using System.Security.Claims;
using Fengling.Platform.Domain.AggregatesModel.GatewayAggregate;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Caching.Memory;
using Yarp.ReverseProxy.Transforms;
using YarpGateway.Data;

namespace YarpGateway.Transforms;

/// <summary>
/// 租户路由转换器
/// 
/// 功能说明：
/// 1. 从 JWT Token 解析租户 ID
/// 2. 根据租户 ID 查找对应的目标端点
/// 3. 优先使用租户专属目标，不存在则回退到默认目标
/// 4. 使用内存缓存优化性能
/// </summary>
public class TenantRoutingTransform : RequestTransform
{
    private readonly IDbContextFactory<GatewayDbContext> _dbContextFactory;
    private readonly IMemoryCache _cache;
    private readonly ILogger<TenantRoutingTransform> _logger;

    // 缓存键前缀
    private const string CacheKeyPrefix = "tenant_destination";
    // 缓存过期时间：5分钟
    private static readonly TimeSpan CacheExpiration = TimeSpan.FromMinutes(5);

    public TenantRoutingTransform(
        IDbContextFactory<GatewayDbContext> dbContextFactory,
        IMemoryCache cache,
        ILogger<TenantRoutingTransform> logger)
    {
        _dbContextFactory = dbContextFactory;
        _cache = cache;
        _logger = logger;
    }

    public override async ValueTask ApplyAsync(RequestTransformContext context)
    {
        // 从 HttpContext 获取 ClusterId（由 TenantRoutingMiddleware 设置）
        if (!context.HttpContext.Items.TryGetValue("DynamicClusterId", out var clusterIdObj) || clusterIdObj is not string clusterId)
        {
            _logger.LogDebug("No DynamicClusterId found in HttpContext, skipping tenant routing");
            return;
        }

        // 从 JWT Token 解析租户 ID
        var tenantId = ExtractTenantFromJwt(context.HttpContext);
        
        if (string.IsNullOrEmpty(tenantId))
        {
            _logger.LogDebug("No tenant ID found in JWT, using default destination for cluster {ClusterId}", clusterId);
            // 没有租户ID时，使用默认目标
            await RouteToDefaultDestinationAsync(context, clusterId);
            return;
        }

        _logger.LogDebug("Processing tenant routing for cluster {ClusterId}, tenant {TenantId}", clusterId, tenantId);

        // 查找租户专属目标
        var tenantDestination = await FindTenantDestinationAsync(clusterId, tenantId);
        
        if (tenantDestination != null)
        {
            _logger.LogDebug("Using tenant-specific destination {DestinationId} ({Address}) for tenant {TenantId}", 
                tenantDestination.DestinationId, tenantDestination.Address, tenantId);
            
            context.ProxyRequest.RequestUri = BuildRequestUri(context.DestinationPrefix, tenantDestination.Address);
        }
        else
        {
            // 回退到默认目标
            _logger.LogDebug("No tenant-specific destination found for tenant {TenantId}, falling back to default", tenantId);
            await RouteToDefaultDestinationAsync(context, clusterId);
        }
    }

    /// <summary>
    /// 从 JWT Token 中提取租户 ID
    /// </summary>
    private static string? ExtractTenantFromJwt(HttpContext httpContext)
    {
        if (httpContext.User?.Identity?.IsAuthenticated != true)
        {
            return null;
        }

        // 尝试从 claims 中获取租户 ID
        var tenantClaim = httpContext.User.Claims.FirstOrDefault(c => 
            c.Type.Equals("tenant", StringComparison.OrdinalIgnoreCase) ||
            c.Type.Equals("tenant_id", StringComparison.OrdinalIgnoreCase) ||
            c.Type.Equals("tenant_code", StringComparison.OrdinalIgnoreCase) ||
            c.Type.Equals("tid", StringComparison.OrdinalIgnoreCase));

        return tenantClaim?.Value;
    }

    /// <summary>
    /// 查找租户专属的目标端点
    /// </summary>
    private async Task<GwDestination?> FindTenantDestinationAsync(string clusterId, string tenantId)
    {
        var cacheKey = $"{CacheKeyPrefix}:{clusterId}:{tenantId}";

        // 尝试从缓存获取
        if (_cache.TryGetValue(cacheKey, out GwDestination? cachedDestination))
        {
            _logger.LogDebug("Cache hit for tenant destination: {CacheKey}", cacheKey);
            return cachedDestination;
        }

        // 从数据库查询
        await using var dbContext = await _dbContextFactory.CreateDbContextAsync();
        
        var cluster = await dbContext.GwClusters
            .AsNoTracking()
            .FirstOrDefaultAsync(c => c.ClusterId == clusterId && c.Status == 1);

        if (cluster == null)
        {
            _logger.LogWarning("Cluster {ClusterId} not found or disabled", clusterId);
            return null;
        }

        // 查找租户专属目标（TenantCode 匹配且状态正常）
        var tenantDestination = cluster.Destinations
            .FirstOrDefault(d => 
                d.Status == 1 && 
                !string.IsNullOrEmpty(d.TenantCode) && 
                d.TenantCode.Equals(tenantId, StringComparison.OrdinalIgnoreCase));

        if (tenantDestination != null)
        {
            // 缓存结果
            var cacheOptions = new MemoryCacheEntryOptions()
                .SetAbsoluteExpiration(CacheExpiration)
                .SetSize(1);
            
            _cache.Set(cacheKey, tenantDestination, cacheOptions);
            _logger.LogDebug("Cached tenant destination for key: {CacheKey}", cacheKey);
        }

        return tenantDestination;
    }

    /// <summary>
    /// 查找默认目标端点（TenantCode 为空）
    /// </summary>
    private async Task<GwDestination?> FindDefaultDestinationAsync(string clusterId)
    {
        var cacheKey = $"{CacheKeyPrefix}:{clusterId}:default";

        // 尝试从缓存获取
        if (_cache.TryGetValue(cacheKey, out GwDestination? cachedDestination))
        {
            _logger.LogDebug("Cache hit for default destination: {CacheKey}", cacheKey);
            return cachedDestination;
        }

        // 从数据库查询
        await using var dbContext = await _dbContextFactory.CreateDbContextAsync();
        
        var cluster = await dbContext.GwClusters
            .AsNoTracking()
            .FirstOrDefaultAsync(c => c.ClusterId == clusterId && c.Status == 1);

        if (cluster == null)
        {
            _logger.LogWarning("Cluster {ClusterId} not found or disabled", clusterId);
            return null;
        }

        // 查找默认目标（TenantCode 为空或 null 且状态正常）
        var defaultDestination = cluster.Destinations
            .FirstOrDefault(d => 
                d.Status == 1 && 
                string.IsNullOrEmpty(d.TenantCode));

        if (defaultDestination != null)
        {
            // 缓存结果
            var cacheOptions = new MemoryCacheEntryOptions()
                .SetAbsoluteExpiration(CacheExpiration)
                .SetSize(1);
            
            _cache.Set(cacheKey, defaultDestination, cacheOptions);
            _logger.LogDebug("Cached default destination for key: {CacheKey}", cacheKey);
        }

        return defaultDestination;
    }

    /// <summary>
    /// 路由到默认目标
    /// </summary>
    private async ValueTask RouteToDefaultDestinationAsync(RequestTransformContext context, string clusterId)
    {
        var defaultDestination = await FindDefaultDestinationAsync(clusterId);
        
        if (defaultDestination != null)
        {
            _logger.LogDebug("Using default destination {DestinationId} ({Address}) for cluster {ClusterId}", 
                defaultDestination.DestinationId, defaultDestination.Address, clusterId);
            
            context.ProxyRequest.RequestUri = BuildRequestUri(context.DestinationPrefix, defaultDestination.Address);
        }
        else
        {
            _logger.LogWarning("No default destination found for cluster {ClusterId}", clusterId);
        }
    }

    /// <summary>
    /// 构建完整的请求 URI
    /// </summary>
    private static Uri BuildRequestUri(string? destinationPrefix, string address)
    {
        // 如果 address 已经是完整 URI，直接使用
        if (Uri.TryCreate(address, UriKind.Absolute, out var absoluteUri))
        {
            return absoluteUri;
        }

        // 否则，与 destinationPrefix 组合
        if (!string.IsNullOrEmpty(destinationPrefix))
        {
            var baseUri = destinationPrefix.TrimEnd('/');
            var path = address.StartsWith('/') ? address : "/" + address;
            return new Uri(baseUri + path);
        }

        // 如果都无法构建，抛出异常
        throw new InvalidOperationException($"Cannot build valid URI from prefix '{destinationPrefix}' and address '{address}'");
    }
}