from tkinter import *

def main():
    color = None
    root = Tk()
    root.title("Traffic Lights")
    root.geometry("640x480")
    # drawArea = Canvas(root, bg="white")
    drawArea = Canvas(root, bg="#cffbffaff")
    drawArea.pack(side=LEFT, fill=BOTH, expand=True, padx=8, pady=8)
    panel = Frame(root)
    panel.pack(side=RIGHT, fill=Y, expand=False, padx=8, pady=8)
    redButton = Button(panel, text="Red")
    redButton.pack(side=TOP, fill=X)
    yellowButton = Button(panel, text="Yellow")
    yellowButton.pack(side=TOP, fill=X)
    greenButton = Button(panel, text="Green")
    greenButton.pack(side=TOP, fill=X)
    blinkingButton = Button(panel, text="Blinking")
    blinkingButton.pack(side=TOP, fill=X)

    blinkDt = 500       # 500 milliseconds = 0.5 s 
    blinking = False
    
    def onRed():
        nonlocal color, blinking
        blinking = False
        color = 0
        drawLights()
        
    def onYellow():
        nonlocal color, blinking
        blinking = False
        color = 1
        drawLights()

    def onGreen():
        nonlocal color, blinking
        blinking = False
        color = 2
        drawLights()

    def onBlinking():
        nonlocal color, blinking
        blinking = True
        color = 1
        drawLights()
        drawArea.after(blinkDt, switchYellow)
        
    def switchYellow():
        nonlocal color, blinking
        if not blinking:
            return
        if color == 1:
            color = (-1)
        else:
            color = 1
        drawLights()
        drawArea.after(blinkDt, switchYellow)
        
    def drawLights():
        w = drawArea.winfo_width()
        h = drawArea.winfo_height()
        drawArea.delete("all")
        x = w/2
        r = 20
        for y in (h/3, h/2, h*2/3):
            drawArea.create_oval(
                x - r, y - r, x + r, y + r, fill=None, outline="black")
        if color == 0:
            y = h/3
            drawArea.create_oval(x - r, y - r, x + r, y + r, fill="red")
        elif color == 1:
            y = h/2
            drawArea.create_oval(x - r, y - r, x + r, y + r, fill="yellow")
        elif color == 2:
            y = h*2/3
            drawArea.create_oval(x - r, y - r, x + r, y + r, fill="green")
    
    redButton.configure(command=onRed)
    yellowButton.configure(command=onYellow)
    greenButton.configure(command=onGreen)
    blinkingButton.configure(command=onBlinking)
    drawLights()
    drawArea.bind("<Configure>", lambda e: drawLights())
    
    root.mainloop()
    
if __name__ == "__main__":
    main()