from tkinter import *
from functools import partial # To prevent unwanted windows

class Converter:
    """
    Temperature conversion tool (deg C to deg F or deg F to deg C)
    """

    def __init__(self):
        """
        Temperature converter GUI
        """

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

        self.to_help_button = Button(self.temp_frame,
                                     text="Help / Info",
                                     bg="#CC6600",
                                     fg="#FFFFFF",
                                     font=("Arial", 12, "bold"), width=12,
                                     command=self.to_help)
        self.to_help_button.grid(row=1, padx=5, pady=5)

    def to_help(self):
        """
        Opens help dialogue box and disables help button
        (so that users can't create multiple help boxes).
        """
        DisplayHelp(self)

class DisplayHelp:

    def __init__(self, partner):
        # setup dialogue box and background colour
        background = "#ffe6cc"
        self.help_box = Toplevel()

        # diable help button
        partner.to_help_button.config(state=DISABLED)

        # If users press cross at top, closes help and
        # 'releases' help button
        self.help_box.protocol("WM_DELETE_WINDOW",
                               partial(self.close_help, partner))

        self.help_frame = Frame(self.help_box, width=300,
                                height=200)
        self.help_frame.grid()

        self.help_heading_label = Label(self.help_frame,
                                     text="Help / Info",
                                      font=("Arial", 14, "bold"),)
        self.help_heading_label.grid(row=0)

        help_text = ("To use the program, simply enter the temperature"
                     "you wish to convert and then choose to convert to "
                     "either degrees Celsius (centigrade) or "
                     "Fahrenheit... \n\n"
                     "Note that -273 degrees C "
                     "(-459 F) is absolute zero (the coldest possible"
                     "temperature). If you try to convert a"
                     "temperature that is less than -273 degrees C,"
                     "you will get an error message. \n\n "
                     "To see your "
                     "calculation history and export it to a text "
                     "file, please click the History / Export button")

        self.help_text_label = Label(self.help_frame,
                                     text=help_text, wraplength=350,
                                     justify="left")
        self.help_text_label.grid(row=1, padx=5, pady=5)

        self.dismiss_button = Button(self.help_frame,
                                     font=("Arial", 12, "bold"),
                                     text="Dismiss", bg="#CC6600",
                                     fg="#FFFFFF", command=partial(self.close_help, partner))
        self.dismiss_button.grid(row=2, padx=10, pady=10)

        # List and loop to set background colour on
        # everything except the buttons.
        recolour_list = [self.help_frame, self.help_heading_label,
                         self.help_text_label]

        for item in recolour_list:
            item.config(bg=background)

    def close_help(self, partner):
        """
        Closes help dialogue box and enables help button
        """
        # Put help button back to normal
        partner.to_help_button.config(state=NORMAL)
        self.help_box.destroy()


# main routine
if __name__ == "__main__":
    root = Tk()
    root.title("Temperature Conversion")
    Converter()
    root.mainloop()