#!/usr/bin/env python3

import logging
import math
from typing import Dict, List, Optional, Tuple
from pathlib import Path

import torch
import torch.nn as nn
from fairseq import checkpoint_utils, utils
from fairseq.data.data_utils import lengths_to_padding_mask
from fairseq.models import (
    FairseqEncoder,
    FairseqEncoderDecoderModel,
    register_model,
    register_model_architecture,
)
from fairseq.models.transformer import Embedding, TransformerDecoder
from fairseq.modules import (
    FairseqDropout,
    LayerNorm,
    PositionalEmbedding,
    TransformerEncoderLayer,
)
from torch import Tensor


logger = logging.getLogger(__name__)


class Conv1dSubsampler(nn.Module):
    """Convolutional subsampler: a stack of 1D convolution (along temporal
    dimension) followed by non-linear activation via gated linear units
    (https://arxiv.org/abs/1911.08460)

    Args:
        in_channels (int): the number of input channels
        mid_channels (int): the number of intermediate channels
        out_channels (int): the number of output channels
        kernel_sizes (List[int]): the kernel size for each convolutional layer
    """

    def __init__(
        self,
        in_channels: int,
        mid_channels: int,
        out_channels: int,
        kernel_sizes: List[int] = (3, 3),
    ):
        super(Conv1dSubsampler, self).__init__()
        self.n_layers = len(kernel_sizes)
        self.conv_layers = nn.ModuleList(
            nn.Conv1d(
                in_channels if i == 0 else mid_channels // 2,
                mid_channels if i < self.n_layers - 1 else out_channels * 2,
                k,
                stride=2,
                padding=k // 2,
            )
            for i, k in enumerate(kernel_sizes)
        )

    def get_out_seq_lens_tensor(self, in_seq_lens_tensor):
        out = in_seq_lens_tensor.clone()
        for _ in range(self.n_layers):
            out = ((out.float() - 1) / 2 + 1).floor().long()
        return out

    def forward(self, src_tokens, src_lengths):
        bsz, in_seq_len, _ = src_tokens.size()  # B x T x (C x D)
        x = src_tokens.transpose(1, 2).contiguous()  # -> B x (C x D) x T
        for conv in self.conv_layers:
            x = conv(x)
            x = nn.functional.glu(x, dim=1)
        _, _, out_seq_len = x.size()
        x = x.transpose(1, 2).transpose(0, 1).contiguous()  # -> T x B x (C x D)
        return x, self.get_out_seq_lens_tensor(src_lengths)


@register_model("s2t_transformer")
class S2TTransformerModel(FairseqEncoderDecoderModel):
    """Adapted Transformer model (https://arxiv.org/abs/1706.03762) for
    speech-to-text tasks. The Transformer encoder/decoder remains the same.
    A trainable input subsampler is prepended to the Transformer encoder to
    project inputs into the encoder dimension as well as downsample input
    sequence for computational efficiency."""

    def __init__(self, encoder, decoder):
        super().__init__(encoder, decoder)

    @staticmethod
    def add_args(parser):
        """Add model-specific arguments to the parser."""
        # input
        parser.add_argument(
            "--conv-kernel-sizes",
            type=str,
            metavar="N",
            help="kernel sizes of Conv1d subsampling layers",
        )
        parser.add_argument(
            "--conv-channels",
            type=int,
            metavar="N",
            help="# of channels in Conv1d subsampling layers",
        )
        # Transformer
        parser.add_argument(
            "--activation-fn",
            type=str,
            default="relu",
            choices=utils.get_available_activation_fns(),
            help="activation function to use",
        )
        parser.add_argument(
            "--dropout", type=float, metavar="D", help="dropout probability"
        )
        parser.add_argument(
            "--attention-dropout",
            type=float,
            metavar="D",
            help="dropout probability for attention weights",
        )
        parser.add_argument(
            "--activation-dropout",
            "--relu-dropout",
            type=float,
            metavar="D",
            help="dropout probability after activation in FFN.",
        )
        parser.add_argument(
            "--encoder-embed-dim",
            type=int,
            metavar="N",
            help="encoder embedding dimension",
        )
        parser.add_argument(
            "--encoder-ffn-embed-dim",
            type=int,
            metavar="N",
            help="encoder embedding dimension for FFN",
        )
        parser.add_argument(
            "--encoder-layers", type=int, metavar="N", help="num encoder layers"
        )
        parser.add_argument(
            "--encoder-attention-heads",
            type=int,
            metavar="N",
            help="num encoder attention heads",
        )
        parser.add_argument(
            "--encoder-normalize-before",
            action="store_true",
            help="apply layernorm before each encoder block",
        )
        parser.add_argument(
            "--decoder-embed-dim",
            type=int,
            metavar="N",
            help="decoder embedding dimension",
        )
        parser.add_argument(
            "--decoder-ffn-embed-dim",
            type=int,
            metavar="N",
            help="decoder embedding dimension for FFN",
        )
        parser.add_argument(
            "--decoder-layers", type=int, metavar="N", help="num decoder layers"
        )
        parser.add_argument(
            "--decoder-attention-heads",
            type=int,
            metavar="N",
            help="num decoder attention heads",
        )
        parser.add_argument(
            "--decoder-normalize-before",
            action="store_true",
            help="apply layernorm before each decoder block",
        )
        parser.add_argument(
            "--share-decoder-input-output-embed",
            action="store_true",
            help="share decoder input and output embeddings",
        )
        parser.add_argument(
            "--layernorm-embedding",
            action="store_true",
            help="add layernorm to embedding",
        )
        parser.add_argument(
            "--no-scale-embedding",
            action="store_true",
            help="if True, dont scale embeddings",
        )
        parser.add_argument(
            "--load-pretrained-encoder-from",
            type=str,
            metavar="STR",
            help="model to take encoder weights from (for initialization)",
        )
        parser.add_argument(
            '--encoder-freezing-updates',
            type=int,
            metavar='N',
            help='freeze encoder for first N updates'
        )

    @classmethod
    def build_encoder(cls, args):
        encoder = S2TTransformerEncoder(args)
        pretraining_path = getattr(args, "load_pretrained_encoder_from", None)
        if pretraining_path is not None:
            if not Path(pretraining_path).exists():
                logger.warning(
                    f"skipped pretraining because {pretraining_path} does not exist"
                )
            else:
                encoder = checkpoint_utils.load_pretrained_component_from_model(
                    component=encoder, checkpoint=pretraining_path
                )
                logger.info(f"loaded pretrained encoder from: {pretraining_path}")
        return encoder

    @classmethod
    def build_decoder(cls, args, task, embed_tokens):
        return TransformerDecoderScriptable(args, task.target_dictionary, embed_tokens)

    @classmethod
    def build_model(cls, args, task):
        """Build a new model instance."""

        # make sure all arguments are present in older models
        base_architecture(args)

        def build_embedding(dictionary, embed_dim):
            num_embeddings = len(dictionary)
            padding_idx = dictionary.pad()
            return Embedding(num_embeddings, embed_dim, padding_idx)

        decoder_embed_tokens = build_embedding(
            task.target_dictionary, args.decoder_embed_dim
        )
        encoder = cls.build_encoder(args)
        decoder = cls.build_decoder(args, task, decoder_embed_tokens)
        return cls(encoder, decoder)

    def get_normalized_probs(
        self,
        net_output: Tuple[Tensor, Optional[Dict[str, List[Optional[Tensor]]]]],
        log_probs: bool,
        sample: Optional[Dict[str, Tensor]] = None,
    ):
        # net_output['encoder_out'] is a (B, T, D) tensor
        lprobs = self.get_normalized_probs_scriptable(net_output, log_probs, sample)
        lprobs.batch_first = True
        return lprobs

    def forward(self, src_tokens, src_lengths, prev_output_tokens):
        """
        The forward method inherited from the base class has a **kwargs
        argument in its input, which is not supported in torchscript. This
        method overwrites the forward method definition without **kwargs.
        """
        encoder_out = self.encoder(src_tokens=src_tokens, src_lengths=src_lengths)
        decoder_out = self.decoder(
            prev_output_tokens=prev_output_tokens, encoder_out=encoder_out
        )
        return decoder_out


class S2TTransformerEncoder(FairseqEncoder):
    """Speech-to-text Transformer encoder that consists of input subsampler and
    Transformer encoder."""

    def __init__(self, args):
        super().__init__(None)

        self.encoder_freezing_updates = args.encoder_freezing_updates
        self.num_updates = 0

        self.dropout_module = FairseqDropout(
            p=args.dropout, module_name=self.__class__.__name__
        )
        self.embed_scale = math.sqrt(args.encoder_embed_dim)
        if args.no_scale_embedding:
            self.embed_scale = 1.0
        self.padding_idx = 1

        self.subsample = Conv1dSubsampler(
            args.input_feat_per_channel * args.input_channels,
            args.conv_channels,
            args.encoder_embed_dim,
            [int(k) for k in args.conv_kernel_sizes.split(",")],
        )

        self.embed_positions = PositionalEmbedding(
            args.max_source_positions, args.encoder_embed_dim, self.padding_idx
        )

        self.transformer_layers = nn.ModuleList(
            [TransformerEncoderLayer(args) for _ in range(args.encoder_layers)]
        )
        if args.encoder_normalize_before:
            self.layer_norm = LayerNorm(args.encoder_embed_dim)
        else:
            self.layer_norm = None

    def _forward(self, src_tokens, src_lengths):
        x, input_lengths = self.subsample(src_tokens, src_lengths)
        x = self.embed_scale * x

        encoder_padding_mask = lengths_to_padding_mask(input_lengths)
        positions = self.embed_positions(encoder_padding_mask).transpose(0, 1)
        x += positions
        x = self.dropout_module(x)

        for layer in self.transformer_layers:
            x = layer(x, encoder_padding_mask)

        if self.layer_norm is not None:
            x = self.layer_norm(x)

        return {
            "encoder_out": [x],  # T x B x C
            "encoder_padding_mask": [encoder_padding_mask] if encoder_padding_mask.any() else [],  # B x T
            "encoder_embedding": [],  # B x T x C
            "encoder_states": [],  # List[T x B x C]
            "src_tokens": [],
            "src_lengths": [],
        }

    def forward(self, src_tokens, src_lengths):
        if self.num_updates < self.encoder_freezing_updates:
            with torch.no_grad():
                x = self._forward(src_tokens, src_lengths)
        else:
            x = self._forward(src_tokens, src_lengths)
        return x

    def reorder_encoder_out(self, encoder_out, new_order):
        new_encoder_out = (
            [] if len(encoder_out["encoder_out"]) == 0
            else [x.index_select(1, new_order) for x in encoder_out["encoder_out"]]
        )

        new_encoder_padding_mask = (
            [] if len(encoder_out["encoder_padding_mask"]) == 0
            else [x.index_select(0, new_order) for x in encoder_out["encoder_padding_mask"]]
        )

        new_encoder_embedding = (
            [] if len(encoder_out["encoder_embedding"]) == 0
            else [x.index_select(0, new_order) for x in encoder_out["encoder_embedding"]]
        )

        encoder_states = encoder_out["encoder_states"]
        if len(encoder_states) > 0:
            for idx, state in enumerate(encoder_states):
                encoder_states[idx] = state.index_select(1, new_order)

        return {
            "encoder_out": new_encoder_out,  # T x B x C
            "encoder_padding_mask": new_encoder_padding_mask,  # B x T
            "encoder_embedding": new_encoder_embedding,  # B x T x C
            "encoder_states": encoder_states,  # List[T x B x C]
            "src_tokens": [],  # B x T
            "src_lengths": [],  # B x 1
        }

    def set_num_updates(self, num_updates):
        super().set_num_updates(num_updates)
        self.num_updates = num_updates


class TransformerDecoderScriptable(TransformerDecoder):
    def extract_features(
        self,
        prev_output_tokens,
        encoder_out: Optional[Dict[str, List[Tensor]]] = None,
        incremental_state: Optional[Dict[str, Dict[str, Optional[Tensor]]]] = None,
        full_context_alignment: bool = False,
        alignment_layer: Optional[int] = None,
        alignment_heads: Optional[int] = None,
    ):
        # call scriptable method from parent class
        x, _ = self.extract_features_scriptable(
            prev_output_tokens,
            encoder_out,
            incremental_state,
            full_context_alignment,
            alignment_layer,
            alignment_heads,
        )
        return x, None


@register_model_architecture(model_name="s2t_transformer", arch_name="s2t_transformer")
def base_architecture(args):
    args.encoder_freezing_updates = getattr(args, "encoder_freezing_updates", 0)
    # Convolutional subsampler
    args.conv_kernel_sizes = getattr(args, "conv_kernel_sizes", "5,5")
    args.conv_channels = getattr(args, "conv_channels", 1024)
    # Transformer
    args.encoder_embed_dim = getattr(args, "encoder_embed_dim", 512)
    args.encoder_ffn_embed_dim = getattr(args, "encoder_ffn_embed_dim", 2048)
    args.encoder_layers = getattr(args, "encoder_layers", 12)
    args.encoder_attention_heads = getattr(args, "encoder_attention_heads", 8)
    args.encoder_normalize_before = getattr(args, "encoder_normalize_before", True)
    args.decoder_embed_dim = getattr(args, "decoder_embed_dim", args.encoder_embed_dim)
    args.decoder_ffn_embed_dim = getattr(
        args, "decoder_ffn_embed_dim", args.encoder_ffn_embed_dim
    )
    args.decoder_layers = getattr(args, "decoder_layers", 6)
    args.decoder_attention_heads = getattr(args, "decoder_attention_heads", 8)
    args.decoder_normalize_before = getattr(args, "decoder_normalize_before", True)
    args.decoder_learned_pos = getattr(args, "decoder_learned_pos", False)
    args.dropout = getattr(args, "dropout", 0.1)
    args.attention_dropout = getattr(args, "attention_dropout", args.dropout)
    args.activation_dropout = getattr(args, "activation_dropout", args.dropout)
    args.activation_fn = getattr(args, "activation_fn", "relu")
    args.adaptive_softmax_cutoff = getattr(args, "adaptive_softmax_cutoff", None)
    args.adaptive_softmax_dropout = getattr(args, "adaptive_softmax_dropout", 0)
    args.share_decoder_input_output_embed = getattr(
        args, "share_decoder_input_output_embed", False
    )
    args.no_token_positional_embeddings = getattr(
        args, "no_token_positional_embeddings", False
    )
    args.adaptive_input = getattr(args, "adaptive_input", False)
    args.decoder_layerdrop = getattr(args, "decoder_layerdrop", 0.0)
    args.decoder_output_dim = getattr(
        args, "decoder_output_dim", args.decoder_embed_dim
    )
    args.decoder_input_dim = getattr(args, "decoder_input_dim", args.decoder_embed_dim)
    args.no_scale_embedding = getattr(args, "no_scale_embedding", False)
    args.quant_noise_pq = getattr(args, "quant_noise_pq", 0)


@register_model_architecture("s2t_transformer", "s2t_transformer_s")
def s2t_transformer_s(args):
    args.encoder_embed_dim = getattr(args, "encoder_embed_dim", 256)
    args.encoder_ffn_embed_dim = getattr(args, "encoder_ffn_embed_dim", 256 * 8)
    args.encoder_attention_heads = getattr(args, "encoder_attention_heads", 4)
    args.decoder_attention_heads = getattr(args, "decoder_attention_heads", 4)
    args.dropout = getattr(args, "dropout", 0.1)
    base_architecture(args)


@register_model_architecture("s2t_transformer", "s2t_transformer_xs")
def s2t_transformer_xs(args):
    args.encoder_layers = getattr(args, "encoder_layers", 6)
    args.decoder_layers = getattr(args, "decoder_layers", 3)
    args.encoder_ffn_embed_dim = getattr(args, "encoder_ffn_embed_dim", 256 * 4)
    args.dropout = getattr(args, "dropout", 0.3)
    s2t_transformer_s(args)


@register_model_architecture("s2t_transformer", "s2t_transformer_sp")
def s2t_transformer_sp(args):
    args.encoder_layers = getattr(args, "encoder_layers", 16)
    s2t_transformer_s(args)


@register_model_architecture("s2t_transformer", "s2t_transformer_m")
def s2t_transformer_m(args):
    args.encoder_embed_dim = getattr(args, "encoder_embed_dim", 512)
    args.encoder_ffn_embed_dim = getattr(args, "encoder_ffn_embed_dim", 512 * 4)
    args.encoder_attention_heads = getattr(args, "encoder_attention_heads", 8)
    args.decoder_attention_heads = getattr(args, "decoder_attention_heads", 8)
    args.dropout = getattr(args, "dropout", 0.15)
    base_architecture(args)


@register_model_architecture("s2t_transformer", "s2t_transformer_mp")
def s2t_transformer_mp(args):
    args.encoder_layers = getattr(args, "encoder_layers", 16)
    s2t_transformer_m(args)


@register_model_architecture("s2t_transformer", "s2t_transformer_l")
def s2t_transformer_l(args):
    args.encoder_embed_dim = getattr(args, "encoder_embed_dim", 1024)
    args.encoder_ffn_embed_dim = getattr(args, "encoder_ffn_embed_dim", 1024 * 4)
    args.encoder_attention_heads = getattr(args, "encoder_attention_heads", 16)
    args.decoder_attention_heads = getattr(args, "decoder_attention_heads", 16)
    args.dropout = getattr(args, "dropout", 0.2)
    base_architecture(args)


@register_model_architecture("s2t_transformer", "s2t_transformer_lp")
def s2t_transformer_lp(args):
    args.encoder_layers = getattr(args, "encoder_layers", 16)
    s2t_transformer_l(args)