persitent data path handling in Unity with fallback

Toolkit

private static string[] _persistentDataPaths;

public static bool IsDirectoryWritable(string path) {
	try {
		if (!Directory.Exists(path)) return false;
		string file = Path.Combine(path, Path.GetRandomFileName());
		using (FileStream fs = File.Create(file, 1)) {}
		File.Delete(file);
		return true;
	} catch {
		return false;
	}
}

private static string GetPersistentDataPath(params string[] components) {
	try {
		string path = Path.DirectorySeparatorChar + string.Join("" + Path.DirectorySeparatorChar, components); 
		if (!Directory.GetParent(path).Exists) return null;
		if (!Directory.Exists(path)) {
			Debug.Log("creating directory: " + path);
			Directory.CreateDirectory(path);
		}
		if (!IsDirectoryWritable(path)) {
			Debug.LogWarning("persistent data path not writable: " + path);
			return null;
		}
		return path;
	} catch (Exception ex) {
		Debug.LogException(ex);
		return null;
	}
}
	
public static string persistentDataPathInternal {
#if UNITY_ANDROID
	get { 
		if (Application.isEditor || !Application.isPlaying) return Application.persistentDataPath;
		string path = null; 
		if (string.IsNullOrEmpty(path)) path = GetPersistentDataPath("storage", "emulated", "0", "Android", "data", Application.bundleIdentifier, "files"); 
		if (string.IsNullOrEmpty(path)) path = GetPersistentDataPath("data", "data", Application.bundleIdentifier, "files");
		return path;
	}
#else
	get { return Application.persistentDataPath; }
#endif
}
	
public static string persistentDataPathExternal {
#if UNITY_ANDROID
	get { 
		if (Application.isEditor || !Application.isPlaying) return null;
		string path = null; 
		if (string.IsNullOrEmpty(path)) path = GetPersistentDataPath("storage", "sdcard0", "Android", "data", Application.bundleIdentifier, "files"); 
		if (string.IsNullOrEmpty(path)) path = GetPersistentDataPath("storage", "sdcard1", "Android", "data", Application.bundleIdentifier, "files"); 
		if (string.IsNullOrEmpty(path)) path = GetPersistentDataPath("mnt", "sdcard", "Android", "data", Application.bundleIdentifier, "files"); 
		return path;
	}
#else
	get { return null; }
#endif
}

public static string[] persistentDataPaths {
	get {
		if (_persistentDataPaths == null) {
			List<string> paths = new List<string>();
			if (!string.IsNullOrEmpty(persistentDataPathInternal)) paths.Add(persistentDataPathInternal);
			if (!string.IsNullOrEmpty(persistentDataPathExternal)) paths.Add(persistentDataPathExternal);
			if (!string.IsNullOrEmpty(Application.persistentDataPath) && !paths.Contains(Application.persistentDataPath)) paths.Add(Application.persistentDataPath);
			_persistentDataPaths = paths.ToArray();
		}
		return _persistentDataPaths;
	}
}

// returns best persistent data path
public static string persistentDataPath {
	get { return persistentDataPaths.Length > 0 ? persistentDataPaths[0] : null; }
}

public static string GetPersistentFile(string relativePath) {
	if (string.IsNullOrEmpty(relativePath)) return null;
	foreach (string path in persistentDataPaths) {
		if (FileExists(path, relativePath)) return Path.Combine(path, relativePath);
	}
	return null;
}

public static bool SaveData(string relativePath, byte[] data) {
	string path = GetPersistentFile(relativePath);
	if (string.IsNullOrEmpty(path)) {
		return SaveData(relativePath, data, 0);
	} else {
		try {
			File.WriteAllBytes(path, data);	
			return true;
		} catch (Exception ex) {
			Debug.LogWarning("couldn't save data to: " + path);
			Debug.LogException(ex);
			// try to delete file again
			if (File.Exists(path)) File.Delete(path);
			return SaveData(relativePath, data, 0);
		}
	}
}

private static bool SaveData(string relativePath, byte[] data, int pathIndex) {
	if (pathIndex < persistentDataPaths.Length) {
		string path = Path.Combine(persistentDataPaths[pathIndex], relativePath);
		try {
			string dir = Path.GetDirectoryName(path);
			if (!Directory.Exists(dir)) {
				Debug.Log("creating directory: " + dir);
				Directory.CreateDirectory(dir);
			}
			File.WriteAllBytes(path, data);			
			return true;
		} catch (Exception ex) {
			Debug.LogWarning("couldn't save data to: " + path);
			Debug.LogException(ex);
			if (File.Exists(path)) File.Delete(path);		// try to delete file again
			return SaveData(relativePath, data, pathIndex + 1);	// try next persistent path
		}
	} else {
		Debug.LogWarning("couldn't save data to any persistent data path");
		return false;
	}
}

public static bool FileExists(string path, string relativePath) {
	return Directory.Exists(path) && File.Exists(Path.Combine(path, relativePath));
}