using Newtonsoft.Json;

namespace OCES.Resonance.Core;

/// <summary>
/// 偏好设置管理器，负责平台路径解析、JSON 持久化以及 <see cref="Preferences"/> 实例的生命周期管理。
/// </summary>
public static class PreferencesManager
{
    /// <summary>当前活动的偏好设置实例，<see cref="Load"/> 调用前为 null</summary>
    public static Preferences? CurrentPreferences { get; set; }

    /// <summary>
    /// 加载偏好设置。先尝试从硬盘反序列化；若文件不存在则创建带平台默认路径的新实例。
    /// </summary>
    public static void Load()
    {
        string preferencesPath = GetDefaultPreferencesPath();

        // 尝试从硬盘加载
        Preferences? loaded = Deserialize(preferencesPath);
        if (loaded != null)
        {
            CurrentPreferences = loaded;
            return;
        }

        // 文件不存在或反序列化失败 → 创建默认实例
        CurrentPreferences = new Preferences
        {
            DatabasePath = GetDefaultDatabasePath(),
        };

        // 立即落盘，确保下次启动能直接读取
        Serialize(CurrentPreferences);
    }

    /// <summary>
    /// 将当前 <see cref="CurrentPreferences"/> 序列化到硬盘。
    /// </summary>
    public static void Save()
    {
        if (CurrentPreferences == null) return;
        Serialize(CurrentPreferences);
    }

    /// <summary>
    /// 根据运行时平台返回数据库文件存放目录。
    /// </summary>
    public static string GetDefaultDatabasePath()
    {
        if (OperatingSystem.IsMacOS())
        {
            string applicationSupport = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
            DirectoryInfo databasePath = new(Path.Combine(applicationSupport, "OCES", "Resonance", "Databases"));
            if (!databasePath.Exists) Directory.CreateDirectory(databasePath.FullName);
            return databasePath.FullName;
        }

        if (OperatingSystem.IsWindows())
        {
            string localAppData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
            DirectoryInfo databasePath = new(Path.Combine(localAppData, "OCES", "Resonance", "Databases"));
            if (!databasePath.Exists) Directory.CreateDirectory(databasePath.FullName);
            return databasePath.FullName;
        }

        if (OperatingSystem.IsLinux())
        {
            string home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
            string xdgDataHome = Environment.GetEnvironmentVariable("XDG_DATA_HOME")
                                 ?? Path.Combine(home, ".local", "share");
            DirectoryInfo databasePath = new(Path.Combine(xdgDataHome, "Resonance", "Databases"));
            if (!databasePath.Exists) Directory.CreateDirectory(databasePath.FullName);
            return databasePath.FullName;
        }

        return string.Empty;
    }

    /// <summary>
    /// 根据运行时平台返回偏好设置 JSON 文件的完整路径。
    /// </summary>
    public static string GetDefaultPreferencesPath()
    {
        if (OperatingSystem.IsMacOS())
        {
            string home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
            return Path.Combine(home, "Library", "Preferences", "com.oces.Resonance.json");
        }

        if (OperatingSystem.IsWindows())
        {
            string roamingAppData = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
            return Path.Combine(roamingAppData, "OCES", "Resonance", "preferences.json");
        }

        if (OperatingSystem.IsLinux())
        {
            string home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
            string xdgConfigHome = Environment.GetEnvironmentVariable("XDG_CONFIG_HOME")
                                   ?? Path.Combine(home, ".config");
            return Path.Combine(xdgConfigHome, "Resonance", "preferences.json");
        }

        return string.Empty;
    }

    /// <summary>
    /// 将 <see cref="Preferences"/> 实例序列化为 JSON 文件，保存到平台默认偏好设置路径。
    /// </summary>
    /// <returns>成功返回 true，失败返回 false</returns>
    static bool Serialize(Preferences preferences)
    {
        try
        {
            string path = GetDefaultPreferencesPath();
            string? directory = Path.GetDirectoryName(path);
            if (!string.IsNullOrEmpty(directory) && !Directory.Exists(directory))
            {
                Directory.CreateDirectory(directory);
            }

            string json = JsonConvert.SerializeObject(preferences, Formatting.Indented);
            File.WriteAllText(path, json);
            return true;
        }
        catch
        {
            // 调用方根据自己的情况处理 false
            return false;
        }
    }

    /// <summary>
    /// 从指定路径读取 JSON 文件并反序列化为 <see cref="Preferences"/> 实例。
    /// </summary>
    /// <returns>反序列化成功返回实例，失败返回 null</returns>
    static Preferences? Deserialize(string preferencesPath)
    {
        try
        {
            if (!File.Exists(preferencesPath))
            {
                return null;
            }

            string json = File.ReadAllText(preferencesPath);
            return JsonConvert.DeserializeObject<Preferences>(json);
        }
        catch
        {
            return null;
        }
    }
}