import time

class Timer:
    def __init__(self):
        self.start_time = 0
        self.end_time = 0
        self.elapsing = False

    def start(self):
        if(self.elapsing):
            return
        self.start_time = time.time()
        self.elapsing = True

    def stop(self):
        if(not self.elapsing):
            return
        self.end_time = time.time()
        self.elapsing = False

    def elapsed_time(self):
        if(self.elapsing):
            return (str)(round(time.time() - self.start_time, 3)) + " seconds"
        return (str)(round(self.end_time - self.start_time, 3)) + " seconds"
    
    def reset(self):
        self.start_time = 0
        self.end_time = 0
        self.elapsing = False