using System;
using System.Threading;
using System.Threading.Tasks;
using AutopilotMonitor.Functions.Helpers;
using Microsoft.Azure.SignalR.Management;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;

namespace AutopilotMonitor.Functions.Services
{
    /// <summary>
    /// Programmatic SignalR message sender for background tasks that run outside
    /// of Azure Function output bindings (e.g., async rule engine, vulnerability correlation).
    /// Uses the Azure SignalR Management SDK to send messages to connected clients.
    /// </summary>
    public class SignalRNotificationService : ISignalRNotificationService, IDisposable
    {
        private readonly ILogger<SignalRNotificationService> _logger;
        private readonly ServiceManager _serviceManager;
        private ServiceHubContext? _hubContext;
        private static readonly SemaphoreSlim _initLock = new(1, 1);

        private const string HubName = "autopilotmonitor";

        /// <summary>
        /// Hard ceiling for every imperative send (hub-context resolution + SendCoreAsync).
        /// Without it a slow/unreachable SignalR endpoint blocks for the SDK's HttpClient
        /// default of 100s, pinning the calling thread (queue worker or Task.Run) for the
        /// full duration. These pushes are observability nudges, never correctness — fail fast.
        /// </summary>
        private static readonly TimeSpan SendTimeout = TimeSpan.FromSeconds(5);

        /// <summary>
        /// Ceiling for client negotiation. More generous than SendTimeout: the first negotiate on a
        /// cold instance also pays the one-time hub-context initialization, and a negotiate failure
        /// is user-visible (the client cannot connect at all), so err toward completing it.
        /// </summary>
        private static readonly TimeSpan NegotiateTimeout = TimeSpan.FromSeconds(10);

        public SignalRNotificationService(IConfiguration configuration, ILogger<SignalRNotificationService> logger)
        {
            _logger = logger;
            var connectionString = configuration["AzureSignalRConnectionString"]
                ?? throw new InvalidOperationException("AzureSignalRConnectionString is not configured");

            _serviceManager = new ServiceManagerBuilder()
                .WithOptions(o =>
                {
                    o.ConnectionString = connectionString;
                    o.ServiceTransportType = ServiceTransportType.Persistent;
                })
                .BuildServiceManager();
        }

        /// <summary>
        /// Notify a session's connected clients that new rule analysis results are available.
        /// Sends to the session-specific SignalR group so only the relevant session detail page reacts.
        /// </summary>
        public async Task NotifyRuleResultsAvailableAsync(string tenantId, string sessionId, int resultCount)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var groupName = $"session-{tenantId}-{sessionId}";

                await hub.Clients.Group(groupName).SendCoreAsync("ruleResultsReady", new object[]
                {
                    new
                    {
                        sessionId,
                        tenantId,
                        ruleResultCount = resultCount,
                        timestamp = DateTime.UtcNow.ToString("o")
                    }
                }, cts.Token);

                _logger.LogDebug("Sent ruleResultsReady to group {Group} ({Count} results)", groupName, resultCount);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send ruleResultsReady notification for session {SessionId}", sessionId);
            }
        }

        /// <summary>
        /// Notify a session's connected clients that vulnerability correlation results are available.
        /// </summary>
        public async Task NotifyVulnerabilityReportAvailableAsync(string tenantId, string sessionId, string overallRisk)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var groupName = $"session-{tenantId}-{sessionId}";

                await hub.Clients.Group(groupName).SendCoreAsync("vulnerabilityReportReady", new object[]
                {
                    new
                    {
                        sessionId,
                        tenantId,
                        overallRisk,
                        timestamp = DateTime.UtcNow.ToString("o")
                    }
                }, cts.Token);

                _logger.LogDebug("Sent vulnerabilityReportReady to group {Group} (risk={Risk})", groupName, overallRisk);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send vulnerabilityReportReady notification for session {SessionId}", sessionId);
            }
        }

        /// <summary>
        /// Notify the session group that the cascade-deletion worker has tombstoned the session
        /// (plan §5 PR4). Receivers (web UI) remove the row and close any open detail pane.
        /// Failures are logged and swallowed — the SignalR push is observability, not correctness;
        /// the audit log entry <c>deletion_completed</c> remains the canonical record.
        /// </summary>
        public async Task NotifySessionDeletedAsync(string tenantId, string sessionId)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var groupName = $"session-{tenantId}-{sessionId}";

                await hub.Clients.Group(groupName).SendCoreAsync("sessionDeleted", new object[]
                {
                    new
                    {
                        sessionId,
                        tenantId,
                        timestamp = DateTime.UtcNow.ToString("o")
                    }
                }, cts.Token);

                _logger.LogDebug("Sent sessionDeleted to group {Group}", groupName);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send sessionDeleted notification for session {SessionId}", sessionId);
            }
        }

        /// <summary>
        /// Push a newly created tenant notification to the appropriate audience-tier group.
        /// Member-tier notifications go to the -notify-member group (joined by all tenant members);
        /// Admin-tier notifications go to the -notify-admin group (joined by Tenant Admins + Global Admins only).
        /// </summary>
        public virtual async Task SendTenantNotificationAsync(string tenantId, NotificationAudience audience, object dto)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var groupName = audience == NotificationAudience.Admin
                    ? SignalRGroupHelper.TenantNotifyAdminGroup(tenantId)
                    : SignalRGroupHelper.TenantNotifyMemberGroup(tenantId);

                await hub.Clients.Group(groupName).SendCoreAsync("tenantNotification", new[] { dto }, cts.Token);
                _logger.LogDebug("Sent tenantNotification to group {Group}", groupName);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send tenantNotification for tenant {TenantId}", tenantId);
            }
        }

        /// <summary>
        /// Push a tenant notification dismissal to all audience-tier groups for the tenant.
        /// We do not know the original audience at dismiss time, so we broadcast to both groups —
        /// receivers filter by id and remove if present (idempotent).
        /// </summary>
        public virtual async Task SendTenantNotificationDismissedAsync(string tenantId, string notificationId)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var memberGroup = SignalRGroupHelper.TenantNotifyMemberGroup(tenantId);
                var adminGroup = SignalRGroupHelper.TenantNotifyAdminGroup(tenantId);
                var payload = new { id = notificationId };

                await Task.WhenAll(
                    hub.Clients.Group(memberGroup).SendCoreAsync("tenantNotificationDismissed", new object[] { payload }, cts.Token),
                    hub.Clients.Group(adminGroup).SendCoreAsync("tenantNotificationDismissed", new object[] { payload }, cts.Token)
                );
                _logger.LogDebug("Sent tenantNotificationDismissed for tenant {TenantId} id {Id}", tenantId, notificationId);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send tenantNotificationDismissed for tenant {TenantId} id {Id}", tenantId, notificationId);
            }
        }

        /// <summary>
        /// Push a "dismiss all" event to all audience-tier groups for the tenant. Receivers clear local state.
        /// </summary>
        public virtual async Task SendTenantNotificationDismissedAllAsync(string tenantId)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var memberGroup = SignalRGroupHelper.TenantNotifyMemberGroup(tenantId);
                var adminGroup = SignalRGroupHelper.TenantNotifyAdminGroup(tenantId);

                await Task.WhenAll(
                    hub.Clients.Group(memberGroup).SendCoreAsync("tenantNotificationsDismissedAll", Array.Empty<object>(), cts.Token),
                    hub.Clients.Group(adminGroup).SendCoreAsync("tenantNotificationsDismissedAll", Array.Empty<object>(), cts.Token)
                );
                _logger.LogDebug("Sent tenantNotificationsDismissedAll for tenant {TenantId}", tenantId);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send tenantNotificationsDismissedAll for tenant {TenantId}", tenantId);
            }
        }

        /// <summary>
        /// Push a newly created global notification to the global-admins group.
        /// </summary>
        public virtual async Task SendGlobalNotificationAsync(object dto)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                await hub.Clients.Group(SignalRGroupHelper.GlobalAdminsGroup).SendCoreAsync("globalNotification", new[] { dto }, cts.Token);
                _logger.LogDebug("Sent globalNotification to group {Group}", SignalRGroupHelper.GlobalAdminsGroup);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send globalNotification");
            }
        }

        public virtual async Task SendGlobalNotificationDismissedAsync(string notificationId)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var payload = new { id = notificationId };
                await hub.Clients.Group(SignalRGroupHelper.GlobalAdminsGroup).SendCoreAsync("globalNotificationDismissed", new object[] { payload }, cts.Token);
                _logger.LogDebug("Sent globalNotificationDismissed for id {Id}", notificationId);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send globalNotificationDismissed for id {Id}", notificationId);
            }
        }

        public virtual async Task SendGlobalNotificationDismissedAllAsync()
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                await hub.Clients.Group(SignalRGroupHelper.GlobalAdminsGroup).SendCoreAsync("globalNotificationsDismissedAll", Array.Empty<object>(), cts.Token);
                _logger.LogDebug("Sent globalNotificationsDismissedAll");
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to send globalNotificationsDismissedAll");
            }
        }

        /// <summary>
        /// Negotiates a client connection with the access token bound to <paramref name="userId"/>
        /// (lowercased UPN) — see <see cref="ISignalRNotificationService.NegotiateClientAsync"/>.
        /// Token generation is local (no service round-trip beyond hub-context init).
        /// </summary>
        public virtual async Task<(string Url, string AccessToken)?> NegotiateClientAsync(string userId)
        {
            try
            {
                using var cts = new CancellationTokenSource(NegotiateTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                var negotiation = await hub.NegotiateAsync(new NegotiationOptions { UserId = userId }, cts.Token);
                if (string.IsNullOrEmpty(negotiation?.Url) || string.IsNullOrEmpty(negotiation.AccessToken))
                {
                    _logger.LogError("SignalR negotiation returned an empty url/token for user {UserId}", userId);
                    return null;
                }
                return (negotiation.Url, negotiation.AccessToken);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "SignalR negotiation failed for user {UserId}", userId);
                return null;
            }
        }

        /// <summary>
        /// Cuts the user's live streams after a revoke (see
        /// <see cref="ISignalRNotificationService.DisconnectUserAsync"/>). Two prongs, because the
        /// Management SDK (1.33) exposes no user-level connection close: (1) strip the user from all
        /// groups server-side, and (2) push "accessRevoked" to the user's connections — the web
        /// client restarts its connection on receipt, and every re-join then re-runs authorization
        /// against the fresh (≤30s-cached) scope. Residual: a tampered client that ignores (2) and
        /// whose connection-scoped memberships survive (1) keeps its streams until the connection
        /// drops. Warning (not Debug) on failure so it reaches App Insights.
        /// </summary>
        public virtual async Task DisconnectUserAsync(string userId)
        {
            try
            {
                using var cts = new CancellationTokenSource(SendTimeout);
                var hub = await GetHubContextAsync(cts.Token);
                await hub.UserGroups.RemoveFromAllGroupsAsync(userId, cts.Token);
                await hub.Clients.User(userId).SendCoreAsync("accessRevoked", new object[]
                {
                    new { timestamp = DateTime.UtcNow.ToString("o") }
                }, cts.Token);
                _logger.LogInformation("Revoked SignalR streams of user {UserId} (group strip + accessRevoked push)", userId);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex,
                    "Failed to cut SignalR streams of user {UserId} after revoke — already-joined connections keep streaming until they drop",
                    userId);
            }
        }

        private async Task<ServiceHubContext> GetHubContextAsync(CancellationToken ct = default)
        {
            if (_hubContext != null) return _hubContext;

            await _initLock.WaitAsync(ct);
            try
            {
                _hubContext ??= await _serviceManager.CreateHubContextAsync(HubName, ct);
                return _hubContext;
            }
            finally
            {
                _initLock.Release();
            }
        }

        public void Dispose()
        {
            (_hubContext as IDisposable)?.Dispose();
            _serviceManager?.Dispose();
        }
    }
}