# Copyright (c) Alibaba, Inc. and its affiliates.
# Copyright 2018 The Google AI Language Team Authors and The HuggingFace Inc. team.
# Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
# 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.

import torch
import torch.nn as nn
import torch.utils.checkpoint
from torch.nn import CrossEntropyLoss
from transformers.activations import ACT2FN

from modelscope.metainfo import Models
from modelscope.models.builder import MODELS
from modelscope.outputs import AttentionFillMaskModelOutput
from modelscope.utils import logger as logging
from modelscope.utils.constant import Tasks
from .backbone import MegatronBertModel, MegatronBertPreTrainedModel
from .configuration import MegatronBertConfig

logger = logging.get_logger()


# Copied from transformers.models.bert.modeling_bert.BertPredictionHeadTransform with Bert->MegatronBert
class MegatronBertPredictionHeadTransform(nn.Module):

    def __init__(self, config):
        super().__init__()
        self.dense = nn.Linear(config.hidden_size, config.hidden_size)
        if isinstance(config.hidden_act, str):
            self.transform_act_fn = ACT2FN[config.hidden_act]
        else:
            self.transform_act_fn = config.hidden_act
        self.LayerNorm = nn.LayerNorm(
            config.hidden_size, eps=config.layer_norm_eps)

    def forward(self, hidden_states: torch.Tensor) -> torch.Tensor:
        hidden_states = self.dense(hidden_states)
        hidden_states = self.transform_act_fn(hidden_states)
        hidden_states = self.LayerNorm(hidden_states)
        return hidden_states


# Copied from transformers.models.bert.modeling_bert.BertLMPredictionHead with Bert->MegatronBert
class MegatronBertLMPredictionHead(nn.Module):

    def __init__(self, config):
        super().__init__()
        self.transform = MegatronBertPredictionHeadTransform(config)

        # The output weights are the same as the input embeddings, but there is
        # an output-only bias for each token.
        self.decoder = nn.Linear(
            config.hidden_size, config.vocab_size, bias=False)

        self.bias = nn.Parameter(torch.zeros(config.vocab_size))

        # Need a link between the two variables so that the bias is correctly resized with `resize_token_embeddings`
        self.decoder.bias = self.bias

    def forward(self, hidden_states):
        hidden_states = self.transform(hidden_states)
        hidden_states = self.decoder(hidden_states)
        return hidden_states


# Copied from transformers.models.bert.modeling_bert.BertOnlyMLMHead with Bert->MegatronBert
class MegatronBertOnlyMLMHead(nn.Module):

    def __init__(self, config):
        super().__init__()
        self.predictions = MegatronBertLMPredictionHead(config)

    def forward(self, sequence_output: torch.Tensor) -> torch.Tensor:
        prediction_scores = self.predictions(sequence_output)
        return prediction_scores


# Copied from transformers.models.bert.modeling_bert.BertOnlyNSPHead with Bert->MegatronBert
class MegatronBertOnlyNSPHead(nn.Module):

    def __init__(self, config):
        super().__init__()
        self.seq_relationship = nn.Linear(config.hidden_size, 2)

    def forward(self, pooled_output):
        seq_relationship_score = self.seq_relationship(pooled_output)
        return seq_relationship_score


# Copied from transformers.models.bert.modeling_bert.BertPreTrainingHeads with Bert->MegatronBert
class MegatronBertPreTrainingHeads(nn.Module):

    def __init__(self, config):
        super().__init__()
        self.predictions = MegatronBertLMPredictionHead(config)
        self.seq_relationship = nn.Linear(config.hidden_size, 2)

    def forward(self, sequence_output, pooled_output):
        prediction_scores = self.predictions(sequence_output)
        seq_relationship_score = self.seq_relationship(pooled_output)
        return prediction_scores, seq_relationship_score


@MODELS.register_module(Tasks.fill_mask, module_name=Models.megatron_bert)
class MegatronBertForMaskedLM(MegatronBertPreTrainedModel):

    _keys_to_ignore_on_load_unexpected = [r'pooler', r'seq_relationship']
    _keys_to_ignore_on_load_missing = [
        r'position_ids', r'predictions.decoder.bias'
    ]

    def __init__(self, config: MegatronBertConfig, **kwargs):
        super().__init__(config)

        if config.is_decoder:
            logger.warning(
                'If you want to use `MegatronBertForMaskedLM` make sure `config.is_decoder=False` for '
                'bi-directional self-attention.')

        self.bert = MegatronBertModel(config, add_pooling_layer=False)
        self.cls = MegatronBertOnlyMLMHead(config)

        # Initialize weights and apply final processing
        self.post_init()

    def get_output_embeddings(self):
        return self.cls.predictions.decoder

    def set_output_embeddings(self, new_embeddings):
        self.cls.predictions.decoder = new_embeddings

    def forward(
        self,
        input_ids=None,
        attention_mask=None,
        token_type_ids=None,
        position_ids=None,
        head_mask=None,
        inputs_embeds=None,
        encoder_hidden_states=None,
        encoder_attention_mask=None,
        labels=None,
        output_attentions=None,
        output_hidden_states=None,
        return_dict=None,
    ):
        r"""
        Args:
            input_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`):
                Indices of input sequence tokens in the vocabulary.

                Indices can be obtained using :class:`~modelscope.models.nlp.structbert.SbertTokenizer`. See
                :meth:`transformers.PreTrainedTokenizer.encode` and :meth:`transformers.PreTrainedTokenizer.__call__`
                for details.

                `What are input IDs? <../glossary.html#input-ids>`__
            attention_mask (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length)`, `optional`):
                Mask to avoid performing attention on padding token indices. Mask values selected in ``[0, 1]``:

                - 1 for tokens that are **not masked**,
                - 0 for tokens that are **masked**.

                `What are attention masks? <../glossary.html#attention-mask>`__
            token_type_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`, `optional`):
                Segment token indices to indicate first and second portions of the inputs. Indices are selected in ``[0,
                1]``:

                - 0 corresponds to a `sentence A` token,
                - 1 corresponds to a `sentence B` token.

                `What are token type IDs? <../glossary.html#token-type-ids>`_
            position_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`, `optional`):
                Indices of positions of each input sequence tokens in the position embeddings. Selected in the range
                ``[0,config.max_position_embeddings - 1]``.

                `What are position IDs? <../glossary.html#position-ids>`_
            head_mask (:obj:`torch.FloatTensor` of shape :obj:`(num_heads,)` or :obj:`(num_layers, num_heads)`,
                `optional`):
                Mask to nullify selected heads of the self-attention modules. Mask values selected in ``[0, 1]``:

                - 1 indicates the head is **not masked**,
                - 0 indicates the head is **masked**.

            inputs_embeds (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length, hidden_size)`,
                `optional`):
                Optionally, instead of passing :obj:`input_ids` you can choose to directly pass an embedded
                representation. This is useful if you want more control over how to convert :obj:`input_ids` indices
                into associated vectors than the model's internal embedding lookup matrix.
            output_attentions (:obj:`bool`, `optional`):
                Whether or not to return the attentions tensors of all attention layers. See ``attentions`` under
                returned tensors for more detail.
            output_hidden_states (:obj:`bool`, `optional`):
                Whether or not to return the hidden states of all layers. See ``hidden_states`` under returned tensors
                for more detail.
            return_dict (:obj:`bool`, `optional`):
                Whether or not to return a :class:`~transformers.ModelOutput` instead of a plain tuple.
            labels (`torch.LongTensor` of shape `(batch_size, sequence_length)`,
            *optional*):
                Labels for computing the masked language modeling loss. Indices
                should be in `[-100, 0, ..., config.vocab_size]` (see `input_ids`
                docstring) Tokens with indices set to `-100` are ignored (masked),
                the loss is only computed for the tokens with labels in `[0, ...,
                config.vocab_size]`

        Returns:
            Returns `modelscope.outputs.AttentionFillMaskModelOutput`

        Examples:
            >>> from modelscope.models import Model
            >>> from modelscope.preprocessors import Preprocessor
            >>> model = Model.from_pretrained('damo/nlp_megatronbert_backbone_base_std')
            >>> preprocessor = Preprocessor.from_pretrained('damo/nlp_megatronbert_backbone_base_std')
            >>> print(model(**preprocessor(('This is a test', 'This is also a test'))))
        """

        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.bert(
            input_ids,
            attention_mask=attention_mask,
            token_type_ids=token_type_ids,
            position_ids=position_ids,
            head_mask=head_mask,
            inputs_embeds=inputs_embeds,
            encoder_hidden_states=encoder_hidden_states,
            encoder_attention_mask=encoder_attention_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        sequence_output = outputs[0]
        prediction_scores = self.cls(sequence_output)

        masked_lm_loss = None
        if labels is not None:
            loss_fct = CrossEntropyLoss()  # -100 index = padding token
            masked_lm_loss = loss_fct(
                prediction_scores.view(-1, self.config.vocab_size),
                labels.view(-1))

        if not return_dict:
            output = (prediction_scores, ) + outputs[2:]
            return ((masked_lm_loss, )
                    + output) if masked_lm_loss is not None else output

        return AttentionFillMaskModelOutput(
            loss=masked_lm_loss,
            logits=prediction_scores,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
            input_ids=input_ids,
        )

    def prepare_inputs_for_generation(self,
                                      input_ids,
                                      attention_mask=None,
                                      **model_kwargs):
        input_shape = input_ids.shape
        effective_batch_size = input_shape[0]

        #  add a dummy token
        if self.config.pad_token_id is None:
            raise ValueError('The PAD token should be defined for generation')
        attention_mask_new_zeros = attention_mask.new_zeros(
            (attention_mask.shape[0], 1))
        attention_mask = torch.cat([attention_mask, attention_mask_new_zeros],
                                   dim=-1)
        dummy_token = torch.full((effective_batch_size, 1),
                                 self.config.pad_token_id,
                                 dtype=torch.long,
                                 device=input_ids.device)
        input_ids = torch.cat([input_ids, dummy_token], dim=1)

        return {'input_ids': input_ids, 'attention_mask': attention_mask}