# import the necessary packages
from .social_distancing_config import NMS_THRESH
from .social_distancing_config import MIN_CONF
import numpy as np
import cv2

def detect_people(frame, net, ln, personIdx=0):
	# grab the dimensions of the frame and  initialize the list of
	# results
	(H, W) = frame.shape[:2]
	results = []

	# construct a blob from the input frame and then perform a forward
	# pass of the YOLO object detector, giving us our bounding boxes
	# and associated probabilities
	blob = cv2.dnn.blobFromImage(frame, 1 / 255.0, (416, 416),
		swapRB=True, crop=False)
	net.setInput(blob)
	layerOutputs = net.forward(ln)

	# initialize our lists of detected bounding boxes, centroids, and
	# confidences, respectively
	boxes = []
	centroids = []
	confidences = []

	# loop over each of the layer outputs
	for output in layerOutputs:
		# loop over each of the detections
		for detection in output:
			# extract the class ID and confidence (i.e., probability)
			# of the current object detection
			scores = detection[5:]
			classID = np.argmax(scores)
			confidence = scores[classID]

			# filter detections by (1) ensuring that the object
			# detected was a person and (2) that the minimum
			# confidence is met
			if classID == personIdx and confidence > MIN_CONF:
				# scale the bounding box coordinates back relative to
				# the size of the image, keeping in mind that YOLO
				# actually returns the center (x, y)-coordinates of
				# the bounding box followed by the boxes' width and
				# height
				box = detection[0:4] * np.array([W, H, W, H])
				(centerX, centerY, width, height) = box.astype("int")

				# use the center (x, y)-coordinates to derive the top
				# and and left corner of the bounding box
				x = int(centerX - (width / 2))
				y = int(centerY - (height / 2))

				# update our list of bounding box coordinates,
				# centroids, and confidences
				boxes.append([x, y, int(width), int(height)])
				centroids.append((centerX, centerY))
				confidences.append(float(confidence))

	# apply non-maxima suppression to suppress weak, overlapping
	# bounding boxes
	idxs = cv2.dnn.NMSBoxes(boxes, confidences, MIN_CONF, NMS_THRESH)

	# ensure at least one detection exists
	if len(idxs) > 0:
		# loop over the indexes we are keeping
		for i in idxs.flatten():
			# extract the bounding box coordinates
			(x, y) = (boxes[i][0], boxes[i][1])
			(w, h) = (boxes[i][2], boxes[i][3])

			# update our results list to consist of the person
			# prediction probability, bounding box coordinates,
			# and the centroid
			r = (confidences[i], (x, y, x + w, y + h), centroids[i])
			results.append(r)

	# return the list of results
	return results