import cv2
import numpy as np


def resize_short(img, target_size):
    """ resize_short """
    percent = float(target_size) / min(img.shape[0], img.shape[1])
    resized_width = int(round(img.shape[1] * percent))
    resized_height = int(round(img.shape[0] * percent))
    resized = cv2.resize(img, (resized_width, resized_height))
    return resized


def crop_image(img, target_size, center):
    """ crop_image """
    height, width = img.shape[:2]
    size = target_size
    if center:
        w_start = (width - size) / 2
        h_start = (height - size) / 2
    else:
        w_start = np.random.randint(0, width - size + 1)
        h_start = np.random.randint(0, height - size + 1)
    w_end = w_start + size
    h_end = h_start + size
    img = img[int(h_start):int(h_end), int(w_start):int(w_end), :]
    return img


def preprocess(img):
    mean = [0.485, 0.456, 0.406]
    std = [0.229, 0.224, 0.225]
    img = resize_short(img, 224)
    img = crop_image(img, 224, True)
    # bgr-> rgb && hwc->chw
    img = img[:, :, ::-1].astype('float32').transpose((2, 0, 1)) / 255
    img_mean = np.array(mean).reshape((3, 1, 1))
    img_std = np.array(std).reshape((3, 1, 1))
    img -= img_mean
    img /= img_std
    return img[np.newaxis, :]
