import tkinter as tk
from tkinter import ttk, messagebox
import difflib
import os
import shutil


class DiffViewer(tk.Toplevel):
    """
    Side-by-side diff viewer for comparing two files.
    """

    def __init__(self, parent, source_path: str, dest_path: str, relative_path: str):
        super().__init__(parent)
        self.source_path = source_path
        self.dest_path = dest_path
        self.relative_path = relative_path
        self.title(f"Diff - {relative_path}")
        self.geometry("1200x800")
        self._setup_ui()
        self._load_and_compare()

    def _setup_ui(self) -> None:
        """
        Initializes the side-by-side layout and buttons.
        """
        # Toolbar
        toolbar = ttk.Frame(self, padding=5)
        toolbar.pack(fill="x", side="top")
        copy_all_btn = ttk.Button(toolbar, text="⤴ Copy Source to Destination", command=self._copy_source_to_dest)
        copy_all_btn.pack(side="left", padx=5)
        # Main diff container
        main_frame = ttk.Frame(self)
        main_frame.pack(fill="both", expand=True, padx=5, pady=5)
        # Left pane (Source)
        self.left_text = tk.Text(main_frame, wrap="none", undo=True)
        self.left_text.pack(side="left", fill="both", expand=True)
        # Right pane (Destination)
        self.right_text = tk.Text(main_frame, wrap="none", undo=True)
        self.right_text.pack(side="left", fill="both", expand=True)
        # Scrollbar for both
        self.v_scroll = ttk.Scrollbar(main_frame, orient="vertical", command=self._sync_scroll)
        self.v_scroll.pack(side="right", fill="y")
        self.left_text.config(yscrollcommand=self.v_scroll.set)
        self.right_text.config(yscrollcommand=self.v_scroll.set)
        # Colors for diff
        self.left_text.tag_config("removed", background="#ffeef0")
        self.right_text.tag_config("added", background="#e6ffed")
        self.left_text.tag_config("changed", background="#fffbdd")
        self.right_text.tag_config("changed", background="#fffbdd")

    def _sync_scroll(self, *args) -> None:
        """
        Synchronizes vertical scrolling between both text widgets.
        """
        self.left_text.yview(*args)
        self.right_text.yview(*args)

    def _load_and_compare(self) -> None:
        """
        Reads files and highlights differences.
        """
        try:
            with open(self.source_path, "r", encoding="utf-8") as f:
                source_lines = f.readlines()
            # Handle case where destination file might not exist (Added files)
            dest_lines = []
            if os.path.exists(self.dest_path):
                with open(self.dest_path, "r", encoding="utf-8") as f:
                    dest_lines = f.readlines()
            diff = difflib.ndiff(dest_lines, source_lines)
            self._display_diff(diff)
        except Exception as e:
            messagebox.showerror("Error", f"Could not read files: {e}")
            self.destroy()

    def _display_diff(self, diff_generator) -> None:
        """
        Parses the diff and populates the text widgets with highlighting.
        """
        self.left_text.config(state="normal")
        self.right_text.config(state="normal")
        for line in diff_generator:
            code = line[:2]
            content = line[2:]
            if code == "  ":
                self.left_text.insert("end", content)
                self.right_text.insert("end", content)
            elif code == "- ":
                self.left_text.insert("end", content, "removed")
                self.right_text.insert("end", "\n")
            elif code == "+ ":
                self.left_text.insert("end", "\n")
                self.right_text.insert("end", content, "added")
            elif code == "? ":
                continue
        self.left_text.config(state="disabled")
        self.right_text.config(state="disabled")

    def _copy_source_to_dest(self) -> None:
        """
        Overwrites the destination file with the source file content.
        """
        confirm = messagebox.askyesno("Confirm", "Overwrite destination file with source content?")
        if confirm:
            try:
                os.makedirs(os.path.dirname(self.dest_path), exist_ok=True)
                shutil.copy2(self.source_path, self.dest_path)
                messagebox.showinfo("Success", "File copied successfully.")
                self.destroy()
            except Exception as e:
                messagebox.showerror("Error", f"Failed to copy file: {e}")