# Copyright (c) OpenMMLab. All rights reserved.
from typing import List, Optional, Union

import torch
from mmengine.model import BaseModel as _BaseModel
from torch import nn

from mmselfsup.registry import MODELS
from mmselfsup.structures import SelfSupDataSample


class BaseModel(_BaseModel):
    """BaseModel for SelfSup.

    All algorithms should inherit this module.

    Args:
        backbone (dict): The backbone module. See
            :mod:`mmcls.models.backbones`.
        neck (dict, optional): The neck module to process features from
            backbone. See :mod:`mmcls.models.necks`. Defaults to None.
        head (dict, optional): The head module to do prediction and calculate
            loss from processed features. See :mod:`mmcls.models.heads`.
            Notice that if the head is not set, almost all methods cannot be
            used except :meth:`extract_feat`. Defaults to None.
        pretrained (str, optional): The pretrained checkpoint path, support
            local path and remote path. Defaults to None.
        data_preprocessor (Union[dict, nn.Module], optional): The config for
            preprocessing input data. If None or no specified type, it will use
            "SelfSupDataPreprocessor" as type.
            See :class:`SelfSupDataPreprocessor` for more details.
            Defaults to None.
        init_cfg (dict, optional): the config to control the initialization.
            Defaults to None.
    """

    def __init__(self,
                 backbone: dict,
                 neck: Optional[dict] = None,
                 head: Optional[dict] = None,
                 pretrained: Optional[str] = None,
                 data_preprocessor: Optional[Union[dict, nn.Module]] = None,
                 init_cfg: Optional[dict] = None):

        if pretrained is not None:
            init_cfg = dict(type='Pretrained', checkpoint=pretrained)

        if data_preprocessor is None:
            data_preprocessor = {}
        # The build process is in MMEngine, so we need to add scope here.
        data_preprocessor.setdefault('type',
                                     'mmselfsup.SelfSupDataPreprocessor')

        super().__init__(
            init_cfg=init_cfg, data_preprocessor=data_preprocessor)

        self.backbone = MODELS.build(backbone)

        if neck is not None:
            self.neck = MODELS.build(neck)

        if head is not None:
            self.head = MODELS.build(head)

    @property
    def with_neck(self) -> bool:
        return hasattr(self, 'neck') and self.neck is not None

    @property
    def with_head(self) -> bool:
        return hasattr(self, 'head') and self.head is not None

    def forward(self,
                inputs: torch.Tensor,
                data_samples: Optional[List[SelfSupDataSample]] = None,
                mode: str = 'tensor'):
        """Returns losses or predictions of training, validation, testing, and
        simple inference process.

        This module overwrites the abstract method in ``BaseModel``.

        Args:
            inputs (torch.Tensor): batch input tensor collated by
                :attr:`data_preprocessor`.
            data_samples (List[BaseDataElement], optional):
                data samples collated by :attr:`data_preprocessor`.
            mode (str): mode should be one of ``loss``, ``predict`` and
                ``tensor``
                - ``loss``: Called by ``train_step`` and return loss ``dict``
                  used for logging
                - ``predict``: Called by ``val_step`` and ``test_step``
                  and return list of ``BaseDataElement`` results used for
                  computing metric.
                - ``tensor``: Called by custom use to get ``Tensor`` type
                  results.
        Returns:
            ForwardResults:
                - If ``mode == loss``, return a ``dict`` of loss tensor used
                  for backward and logging.
                - If ``mode == predict``, return a ``list`` of
                  :obj:`BaseDataElement` for computing metric
                  and getting inference result.
                - If ``mode == tensor``, return a tensor or ``tuple`` of tensor
                  or ``dict of tensor for custom use.
        """
        if mode == 'tensor':
            feats = self.extract_feat(inputs)
            return feats
        elif mode == 'loss':
            return self.loss(inputs, data_samples)
        elif mode == 'predict':
            return self.predict(inputs, data_samples)
        else:
            raise RuntimeError(f'Invalid mode "{mode}".')

    def extract_feat(self, inputs):
        """Extract features from the input tensor with shape (N, C, ...).

        This is a abstract method, and subclass should overwrite this methods
        if needed.

        Args:
            inputs (Tensor): A batch of inputs. The shape of it should be
                ``(num_samples, num_channels, *img_shape)``.

        Returns:
            tuple | Tensor: The output of specified stage.
            The output depends on detailed implementation.
        """
        raise NotImplementedError

    def loss(self, inputs: torch.Tensor,
             data_samples: List[SelfSupDataSample]) -> dict:
        """Calculate losses from a batch of inputs and data samples.

        This is a abstract method, and subclass should overwrite this methods
        if needed.

        Args:
            inputs (torch.Tensor): The input tensor with shape
                (N, C, ...) in general.
            data_samples (List[SelfSupDataSample]): The annotation data of
                every samples.

        Returns:
            dict[str, Tensor]: A dictionary of loss components.
        """
        raise NotImplementedError

    def predict(self,
                inputs: tuple,
                data_samples: Optional[List[SelfSupDataSample]] = None,
                **kwargs) -> List[SelfSupDataSample]:
        """Predict results from the extracted features.

        This module returns the logits before loss, which are used to compute
        all kinds of metrics. This is a abstract method, and subclass should
        overwrite this methods if needed.

        Args:
            feats (tuple): The features extracted from the backbone.
            data_samples (List[BaseDataElement], optional): The annotation
                data of every samples. Defaults to None.
            **kwargs: Other keyword arguments accepted by the ``predict``
                method of :attr:`head`.
        """
        raise NotImplementedError
