from tkinter import *

# Trial 2 - Two OptionMenu dropdowns built from a list
# Purpose: Learn how to use a list of options and build TWO linked dropdowns
#          This is how the distance converter handles from/to unit selection

# Unit options stored in a list (mirrors all_constants.UNITS)
UNITS = ["km", "m", "cm", "mm"]


class DropdownTrial:

    def __init__(self):

        self.frame = Frame(padx=10, pady=10)
        self.frame.grid()

        self.heading = Label(self.frame,
                             text="Dropdown Trial - v2 (Two Dropdowns)",
                             font=("Arial", "16", "bold"))
        self.heading.grid(row=0)

        # --- From unit row ---
        self.from_frame = Frame(self.frame)
        self.from_frame.grid(row=1, pady=5)

        Label(self.from_frame,
              text="Convert from:",
              font=("Arial", "12")).grid(row=0, column=0, padx=(0, 10))

        self.from_var = StringVar(value=UNITS[0])  # default: km

        # Unpack the list using * so each item becomes a separate argument
        self.from_menu = OptionMenu(self.from_frame, self.from_var, *UNITS)
        self.from_menu.config(font=("Arial", "12"), width=5)
        self.from_menu.grid(row=0, column=1)

        # --- To unit row ---
        self.to_frame = Frame(self.frame)
        self.to_frame.grid(row=2, pady=5)

        Label(self.to_frame,
              text="Convert to:    ",
              font=("Arial", "12")).grid(row=0, column=0, padx=(0, 10))

        self.to_var = StringVar(value=UNITS[1])  # default: m

        self.to_menu = OptionMenu(self.to_frame, self.to_var, *UNITS)
        self.to_menu.config(font=("Arial", "12"), width=5)
        self.to_menu.grid(row=0, column=1)

        # --- Check button ---
        self.check_button = Button(self.frame,
                                   text="Show Selection",
                                   font=("Arial", "12", "bold"),
                                   bg="#009900", fg="#FFFFFF",
                                   width=14,
                                   command=self.show_selected)
        self.check_button.grid(row=3, pady=10)

        self.result_label = Label(self.frame,
                                  text="",
                                  font=("Arial", "12"))
        self.result_label.grid(row=4)

    def show_selected(self):
        from_unit = self.from_var.get()
        to_unit = self.to_var.get()

        # Check for same-unit selection - important validation!
        if from_unit == to_unit:
            self.result_label.config(
                text="Error: please choose two different units",
                fg="#9C0000"
            )
        else:
            self.result_label.config(
                text=f"Converting from {from_unit} to {to_unit}",
                fg="#004C99"
            )


# main routine
if __name__ == "__main__":
    root = Tk()
    root.title("Dropdown Trial v2")
    DropdownTrial()
    root.mainloop()