from tkinter import *
from tkinter import ttk

status = 1

def switch_status(newS: int = None):
    global status
    if not newS:
        if status == 1:
            status = 2
        else:
            status = 1
    else:
        status = newS
    update_statusbar()

def update_statusbar():
    global status
    if status == 1:
        frame_statusbar['style'] = 'aFrame.TFrame'
    elif status == 2:
        frame_statusbar['style'] = 'bFrame.TFrame'
    else:
        frame_statusbar['style'] = 'bFrame.TFrame'

def calculate(*args):
    try:
        stringvalue = feet.get()
        stringvalue = stringvalue.replace(",",".")
        value = float(stringvalue)
        m_value = 0.3048 * value
        m_value = round(m_value, 2)
        meters.set(m_value)
        switch_status(2)
    except ValueError:
        pass
    return True

def check_entry(what):
    switch_status(1)
    if what == "":
        # Nichts eingegeben
        return True
    else:
        try:
            # DEBUG
            print(what)
            float(what)
            return True
        except ValueError:
            return False

# Hauptfenster
root = Tk()
root.title("Feet to Meters")
check_entry_wrapper = root.register(check_entry)

# Rahmen im Hauptfenster (aus ttk für Farbanpassung)
mainframe = ttk.Frame(root, padding = "3 3 12 12")

mainframe.grid(column = 0, row = 0, sticky = NW)
root.columnconfigure(0, weight = 1)
root.rowconfigure(0, weight = 1)

# Eingabefeld für Länge in feet
feet = StringVar()
feet_entry = ttk.Entry(mainframe, width = 7, textvariable = feet,
                       validatecommand = (check_entry_wrapper, '%P'),
                       validate = 'key')
feet_entry.grid(column = 2, row = 1, sticky = (W, E))

# Einheit-Label für Eingabefeld der Länge in feet
ttk.Label(mainframe, text = "feet").grid(column = 3, row = 1, sticky = W)

# Label für Ausgabefeld der Länge in Metern
ttk.Label(mainframe, text = "ist äquivalent zu").grid(column = 1, row = 2, sticky = E)

# Einheit-Label für Ausgabefeld der Länge in Metern
ttk.Label(mainframe, text = "Meter").grid(column = 3, row = 2, sticky = W)

# Ausgabefeld für Länge in Metern
meters = StringVar()
meters_entry = ttk.Entry(mainframe, width = 7, textvariable = meters)
meters_entry.grid(column = 2, row = 2, sticky = (W,E))
meters_entry.configure(state = 'readonly') # keine Eingabe, aber selektierbar

# Button für Berechnung

button_calc = ttk.Button(mainframe, text = "Berechne", command = calculate)
button_calc.grid(column = 3, row = 3, sticky = W)

# schönere Abstände
for child in mainframe.winfo_children():
    child.grid_configure(padx = 5, pady = 5)

# Statusbar
s = ttk.Style()
s.configure('aFrame.TFrame', background = "yellow")
s.configure('bFrame.TFrame', background = "green")
s.configure('cFrame.TFrame', background = "red")
frame_statusbar = ttk.Frame(root)
frame_statusbar['relief'] = 'sunken'
frame_statusbar['height'] = 12
frame_statusbar['style'] = 'aFrame.TFrame'
frame_statusbar.grid_propagate(0) # Feste Größe an Grid-Packer weitergeben
frame_statusbar.grid(column = 0, row = 1, sticky = W+S+E)

# Setze Fokus in Eingabefeld
feet_entry.focus()

root.bind("<Return>", calculate)
root.bind("<KP_Enter>", calculate)

root.mainloop()