//Unity某些版本某些android机型,获取Application.persistentDataPath可能会返回空
//一些用Java获取外部路径的，也可能会在低端机上遇到UnauthorizedAccessException
//这个老外TheGering的方案比较完善，足以覆盖Android上所有的情况。

#region Android Java获取persistentDataPath以解决Unity获取路径为空的问题

    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));
    }
    #endregion