using System.IO;
using Newtonsoft.Json;
using Prism.Mvvm;
using Store.Management.Framework.Configs;

namespace Store.Management.Framework.Services;

public interface ISettingsServiceBase<T> where T : class
{
	T Model { get; }
	string FilePath { get; }
	T GetDefaultModel();
	void LoadSettings();
	Task LoadSettingsAsync();
	void SaveSettings();
	Task SaveSettingsAsync();
}

/// <summary>
/// JSON 配置服务。缺失文件保留当前配置，加载失败保留旧模型并抛出异常。
/// 保存通过同目录临时文件替换目标；模型变更应在所属 UI 线程调用。
/// </summary>
public abstract class JsonSettingsServiceBase<T> : BindableBase, ISettingsServiceBase<T> where T : class
{
	private readonly SemaphoreSlim _gate = new(1, 1);
	private T? _model;
	/// <summary>默认按模型类型名保存到用户配置目录，派生类可覆盖文件名或完整路径。</summary>
	public virtual string FilePath => FolderConfig.GetSettingsFilePath(typeof(T).Name + ".json");
	public abstract T GetDefaultModel();
	public T Model
	{
		get => _model ??= GetDefaultModel() ?? throw new InvalidOperationException("默认配置不能为空。");
		protected set
		{
			ArgumentNullException.ThrowIfNull(value);
			SetProperty(ref _model, value);
		}
	}

	public void LoadSettings()
	{
		T? loaded = LoadModelAsync().GetAwaiter().GetResult();
		if (loaded is not null) Model = loaded;
	}
	public void SaveSettings() => SaveSettingsAsync().GetAwaiter().GetResult();

	public async Task LoadSettingsAsync()
	{
		T? loaded = await LoadModelAsync();
		if (loaded is not null) Model = loaded;
	}

	private async Task<T?> LoadModelAsync()
	{
		T? loaded = null;
		await _gate.WaitAsync().ConfigureAwait(false);
		try
		{
			string path = GetFullPath();
			try
			{
				string json = await File.ReadAllTextAsync(path).ConfigureAwait(false);
				loaded = JsonConvert.DeserializeObject<T>(json)
					?? throw new JsonSerializationException($"配置文件不能为 null：{path}");
			}
			catch (FileNotFoundException) { }
			catch (DirectoryNotFoundException) { }
		}
		finally { _gate.Release(); }
		return loaded;
	}

	public async Task SaveSettingsAsync()
	{
		// 在首次等待前读取模型，避免在后台线程初始化默认模型。
		string json = JsonConvert.SerializeObject(Model, Formatting.Indented);
		await _gate.WaitAsync().ConfigureAwait(false);
		string? temporaryPath = null;
		try
		{
			string path = GetFullPath();
			Directory.CreateDirectory(Path.GetDirectoryName(path)!);
			temporaryPath = path + "." + Guid.NewGuid().ToString("N") + ".tmp";
			await File.WriteAllTextAsync(temporaryPath, json).ConfigureAwait(false);
			File.Move(temporaryPath, path, overwrite: true);
		}
		finally
		{
			try { if (temporaryPath is not null && File.Exists(temporaryPath)) File.Delete(temporaryPath); }
			finally { _gate.Release(); }
		}
	}

	private string GetFullPath()
	{
		ArgumentException.ThrowIfNullOrWhiteSpace(FilePath);
		return Path.GetFullPath(FilePath);
	}
}