# Copyright 2022 The Plenoptix Team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
Sampler.
"""

import math

import torch
from torch import nn

import pyrad_cuda


class LLTMFunction(torch.autograd.Function):
    @staticmethod
    def forward(ctx, input, weights, bias, old_h, old_cell):
        outputs = pyrad_cuda.forward(input, weights, bias, old_h, old_cell)
        new_h, new_cell = outputs[:2]
        variables = outputs[1:] + [weights]
        ctx.save_for_backward(*variables)

        return new_h, new_cell

    @staticmethod
    def backward(ctx, grad_h, grad_cell):
        outputs = pyrad_cuda.backward(grad_h.contiguous(), grad_cell.contiguous(), *ctx.saved_variables)
        d_old_h, d_input, d_weights, d_bias, d_old_cell, d_gates = outputs
        return d_input, d_weights, d_bias, d_old_h, d_old_cell


class Sampler(nn.Module):
    def __init__(self, input_features, state_size):
        super().__init__()
        self.input_features = input_features
        self.state_size = state_size
        self.weights = nn.Parameter(torch.Tensor(3 * state_size, input_features + state_size))
        self.bias = nn.Parameter(torch.Tensor(1, 3 * state_size))
        self.reset_parameters()

    def reset_parameters(self):
        stdv = 1.0 / math.sqrt(self.state_size)
        for weight in self.parameters():
            weight.data.uniform_(-stdv, +stdv)

    def forward(self, input, state):
        return LLTMFunction.apply(input, self.weights, self.bias, *state)