using Microsoft.Extensions.Logging;
using Opc.Ua;
using Opc.Ua.Configuration;
using ZB.MOM.WW.OtOpcUa.Core.Hosting;
using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
using ZB.MOM.WW.OtOpcUa.Core.Resilience;
using ZB.MOM.WW.OtOpcUa.Server.Security;

namespace ZB.MOM.WW.OtOpcUa.Server.OpcUa;

/// <summary>
///     Wraps <see cref="ApplicationInstance"/> to bring the OPC UA server online — builds an
///     <see cref="ApplicationConfiguration"/> programmatically (no external XML file), ensures
///     the application certificate exists in the PKI store (auto-generates self-signed on first
///     run), starts the server, then walks each <see cref="DriverNodeManager"/> and invokes
///     <see cref="GenericDriverNodeManager.BuildAddressSpaceAsync"/> against it so the driver's
///     discovery streams into the already-running server's address space.
/// </summary>
public sealed class OpcUaApplicationHost : IAsyncDisposable
{
    private readonly OpcUaServerOptions _options;
    private readonly DriverHost _driverHost;
    private readonly IUserAuthenticator _authenticator;
    private readonly DriverResiliencePipelineBuilder _pipelineBuilder;
    private readonly ILoggerFactory _loggerFactory;
    private readonly ILogger<OpcUaApplicationHost> _logger;
    private ApplicationInstance? _application;
    private OtOpcUaServer? _server;
    private bool _disposed;

    public OpcUaApplicationHost(OpcUaServerOptions options, DriverHost driverHost,
        IUserAuthenticator authenticator, ILoggerFactory loggerFactory, ILogger<OpcUaApplicationHost> logger,
        DriverResiliencePipelineBuilder? pipelineBuilder = null)
    {
        _options = options;
        _driverHost = driverHost;
        _authenticator = authenticator;
        _pipelineBuilder = pipelineBuilder ?? new DriverResiliencePipelineBuilder();
        _loggerFactory = loggerFactory;
        _logger = logger;
    }

    public OtOpcUaServer? Server => _server;

    /// <summary>
    ///     Builds the <see cref="ApplicationConfiguration"/>, validates/creates the application
    ///     certificate, constructs + starts the <see cref="OtOpcUaServer"/>, then drives
    ///     <see cref="GenericDriverNodeManager.BuildAddressSpaceAsync"/> per registered driver so
    ///     the address space is populated before the first client connects.
    /// </summary>
    public async Task StartAsync(CancellationToken ct)
    {
        _application = new ApplicationInstance
        {
            ApplicationName = _options.ApplicationName,
            ApplicationType = ApplicationType.Server,
            ApplicationConfiguration = BuildConfiguration(),
        };

        var hasCert = await _application.CheckApplicationInstanceCertificate(silent: true, minimumKeySize: CertificateFactory.DefaultKeySize).ConfigureAwait(false);
        if (!hasCert)
            throw new InvalidOperationException(
                $"OPC UA application certificate could not be validated or created in {_options.PkiStoreRoot}");

        _server = new OtOpcUaServer(_driverHost, _authenticator, _pipelineBuilder, _loggerFactory);
        await _application.Start(_server).ConfigureAwait(false);

        _logger.LogInformation("OPC UA server started — endpoint={Endpoint} driverCount={Count}",
            _options.EndpointUrl, _server.DriverNodeManagers.Count);

        // Drive each driver's discovery through its node manager. The node manager IS the
        // IAddressSpaceBuilder; GenericDriverNodeManager captures alarm-condition sinks into
        // its internal map and wires OnAlarmEvent → sink routing.
        foreach (var nodeManager in _server.DriverNodeManagers)
        {
            var driverId = nodeManager.Driver.DriverInstanceId;
            try
            {
                var generic = new GenericDriverNodeManager(nodeManager.Driver);
                await generic.BuildAddressSpaceAsync(nodeManager, ct).ConfigureAwait(false);
                _logger.LogInformation("Address space populated for driver {Driver}", driverId);
            }
            catch (Exception ex)
            {
                // Per decision #12: driver exceptions isolate — log and keep the server serving
                // the other drivers' subtrees. Re-building this one takes a Reinitialize call.
                _logger.LogError(ex, "Discovery failed for driver {Driver}; subtree faulted", driverId);
            }
        }
    }

    private ApplicationConfiguration BuildConfiguration()
    {
        Directory.CreateDirectory(_options.PkiStoreRoot);

        var cfg = new ApplicationConfiguration
        {
            ApplicationName = _options.ApplicationName,
            ApplicationUri = _options.ApplicationUri,
            ApplicationType = ApplicationType.Server,
            ProductUri = "urn:OtOpcUa:Server",

            SecurityConfiguration = new SecurityConfiguration
            {
                ApplicationCertificate = new CertificateIdentifier
                {
                    StoreType = CertificateStoreType.Directory,
                    StorePath = Path.Combine(_options.PkiStoreRoot, "own"),
                    SubjectName = "CN=" + _options.ApplicationName,
                },
                TrustedIssuerCertificates = new CertificateTrustList
                {
                    StoreType = CertificateStoreType.Directory,
                    StorePath = Path.Combine(_options.PkiStoreRoot, "issuers"),
                },
                TrustedPeerCertificates = new CertificateTrustList
                {
                    StoreType = CertificateStoreType.Directory,
                    StorePath = Path.Combine(_options.PkiStoreRoot, "trusted"),
                },
                RejectedCertificateStore = new CertificateTrustList
                {
                    StoreType = CertificateStoreType.Directory,
                    StorePath = Path.Combine(_options.PkiStoreRoot, "rejected"),
                },
                AutoAcceptUntrustedCertificates = _options.AutoAcceptUntrustedClientCertificates,
                AddAppCertToTrustedStore = true,
            },

            TransportConfigurations = new TransportConfigurationCollection(),
            TransportQuotas = new TransportQuotas { OperationTimeout = 15000 },

            ServerConfiguration = new ServerConfiguration
            {
                BaseAddresses = new StringCollection { _options.EndpointUrl },
                SecurityPolicies = BuildSecurityPolicies(),
                UserTokenPolicies = BuildUserTokenPolicies(),
                MinRequestThreadCount = 5,
                MaxRequestThreadCount = 100,
                MaxQueuedRequestCount = 200,
            },

            TraceConfiguration = new TraceConfiguration(),
        };

        cfg.Validate(ApplicationType.Server).GetAwaiter().GetResult();

        if (cfg.SecurityConfiguration.AutoAcceptUntrustedCertificates)
        {
            cfg.CertificateValidator.CertificateValidation += (_, e) =>
            {
                if (e.Error.StatusCode == StatusCodes.BadCertificateUntrusted)
                    e.Accept = true;
            };
        }

        return cfg;
    }

    private ServerSecurityPolicyCollection BuildSecurityPolicies()
    {
        var policies = new ServerSecurityPolicyCollection
        {
            // Keep the None policy present so legacy clients can discover + browse. Locked-down
            // deployments remove this by setting Ldap.Enabled=true + dropping None here; left in
            // for PR 19 so the PR 17 test harness continues to pass unchanged.
            new ServerSecurityPolicy
            {
                SecurityMode = MessageSecurityMode.None,
                SecurityPolicyUri = SecurityPolicies.None,
            },
        };

        if (_options.SecurityProfile == OpcUaSecurityProfile.Basic256Sha256SignAndEncrypt)
        {
            policies.Add(new ServerSecurityPolicy
            {
                SecurityMode = MessageSecurityMode.SignAndEncrypt,
                SecurityPolicyUri = SecurityPolicies.Basic256Sha256,
            });
        }

        return policies;
    }

    private UserTokenPolicyCollection BuildUserTokenPolicies()
    {
        var tokens = new UserTokenPolicyCollection
        {
            new UserTokenPolicy(UserTokenType.Anonymous)
            {
                PolicyId = "Anonymous",
                SecurityPolicyUri = SecurityPolicies.None,
            },
        };

        if (_options.SecurityProfile == OpcUaSecurityProfile.Basic256Sha256SignAndEncrypt
            && _options.Ldap.Enabled)
        {
            tokens.Add(new UserTokenPolicy(UserTokenType.UserName)
            {
                PolicyId = "UserName",
                // Passwords must ride an encrypted channel — scope this token to Basic256Sha256
                // so the stack rejects any attempt to send UserName over the None endpoint.
                SecurityPolicyUri = SecurityPolicies.Basic256Sha256,
            });
        }

        return tokens;
    }

    public async ValueTask DisposeAsync()
    {
        if (_disposed) return;
        _disposed = true;
        try
        {
            _server?.Stop();
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "OPC UA server stop threw during dispose");
        }
        await Task.CompletedTask;
    }
}