import numpy as np

from ...phi import math
from ...phi.geom import GridCell, Geometry
from ...phi.math import random_normal, Tensor
from ._field import Field


class Noise(Field):

    def __init__(self, shape=math.EMPTY_SHAPE, scale=10, smoothness=1.0, **dims):
        """
        Generates random noise fluctuations which can be configured in physical size and smoothness.
            Each time values are sampled from a Noise field, a new noise field is generated.

            Noise is typically used as an initializer for CenteredGrids or StaggeredGrids.

        Args:
          channels: Number of independent random scalar fields this Field consists of
          scale: Size of noise fluctuations in physical units
          smoothness: Determines how quickly high frequencies die out
        """
        self.scale = scale
        self.smoothness = smoothness
        self._shape = shape & math.shape(**dims)

    @property
    def shape(self):
        return self._shape

    def sample_in(self, geometry: Geometry, reduce_channels=()) -> Tensor:
        if reduce_channels:
            shape = self._shape.non_channel.without(reduce_channels)
            assert len(reduce_channels) == 1
            geoms = geometry.unstack(reduce_channels[0])
            assert all(isinstance(g, GridCell) for g in geoms)
            components = [self.grid_sample(g.resolution, g.grid_size, shape) for g in geoms]
            return math.channel_stack(components, 'vector')
        if isinstance(geometry, GridCell):
            return self.grid_sample(geometry.resolution, geometry.grid_size)
        raise NotImplementedError(f"{type(geometry)} not supported. Only GridCell allowed.")

    def sample_at(self, points, reduce_channels=()) -> math.Tensor:
        raise NotImplementedError()

    def grid_sample(self, resolution: math.Shape, size, shape: math.Shape = None):
        shape = (self._shape if shape is None else shape).combined(resolution)
        rndj = math.to_complex(random_normal(shape)) + 1j * math.to_complex(random_normal(shape))  # Note: there is no complex32
        with math.NUMPY_BACKEND:
            k = math.fftfreq(resolution) * resolution / size * self.scale  # in physical units
            k = math.vec_squared(k)
        lowest_frequency = 0.1
        weight_mask = 1 / (1 + math.exp((lowest_frequency - k) * 1e3))  # High pass filter
        # --- Compute 1/k ---
        k.native()[(0,) * len(k.shape)] = np.inf
        inv_k = 1 / k
        inv_k.native()[(0,) * len(k.shape)] = 0
        # --- Compute result ---
        fft = rndj * inv_k ** self.smoothness * weight_mask
        array = math.real(math.ifft(fft))
        array /= math.std(array, dim=array.shape.non_batch)
        array -= math.mean(array, dim=array.shape.non_batch)
        array = math.to_float(array)
        return array

    def unstack(self, dimension: str) -> tuple:
        count = self.shape.get_size(dimension)
        reduced_shape = self.shape.without(dimension)
        return (Noise(reduced_shape, self.scale, self.smoothness),) * count

    def __repr__(self):
        return "%s, scale=%f, smoothness=%f" % (self._shape, self.scale, self.smoothness)
