using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using StellaOps.Router.Common.Abstractions;
using StellaOps.Router.Common.Models;
using StellaOps.Router.Gateway.OpenApi;
using StellaOps.Router.Transport.InMemory;

namespace StellaOps.Router.Gateway.Services;

/// <summary>
/// Manages microservice connections and updates routing state.
/// </summary>
internal sealed class ConnectionManager : IHostedService
{
    private readonly InMemoryTransportServer _transportServer;
    private readonly InMemoryConnectionRegistry _connectionRegistry;
    private readonly IGlobalRoutingState _routingState;
    private readonly IRouterOpenApiDocumentCache? _openApiCache;
    private readonly ILogger<ConnectionManager> _logger;

    public ConnectionManager(
        InMemoryTransportServer transportServer,
        InMemoryConnectionRegistry connectionRegistry,
        IGlobalRoutingState routingState,
        ILogger<ConnectionManager> logger,
        IRouterOpenApiDocumentCache? openApiCache = null)
    {
        _transportServer = transportServer;
        _connectionRegistry = connectionRegistry;
        _routingState = routingState;
        _openApiCache = openApiCache;
        _logger = logger;
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        // Subscribe to transport server events
        _transportServer.OnHelloReceived += HandleHelloReceivedAsync;
        _transportServer.OnHeartbeatReceived += HandleHeartbeatReceivedAsync;
        _transportServer.OnConnectionClosed += HandleConnectionClosedAsync;

        // Start the transport server
        await _transportServer.StartAsync(cancellationToken);

        _logger.LogInformation("Connection manager started");
    }

    public async Task StopAsync(CancellationToken cancellationToken)
    {
        await _transportServer.StopAsync(cancellationToken);

        _transportServer.OnHelloReceived -= HandleHelloReceivedAsync;
        _transportServer.OnHeartbeatReceived -= HandleHeartbeatReceivedAsync;
        _transportServer.OnConnectionClosed -= HandleConnectionClosedAsync;

        _logger.LogInformation("Connection manager stopped");
    }

    private Task HandleHelloReceivedAsync(ConnectionState connectionState, HelloPayload payload)
    {
        if (!TryValidateHelloPayload(payload, out var validationError))
        {
            _logger.LogWarning(
                "Rejecting HELLO for connection {ConnectionId}: {Error}",
                connectionState.ConnectionId,
                validationError);

            _connectionRegistry.RemoveChannel(connectionState.ConnectionId);
            return Task.CompletedTask;
        }

        _logger.LogInformation(
            "Connection registered: {ConnectionId} from {ServiceName}/{Version} with {EndpointCount} endpoints, {SchemaCount} schemas",
            connectionState.ConnectionId,
            connectionState.Instance.ServiceName,
            connectionState.Instance.Version,
            connectionState.Endpoints.Count,
            connectionState.Schemas.Count);

        // Add the connection to the routing state
        _routingState.AddConnection(connectionState);

        // Start listening to this connection for frames
        _transportServer.StartListeningToConnection(connectionState.ConnectionId);

        // Invalidate OpenAPI cache when connections change
        _openApiCache?.Invalidate();

        return Task.CompletedTask;
    }

    private static bool TryValidateHelloPayload(HelloPayload payload, out string error)
    {
        if (string.IsNullOrWhiteSpace(payload.Instance.ServiceName))
        {
            error = "Instance.ServiceName is required";
            return false;
        }

        if (string.IsNullOrWhiteSpace(payload.Instance.Version))
        {
            error = "Instance.Version is required";
            return false;
        }

        if (string.IsNullOrWhiteSpace(payload.Instance.Region))
        {
            error = "Instance.Region is required";
            return false;
        }

        if (string.IsNullOrWhiteSpace(payload.Instance.InstanceId))
        {
            error = "Instance.InstanceId is required";
            return false;
        }

        var seen = new HashSet<(string Method, string Path)>(new EndpointKeyComparer());

        foreach (var endpoint in payload.Endpoints)
        {
            if (string.IsNullOrWhiteSpace(endpoint.Method))
            {
                error = "Endpoint.Method is required";
                return false;
            }

            if (string.IsNullOrWhiteSpace(endpoint.Path) || !endpoint.Path.StartsWith('/'))
            {
                error = "Endpoint.Path must start with '/'";
                return false;
            }

            if (!string.Equals(endpoint.ServiceName, payload.Instance.ServiceName, StringComparison.OrdinalIgnoreCase) ||
                !string.Equals(endpoint.Version, payload.Instance.Version, StringComparison.Ordinal))
            {
                error = "Endpoint.ServiceName/Version must match HelloPayload.Instance";
                return false;
            }

            if (!seen.Add((endpoint.Method, endpoint.Path)))
            {
                error = $"Duplicate endpoint registration for {endpoint.Method} {endpoint.Path}";
                return false;
            }

            if (endpoint.SchemaInfo is not null)
            {
                if (endpoint.SchemaInfo.RequestSchemaId is not null &&
                    !payload.Schemas.ContainsKey(endpoint.SchemaInfo.RequestSchemaId))
                {
                    error = $"Endpoint schema reference missing: requestSchemaId='{endpoint.SchemaInfo.RequestSchemaId}'";
                    return false;
                }

                if (endpoint.SchemaInfo.ResponseSchemaId is not null &&
                    !payload.Schemas.ContainsKey(endpoint.SchemaInfo.ResponseSchemaId))
                {
                    error = $"Endpoint schema reference missing: responseSchemaId='{endpoint.SchemaInfo.ResponseSchemaId}'";
                    return false;
                }
            }
        }

        error = string.Empty;
        return true;
    }

    private sealed class EndpointKeyComparer : IEqualityComparer<(string Method, string Path)>
    {
        public bool Equals((string Method, string Path) x, (string Method, string Path) y)
        {
            return string.Equals(x.Method, y.Method, StringComparison.OrdinalIgnoreCase) &&
                   string.Equals(x.Path, y.Path, StringComparison.OrdinalIgnoreCase);
        }

        public int GetHashCode((string Method, string Path) obj)
        {
            return HashCode.Combine(
                StringComparer.OrdinalIgnoreCase.GetHashCode(obj.Method),
                StringComparer.OrdinalIgnoreCase.GetHashCode(obj.Path));
        }
    }

    private Task HandleHeartbeatReceivedAsync(ConnectionState connectionState, HeartbeatPayload payload)
    {
        _logger.LogDebug(
            "Heartbeat received from {ConnectionId}: status={Status}",
            connectionState.ConnectionId,
            payload.Status);

        // Update connection state
        _routingState.UpdateConnection(connectionState.ConnectionId, conn =>
        {
            conn.Status = payload.Status;
            conn.LastHeartbeatUtc = DateTime.UtcNow;
        });

        return Task.CompletedTask;
    }

    private Task HandleConnectionClosedAsync(string connectionId)
    {
        _logger.LogInformation("Connection closed: {ConnectionId}", connectionId);

        // Remove from routing state
        _routingState.RemoveConnection(connectionId);

        // Invalidate OpenAPI cache when connections change
        _openApiCache?.Invalidate();

        return Task.CompletedTask;
    }
}