import numpy as np


def decode(loc, priors, variances):
    """Decode locations from predictions using priors to undo
    the encoding we did for offset regression at train time.
    Args:
        loc (tensor): location predictions for loc layers,
            Shape: [num_priors,4]
        priors (tensor): Prior boxes in center-offset form.
            Shape: [num_priors,4].
        variances: (list[float]) Variances of priorboxes
    Return:
        decoded bounding box predictions
    """

    boxes = None

    boxes = np.concatenate(
        (
            priors[:, :2] + loc[:, :2] * variances[0] * priors[:, 2:],
            priors[:, 2:] * np.exp(loc[:, 2:] * variances[1]),
        ),
        axis=1,
    )

    boxes[:, :2] -= boxes[:, 2:] / 2
    boxes[:, 2:] += boxes[:, :2]
    return boxes


def decode_landm(pre, priors, variances):
    """Decode landm from predictions using priors to undo
    the encoding we did for offset regression at train time.
    Args:
        pre (tensor): landm predictions for loc layers,
            Shape: [num_priors,10]
        priors (tensor): Prior boxes in center-offset form.
            Shape: [num_priors,4].
        variances: (list[float]) Variances of priorboxes
    Return:
        decoded landm predictions
    """
    landms = None

    landms = np.concatenate(
        (
            priors[:, :2] + pre[:, :2] * variances[0] * priors[:, 2:],
            priors[:, :2] + pre[:, 2:4] * variances[0] * priors[:, 2:],
            priors[:, :2] + pre[:, 4:6] * variances[0] * priors[:, 2:],
            priors[:, :2] + pre[:, 6:8] * variances[0] * priors[:, 2:],
            priors[:, :2] + pre[:, 8:10] * variances[0] * priors[:, 2:],
        ),
        axis=1,
    )

    return landms