# --------------------------------------------------------
# The YiTrans End-to-End Speech Translation System for IWSLT 2022 Offline Shared Task (https://arxiv.org/abs/2206.05777)
# Github source: https://github.com/microsoft/SpeechT5/tree/main/YiTrans
# Copyright (c) 2022 Microsoft
# Licensed under The MIT License [see LICENSE for details]
# Based on fairseq code bases
# https://github.com/facebookresearch/fairseq
# --------------------------------------------------------
"""
    Modified from https://github.com/facebookresearch/fairseq/blob/main/fairseq/modules/transformer_layer.py
    https://github.com/microsoft/SpeechT5/blob/main/Speech2C/speech2c/models/modules/transformer_decoder_layer.py
"""

from typing import Dict, List, Optional

import torch
from torch import Tensor
from fairseq.modules.transformer_layer import TransformerDecoderLayerBase as FairseqTransformerDecoderLayerBase
from fairseq.modules import LayerNorm

from yitrans_iwslt22.modules.multihead_attention import MultiheadAttention


class TransformerDecoderLayerBase(FairseqTransformerDecoderLayerBase):
    """Decoder layer block.

    In the original paper each operation (multi-head attention, encoder
    attention or FFN) is postprocessed with: `dropout -> add residual ->
    layernorm`. In the tensor2tensor code they suggest that learning is more
    robust when preprocessing each layer with layernorm and postprocessing with:
    `dropout -> add residual`. We default to the approach in the paper, but the
    tensor2tensor approach can be enabled by setting
    *cfg.decoder.normalize_before* to ``True``.

    Args:
        args (argparse.Namespace): parsed command-line arguments
        no_encoder_attn (bool, optional): whether to attend to encoder outputs
            (default: False).
    """

    def __init__(
        self, cfg, no_encoder_attn=False, add_bias_kv=False, add_zero_attn=False, has_relative_attention_bias=False
    ):
        super().__init__(
            cfg,
            no_encoder_attn,
            add_bias_kv,
            add_zero_attn,
        )

        if has_relative_attention_bias:
            self.norm_k = LayerNorm(self.embed_dim // cfg.decoder.attention_heads)

    def build_self_attention(
        self, embed_dim, cfg, add_bias_kv=False, add_zero_attn=False
    ):
        return MultiheadAttention(
            embed_dim,
            cfg.decoder.attention_heads,
            dropout=cfg.attention_dropout,
            add_bias_kv=add_bias_kv,
            add_zero_attn=add_zero_attn,
            self_attention=not cfg.cross_self_attention,
            q_noise=self.quant_noise,
            qn_block_size=self.quant_noise_block_size,
        )

    def forward(
        self,
        x,
        encoder_out: Optional[torch.Tensor] = None,
        encoder_padding_mask: Optional[torch.Tensor] = None,
        incremental_state: Optional[Dict[str, Dict[str, Optional[Tensor]]]] = None,
        prev_self_attn_state: Optional[List[torch.Tensor]] = None,
        prev_attn_state: Optional[List[torch.Tensor]] = None,
        self_attn_mask: Optional[torch.Tensor] = None,
        self_attn_padding_mask: Optional[torch.Tensor] = None,
        need_attn: bool = False,
        need_head_weights: bool = False,
        pos_bias=None,
    ):
        """
        Args:
            x (Tensor): input to the layer of shape `(seq_len, batch, embed_dim)`
            encoder_padding_mask (ByteTensor, optional): binary
                ByteTensor of shape `(batch, src_len)` where padding
                elements are indicated by ``1``.
            need_attn (bool, optional): return attention weights
            need_head_weights (bool, optional): return attention weights
                for each head (default: return average over heads).
        Returns:
            encoded output of shape `(seq_len, batch, embed_dim)`
        """
        if need_head_weights:
            need_attn = True

        residual = x
        if self.normalize_before:
            x = self.self_attn_layer_norm(x)
            if pos_bias is not None:
                pos_bias = self.norm_k(pos_bias)
        if prev_self_attn_state is not None:
            prev_key, prev_value = prev_self_attn_state[:2]
            saved_state: Dict[str, Optional[Tensor]] = {
                "prev_key": prev_key,
                "prev_value": prev_value,
            }
            if len(prev_self_attn_state) >= 3:
                saved_state["prev_key_padding_mask"] = prev_self_attn_state[2]
            assert incremental_state is not None
            self.self_attn._set_input_buffer(incremental_state, saved_state)
        _self_attn_input_buffer = self.self_attn._get_input_buffer(incremental_state)
        if self.cross_self_attention and not (
            incremental_state is not None
            and _self_attn_input_buffer is not None
            and "prev_key" in _self_attn_input_buffer
        ):
            if self_attn_mask is not None:
                assert encoder_out is not None
                self_attn_mask = torch.cat(
                    (x.new_zeros(x.size(0), encoder_out.size(0)), self_attn_mask), dim=1
                )
            if self_attn_padding_mask is not None:
                if encoder_padding_mask is None:
                    assert encoder_out is not None
                    encoder_padding_mask = self_attn_padding_mask.new_zeros(
                        encoder_out.size(1), encoder_out.size(0)
                    )
                self_attn_padding_mask = torch.cat(
                    (encoder_padding_mask, self_attn_padding_mask), dim=1
                )
            assert encoder_out is not None
            y = torch.cat((encoder_out, x), dim=0)
        else:
            y = x

        x, attn = self.self_attn(
            query=x,
            key=y,
            value=y,
            key_padding_mask=self_attn_padding_mask,
            incremental_state=incremental_state,
            need_weights=False,
            attn_mask=self_attn_mask,
            position_bias=pos_bias,
        )
        if self.c_attn is not None:
            tgt_len, bsz = x.size(0), x.size(1)
            x = x.view(tgt_len, bsz, self.nh, self.head_dim)
            x = torch.einsum("tbhd,h->tbhd", x, self.c_attn)
            x = x.reshape(tgt_len, bsz, self.embed_dim)
        if self.attn_ln is not None:
            x = self.attn_ln(x)
        x = self.dropout_module(x)
        x = self.residual_connection(x, residual)
        if not self.normalize_before:
            x = self.self_attn_layer_norm(x)

        if self.encoder_attn is not None and encoder_out is not None:
            residual = x
            if self.normalize_before:
                x = self.encoder_attn_layer_norm(x)
            if prev_attn_state is not None:
                prev_key, prev_value = prev_attn_state[:2]
                saved_state: Dict[str, Optional[Tensor]] = {
                    "prev_key": prev_key,
                    "prev_value": prev_value,
                }
                if len(prev_attn_state) >= 3:
                    saved_state["prev_key_padding_mask"] = prev_attn_state[2]
                assert incremental_state is not None
                self.encoder_attn._set_input_buffer(incremental_state, saved_state)

            x, attn = self.encoder_attn(
                query=x,
                key=encoder_out,
                value=encoder_out,
                key_padding_mask=encoder_padding_mask,
                incremental_state=incremental_state,
                static_kv=True,
                need_weights=need_attn or (not self.training and self.need_attn),
                need_head_weights=need_head_weights,
            )
            x = self.dropout_module(x)
            x = self.residual_connection(x, residual)
            if not self.normalize_before:
                x = self.encoder_attn_layer_norm(x)

        residual = x
        if self.normalize_before:
            x = self.final_layer_norm(x)

        x = self.activation_fn(self.fc1(x))
        x = self.activation_dropout_module(x)
        if self.ffn_layernorm is not None:
            x = self.ffn_layernorm(x)
        x = self.fc2(x)
        x = self.dropout_module(x)
        if self.w_resid is not None:
            residual = torch.mul(self.w_resid, residual)
        x = self.residual_connection(x, residual)
        if not self.normalize_before:
            x = self.final_layer_norm(x)
        if self.onnx_trace and incremental_state is not None:
            saved_state = self.self_attn._get_input_buffer(incremental_state)
            assert saved_state is not None
            if self_attn_padding_mask is not None:
                self_attn_state = [
                    saved_state["prev_key"],
                    saved_state["prev_value"],
                    saved_state["prev_key_padding_mask"],
                ]
            else:
                self_attn_state = [saved_state["prev_key"], saved_state["prev_value"]]
            return x, attn, self_attn_state
        return x, attn, None

    def make_generation_fast_(self, need_attn: bool = False, **kwargs):
        self.need_attn = need_attn
