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# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.

from abc import ABCMeta
from typing import List, Optional, Tuple

from mmengine.model import BaseModule
from torch import Tensor

from mmdet.registry import MODELS, TASK_UTILS
from mmdet.structures import TrackSampleList
from mmdet.structures.bbox import bbox2roi
from mmdet.utils import InstanceList


@MODELS.register_module()
class RoITrackHead(BaseModule, metaclass=ABCMeta):
    """The roi track head.

    This module is used in multi-object tracking methods, such as MaskTrack
    R-CNN.

    Args:
        roi_extractor (dict): Configuration of roi extractor. Defaults to None.
        embed_head (dict): Configuration of embed head. Defaults to None.
        train_cfg (dict): Configuration when training. Defaults to None.
        test_cfg (dict): Configuration when testing. Defaults to None.
        init_cfg (dict): Configuration of initialization. Defaults to None.
    """

    def __init__(self,
                 roi_extractor: Optional[dict] = None,
                 embed_head: Optional[dict] = None,
                 regress_head: Optional[dict] = None,
                 train_cfg: Optional[dict] = None,
                 test_cfg: Optional[dict] = None,
                 init_cfg: Optional[dict] = None,
                 *args,
                 **kwargs):
        super().__init__(init_cfg=init_cfg)
        self.train_cfg = train_cfg
        self.test_cfg = test_cfg

        if embed_head is not None:
            self.init_embed_head(roi_extractor, embed_head)

        if regress_head is not None:
            raise NotImplementedError('Regression head is not supported yet.')

        self.init_assigner_sampler()

    def init_embed_head(self, roi_extractor, embed_head) -> None:
        """Initialize ``embed_head``"""
        self.roi_extractor = MODELS.build(roi_extractor)
        self.embed_head = MODELS.build(embed_head)

    def init_assigner_sampler(self) -> None:
        """Initialize assigner and sampler."""
        self.bbox_assigner = None
        self.bbox_sampler = None
        if self.train_cfg:
            self.bbox_assigner = TASK_UTILS.build(self.train_cfg.assigner)
            self.bbox_sampler = TASK_UTILS.build(
                self.train_cfg.sampler, default_args=dict(context=self))

    @property
    def with_track(self) -> bool:
        """bool: whether the multi-object tracker has an embed head"""
        return hasattr(self, 'embed_head') and self.embed_head is not None

    def extract_roi_feats(
            self, feats: List[Tensor],
            bboxes: List[Tensor]) -> Tuple[Tuple[Tensor], List[int]]:
        """Extract roi features.

        Args:
            feats (list[Tensor]): list of multi-level image features.
            bboxes (list[Tensor]): list of bboxes in sampling result.

        Returns:
            tuple[tuple[Tensor], list[int]]: The extracted roi features and
            the number of bboxes in each image.
        """
        rois = bbox2roi(bboxes)
        bbox_feats = self.roi_extractor(feats[:self.roi_extractor.num_inputs],
                                        rois)
        num_bbox_per_img = [len(bbox) for bbox in bboxes]
        return bbox_feats, num_bbox_per_img

    def loss(self, key_feats: List[Tensor], ref_feats: List[Tensor],
             rpn_results_list: InstanceList, data_samples: TrackSampleList,
             **kwargs) -> dict:
        """Calculate losses from a batch of inputs and data samples.

        Args:
            key_feats (list[Tensor]): list of multi-level image features.
            ref_feats (list[Tensor]): list of multi-level ref_img features.
            rpn_results_list (list[:obj:`InstanceData`]): List of region
                proposals.
            data_samples (list[:obj:`TrackDataSample`]): The batch
                data samples. It usually includes information such
                as `gt_instance`.

        Returns:
            dict: A dictionary of loss components.
        """
        assert self.with_track
        batch_gt_instances = []
        ref_batch_gt_instances = []
        batch_gt_instances_ignore = []
        gt_instance_ids = []
        ref_gt_instance_ids = []
        for track_data_sample in data_samples:
            key_data_sample = track_data_sample.get_key_frames()[0]
            ref_data_sample = track_data_sample.get_ref_frames()[0]
            batch_gt_instances.append(key_data_sample.gt_instances)
            ref_batch_gt_instances.append(ref_data_sample.gt_instances)
            if 'ignored_instances' in key_data_sample:
                batch_gt_instances_ignore.append(
                    key_data_sample.ignored_instances)
            else:
                batch_gt_instances_ignore.append(None)

            gt_instance_ids.append(key_data_sample.gt_instances.instances_ids)
            ref_gt_instance_ids.append(
                ref_data_sample.gt_instances.instances_ids)

        losses = dict()
        num_imgs = len(data_samples)
        if batch_gt_instances_ignore is None:
            batch_gt_instances_ignore = [None] * num_imgs
        sampling_results = []
        for i in range(num_imgs):
            rpn_results = rpn_results_list[i]

            assign_result = self.bbox_assigner.assign(
                rpn_results, batch_gt_instances[i],
                batch_gt_instances_ignore[i])
            sampling_result = self.bbox_sampler.sample(
                assign_result,
                rpn_results,
                batch_gt_instances[i],
                feats=[lvl_feat[i][None] for lvl_feat in key_feats])
            sampling_results.append(sampling_result)

        bboxes = [res.bboxes for res in sampling_results]
        bbox_feats, num_bbox_per_img = self.extract_roi_feats(
            key_feats, bboxes)

        # batch_size is 1
        ref_gt_bboxes = [
            ref_batch_gt_instance.bboxes
            for ref_batch_gt_instance in ref_batch_gt_instances
        ]
        ref_bbox_feats, num_bbox_per_ref_img = self.extract_roi_feats(
            ref_feats, ref_gt_bboxes)

        loss_track = self.embed_head.loss(bbox_feats, ref_bbox_feats,
                                          num_bbox_per_img,
                                          num_bbox_per_ref_img,
                                          sampling_results, gt_instance_ids,
                                          ref_gt_instance_ids)
        losses.update(loss_track)

        return losses

    def predict(self, roi_feats: Tensor,
                prev_roi_feats: Tensor) -> List[Tensor]:
        """Perform forward propagation of the tracking head and predict
        tracking results on the features of the upstream network.

        Args:
            roi_feats (Tensor): Feature map of current images rois.
            prev_roi_feats (Tensor): Feature map of previous images rois.

        Returns:
            list[Tensor]: The predicted similarity_logits of each pair of key
            image and reference image.
        """
        return self.embed_head.predict(roi_feats, prev_roi_feats)[0]