C# Hex Swapper

using System;
using System.IO;
using System.Text;

class HexReplace
{
    static void Main()
    {
        Console.WriteLine("Enter the path to the .ucas file:");
        string filePath = Console.ReadLine();

        Console.WriteLine("Enter the hex value to replace:");
        string hexToReplace = Console.ReadLine();

        Console.WriteLine("Enter the new hex value:");
        string newHexValue = Console.ReadLine();

        if (hexToReplace.Length != newHexValue.Length)
        {
            Console.WriteLine("Error: The lengths of the hex values should be the same.");
            return;
        }

        try
        {
            // Read the content of the file
            string fileContent = File.ReadAllText(filePath);

            // Search and replace the hex value
            string updatedContent = ReplaceHexValue(fileContent, hexToReplace, newHexValue);

            // Write the updated content back to the file
            File.WriteAllText(filePath, updatedContent);

            Console.WriteLine("Hex value replaced successfully.");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"An error occurred: {ex.Message}");
        }
    }

    static string ReplaceHexValue(string input, string hexToReplace, string newHexValue)
    {
        // Convert hex strings to byte arrays
        byte[] hexBytesToReplace = StringToByteArray(hexToReplace);
        byte[] newHexBytes = StringToByteArray(newHexValue);

        // Replace the hex value in the input string
        int index = input.IndexOf(hexBytesToReplace, StringComparison.OrdinalIgnoreCase);
        while (index != -1)
        {
            input = input.Remove(index, hexBytesToReplace.Length);
            input = input.Insert(index, ByteArrayToString(newHexBytes));
            index = input.IndexOf(hexBytesToReplace, index + newHexBytes.Length, StringComparison.OrdinalIgnoreCase);
        }

        return input;
    }

    static byte[] StringToByteArray(string hex)
    {
        return Enumerable.Range(0, hex.Length)
                         .Where(x => x % 2 == 0)
                         .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
                         .ToArray();
    }

    static string ByteArrayToString(byte[] byteArray)
    {
        StringBuilder hex = new StringBuilder(byteArray.Length * 2);
        foreach (byte b in byteArray)
        {
            hex.AppendFormat("{0:x2}", b);
        }
        return hex.ToString();
    }
}