using System.Text.Json;
using Microsoft.EntityFrameworkCore;
using YarpGateway.Data;
using YarpGateway.Models;

namespace YarpGateway.Services;

public class KubernetesPendingSyncService : BackgroundService
{
    private readonly IServiceProvider _serviceProvider;
    private readonly ILogger<KubernetesPendingSyncService> _logger;
    private readonly TimeSpan _syncInterval = TimeSpan.FromSeconds(30);
    private readonly TimeSpan _staleThreshold = TimeSpan.FromHours(24);

    public KubernetesPendingSyncService(
        IServiceProvider serviceProvider,
        ILogger<KubernetesPendingSyncService> logger)
    {
        _serviceProvider = serviceProvider;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("Starting K8s pending service sync background task");

        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                await SyncPendingServicesAsync(stoppingToken);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error during K8s pending service sync");
            }

            await Task.Delay(_syncInterval, stoppingToken);
        }
    }

    private async Task SyncPendingServicesAsync(CancellationToken ct)
    {
        using var scope = _serviceProvider.CreateScope();
        var providers = scope.ServiceProvider.GetServices<Fengling.ServiceDiscovery.IServiceDiscoveryProvider>();
        var k8sProvider = providers.FirstOrDefault(p => p.ProviderName == "Kubernetes");
        
        if (k8sProvider == null)
        {
            _logger.LogWarning("No Kubernetes service discovery provider found");
            return;
        }
        
        var dbContextFactory = scope.ServiceProvider.GetRequiredService<IDbContextFactory<GatewayDbContext>>();

        var discoveredServices = await k8sProvider.GetServicesAsync(ct);
        
        await using var db = await dbContextFactory.CreateDbContextAsync(ct);

        var existingPending = await db.PendingServiceDiscoveries
            .Where(p => !p.IsDeleted && p.Status == (int)PendingServiceStatus.Pending)
            .ToListAsync(ct);

        var existingDict = existingPending
            .ToDictionary(p => $"{p.K8sServiceName}|{p.K8sNamespace}");

        var discoveredSet = discoveredServices
            .Select(s => $"{s.Name}|{s.Namespace}")
            .ToHashSet();

        var addedCount = 0;
        var updatedCount = 0;
        var cleanedCount = 0;

        foreach (var item in existingDict)
        {
            var key = item.Key;
            
            if (!discoveredSet.Contains(key))
            {
                var pending = item.Value;
                
                if (DateTime.UtcNow - pending.DiscoveredAt > _staleThreshold)
                {
                    pending.IsDeleted = true;
                    pending.Version++;
                    cleanedCount++;
                    _logger.LogInformation("Cleaned up stale pending service {ServiceName} in namespace {Namespace}",
                        pending.K8sServiceName, pending.K8sNamespace);
                }
                else
                {
                    pending.Status = (int)PendingServiceStatus.K8sServiceNotFound;
                    pending.Version++;
                    _logger.LogInformation("Pending service {ServiceName} in namespace {Namespace} not found in K8s, marked as not found",
                        pending.K8sServiceName, pending.K8sNamespace);
                }
            }
        }

        if (discoveredServices.Count > 0)
        {
            var discoveredDict = discoveredServices.ToDictionary(
                s => $"{s.Name}|{s.Namespace}",
                s => s);

            foreach (var item in discoveredDict)
            {
                var key = item.Key;
                var service = item.Value;
                
                if (existingDict.TryGetValue(key, out var existing))
                {
                    if (existing.Status == (int)PendingServiceStatus.K8sServiceNotFound)
                    {
                        existing.Status = (int)PendingServiceStatus.Pending;
                        existing.Version++;
                        updatedCount++;
                    }
                    
                    var portsJson = JsonSerializer.Serialize(service.Ports);
                    var labelsJson = JsonSerializer.Serialize(service.Labels);

                    if (existing.DiscoveredPorts != portsJson || existing.Labels != labelsJson)
                    {
                        existing.DiscoveredPorts = portsJson;
                        existing.Labels = labelsJson;
                        existing.K8sClusterIP = service.ClusterIP;
                        existing.PodCount = service.Ports.Count;
                        existing.Version++;
                        updatedCount++;
                    }
                }
                else
                {
                    var newPending = new GwPendingServiceDiscovery
                    {
                        K8sServiceName = service.Name,
                        K8sNamespace = service.Namespace,
                        K8sClusterIP = service.ClusterIP,
                        DiscoveredPorts = JsonSerializer.Serialize(service.Ports),
                        Labels = JsonSerializer.Serialize(service.Labels),
                        PodCount = service.Ports.Count,
                        Status = (int)PendingServiceStatus.Pending,
                        DiscoveredAt = DateTime.UtcNow,
                        Version = 1
                    };
                    db.PendingServiceDiscoveries.Add(newPending);
                    addedCount++;
                }
            }
        }

        if (addedCount > 0 || updatedCount > 0 || cleanedCount > 0)
        {
            await db.SaveChangesAsync(ct);
            _logger.LogInformation("K8s sync completed: {Added} new, {Updated} updated, {Cleaned} cleaned",
                addedCount, updatedCount, cleanedCount);
        }
    }
}