from abc import ABCMeta, abstractmethod

import torch.nn as nn


class BaseDetector(nn.Module, metaclass=ABCMeta):
    """Base class for detectors"""

    def __init__(self):
        super(BaseDetector, self).__init__()
        self.fp16_enabled = False

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

    @property
    def with_voxel_encoder(self):
        return hasattr(self,
                       'voxel_encoder') and self.voxel_encoder is not None

    @property
    def with_middle_encoder(self):
        return hasattr(self,
                       'middle_encoder') and self.middle_encoder is not None

    @property
    def with_shared_head(self):
        return hasattr(self, 'shared_head') and self.shared_head is not None

    @property
    def with_bbox(self):
        return hasattr(self, 'bbox_head') and self.bbox_head is not None

    @property
    def with_mask(self):
        return hasattr(self, 'mask_head') and self.mask_head is not None

    @abstractmethod
    def extract_feat(self, imgs):
        pass

    def extract_feats(self, imgs):
        assert isinstance(imgs, list)
        for img in imgs:
            yield self.extract_feat(img)

    @abstractmethod
    def forward_train(self, **kwargs):
        pass

    @abstractmethod
    def simple_test(self, **kwargs):
        pass

    @abstractmethod
    def aug_test(self, **kwargs):
        pass

    def init_weights(self, pretrained=None):
        if pretrained is not None:
            from mmdet3d.apis import get_root_logger
            logger = get_root_logger()
            logger.info('load model from: {}'.format(pretrained))

    def forward_test(self, imgs, img_metas, **kwargs):
        """
        Args:
            imgs (List[Tensor]): the outer list indicates test-time
                augmentations and inner Tensor should have a shape NxCxHxW,
                which contains all images in the batch.
            img_meta (List[List[dict]]): the outer list indicates test-time
                augs (multiscale, flip, etc.) and the inner list indicates
                images in a batch
        """
        for var, name in [(imgs, 'imgs'), (img_metas, 'img_metas')]:
            if not isinstance(var, list):
                raise TypeError('{} must be a list, but got {}'.format(
                    name, type(var)))

        num_augs = len(imgs)
        if num_augs != len(img_metas):
            raise ValueError(
                'num of augmentations ({}) != num of image meta ({})'.format(
                    len(imgs), len(img_metas)))
        # TODO: remove the restriction of imgs_per_gpu == 1 when prepared
        imgs_per_gpu = imgs[0].size(0)
        assert imgs_per_gpu == 1

        if num_augs == 1:
            return self.simple_test(imgs[0], img_metas[0], **kwargs)
        else:
            return self.aug_test(imgs, img_metas, **kwargs)

    def forward(self, img, img_meta, return_loss=True, **kwargs):
        """
        Calls either forward_train or forward_test depending on whether
        return_loss=True. Note this setting will change the expected inputs.
        When `return_loss=True`, img and img_meta are single-nested (i.e.
        Tensor and List[dict]), and when `resturn_loss=False`, img and img_meta
        should be double nested (i.e.  List[Tensor], List[List[dict]]), with
        the outer list indicating test time augmentations.
        """

        # TODO: current version only support 2D detector now, find
        # a better way to be compatible with both
        if return_loss:
            return self.forward_train(img, img_meta, **kwargs)
        else:
            return self.forward_test(img, img_meta, **kwargs)