import torch
from torch import nn
from transformers import PreTrainedModel
from transformers.modeling_outputs import CausalLMOutputWithPast
from torch.nn import CrossEntropyLoss
from typing import Optional
from .configuration_minGRULM import MinGRULMConfig
from minGRU_pytorch.minGRULM import minGRULM


class MinGRULMPreTrainedModel(PreTrainedModel):
    config_class = MinGRULMConfig
    base_model_prefix = "model"

    def _init_weights(self, module):
        std = 0.02
        if isinstance(module, nn.Linear):
            module.weight.data.normal_(mean=0.0, std=std)
            if module.bias is not None:
                module.bias.data.zero_()
        elif isinstance(module, nn.Embedding):
            module.weight.data.normal_(mean=0.0, std=std)
            if module.padding_idx is not None:
                module.weight.data[module.padding_idx].zero_()


class MinGRULMForCausalLM(MinGRULMPreTrainedModel):
    def __init__(self, config: MinGRULMConfig):
        super().__init__(config)

        # Load model from minGRULM library
        self.model = minGRULM(
            num_tokens=config.vocab_size,
            dim=config.d_model,
            depth=config.n_layer,
            ff_mult=config.ff_mult,
            min_gru_expansion=config.expand,
            enable_conv=config.enable_conv,
        )

        self.lm_head = nn.Linear(config.d_model, config.vocab_size, bias=False)
        self.post_init()

    def get_input_embeddings(self):
        return self.model.token_emb

    def set_input_embeddings(self, value):
        self.model.token_emb = value

    def get_output_embeddings(self):
        return self.lm_head

    def forward(
        self,
        input_ids: torch.LongTensor,
        labels: Optional[torch.LongTensor] = None,
        return_dict: Optional[bool] = True,
    ):
        # Forward pass through the model
        logits = self.model(input_ids)

        loss = None
        if labels is not None:
            shift_logits = logits[..., :-1, :].contiguous()
            shift_labels = labels[..., 1:].contiguous()
            loss_fct = CrossEntropyLoss()
            loss = loss_fct(
                shift_logits.view(-1, self.config.vocab_size),
                shift_labels.view(-1),
            )

        if not return_dict:
            return (loss, logits) if loss is not None else (logits,)

        return CausalLMOutputWithPast(
            loss=loss,
            logits=logits,
        )