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


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


class Converter:
    """
    Temperature conversion tool (°C to °F or °F to °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", "14", "bold"), width=12,
                                     command=partial(to_help, self)
                                     )
        self.to_help_button.grid(row=1, padx=5, pady=5)


class DisplayHelp:
    """
    Displays help dialogue box
    """

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

        # disable 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=10)

        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 converter")
    Converter()
    root.mainloop()