import numpy as np
import time

def IoU(box, boxes):
    """Compute IoU between detect box and gt boxes

    Parameters:
    ----------
    box: numpy array , shape (5, ): x1, y1, x2, y2, score
        input box
    boxes: numpy array, shape (n, 4): x1, y1, x2, y2
        input ground truth boxes

    Returns:
    -------
    ovr: numpy.array, shape (n, )
        IoU
    """
    box_area = (box[2] - box[0] + 1) * (box[3] - box[1] + 1)
    area = (boxes[:, 2] - boxes[:, 0] + 1) * (boxes[:, 3] - boxes[:, 1] + 1)
    xx1 = np.maximum(box[0], boxes[:, 0])
    yy1 = np.maximum(box[1], boxes[:, 1])
    xx2 = np.minimum(box[2], boxes[:, 2])
    yy2 = np.minimum(box[3], boxes[:, 3])

    # compute the width and height of the bounding box
    w = np.maximum(0, xx2 - xx1 + 1)
    h = np.maximum(0, yy2 - yy1 + 1)

    inter = w * h
    ovr = np.true_divide(inter,(box_area + area - inter))
    #ovr = inter / (box_area + area - inter)
    return ovr


def convert_to_square(bbox):
    """Convert bbox to square

    Parameters:
    ----------
    bbox: numpy array , shape n x 5
        input bbox

    Returns:
    -------
    square bbox
    """
    square_bbox = bbox.copy()

    h = bbox[:, 3] - bbox[:, 1] + 1
    w = bbox[:, 2] - bbox[:, 0] + 1
    max_side = np.maximum(h,w)
    square_bbox[:, 0] = bbox[:, 0] + w*0.5 - max_side*0.5
    square_bbox[:, 1] = bbox[:, 1] + h*0.5 - max_side*0.5
    square_bbox[:, 2] = square_bbox[:, 0] + max_side - 1
    square_bbox[:, 3] = square_bbox[:, 1] + max_side - 1
    return square_bbox

# non-maximum suppression: eleminates the box which have large interception with the box which have the largest score
def nms(dets, thresh, mode="Union"):
    """
    greedily select boxes with high confidence
    keep boxes overlap <= thresh
    rule out overlap > thresh
    :param dets: [[x1, y1, x2, y2 score]]
    :param thresh: retain overlap <= thresh
    :return: indexes to keep
    """
    x1 = dets[:, 0]
    y1 = dets[:, 1]
    x2 = dets[:, 2]
    y2 = dets[:, 3]
    scores = dets[:, 4]

    # shape of x1 = (454,), shape of scores = (454,)
    # print("shape of x1 = {0}, shape of scores = {1}".format(x1.shape, scores.shape))
    # time.sleep(5)

    areas = (x2 - x1 + 1) * (y2 - y1 + 1)
    order = scores.argsort()[::-1] # argsort: ascending order then [::-1] reverse the order --> descending order
    # print("shape of order {0}".format(order.size)) # (454,)
    # time.sleep(5)

    # eleminates the box which have large interception with the box which have the largest score in order
    # matain the box with largest score and boxes don't have large interception with it
    keep = []
    while order.size > 0:
        i = order[0]
        keep.append(i)
        xx1 = np.maximum(x1[i], x1[order[1:]])
        yy1 = np.maximum(y1[i], y1[order[1:]])
        xx2 = np.minimum(x2[i], x2[order[1:]])
        yy2 = np.minimum(y2[i], y2[order[1:]])

        w = np.maximum(0.0, xx2 - xx1 + 1)
        h = np.maximum(0.0, yy2 - yy1 + 1)
        inter = w * h

        # cacaulate the IOU between box which have largest score with other boxes
        if mode == "Union":
            # area[i]: the area of largest score
            ovr = inter / (areas[i] + areas[order[1:]] - inter)
        elif mode == "Minimum":
            ovr = inter / np.minimum(areas[i], areas[order[1:]])
        

        inds = np.where(ovr <= thresh)[0]
        order = order[inds + 1] # +1: eliminates the first element in order
        # print(inds)
        # print("shape of order {0}".format(order.shape))  # (454,)
        # time.sleep(2)

    return keep