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# Copyright (c) OpenMMLab. All rights reserved.
import numpy as np


def temporal_iou(proposal_min, proposal_max, gt_min, gt_max):
    """Compute IoU score between a groundtruth bbox and the proposals.

    Args:
        proposal_min (list[float]): List of temporal anchor min.
        proposal_max (list[float]): List of temporal anchor max.
        gt_min (float): Groundtruth temporal box min.
        gt_max (float): Groundtruth temporal box max.

    Returns:
        list[float]: List of iou scores.
    """
    len_anchors = proposal_max - proposal_min
    int_tmin = np.maximum(proposal_min, gt_min)
    int_tmax = np.minimum(proposal_max, gt_max)
    inter_len = np.maximum(int_tmax - int_tmin, 0.)
    union_len = len_anchors - inter_len + gt_max - gt_min
    jaccard = np.divide(inter_len, union_len)
    return jaccard


def temporal_iop(proposal_min, proposal_max, gt_min, gt_max):
    """Compute IoP score between a groundtruth bbox and the proposals.

    Compute the IoP which is defined as the overlap ratio with
    groundtruth proportional to the duration of this proposal.

    Args:
        proposal_min (list[float]): List of temporal anchor min.
        proposal_max (list[float]): List of temporal anchor max.
        gt_min (float): Groundtruth temporal box min.
        gt_max (float): Groundtruth temporal box max.

    Returns:
        list[float]: List of intersection over anchor scores.
    """
    len_anchors = np.array(proposal_max - proposal_min)
    int_tmin = np.maximum(proposal_min, gt_min)
    int_tmax = np.minimum(proposal_max, gt_max)
    inter_len = np.maximum(int_tmax - int_tmin, 0.)
    scores = np.divide(inter_len, len_anchors)
    return scores


def soft_nms(proposals, alpha, low_threshold, high_threshold, top_k):
    """Soft NMS for temporal proposals.

    Args:
        proposals (np.ndarray): Proposals generated by network.
        alpha (float): Alpha value of Gaussian decaying function.
        low_threshold (float): Low threshold for soft nms.
        high_threshold (float): High threshold for soft nms.
        top_k (int): Top k values to be considered.

    Returns:
        np.ndarray: The updated proposals.
    """
    proposals = proposals[proposals[:, -1].argsort()[::-1]]
    tstart = list(proposals[:, 0])
    tend = list(proposals[:, 1])
    tscore = list(proposals[:, -1])
    rstart = []
    rend = []
    rscore = []

    while len(tscore) > 0 and len(rscore) <= top_k:
        max_index = np.argmax(tscore)
        max_width = tend[max_index] - tstart[max_index]
        iou_list = temporal_iou(tstart[max_index], tend[max_index],
                                np.array(tstart), np.array(tend))
        iou_exp_list = np.exp(-np.square(iou_list) / alpha)

        for idx, _ in enumerate(tscore):
            if idx != max_index:
                current_iou = iou_list[idx]
                if current_iou > low_threshold + (high_threshold -
                                                  low_threshold) * max_width:
                    tscore[idx] = tscore[idx] * iou_exp_list[idx]

        rstart.append(tstart[max_index])
        rend.append(tend[max_index])
        rscore.append(tscore[max_index])
        tstart.pop(max_index)
        tend.pop(max_index)
        tscore.pop(max_index)

    rstart = np.array(rstart).reshape(-1, 1)
    rend = np.array(rend).reshape(-1, 1)
    rscore = np.array(rscore).reshape(-1, 1)
    new_proposals = np.concatenate((rstart, rend, rscore), axis=1)
    return new_proposals