def electron_configuration(electron_num):
    """
    Determines the electron configuration for a given atomic number.
    Uses standard orbital filling order and handles some exceptions.
    """
    # Define the order in which orbitals fill
    filling_order = ["1s", "2s", "2p", "3s", "3p", "4s", "3d", "4p",
                     "5s", "4d", "5p", "6s", "4f", "5d", "6p", "7s",
                     "5f", "6d", "7p", "8s"]

    configuration = []  # Store the final configuration here
    remaining_electrons = electron_num  # Track electrons left to assign
    i = 0  # Index in filling_order

    while remaining_electrons > 0: # Repeat until we run out of electrons
        subshell = filling_order[i][1]  # 's', 'p', 'd', or 'f'
        # Maximum electrons allowed in this subshell
        shell_capacity = {"s": 2, "p": 6, "d": 10, "f": 14}[subshell]
        # Find how many electrons can be placed in the orbital
        electrons_in_subshell = min(shell_capacity, remaining_electrons)

        # Append orbital and electron count to configuration
        configuration.append(filling_order[i] + str(electrons_in_subshell))
        # Subtract placed electrons from remaining
        remaining_electrons -= electrons_in_subshell
        i += 1  # Move to next orbital in filling order

    # Sort orbitals to show them in increasing shell order
    configuration.sort()
    return configuration

def convert_superscript(number):
    """
    Converts a number into Unicode superscript.
    Example: 2 to '²'
    """
    return "¹²³⁴⁵⁶⁷⁸⁹⁰"["1234567890".find(str(number))]

def integer_test(string):
    """
    Returns True if string contains only digits.
    """
    for char in string:
        if char not in "0123456789":
            return False
    return True


def remove_letters(string):
    """
    Remove all non-numeric characters from input.
    """
    return "".join([c for c in string if c in "0123456789"])

def draw_bohr_model():
    GRAPH_SIZE = (400, 400)

    # Define PySimpleGUI layout. This is used to tell PySimpleGUI what elemets to put on the screen.
    layout = [
        [sg.Text("Atomic Number of Element:"),
         sg.Input("", size=(5,20), key="inp"),
         sg.Button("Show Electron Configuration", bind_return_key=True, key="start")],
        [sg.Text("Electron Configuration:\n\n", font=("Helvetica", 14), key="config")],
        [sg.Graph(canvas_size=GRAPH_SIZE,
                  graph_bottom_left=(0,0),
                  graph_top_right=(GRAPH_SIZE[0]+150, GRAPH_SIZE[1]+150),
                  background_color="white",
                  key="GRAPH")]
    ]

    # Create window
    window = sg.Window("Bohr Model", layout, finalize=True)
    graph = window["GRAPH"]

    while True:
        event, values = window.read()
        if event == sg.WIN_CLOSED: # Close window on user's request
            break

        inp = values["inp"]
        # Only accept numeric inputs 1-118
        if event == "start" and inp.isdigit() and 1 <= int(inp) <= 118:
            configuration = electron_configuration(int(inp))
            graph.erase()  # Clear previous drawings

            # Draw nucleus in the center
            graph.draw_circle((275, 275), 30, fill_color="red")

            # Draw electrons
            prev_shell = 1
            electrons_num = 0
            for orbital in configuration:
                shell = int(orbital[0]) 
                if shell != prev_shell:
                    # Draw shell circle/ring
                    angle_increment = 2 * pi / electrons_num
                    graph.draw_circle((275, 275), (prev_shell+1)*30)
                    # Space electrons out evenly and droaw them
                    for j in range(electrons_num):
                        x = cos(angle_increment*j - pi/2)*(prev_shell+1)*30 + 275
                        y = sin(angle_increment*j - pi/2)*(prev_shell+1)*30 + 275
                        graph.draw_circle((x, y), 7, fill_color="blue")
                    prev_shell = shell
                    electrons_num = 0
                electrons_num += int(orbital[2:])