using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using CoreAgent.WebSocketTransport.Models;

namespace CoreAgent.WebSocketTransport.Middleware;

/// <summary>
/// 缓存中间件
/// 使用 IMemoryCache 缓存静态消息（如 CONFIG_ 消息），支持 TTL
/// </summary>
public class CacheMiddleware : IMessageMiddleware
{
    private readonly IMemoryCache _cache;
    private readonly ILogger<CacheMiddleware> _logger;
    private readonly WebSocketConfig _config;
    private static readonly string[] _cacheablePrefixes = { "CONFIG_", "SETTINGS_" };

    public CacheMiddleware(IMemoryCache cache, ILogger<CacheMiddleware> logger, IOptions<WebSocketConfig> config)
    {
        _cache = cache ?? throw new ArgumentNullException(nameof(cache));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _config = config?.Value ?? throw new ArgumentNullException(nameof(config));
    }

    /// <summary>
    /// 处理发送消息，不进行缓存操作
    /// </summary>
    public Task<T?> ProcessSendAsync<T>(T message, CancellationToken cancellationToken = default)
    {
        // 发送消息不进行缓存，直接返回
        return Task.FromResult<T?>(message);
    }

    /// <summary>
    /// 处理接收消息，缓存符合条件的消息
    /// </summary>
    public Task<T?> ProcessReceiveAsync<T>(T message, CancellationToken cancellationToken = default)
    {
        if (message == null)
        {
            return Task.FromResult<T?>(default);
        }

        var messageStr = message.ToString();
        
        // 检查是否为可缓存消息
        if (IsCacheableMessage(messageStr))
        {
            var cacheKey = GenerateCacheKey(messageStr);
            
            // 尝试从缓存获取
            if (_cache.TryGetValue(cacheKey, out T? cachedMessage))
            {
                _logger.LogDebug("缓存命中: {CacheKey}", cacheKey);
                return Task.FromResult<T?>(cachedMessage);
            }

            // 缓存消息
            var cacheOptions = new MemoryCacheEntryOptions
            {
                AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(_config.CacheTtlMinutes),
                SlidingExpiration = TimeSpan.FromMinutes(_config.CacheTtlMinutes / 2)
            };

            _cache.Set(cacheKey, message, cacheOptions);
            _logger.LogDebug("消息已缓存: {CacheKey}, TTL: {TtlMinutes}分钟", 
                cacheKey, _config.CacheTtlMinutes);
        }

        return Task.FromResult<T?>(message);
    }

    /// <summary>
    /// 判断是否为可缓存消息
    /// </summary>
    private static bool IsCacheableMessage(string? message)
    {
        if (string.IsNullOrEmpty(message))
            return false;

        return _cacheablePrefixes.Any(prefix => 
            message.StartsWith(prefix, StringComparison.OrdinalIgnoreCase));
    }

    /// <summary>
    /// 生成缓存键
    /// </summary>
    private static string GenerateCacheKey(string? message)
    {
        return $"websocket_cache_{message?.GetHashCode() ?? 0}";
    }
}