"""

Implementation of the spectral normalization for the weight matrix

"""

import torch
import torch.nn as nn
from torch.nn import Parameter


class SpectralNorm(nn.Module):

    def __init__(self, module, name_module='weight', power_iterations=1):
        super(SpectralNorm, self).__init__()
        self.module= module
        self.name = name_module
        self.power_iter = power_iterations

        if not self._made_params():
            self._make_params()


    def update_u_v(self):
        """
        Updating the parameters u and v which would be used for the
        calculation of the spectral norm.
        :return:
        """

        u = getattr(self.module, self.name + "_u")
        v = getattr(self.module, self.name + "_v")
        w = getattr(self.module, self.name + "_bar")

        height = w.data.shape[0]
        for _ in range(self.power_iterations):
            v.data = self.l2normalize(torch.mv(torch.t(w.view(height, -1).data), u.data))
            u.data = self.l2normalize(torch.mv(w.view(height, -1).data, v.data))

        # sigma = torch.dot(u.data, torch.mv(w.view(height,-1).data, v.data))
        sigma = u.dot(w.view(height, -1).mv(v))

        setattr(self.module, self.name, w / sigma.expand_as(w))


    def l2normalize(self, v, eps=1e-12):
        return v / (v.norm() + eps)

    def _made_params(self):
        try:
            u = getattr(self.module, self.name + "_u")
            v = getattr(self.module, self.name + "_v")
            w = getattr(self.module, self.name + "_bar")
            return True
        except AttributeError:
            return False

    def _make_params(self):
        w = getattr(self.module, self.name)

        height = w.data.shape[0]
        width = w.view(height, -1).data.shape[1]

        u = Parameter(w.data.new(height).normal_(0, 1), requires_grad=False)
        v = Parameter(w.data.new(width).normal_(0, 1), requires_grad=False)
        u.data = self.l2normalize(u.data)
        v.data = self.l2normalize(v.data)
        w_bar = Parameter(w.data)

        del self.module._parameters[self.name]
        self.module.register_parameter(self.name + "_u", u)
        self.module.register_parameter(self.name + "_v", v)
        self.module.register_parameter(self.name + "_bar", w_bar)

    def forward(self, *args):
        self.update_u_v()
        return self.module.forward(*args)