from tkinter import *
import all_constants as c
import conversion_rounding as cr


class Converter:
    """
    Distance conversion tool (km, m, cm, mm)
    """

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

        self.all_calculations_list = []

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

        self.dist_heading = Label(self.dist_frame,
                                  text="Distance Converter",
                                  font=("Arial", "16", "bold"))
        self.dist_heading.grid(row=0, columnspan=2)

        instructions = ("Please enter a distance below, choose the units "
                        "to convert from and to, then press Convert.")
        self.dist_instructions = Label(self.dist_frame,
                                       text=instructions,
                                       wraplength=250, width=40,
                                       justify="left")
        self.dist_instructions.grid(row=1, columnspan=2)

        # Input row: entry + from-unit dropdown
        self.input_subframe = Frame(self.dist_frame)
        self.input_subframe.grid(row=2, pady=10)

        self.dist_entry = Entry(self.input_subframe, font=("Arial", "14"), width=14)
        self.dist_entry.grid(row=0, column=0, padx=(0, 10))

        self.from_unit_var = StringVar(value=c.UNITS[0])
        self.from_unit_menu = OptionMenu(self.input_subframe, self.from_unit_var, *c.UNITS)
        self.from_unit_menu.config(font=("Arial", "12"), width=5)
        self.from_unit_menu.grid(row=0, column=1)

        # "to" label + to-unit dropdown
        self.to_subframe = Frame(self.dist_frame)
        self.to_subframe.grid(row=3, pady=(0, 10))

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

        self.to_unit_var = StringVar(value=c.UNITS[1])
        self.to_unit_menu = OptionMenu(self.to_subframe, self.to_unit_var, *c.UNITS)
        self.to_unit_menu.config(font=("Arial", "12"), width=5)
        self.to_unit_menu.grid(row=0, column=1)

        error = "Please enter a number"
        self.answer_error = Label(self.dist_frame, text=error,
                                  fg="#9C0000", font=("Arial", "14", "bold"))
        self.answer_error.grid(row=4)

        # Conversion, help and history / export buttons
        self.button_frame = Frame(self.dist_frame)
        self.button_frame.grid(row=5)

        # button list (button text | bg colour | command | row | column)
        button_details_list = [
            ["Convert",          "#009900", lambda: self.check_distance(), 0, 0],
            ["Clear",            "#666666", self.clear_entry,              0, 1],
            ["Help / Info",      "#CC6600", "",                            1, 0],
            ["History / Export", "#004C99", "",                            1, 1]
        ]

        # List to hold buttons once they have been made
        self.button_ref_list = []

        for item in button_details_list:
            self.make_button = Button(self.button_frame,
                                      text=item[0], bg=item[1],
                                      fg="#FFFFFF", font=("Arial", "12", "bold"),
                                      width=12, command=item[2])
            self.make_button.grid(row=item[3], column=item[4], padx=5, pady=5)

            self.button_ref_list.append(self.make_button)

        # retrieve 'history / export' button and disable it at the start
        self.to_history_button = self.button_ref_list[3]
        self.to_history_button.config(state=DISABLED)

    def check_distance(self):
        """
        Checks distance is valid and either invokes calculation
        function or shows a custom error
        """

        # Retrieve distance to be converted
        to_convert = self.dist_entry.get()

        # Reset label and entry box (if we have error)
        self.answer_error.config(fg="#004C99", font=("Arial", "13", "bold"))
        self.dist_entry.config(bg="#FFFFFF")

        error = "Please enter a valid positive number"
        has_errors = "no"

        try:
            to_convert = float(to_convert)
            if to_convert < 0:
                error = "Please enter a number greater than or equal to 0"
                has_errors = "yes"
            elif self.from_unit_var.get() == self.to_unit_var.get():
                error = "Please choose two different units to convert between"
                has_errors = "yes"
            else:
                error = ""
                self.convert(to_convert)

        except ValueError:
            has_errors = "yes"

        # display error if necessary
        if has_errors == "yes":
            self.answer_error.config(text=error, fg="#9C0000")
            self.dist_entry.config(bg="#F4CCCC")
            self.dist_entry.delete(0, END)

    def convert(self, to_convert):
        """
        Converts distances and updates answer label. Also stores
        calculations for Export / History feature
        """
        from_unit = self.from_unit_var.get()
        to_unit = self.to_unit_var.get()

        answer = cr.convert_distance(to_convert, from_unit, to_unit)
        answer_statement = f"{to_convert} {from_unit} = {answer} {to_unit}"

        # enable history export button as soon as we have a valid calculation
        self.to_history_button.config(state=NORMAL)

        self.answer_error.config(text=answer_statement)
        self.all_calculations_list.append(answer_statement)
        print(self.all_calculations_list)

    def clear_entry(self):
        """Clears the entry box and resets the answer label."""
        self.dist_entry.delete(0, END)
        self.dist_entry.config(bg="#FFFFFF")
        self.answer_error.config(text="Please enter a number",
                                 fg="#9C0000", font=("Arial", "13", "bold"))


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