import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)


maxParkingSpaces=10
parkingSpaces=maxParkingSpaces
TRIG = 13
ECHO = 15
GREEN = 37
RED = 35

print "Distance Measurement In Progress"

GPIO.setup(TRIG,GPIO.OUT)
GPIO.setup(15,GPIO.IN)
GPIO.setup(11,GPIO.IN)
GPIO.setup(RED,GPIO.OUT)
GPIO.setup(GREEN,GPIO.OUT)


GPIO.output(TRIG, False)
print "Waiting For Sensor To Settle"
time.sleep(2)

lastEntryDistance=0
lastExitDistance=0

if parkingSpaces>0:
        GPIO.output(GREEN,GPIO.HIGH)
        GPIO.output(RED,GPIO.LOW)

try:
        while 1:
                if ECHO == 15:
                        ECHO=11
                else :
                        ECHO =15

                time.sleep(0.3)
                GPIO.output(TRIG, True)
                time.sleep(0.00001)
                GPIO.output(TRIG, False)

                while GPIO.input(ECHO)==0:
                  pulse_start = time.time()

                while GPIO.input(ECHO)==1:
                  pulse_end = time.time()


                pulse_duration = pulse_end - pulse_start
                distance = pulse_duration * 17150

                distance = round(distance, 2)


                if ECHO == 15:
                        print "Distance Entry:",distance,"cm"
                        if distance < 16 and lastEntryDistance>16:
                                parkingSpaces = parkingSpaces - 1
                        lastEntryDistance=distance
                else :
                        print "Distance Exit:",distance,"cm"
                        if distance < 16 and lastExitDistance>16 and parkingSpaces<maxParkingSpaces:
                                parkingSpaces = parkingSpaces + 1
                        lastExitDistance=distance

                if parkingSpaces>0 :
                        print "Parking Spaces Available : ",parkingSpaces
                else:
                        print "Parking Spaces Available : 0"

                if parkingSpaces<=0:
                        GPIO.output(GREEN,GPIO.LOW)
                        GPIO.output(RED,GPIO.HIGH)
                else:
                        GPIO.output(GREEN,GPIO.HIGH)
                        GPIO.output(RED,GPIO.LOW)
except KeyboardInterrupt:
        GPIO.cleanup()