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from torch import nn, Tensor, tensor
from typing import Union, List, Optional

from transformers import PreTrainedModel
from transformers.modeling_outputs import (
    BaseModelOutputWithPoolingAndNoAttention, 
    ImageClassifierOutputWithNoAttention
)
from timm import create_model

from .configuration_efficientnet import EfficientNetConfig


class EfficientNetModel(PreTrainedModel):
    """

    EfficientNet model wrapper using Hugging Face's PreTrainedModel.



    This class initializes an EfficientNet model from `timm` library 

    and defines a forward method that extracts feature representations.



    Attributes

    ----------

        config:  

            Configuration object containing model parameters.

        model:   

            Instantiated EfficientNet model.

    """
    config_class = EfficientNetConfig

    def __init__(self, config):
        super().__init__(config)
        self.config = config
        self.model = create_model(
            config.model_name, 
            pretrained = config.pretrained, 
            num_classes = config.num_classes, 
            global_pool = config.global_pool,
        )
        
    def forward(self, pixel_values: Tensor) -> BaseModelOutputWithPoolingAndNoAttention:
        """

        Parameters

        ----------

            pixel_values : torch.Tensor

                Input tensor representing image pixel values.



        Returns

        -------

            BaseModelOutputWithPoolingAndNoAttention

                Object containing the `last_hidden_state` and `pooled_output`.

        """
        last_hidden_state = self.model.forward_features(pixel_values)
        pooler_output = self.model.forward_head(last_hidden_state, pre_logits=True)
        
        return BaseModelOutputWithPoolingAndNoAttention(
            last_hidden_state = last_hidden_state,
            pooler_output=pooler_output
        )


class EfficientNetModelForImageClassification(PreTrainedModel):
    """

    EfficientNet model wrapper using Hugging Face's PreTrainedModel.



    This class initializes an EfficientNet model from `timm` library 

    and defines a forward method that return logits.



    It supports training when labels are provided



    Attributes

    ----------

        config :  

            Configuration object containing model parameters.

        model :   

            Instantiated EfficientNet model.

    """
    config_class = EfficientNetConfig

    def __init__(self, config):
        super().__init__(config)
        self.config = config
        self.model = create_model(
            config.model_name, 
            pretrained = config.pretrained, 
            num_classes = config.num_classes, 
            global_pool = config.global_pool,
        )
        
    def compute_loss(self, logits, labels=None):
        loss = None
        if labels is None:
            pass
        else:
            labels = tensor(labels)
            ce_loss = nn.CrossEntropyLoss()
            loss = ce_loss(logits, labels)

        return loss
    
    def forward(

        self, 

        pixel_values: Tensor, 

        labels: Optional[Union[List[int], Tensor]] = None,

    ) -> ImageClassifierOutputWithNoAttention:
        """

        Parameters

        ----------

            pixel_values : torch.Tensor

                Input tensor representing image pixel values.

            labels : Optional[Union[List[int], torch.Tensor]]

                Ground truth labels for training and computing loss. 

                List of integers/tensor representing class IDs.



        Returns

        -------

            ImageClassifierOutputWithNoAttention

                Object containing `logits` and `loss`.

        """
        logits = self.model(pixel_values)

        loss = self.compute_loss(logits, labels)

        return ImageClassifierOutputWithNoAttention(
            loss = loss,
            logits = logits,
        )
    

__all__ = [
    "EfficientNetModel",
    "EfficientNetModelForImageClassification"
]