# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
"""
Utilities for bounding box manipulation and GIoU.
"""
import torch
from torchvision.ops.boxes import box_area


def get_ious(bboxes1,
             bboxes2,
             box_mode="xyxy",
             iou_type="iou"):
    """
    Compute iou loss of type ['iou', 'giou', 'linear_iou']

    Args:
        inputs (tensor): pred values
        targets (tensor): target values
        weight (tensor): loss weight
        box_mode (str): 'xyxy' or 'ltrb', 'ltrb' is currently supported.
        loss_type (str): 'giou' or 'iou' or 'linear_iou'
        reduction (str): reduction manner

    Returns:
        loss (tensor): computed iou loss.
    """
    if box_mode == "ltrb":
        bboxes1 = torch.cat((-bboxes1[..., :2], bboxes1[..., 2:]), dim=-1)
        bboxes2 = torch.cat((-bboxes2[..., :2], bboxes2[..., 2:]), dim=-1)
    elif box_mode != "xyxy":
        raise NotImplementedError

    eps = torch.finfo(torch.float32).eps

    bboxes1_area = (bboxes1[..., 2] - bboxes1[..., 0]).clamp_(min=0) \
        * (bboxes1[..., 3] - bboxes1[..., 1]).clamp_(min=0)
    bboxes2_area = (bboxes2[..., 2] - bboxes2[..., 0]).clamp_(min=0) \
        * (bboxes2[..., 3] - bboxes2[..., 1]).clamp_(min=0)

    w_intersect = (torch.min(bboxes1[..., 2], bboxes2[..., 2])
                   - torch.max(bboxes1[..., 0], bboxes2[..., 0])).clamp_(min=0)
    h_intersect = (torch.min(bboxes1[..., 3], bboxes2[..., 3])
                   - torch.max(bboxes1[..., 1], bboxes2[..., 1])).clamp_(min=0)

    area_intersect = w_intersect * h_intersect
    area_union = bboxes2_area + bboxes1_area - area_intersect
    ious = area_intersect / area_union.clamp(min=eps)

    if iou_type == "iou":
        return ious
    elif iou_type == "giou":
        g_w_intersect = torch.max(bboxes1[..., 2], bboxes2[..., 2]) \
            - torch.min(bboxes1[..., 0], bboxes2[..., 0])
        g_h_intersect = torch.max(bboxes1[..., 3], bboxes2[..., 3]) \
            - torch.min(bboxes1[..., 1], bboxes2[..., 1])
        ac_uion = g_w_intersect * g_h_intersect
        gious = ious - (ac_uion - area_union) / ac_uion.clamp(min=eps)
        return gious
    else:
        raise NotImplementedError

def box_cxcywh_to_xyxy(x):
    x_c, y_c, w, h = x.unbind(-1)
    b = [(x_c - 0.5 * w), (y_c - 0.5 * h),
         (x_c + 0.5 * w), (y_c + 0.5 * h)]
    return torch.stack(b, dim=-1)

def box_xyxy_to_cxcywh(x):
    x0, y0, x1, y1 = x.unbind(-1)
    b = [(x0 + x1) / 2, (y0 + y1) / 2,
         (x1 - x0), (y1 - y0)]
    return torch.stack(b, dim=-1)

# modified from torchvision to also return the union
def box_iou(boxes1, boxes2):
    area1 = box_area(boxes1)
    area2 = box_area(boxes2)

    lt = torch.max(boxes1[:, None, :2], boxes2[:, :2])  # [N,M,2]
    rb = torch.min(boxes1[:, None, 2:], boxes2[:, 2:])  # [N,M,2]

    wh = (rb - lt).clamp(min=0)  # [N,M,2]
    inter = wh[:, :, 0] * wh[:, :, 1]  # [N,M]

    union = area1[:, None] + area2 - inter
    union[union == 0.0] = 1.0

    iou = inter / union
    
    return iou, union

def generalized_box_iou(boxes1, boxes2):
    """
    Generalized IoU from https://giou.stanford.edu/

    The boxes should be in [x0, y0, x1, y1] format

    Returns a [N, M] pairwise matrix, where N = len(boxes1)
    and M = len(boxes2)
    """
    # degenerate boxes gives inf / nan results
    # so do an early check
    assert (boxes1[:, 2:] >= boxes1[:, :2]).all()
    assert (boxes2[:, 2:] >= boxes2[:, :2]).all()
    iou, union = box_iou(boxes1, boxes2)

    lt = torch.min(boxes1[:, None, :2], boxes2[:, :2])
    rb = torch.max(boxes1[:, None, 2:], boxes2[:, 2:])

    wh = (rb - lt).clamp(min=0)  # [N,M,2]
    area = wh[:, :, 0] * wh[:, :, 1]

    return iou - (area - union) / area
