Recursively searches for a file with the specified name within a directory and its subdirectories.

FindFileInDirectory.cs

/// <summary>
/// Recursively searches for a file with the specified name within a directory and its subdirectories.
/// </summary>
/// <param name="directoryPath">The path of the directory to start the search from.</param>
/// <param name="fileName">The name of the file to search for.</param>
/// <returns>The full path of the found file or null if the file is not found.</returns>
public static string FindFileInDirectory(string directoryPath, string fileName)
{
    if (string.IsNullOrWhiteSpace(directoryPath) || string.IsNullOrWhiteSpace(fileName))
    {
        throw new ArgumentException("Directory path and file name must be provided.");
    }

    if (!Directory.Exists(directoryPath))
    {
        throw new DirectoryNotFoundException($"The directory '{directoryPath}' does not exist.");
    }

    foreach (var file in Directory.GetFiles(directoryPath))
    {
        if (Path.GetFileName(file) == fileName) return file;
    }

    foreach (var subDirectory in Directory.GetDirectories(directoryPath))
    {
        string foundFilePath = FindFileInDirectory(subDirectory, fileName);
        if (foundFilePath != null) return foundFilePath;
    }

    return null;
}