from tkinter import *

# Trial - Entry Validation v2
# Purpose: Refine the validation to use the has_errors flag pattern,
#          which is cleaner when there are multiple things to check.
#          This matches the pattern used in the Distance Converter.

class ValidationTrial:

    def __init__(self):

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

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

        instructions = ("This version uses the has_errors flag pattern. "
                        "It also checks if from and to units are the same.")
        Label(self.frame,
              text=instructions,
              wraplength=300,
              font=("Arial", "11"),
              fg="#666666").grid(row=1, pady=5)

        # Entry row
        self.input_row = Frame(self.frame)
        self.input_row.grid(row=2, pady=10)

        self.entry = Entry(self.input_row, font=("Arial", "14"), width=12)
        self.entry.grid(row=0, column=0, padx=(0, 10))

        self.from_var = StringVar(value="km")
        OptionMenu(self.input_row, self.from_var,
                   "km", "m", "cm", "mm").grid(row=0, column=1)

        # To unit row
        self.to_row = Frame(self.frame)
        self.to_row.grid(row=3, pady=5)

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

        self.to_var = StringVar(value="m")
        OptionMenu(self.to_row, self.to_var,
                   "km", "m", "cm", "mm").grid(row=0, column=1)

        # Answer / error label
        self.answer_error = Label(self.frame,
                                  text="Enter a distance above",
                                  font=("Arial", "13", "bold"),
                                  fg="#9C0000")
        self.answer_error.grid(row=4, pady=5)

        # Button row
        btn_frame = Frame(self.frame)
        btn_frame.grid(row=5, pady=5)

        Button(btn_frame,
               text="Convert",
               font=("Arial", "12", "bold"),
               bg="#009900", fg="#FFFFFF", width=10,
               command=self.check_input).grid(row=0, column=0, padx=5)

        Button(btn_frame,
               text="Clear",
               font=("Arial", "12", "bold"),
               bg="#666666", fg="#FFFFFF", width=10,
               command=self.clear_entry).grid(row=0, column=1, padx=5)

    def check_input(self):
        """
        Uses a has_errors flag so multiple checks can be done cleanly.
        The error message is set inside each check, then displayed once
        at the end if has_errors == 'yes'.
        """

        raw = self.entry.get()
        from_unit = self.from_var.get()
        to_unit = self.to_var.get()

        # Reset styling first
        self.answer_error.config(fg="#004C99",
                                 font=("Arial", "13", "bold"))
        self.entry.config(bg="#FFFFFF")

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

        try:
            value = float(raw)

            if value < 0:
                error = "Please enter a number greater than or equal to 0"
                has_errors = "yes"

            elif from_unit == to_unit:
                error = "Please choose two different units"
                has_errors = "yes"

            else:
                # All good - simulate a conversion result
                self.answer_error.config(
                    text=f"Valid: converting {value} {from_unit} to {to_unit}",
                    fg="#004C99"
                )

        except ValueError:
            has_errors = "yes"

        # Display error if any check failed
        if has_errors == "yes":
            self.answer_error.config(text=error, fg="#9C0000")
            self.entry.config(bg="#F4CCCC")
            self.entry.delete(0, END)

    def clear_entry(self):
        self.entry.delete(0, END)
        self.entry.config(bg="#FFFFFF")
        self.answer_error.config(
            text="Enter a distance above",
            fg="#9C0000",
            font=("Arial", "13", "bold")
        )


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