from tkinter import *

# Trial - Entry Box
# Purpose: Learn how the Entry widget works - creating it,
#          styling it for errors, and clearing it.
#          This is the same pattern used in the Distance Converter.

class EntryTrial:

    def __init__(self):

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

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

        instructions = ("Press Simulate Error to see the entry turn pink "
                        "and clear. Press Reset to restore it.")
        Label(self.frame,
              text=instructions,
              wraplength=300,
              font=("Arial", "11"),
              fg="#666666").grid(row=1, pady=5)

        # --- The entry box ---
        # font sets the text size inside the box
        # width sets how many characters wide it appears
        self.dist_entry = Entry(self.frame,
                                font=("Arial", "14"),
                                width=20)
        self.dist_entry.grid(row=2, padx=10, pady=10)

        # --- Answer / error label ---
        # Starts red (error state) - same as the Distance Converter
        self.answer_error = Label(self.frame,
                                  text="Please enter a number",
                                  font=("Arial", "13", "bold"),
                                  fg="#9C0000")
        self.answer_error.grid(row=3, pady=5)

        # --- Buttons ---
        btn_frame = Frame(self.frame)
        btn_frame.grid(row=4, pady=10)

        # Read button - shows what was typed in the entry
        Button(btn_frame,
               text="Read Entry",
               font=("Arial", "11", "bold"),
               bg="#004C99", fg="#FFFFFF", width=18,
               command=self.read_entry).grid(row=0, column=0,
                                             padx=5, pady=4)

        # Simulate error - turns entry pink and clears it
        Button(btn_frame,
               text="Simulate Error",
               font=("Arial", "11", "bold"),
               bg="#9C0000", fg="#FFFFFF", width=18,
               command=self.simulate_error).grid(row=1, column=0,
                                                 padx=5, pady=4)

        # Reset - puts entry and label back to normal
        Button(btn_frame,
               text="Reset / Clear",
               font=("Arial", "11", "bold"),
               bg="#666666", fg="#FFFFFF", width=18,
               command=self.reset_entry).grid(row=2, column=0,
                                              padx=5, pady=4)

    def read_entry(self):
        """
        Reads whatever is currently typed in the entry box.
        Only accepts positive whole numbers and decimals.
        - Non-numeric input is caught by the ValueError exception
        - Negative numbers are caught by the value < 0 check
        - Zero and positive numbers (including decimals) are accepted
        """
        raw = self.dist_entry.get()

        # Reset entry box colour first
        self.dist_entry.config(bg="#FFFFFF")

        try:
            value = float(raw)

            if value < 0:
                # Number was entered but it is negative
                self.answer_error.config(
                    text="Please enter a positive number",
                    fg="#9C0000"
                )
                self.dist_entry.config(bg="#F4CCCC")
                self.dist_entry.delete(0, END)

            else:
                # Valid positive number or zero
                self.answer_error.config(
                    text=f"You entered: {value}",
                    fg="#004C99"
                )

        except ValueError:
            # Input could not be converted to a number at all
            self.answer_error.config(
                text="Please enter a number, not text",
                fg="#9C0000"
            )
            self.dist_entry.config(bg="#F4CCCC")
            self.dist_entry.delete(0, END)

    def simulate_error(self):
        """
        When validation fails in check_distance(), two things happen:
        1. Entry background turns pink (#F4CCCC)
        2. Entry is cleared using .delete(0, END)
           - 0 means start from the first character
           - END is a tkinter constant meaning 'the last character'
        """
        self.answer_error.config(
            text="Error! Entry cleared and turned pink.",
            fg="#9C0000"
        )
        self.dist_entry.config(bg="#F4CCCC")
        self.dist_entry.delete(0, END)

    def reset_entry(self):
        """
        The clear_entry() method in the Distance Converter does this -
        resets the background to white and clears any text.
        Also resets the label back to the default error state.
        """
        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("Entry Box Trial")
    EntryTrial()
    root.mainloop()