import threading
import time

import RPi.GPIO as GPIO

aSetOfFunctionData =[
    "some data to be sent to USB",
    "some more data to be sent to USB",
    "knock, knock",

    ]

def getNextFunctionData():
    for functionData in aSetOfFunctionData:
        yield functionData

START_PIN = 17
STOP_PIN = 18
NEXT_PIN = 19

def setupBoard():
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(START_PIN, GPIO.IN) # START BUTTON
    GPIO.setup(STOP_PIN, GPIO.IN) # STOP BUTTON
    GPIO.setup(NEXT_PIN, GPIO.IN) # NEXT BUTTON

def sendFunctionDataToUSB(functionData):
    # USB communication code
    pass

class ButtonProcessor(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.stopEvent = threading.Event()

    def run(self):
        startTime = 0
        while not self.stopEvent.is_set():
            startPressed = GPIO.input(START_PIN)
            stopPressed = GPIO.input(STOP_PIN)
            nextPressed = GPIO.input(NEXT_PIN)
            if stopPressed:
                self.stop()
            elif startPressed:
                startTime = time.time()
                sendFunctionDataToUSB(getNextFunctionData())
            elif nextPressed:
                sendFunctionDataToUSB(getNextFunctionData())

            if startTime and time.time()-startTime >10:
                startTime = 0
                sendFunctionDataToUSB(getNextFunctionData())

            self.stopEvent.wait(0.05)

    def stop(self):
        self.event.set()

setupBoard()
processor = ButtonProcessor()
processor.start()

time.sleep(120) # this simulation will self-destruct in 2 minutes.

processor.stop()