NFP, dt))
    m_pos = (m >= 0).astype(int)
    m_abs = jnp.abs(m) * NFP
    shift = m_pos * jnp.pi / 2 + dt * jnp.pi / 2
    return m_abs**dt * jnp.sin(m_abs * theta + shift)


@jit
@jnp.vectorize
def _binom(n, k):
    """Binomial coefficient.

    Implementation is only correct for positive integer n,k and n>=k

    Parameters
    ----------
    n : int, array-like
        number of things to choose from
    k : int, array-like
        number of things chosen

    Returns
    -------
    val : int, float, array-like
        number of possible combinations
    """
    # adapted from scipy:
    # https://github.com/scipy/scipy/blob/701ffcc8a6f04509d115aac5e5681c538b5265a2/
    # scipy/special/orthogonal_eval.pxd#L68

    n, k = map(jnp.asarray, (n, k))

    def _binom_body_fun(i, b_n):
        b, n = b_n
        num = n + 1 - i
        den = i
        return (b * num / den, n)

    kx = k.astype(int)
    b, n = fori_loop(1, 1 + kx, _binom_body_fun, (1.0, n))
    return b


@jit
@jnp.vectorize
def _jacobi(n, alpha, beta, x, dx=0):
    """Jacobi polynomial evaluation.

    Implementation is only correct for non-negative integer coefficients,
    returns 0 otherwise.

    Parameters
    ----------
    n : int, array_like
        Degree of the polynomial.
    alpha : int, array_like
        Parameter
    beta : int, array_like
        Parameter
    x : float, array_like
        Points at which to evaluate the polynomial

    Returns
    -------
    P : ndarray
        Values of the Jacobi polynomial
    """
    # adapted from scipy:
    # https://github.com/scipy/scipy/blob/701ffcc8a6f04509d115aac5e5681c538b5265a2/
    # scipy/special/orthogonal_eval.pxd#L144

    def _jacobi_body_fun(kk, d_p_a_b_x):
        d, p, alpha, beta, x = d_p_a_b_x
        k = kk + 1.0
        t = 2 * k + alpha + beta
        d = (
            (t * (t + 1) * (t + 2)) * (x - 1) * p + 2 * k * (k + beta) * (t + 2) * d
        ) / (2 * (k + alpha + 1) * (k + alpha + beta + 1) * t)
        p = d + p
        return (d, p, alpha, beta, x)

    n, alpha, beta, x = map(jnp.asarray, (n, alpha, beta, x))

    # coefficient for derivative
    c = (
        gammaln(alpha + beta + n + 1 + dx)
        - dx * jnp.log(2)
        - gammaln(alpha + beta + n + 1)
    )
    c = jnp.exp(c)
    # taking derivative is same as coeff*jacobi but for shifted n,a,b
    n -= dx
    alpha += dx
    beta += dx

    d = (alpha + beta + 2) * (x - 1) / (2 * (alpha + 1))
    p = d + 1
    d, p, alpha, beta, x = fori_loop(
        0, jnp.maximum(n - 1, 0).astype(int), _jacobi_body_fun, (d, p, alpha, beta, x)
    )
    out = _binom(n + alpha, n) * p
    # should be complex for n<0, but it gets replaced elsewhere so just return 0 here
    out = jnp.where(n < 0, 0, out)
    # other edge cases
    out = jnp.where(n == 0, 1.0, out)
    out = jnp.where(n == 1, 0.5 * (2 * (alpha + 1) + (alpha + beta + 2) * (x - 1)), out)
    return c * out


def zernike_norm(l, m):
    """Norm of a Zernike polynomial with l, m indexing.

    Parameters
    ----------
    l,m : int
        radial and azimuthal mode numbers.

    Returns
    -------
    norm : float
        the integral (Z^m_l)^2 r dr dt, r=[0,1], t=[0,2*pi]

    """
    return np.sqrt((2 * (l + 1)) / (np.pi * (1 + int(m == 0))))
