using Microsoft.Extensions.Caching.Memory;
using System.Collections.Concurrent;

namespace StoreHub.Framework.Security;

/// <summary>
/// 基于 <see cref="IMemoryCache"/> 的在线用户会话存储。
/// </summary>
public class OnlineUserStore : IOnlineUserStore
{
	private const string CacheKeyPrefix = "online:user:";
	private readonly IMemoryCache _cache;
	// 在线人员索引：IMemoryCache 不提供公共枚举 API，这里用字典维护便于查询在线列表
	private readonly ConcurrentDictionary<string, OnlineUserInfo> _onlineIndex = new(StringComparer.Ordinal);

	public OnlineUserStore(IMemoryCache cache)
	{
		_cache = cache;
	}

	/// <inheritdoc />
	public void SignIn(OnlineUserInfo info)
	{
		ArgumentNullException.ThrowIfNull(info);

		// 以登录账户为键覆盖写入：旧会话（jti）被顶替，实现单点登录
		_cache.Set(GetKey(info.UserName), info, new MemoryCacheEntryOptions
		{
			// 缓存条目与令牌同时过期，过期后自动失效
			AbsoluteExpiration = info.ExpiresAt,
		});
		_onlineIndex[info.UserName] = info;
	}

	/// <inheritdoc />
	public bool IsTokenActive(string userName, string jti)
	{
		if (string.IsNullOrWhiteSpace(userName) || string.IsNullOrWhiteSpace(jti))
		{
			return false;
		}

		return _cache.TryGetValue(GetKey(userName), out OnlineUserInfo? info)
			&& info is not null
			&& string.Equals(info.Jti, jti, StringComparison.Ordinal);
	}

	/// <inheritdoc />
	public void SignOut(string userName)
	{
		_cache.Remove(GetKey(userName));
		_onlineIndex.TryRemove(userName, out _);
	}

	/// <inheritdoc />
	public IReadOnlyList<OnlineUserInfo> GetOnlineUsers()
	{
		DateTime now = DateTime.Now;
		List<OnlineUserInfo> result = [];
		foreach (KeyValuePair<string, OnlineUserInfo> pair in _onlineIndex)
		{
			if (pair.Value.ExpiresAt > now)
			{
				result.Add(pair.Value);
			}
			else
			{
				_onlineIndex.TryRemove(pair.Key, out _);
			}
		}

		return result;
	}

	/// <inheritdoc />
	public int Count => GetOnlineUsers().Count;

	private static string GetKey(string userName) => $"{CacheKeyPrefix}{userName}";
}