import mmcv
import torch

from mmdet.models.dense_heads import GuidedAnchorHead


def test_ga_anchor_head_loss():
    """Tests anchor head loss when truth is empty and non-empty."""
    s = 256
    img_metas = [{
        'img_shape': (s, s, 3),
        'scale_factor': 1,
        'pad_shape': (s, s, 3)
    }]

    cfg = mmcv.Config(
        dict(
            assigner=dict(
                type='MaxIoUAssigner',
                pos_iou_thr=0.7,
                neg_iou_thr=0.3,
                min_pos_iou=0.3,
                match_low_quality=True,
                ignore_iof_thr=-1),
            sampler=dict(
                type='RandomSampler',
                num=256,
                pos_fraction=0.5,
                neg_pos_ub=-1,
                add_gt_as_proposals=False),
            ga_assigner=dict(
                type='ApproxMaxIoUAssigner',
                pos_iou_thr=0.7,
                neg_iou_thr=0.3,
                min_pos_iou=0.3,
                ignore_iof_thr=-1),
            ga_sampler=dict(
                type='RandomSampler',
                num=256,
                pos_fraction=0.5,
                neg_pos_ub=-1,
                add_gt_as_proposals=False),
            allowed_border=-1,
            center_ratio=0.2,
            ignore_ratio=0.5,
            pos_weight=-1,
            debug=False))
    head = GuidedAnchorHead(num_classes=4, in_channels=4, train_cfg=cfg)

    # Anchor head expects a multiple levels of features per image
    if torch.cuda.is_available():
        head.cuda()
        feat = [
            torch.rand(1, 4, s // (2**(i + 2)), s // (2**(i + 2))).cuda()
            for i in range(len(head.approx_anchor_generator.base_anchors))
        ]
        cls_scores, bbox_preds, shape_preds, loc_preds = head.forward(feat)

        # Test that empty ground truth encourages the network to predict
        # background
        gt_bboxes = [torch.empty((0, 4)).cuda()]
        gt_labels = [torch.LongTensor([]).cuda()]

        gt_bboxes_ignore = None

        empty_gt_losses = head.loss(cls_scores, bbox_preds, shape_preds,
                                    loc_preds, gt_bboxes, gt_labels, img_metas,
                                    gt_bboxes_ignore)

        # When there is no truth, the cls loss should be nonzero but there
        # should be no box loss.
        empty_cls_loss = sum(empty_gt_losses['loss_cls'])
        empty_box_loss = sum(empty_gt_losses['loss_bbox'])
        assert empty_cls_loss.item() > 0, 'cls loss should be non-zero'
        assert empty_box_loss.item() == 0, (
            'there should be no box loss when there are no true boxes')

        # When truth is non-empty then both cls and box loss should be nonzero
        # for random inputs
        gt_bboxes = [
            torch.Tensor([[23.6667, 23.8757, 238.6326, 151.8874]]).cuda(),
        ]
        gt_labels = [torch.LongTensor([2]).cuda()]
        one_gt_losses = head.loss(cls_scores, bbox_preds, shape_preds,
                                  loc_preds, gt_bboxes, gt_labels, img_metas,
                                  gt_bboxes_ignore)
        onegt_cls_loss = sum(one_gt_losses['loss_cls'])
        onegt_box_loss = sum(one_gt_losses['loss_bbox'])
        assert onegt_cls_loss.item() > 0, 'cls loss should be non-zero'
        assert onegt_box_loss.item() > 0, 'box loss should be non-zero'
