# Copyright (c) Alibaba, Inc. and its affiliates.
# The AIRDet implementation is also open-sourced by the authors, and available at https://github.com/tinyvision/AIRDet.

import numpy as np
import torch
import torchvision

__all__ = [
    'filter_box',
    'postprocess_airdet',
    'bboxes_iou',
    'matrix_iou',
    'adjust_box_anns',
    'xyxy2xywh',
    'xyxy2cxcywh',
]


def multiclass_nms(multi_bboxes,
                   multi_scores,
                   score_thr,
                   iou_thr,
                   max_num=100,
                   score_factors=None):
    """NMS for multi-class bboxes.

    Args:
        multi_bboxes (Tensor): shape (n, #class*4) or (n, 4)
        multi_scores (Tensor): shape (n, #class), where the last column
            contains scores of the background class, but this will be ignored.
        score_thr (float): bbox threshold, bboxes with scores lower than it
            will not be considered.
        nms_thr (float): NMS IoU threshold
        max_num (int): if there are more than max_num bboxes after NMS,
            only top max_num will be kept.
        score_factors (Tensor): The factors multiplied to scores before
            applying NMS

    Returns:
        tuple: (bboxes, labels), tensors of shape (k, 5) and (k, 1). Labels \
            are 0-based.
    """
    num_classes = multi_scores.size(1)
    # exclude background category
    if multi_bboxes.shape[1] > 4:
        bboxes = multi_bboxes.view(multi_scores.size(0), -1, 4)
    else:
        bboxes = multi_bboxes[:, None].expand(
            multi_scores.size(0), num_classes, 4)
    scores = multi_scores
    # filter out boxes with low scores
    valid_mask = scores > score_thr  # 1000 * 80 bool

    # We use masked_select for ONNX exporting purpose,
    # which is equivalent to bboxes = bboxes[valid_mask]
    # (TODO): as ONNX does not support repeat now,
    # we have to use this ugly code
    # bboxes -> 1000, 4
    bboxes = torch.masked_select(
        bboxes,
        torch.stack((valid_mask, valid_mask, valid_mask, valid_mask),
                    -1)).view(-1, 4)  # mask->  1000*80*4, 80000*4
    if score_factors is not None:
        scores = scores * score_factors[:, None]
    scores = torch.masked_select(scores, valid_mask)
    labels = valid_mask.nonzero(as_tuple=False)[:, 1]

    if bboxes.numel() == 0:
        bboxes = multi_bboxes.new_zeros((0, 5))
        labels = multi_bboxes.new_zeros((0, ), dtype=torch.long)
        scores = multi_bboxes.new_zeros((0, ))

        return bboxes, scores, labels

    keep = torchvision.ops.batched_nms(bboxes, scores, labels, iou_thr)

    if max_num > 0:
        keep = keep[:max_num]

    return bboxes[keep], scores[keep], labels[keep]


def filter_box(output, scale_range):
    """
    output: (N, 5+class) shape
    """
    min_scale, max_scale = scale_range
    w = output[:, 2] - output[:, 0]
    h = output[:, 3] - output[:, 1]
    keep = (w * h > min_scale * min_scale) & (w * h < max_scale * max_scale)
    return output[keep]


def filter_results(boxlist, num_classes, nms_thre):
    boxes = boxlist.bbox
    scores = boxlist.get_field('scores')
    cls = boxlist.get_field('labels')
    nms_out_index = torchvision.ops.batched_nms(
        boxes,
        scores,
        cls,
        nms_thre,
    )
    boxlist = boxlist[nms_out_index]

    return boxlist


def postprocess_airdet(prediction,
                       num_classes,
                       conf_thre=0.7,
                       nms_thre=0.45,
                       imgs=None):
    box_corner = prediction.new(prediction.shape)
    box_corner[:, :, 0] = prediction[:, :, 0] - prediction[:, :, 2] / 2
    box_corner[:, :, 1] = prediction[:, :, 1] - prediction[:, :, 3] / 2
    box_corner[:, :, 2] = prediction[:, :, 0] + prediction[:, :, 2] / 2
    box_corner[:, :, 3] = prediction[:, :, 1] + prediction[:, :, 3] / 2
    prediction[:, :, :4] = box_corner[:, :, :4]
    output = [None for _ in range(len(prediction))]
    for i, image_pred in enumerate(prediction):
        # If none are remaining => process next image
        if not image_pred.size(0):
            continue
        multi_bboxes = image_pred[:, :4]
        multi_scores = image_pred[:, 5:]
        detections, scores, labels = multiclass_nms(multi_bboxes, multi_scores,
                                                    conf_thre, nms_thre, 500)
        detections = torch.cat(
            (detections, scores[:, None], scores[:, None], labels[:, None]),
            dim=1)

        if output[i] is None:
            output[i] = detections
        else:
            output[i] = torch.cat((output[i], detections))
    return output


def bboxes_iou(bboxes_a, bboxes_b, xyxy=True):
    if bboxes_a.shape[1] != 4 or bboxes_b.shape[1] != 4:
        raise IndexError

    if xyxy:
        tl = torch.max(bboxes_a[:, None, :2], bboxes_b[:, :2])
        br = torch.min(bboxes_a[:, None, 2:], bboxes_b[:, 2:])
        area_a = torch.prod(bboxes_a[:, 2:] - bboxes_a[:, :2], 1)
        area_b = torch.prod(bboxes_b[:, 2:] - bboxes_b[:, :2], 1)
    else:
        tl = torch.max(
            (bboxes_a[:, None, :2] - bboxes_a[:, None, 2:] / 2),
            (bboxes_b[:, :2] - bboxes_b[:, 2:] / 2),
        )
        br = torch.min(
            (bboxes_a[:, None, :2] + bboxes_a[:, None, 2:] / 2),
            (bboxes_b[:, :2] + bboxes_b[:, 2:] / 2),
        )

        area_a = torch.prod(bboxes_a[:, 2:], 1)
        area_b = torch.prod(bboxes_b[:, 2:], 1)
    en = (tl < br).type(tl.type()).prod(dim=2)
    area_i = torch.prod(br - tl, 2) * en  # * ((tl < br).all())
    return area_i / (area_a[:, None] + area_b - area_i)


def matrix_iou(a, b):
    """
    return iou of a and b, numpy version for data augenmentation
    """
    lt = np.maximum(a[:, np.newaxis, :2], b[:, :2])
    rb = np.minimum(a[:, np.newaxis, 2:], b[:, 2:])

    area_i = np.prod(rb - lt, axis=2) * (lt < rb).all(axis=2)
    area_a = np.prod(a[:, 2:] - a[:, :2], axis=1)
    area_b = np.prod(b[:, 2:] - b[:, :2], axis=1)
    return area_i / (area_a[:, np.newaxis] + area_b - area_i + 1e-12)


def adjust_box_anns(bbox, scale_ratio, padw, padh, w_max, h_max):
    bbox[:, 0::2] = np.clip(bbox[:, 0::2] * scale_ratio + padw, 0, w_max)
    bbox[:, 1::2] = np.clip(bbox[:, 1::2] * scale_ratio + padh, 0, h_max)
    return bbox


def xyxy2xywh(bboxes):
    bboxes[:, 2] = bboxes[:, 2] - bboxes[:, 0]
    bboxes[:, 3] = bboxes[:, 3] - bboxes[:, 1]
    return bboxes


def xyxy2cxcywh(bboxes):
    bboxes[:, 2] = bboxes[:, 2] - bboxes[:, 0]
    bboxes[:, 3] = bboxes[:, 3] - bboxes[:, 1]
    bboxes[:, 0] = bboxes[:, 0] + bboxes[:, 2] * 0.5
    bboxes[:, 1] = bboxes[:, 1] + bboxes[:, 3] * 0.5
    return bboxes
