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import abc
from typing import List, Tuple, Union, Optional
import math

import torch


def get_filter_basis(kernel_shape: Union[int, List[int], Tuple[int, int]], basis_type: str):
    """Factory function to generate the appropriate filter basis"""

    if basis_type == "piecewise linear":
        return PiecewiseLinearFilterBasis(kernel_shape=kernel_shape)
    else:
        raise ValueError(f"Unknown basis_type {basis_type}")


class AbstractFilterBasis(metaclass=abc.ABCMeta):
    """
    Abstract base class for a filter basis
    """

    def __init__(
        self,
        kernel_shape: Union[int, List[int], Tuple[int, int]],
    ):

        self.kernel_shape = kernel_shape

    @property
    @abc.abstractmethod
    def kernel_size(self):
        raise NotImplementedError

    @abc.abstractmethod
    def compute_support_vals(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float):
        """
        Computes the index set that falls into the kernel's support and returns both indices and values. This routine is designed for sparse evaluations of the filter basis
        """
        raise NotImplementedError


class PiecewiseLinearFilterBasis(AbstractFilterBasis):
    """
    Tensor-product basis on a disk constructed from piecewise linear basis functions.
    """

    def __init__(
        self,
        kernel_shape: Union[int, List[int], Tuple[int, int]],
    ):

        if isinstance(kernel_shape, int):
            kernel_shape = [kernel_shape]
        if len(kernel_shape) == 1:
            kernel_shape = [kernel_shape[0], 1]
        elif len(kernel_shape) != 2:
            raise ValueError(f"expected kernel_shape to be a list or tuple of length 1 or 2 buu got {kernel_shape} instead.")

        super().__init__(kernel_shape=kernel_shape)

    @property
    def kernel_size(self):
        return (self.kernel_shape[0] // 2) * self.kernel_shape[1] + self.kernel_shape[0] % 2

    def _compute_support_vals_isotropic(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float):
        """
        Computes the index set that falls into the isotropic kernel's support and returns both indices and values.
        """

        # enumerator for basis function
        ikernel = torch.arange(self.kernel_size).reshape(-1, 1, 1)

        # collocation points
        nr = self.kernel_shape[0]
        dr = 2 * r_cutoff / (nr + 1)

        # compute the support
        if nr % 2 == 1:
            ir = ikernel * dr
        else:
            ir = (ikernel + 0.5) * dr

        # find the indices where the rotated position falls into the support of the kernel
        iidx = torch.argwhere(((r - ir).abs() <= dr) & (r <= r_cutoff))
        vals = 1 - (r[iidx[:, 1], iidx[:, 2]] - ir[iidx[:, 0], 0, 0]).abs() / dr

        return iidx, vals

    def _compute_support_vals_anisotropic(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float):
        """
        Computes the index set that falls into the isotropic kernel's support and returns both indices and values.
        """

        # enumerator for basis function
        ikernel = torch.arange(self.kernel_size).reshape(-1, 1, 1)

        # collocation points
        nr = self.kernel_shape[0]
        nphi = self.kernel_shape[1]
        dr = 2 * r_cutoff / (nr + 1)
        dphi = 2.0 * math.pi / nphi

        # disambiguate even and uneven cases and compute the support
        if nr % 2 == 1:
            ir = ((ikernel - 1) // nphi + 1) * dr
            iphi = ((ikernel - 1) % nphi) * dphi
        else:
            ir = (ikernel // nphi + 0.5) * dr
            iphi = (ikernel % nphi) * dphi

        # find the indices where the rotated position falls into the support of the kernel
        if nr % 2 == 1:
            # find the support
            cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
            cond_phi = (ikernel == 0) | ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
            # find indices where conditions are met
            iidx = torch.argwhere(cond_r & cond_phi)
            # compute the distance to the collocation points
            dist_r = (r[iidx[:, 1], iidx[:, 2]] - ir[iidx[:, 0], 0, 0]).abs()
            dist_phi = (phi[iidx[:, 1], iidx[:, 2]] - iphi[iidx[:, 0], 0, 0]).abs()
            # compute the value of the basis functions
            vals = 1 - dist_r / dr
            vals *= torch.where(
                (iidx[:, 0] > 0),
                (1 - torch.minimum(dist_phi, (2 * math.pi - dist_phi)) / dphi),
                1.0,
            )

        else:
            # in the even case, the inner casis functions overlap into areas with a negative areas
            rn = -r
            phin = torch.where(phi + math.pi >= 2 * math.pi, phi - math.pi, phi + math.pi)
            # find the support
            cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
            cond_phi = ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
            cond_rn = ((rn - ir).abs() <= dr) & (rn <= r_cutoff)
            cond_phin = ((phin - iphi).abs() <= dphi) | ((2 * math.pi - (phin - iphi).abs()) <= dphi)
            # find indices where conditions are met
            iidx = torch.argwhere((cond_r & cond_phi) | (cond_rn & cond_phin))
            dist_r = (r[iidx[:, 1], iidx[:, 2]] - ir[iidx[:, 0], 0, 0]).abs()
            dist_phi = (phi[iidx[:, 1], iidx[:, 2]] - iphi[iidx[:, 0], 0, 0]).abs()
            dist_rn = (rn[iidx[:, 1], iidx[:, 2]] - ir[iidx[:, 0], 0, 0]).abs()
            dist_phin = (phin[iidx[:, 1], iidx[:, 2]] - iphi[iidx[:, 0], 0, 0]).abs()
            # compute the value of the basis functions
            vals = cond_r[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - dist_r / dr)
            vals *= cond_phi[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - torch.minimum(dist_phi, (2 * math.pi - dist_phi)) / dphi)
            valsn = cond_rn[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - dist_rn / dr)
            valsn *= cond_phin[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - torch.minimum(dist_phin, (2 * math.pi - dist_phin)) / dphi)
            vals += valsn

        return iidx, vals

    def compute_support_vals(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float):

        if self.kernel_shape[1] > 1:
            return self._compute_support_vals_anisotropic(r, phi, r_cutoff=r_cutoff)
        else:
            return self._compute_support_vals_isotropic(r, phi, r_cutoff=r_cutoff)
