class SegmentationValidator(DetectionValidator):

    def __init__(self, dataloader=None, save_dir=None, pbar=None, args=None, _callbacks=None):
        """Initialize SegmentationValidator and set task to 'segment', metrics to SegmentMetrics."""
        super().__init__(dataloader, save_dir, pbar, args, _callbacks)
        self.args.task = 'segment'
        self.metrics = SegmentMetrics(save_dir=self.save_dir, on_plot=self.on_plot)

    def preprocess(self, batch):
        """Preprocesses batch by converting masks to float and sending to device."""
        batch = super().preprocess(batch)
        batch['masks'] = batch['masks'].to(self.device).float()
        return batch

    def init_metrics(self, model):
        """Initialize metrics and select mask processing function based on save_json flag."""
        super().init_metrics(model)
        self.plot_masks = []
        if self.args.save_json:
            check_requirements('pycocotools>=2.0.6')
            self.process = ops.process_mask_upsample  # more accurate
        else:
            self.process = ops.process_mask  # faster

    def get_desc(self):
        """Return a formatted description of evaluation metrics."""
        return ('%22s' + '%11s' * 10) % ('Class', 'Images', 'Instances', 'Box(P', 'R', 'mAP50', 'mAP50-95)', 'Mask(P',
                                         'R', 'mAP50', 'mAP50-95)')

    def postprocess(self, preds):
        """Postprocesses YOLO predictions and returns output detections with proto."""
        p = ops.non_max_suppression(preds[0],
                                    self.args.conf,
                                    self.args.iou,
                                    labels=self.lb,
                                    multi_label=True,
                                    agnostic=self.args.single_cls,
                                    max_det=self.args.max_det,
                                    nc=self.nc)
        proto = preds[1][-1] if len(preds[1]) == 3 else preds[1]  # second output is len 3 if pt, but only 1 if exported
        return p, proto

    def update_metrics(self, preds, batch):
        """Metrics."""
        for si, (pred, proto) in enumerate(zip(preds[0], preds[1])):
            idx = batch['batch_idx'] == si
            cls = batch['cls'][idx]
            bbox = batch['bboxes'][idx]
            nl, npr = cls.shape[0], pred.shape[0]  # number of labels, predictions
            shape = batch['ori_shape'][si]
            correct_masks = torch.zeros(npr, self.niou, dtype=torch.bool, device=self.device)  # init
            correct_bboxes = torch.zeros(npr, self.niou, dtype=torch.bool, device=self.device)  # init
            self.seen += 1

            if npr == 0:
                if nl:
                    self.stats.append((correct_bboxes, correct_masks, *torch.zeros(
                        (2, 0), device=self.device), cls.squeeze(-1)))
                    if self.args.plots:
                        self.confusion_matrix.process_batch(detections=None, labels=cls.squeeze(-1))
                continue

            # Masks
            midx = [si] if self.args.overlap_mask else idx
            gt_masks = batch['masks'][midx]
            pred_masks = self.process(proto, pred[:, 6:], pred[:, :4], shape=batch['img'][si].shape[1:])

            # Predictions
            if self.args.single_cls:
                pred[:, 5] = 0
            predn = pred.clone()
            ops.scale_boxes(batch['img'][si].shape[1:], predn[:, :4], shape,
                            ratio_pad=batch['ratio_pad'][si])  # native-space pred

            # Evaluate
            if nl:
                height, width = batch['img'].shape[2:]
                tbox = ops.xywh2xyxy(bbox) * torch.tensor(
                    (width, height, width, height), device=self.device)  # target boxes
                ops.scale_boxes(batch['img'][si].shape[1:], tbox, shape,
                                ratio_pad=batch['ratio_pad'][si])  # native-space labels
                labelsn = torch.cat((cls, tbox), 1)  # native-space labels
                correct_bboxes = self._process_batch(predn, labelsn)
                # TODO: maybe remove these `self.` arguments as they already are member variable
                correct_masks = self._process_batch(predn,
                                                    labelsn,
                                                    pred_masks,
                                                    gt_masks,
                                                    overlap=self.args.overlap_mask,
                                                    masks=True)
                if self.args.plots:
                    self.confusion_matrix.process_batch(predn, labelsn)

            # Append correct_masks, correct_boxes, pconf, pcls, tcls
            self.stats.append((correct_bboxes, correct_masks, pred[:, 4], pred[:, 5], cls.squeeze(-1)))

            pred_masks = torch.as_tensor(pred_masks, dtype=torch.uint8)
            if self.args.plots and self.batch_i < 3:
                self.plot_masks.append(pred_masks[:15].cpu())  # filter top 15 to plot

            # Save
            if self.args.save_json:
                pred_masks = ops.scale_image(pred_masks.permute(1, 2, 0).contiguous().cpu().numpy(),
                                             shape,
                                             ratio_pad=batch['ratio_pad'][si])
                self.pred_to_json(predn, batch['im_file'][si], pred_masks)
            # if self.args.save_txt:
            #    save_one_txt(predn, save_conf, shape, file=save_dir / 'labels' / f'{path.stem}.txt')

    def finalize_metrics(self, *args, **kwargs):
        """Sets speed and confusion matrix for evaluation metrics."""
        self.metrics.speed = self.speed
        self.metrics.confusion_matrix = self.confusion_matrix

    def _process_batch(self, detections, labels, pred_masks=None, gt_masks=None, overlap=False, masks=False):
        """
        Return correct prediction matrix
        Arguments:
            detections (array[N, 6]), x1, y1, x2, y2, conf, class
            labels (array[M, 5]), class, x1, y1, x2, y2
        Returns:
            correct (array[N, 10]), for 10 IoU levels
        """
        if masks:
            if overlap:
                nl = len(labels)
                index = torch.arange(nl, device=gt_masks.device).view(nl, 1, 1) + 1
                gt_masks = gt_masks.repeat(nl, 1, 1)  # shape(1,640,640) -> (n,640,640)
                gt_masks = torch.where(gt_masks == index, 1.0, 0.0)
            if gt_masks.shape[1:] != pred_masks.shape[1:]:
                gt_masks = F.interpolate(gt_masks[None], pred_masks.shape[1:], mode='bilinear', align_corners=False)[0]
                gt_masks = gt_masks.gt_(0.5)
            iou = mask_iou(gt_masks.view(gt_masks.shape[0], -1), pred_masks.view(pred_masks.shape[0], -1))
        else:  # boxes
            iou = box_iou(labels[:, 1:], detections[:, :4])

        correct = np.zeros((detections.shape[0], self.iouv.shape[0])).astype(bool)
        correct_class = labels[:, 0:1] == detections[:, 5]
        for i in range(len(self.iouv)):
            x = torch.where((iou >= self.iouv[i]) & correct_class)  # IoU > threshold and classes match
            if x[0].shape[0]:
                matches = torch.cat((torch.stack(x, 1), iou[x[0], x[1]][:, None]),
                                    1).cpu().numpy()  # [label, detect, iou]
                if x[0].shape[0] > 1:
                    matches = matches[matches[:, 2].argsort()[::-1]]
                    matches = matches[np.unique(matches[:, 1], return_index=True)[1]]
                    # matches = matches[matches[:, 2].argsort()[::-1]]
                    matches = matches[np.unique(matches[:, 0], return_index=True)[1]]
                correct[matches[:, 1].astype(int), i] = True
        return torch.tensor(correct, dtype=torch.bool, device=detections.device)

    def plot_val_samples(self, batch, ni):
        """Plots validation samples with bounding box labels."""
        plot_images(batch['img'],
                    batch['batch_idx'],
                    batch['cls'].squeeze(-1),
                    batch['bboxes'],
                    batch['masks'],
                    paths=batch['im_file'],
                    fname=self.save_dir / f'val_batch{ni}_labels.jpg',
                    names=self.names,
                    on_plot=self.on_plot)

    def plot_predictions(self, batch, preds, ni):
        """Plots batch predictions with masks and bounding boxes."""
        plot_images(batch['img'],
                    *output_to_target(preds[0], max_det=15),
                    torch.cat(self.plot_masks, dim=0) if len(self.plot_masks) else self.plot_masks,
                    paths=batch['im_file'],
                    fname=self.save_dir / f'val_batch{ni}_pred.jpg',
                    names=self.names,
                    on_plot=self.on_plot)  # pred
        self.plot_masks.clear()

    def pred_to_json(self, predn, filename, pred_masks):
        """Save one JSON result."""
        # Example result = {"image_id": 42, "category_id": 18, "bbox": [258.15, 41.29, 348.26, 243.78], "score": 0.236}
        from pycocotools.mask import encode  # noqa

        def single_encode(x):
            """Encode predicted masks as RLE and append results to jdict."""
            rle = encode(np.asarray(x[:, :, None], order='F', dtype='uint8'))[0]
            rle['counts'] = rle['counts'].decode('utf-8')
            return rle

        stem = Path(filename).stem
        image_id = int(stem) if stem.isnumeric() else stem
        box = ops.xyxy2xywh(predn[:, :4])  # xywh
        box[:, :2] -= box[:, 2:] / 2  # xy center to top-left corner
        pred_masks = np.transpose(pred_masks, (2, 0, 1))
        with ThreadPool(NUM_THREADS) as pool:
            rles = pool.map(single_encode, pred_masks)
        for i, (p, b) in enumerate(zip(predn.tolist(), box.tolist())):
            self.jdict.append({
                'image_id': image_id,
                'category_id': self.class_map[int(p[5])],
                'bbox': [round(x, 3) for x in b],
                'score': round(p[4], 5),
                'segmentation': rles[i]})

    def eval_json(self, stats):
        """Return COCO-style object detection evaluation metrics."""
        if self.args.save_json and self.is_coco and len(self.jdict):
            anno_json = self.data['path'] / 'annotations/instances_val2017.json'  # annotations
            pred_json = self.save_dir / 'predictions.json'  # predictions
            LOGGER.info(f'\nEvaluating pycocotools mAP using {pred_json} and {anno_json}...')
            try:  # https://github.com/cocodataset/cocoapi/blob/master/PythonAPI/pycocoEvalDemo.ipynb
                check_requirements('pycocotools>=2.0.6')
                from pycocotools.coco import COCO  # noqa
                from pycocotools.cocoeval import COCOeval  # noqa

                for x in anno_json, pred_json:
                    assert x.is_file(), f'{x} file not found'
                anno = COCO(str(anno_json))  # init annotations api
                pred = anno.loadRes(str(pred_json))  # init predictions api (must pass string, not Path)
                for i, eval in enumerate([COCOeval(anno, pred, 'bbox'), COCOeval(anno, pred, 'segm')]):
                    if self.is_coco:
                        eval.params.imgIds = [int(Path(x).stem) for x in self.dataloader.dataset.im_files]  # im to eval
                    eval.evaluate()
                    eval.accumulate()
                    eval.summarize()
                    idx = i * 4 + 2
                    stats[self.metrics.keys[idx + 1]], stats[
                        self.metrics.keys[idx]] = eval.stats[:2]  # update mAP50-95 and mAP50
            except Exception as e:
                LOGGER.warning(f'pycocotools unable to run: {e}')
        return stats