# Source: https://github.com/bochinski/iou-tracker

from .utils import iou


def track_iou(detections, sigma_l, sigma_h, sigma_iou, t_min):
    """
    Simple IOU based tracker.
    See "High-Speed Tracking-by-Detection Without Using Image Information by E. Bochinski, V. Eiselein, T. Sikora" for
    more information.

    Args:
         detections (list): list of detections per frame, usually generated by util.load_mot
         sigma_l (float): low detection threshold.
         sigma_h (float): high detection threshold.
         sigma_iou (float): IOU threshold.
         t_min (float): minimum track length in frames.

    Returns:
        list: list of tracks.
    """

    tracks_active = []
    tracks_finished = []

    for frame_num, detections_frame in enumerate(detections, start=1):
        # apply low threshold to detections
        dets = [det for det in detections_frame if det['score'] >= sigma_l]

        updated_tracks = []
        for track in tracks_active:
            if len(dets) > 0:
                # get det with highest iou
                best_match = max(dets, key=lambda x: iou(track['bboxes'][-1], x['bbox']))
                if iou(track['bboxes'][-1], best_match['bbox']) >= sigma_iou:
                    track['bboxes'].append(best_match['bbox'])
                    track['max_score'] = max(track['max_score'], best_match['score'])

                    updated_tracks.append(track)

                    # remove from best matching detection from detections
                    del dets[dets.index(best_match)]

            # if track was not updated
            if len(updated_tracks) == 0 or track is not updated_tracks[-1]:
                # finish track when the conditions are met
                if track['max_score'] >= sigma_h and len(track['bboxes']) >= t_min:
                    tracks_finished.append(track)

        # create new tracks
        new_tracks = [{'bboxes': [det['bbox']], 'max_score': det['score'], 'start_frame': frame_num} for det in dets]
        tracks_active = updated_tracks + new_tracks

    # finish all remaining active tracks
    tracks_finished += [track for track in tracks_active
                        if track['max_score'] >= sigma_h and len(track['bboxes']) >= t_min]

    return tracks_finished