#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# Copyright 2019 Tomoki Hayashi
#  Apache 2.0  (http://www.apache.org/licenses/LICENSE-2.0)

"""Duration predictor related loss."""

import torch
from typing import Optional
from core.modules import LayerNorm
from core.modules import SepConv1d

class DurationPredictor(torch.nn.Module):
    """Duration predictor module.

    This is a module of duration predictor described in `FastSpeech: Fast, Robust and Controllable Text to Speech`_.
    The duration predictor predicts a duration of each frame in log domain from the hidden embeddings of encoder.

    .. _`FastSpeech: Fast, Robust and Controllable Text to Speech`:
        https://arxiv.org/pdf/1905.09263.pdf

    Note:
        The calculation domain of outputs is different between in `forward` and in `inference`. In `forward`,
        the outputs are calculated in log domain but in `inference`, those are calculated in linear domain.

    """

    def __init__(self, idim, n_layers=2, n_chans=256, kernel_size=3, dropout_rate=0.1, offset=1.0):
        """Initilize duration predictor module.

        Args:
            idim (int): Input dimension.
            n_layers (int, optional): Number of convolutional layers.
            n_chans (int, optional): Number of channels of convolutional layers.
            kernel_size (int, optional): Kernel size of convolutional layers.
            dropout_rate (float, optional): Dropout rate.
            offset (float, optional): Offset value to avoid nan in log domain.

        """
        super(DurationPredictor, self).__init__()
        self.offset = offset
        self.conv = torch.nn.ModuleList()
        for idx in range(n_layers):
            in_chans = idim if idx == 0 else n_chans
            self.conv += [torch.nn.Sequential(
                SepConv1d(in_chans, n_chans, kernel_size, stride=1, padding=(kernel_size - 1) // 2),
                torch.nn.ReLU(),
                LayerNorm(n_chans),
                torch.nn.Dropout(dropout_rate)
            )]
        self.linear = torch.nn.Linear(n_chans, 1)

    def _forward(self, xs: torch.Tensor, x_masks: Optional[torch.Tensor] = None, is_inference: bool=False):
        xs = xs.transpose(1, -1)  # (B, idim, Tmax)
        for f in self.conv:
            xs = f(xs)  # (B, C, Tmax)

        # NOTE: calculate in log domain
        xs = self.linear(xs.transpose(1, -1)).squeeze(-1)  # (B, Tmax)

        if is_inference:
            # NOTE: calculate in linear domain
            xs = torch.clamp(torch.round(xs.exp() - self.offset), min=0).long()  # avoid negative value

        if x_masks is not None:
            xs = xs.masked_fill(x_masks, 0.0)

        return xs

    def forward(self, xs: torch.Tensor, x_masks: Optional[torch.Tensor] = None):
        """Calculate forward propagation.

        Args:
            xs (Tensor): Batch of input sequences (B, Tmax, idim).
            x_masks (ByteTensor, optional): Batch of masks indicating padded part (B, Tmax).

        Returns:
            Tensor: Batch of predicted durations in log domain (B, Tmax).

        """
        return self._forward(xs, x_masks, False)

    def inference(self, xs, x_masks: Optional[torch.Tensor] = None):
        """Inference duration.

        Args:
            xs (Tensor): Batch of input sequences (B, Tmax, idim).
            x_masks (ByteTensor, optional): Batch of masks indicating padded part (B, Tmax).

        Returns:
            LongTensor: Batch of predicted durations in linear domain (B, Tmax).

        """
        return self._forward(xs, x_masks, True)


class DurationPredictorLoss(torch.nn.Module):
    """Loss function module for duration predictor.

    The loss value is Calculated in log domain to make it Gaussian.

    """

    def __init__(self, offset=1.0):
        """Initilize duration predictor loss module.

        Args:
            offset (float, optional): Offset value to avoid nan in log domain.

        """
        super(DurationPredictorLoss, self).__init__()
        self.criterion = torch.nn.MSELoss()
        self.offset = offset

    def forward(self, outputs, targets):
        """Calculate forward propagation.

        Args:
            outputs (Tensor): Batch of prediction durations in log domain (B, T)
            targets (LongTensor): Batch of groundtruth durations in linear domain (B, T)

        Returns:
            Tensor: Mean squared error loss value.

        Note:
            `outputs` is in log domain but `targets` is in linear domain.

        """
        # NOTE: outputs is in log domain while targets in linear
        targets = torch.log(targets.float() + self.offset)
        loss = self.criterion(outputs, targets)

        return loss
