Service Discovery

<Matrix xmlns="http://schemas.matrix.com/network/2024">
    <ServiceDiscovery>
        <!-- Define discovery zones -->
        <DiscoveryZone Name="Production">
            <Registry Address="tcp://registry.prod:5000"
                     ReplicationFactor="3"
                     ConsistencyLevel="Strong" />
                     
            <HealthCheck Interval="00:00:30"
                        Timeout="00:00:05"
                        FailureThreshold="3" />
        </DiscoveryZone>

        <!-- Service registration -->
        <ServiceRegistration AutoRegister="true">
            <Registration.Metadata>
                <ServiceMetadata Version="1.0.0"
                               Region="us-west"
                               Tier="Backend" />
            </Registration.Metadata>
        </ServiceRegistration>
    </ServiceDiscovery>

    <!-- Service with discovery settings -->
    <ServiceNode Name="OrderProcessor"
                 DiscoveryMode="Dynamic"
                 DiscoveryScope="Zone">
        <ServiceNode.DiscoveryTags>
            <Tag Key="Service" Value="Orders" />
            <Tag Key="Version" Value="2.0" />
            <Tag Key="Capability" Value="Processing" />
        </ServiceNode.DiscoveryTags>
    </ServiceNode>
</Matrix>

public class ServiceDiscoveryManager : CommunicationElement
{
    private readonly IServiceRegistry _registry;
    private readonly IHealthCheck _healthCheck;
    private readonly ConcurrentDictionary<string, ServiceRegistration> _registrations;

    public async Task RegisterServiceAsync(ServiceNode service)
    {
        var registration = new ServiceRegistration
        {
            ServiceId = service.Id,
            Name = service.Name,
            Endpoints = service.GetEndpoints(),
            Metadata = service.GetMetadata(),
            Tags = service.DiscoveryTags,
            HealthCheck = CreateHealthCheck(service)
        };

        await _registry.RegisterAsync(registration);
        _registrations.TryAdd(service.Id, registration);

        // Start health checking
        await _healthCheck.StartAsync(registration);
    }

    public async Task<IEnumerable<ServiceNode>> DiscoverServicesAsync(
        ServiceQuery query)
    {
        var results = await _registry.QueryAsync(query);
        
        return results.Select(r => 
            CreateServiceNode(r.ServiceId, r.Endpoints, r.Metadata));
    }

    private HealthCheck CreateHealthCheck(ServiceNode service)
    {
        return new HealthCheck
        {
            Endpoint = service.GetHealthCheckEndpoint(),
            Interval = service.HealthCheckInterval,
            Timeout = service.HealthCheckTimeout,
            FailureThreshold = service.FailureThreshold,
            Handler = async () => await CheckServiceHealth(service)
        };
    }
}

public class ServiceQuery : CommunicationElement
{
    public static readonly DependencyProperty TagsProperty =
        DependencyProperty.Register(
            "Tags",
            typeof(TagCollection),
            typeof(ServiceQuery)
        );

    public static readonly DependencyProperty ScopeProperty =
        DependencyProperty.Register(
            "Scope",
            typeof(DiscoveryScope),
            typeof(ServiceQuery)
        );

    public TagCollection Tags
    {
        get => (TagCollection)GetValue(TagsProperty);
        set => SetValue(TagsProperty, value);
    }

    public DiscoveryScope Scope
    {
        get => (DiscoveryScope)GetValue(ScopeProperty);
        set => SetValue(ScopeProperty, value);
    }

    public async Task<IEnumerable<ServiceNode>> ExecuteAsync(
        IServiceRegistry registry)
    {
        var filter = BuildQueryFilter();
        var results = await registry.QueryAsync(filter);

        return results.Select(CreateServiceNode);
    }
}

public class ServiceResolver : CommunicationElement
{
    private readonly IServiceDiscovery _discovery;
    private readonly ILoadBalancer _loadBalancer;

    public async Task<ServiceEndpoint> ResolveEndpointAsync(
        ServiceQuery query)
    {
        // Find matching services
        var services = await _discovery.DiscoverServicesAsync(query);
        
        if (!services.Any())
            throw new ServiceNotFoundException(query);

        // Apply load balancing
        var selected = await _loadBalancer.SelectServiceAsync(services);
        
        // Return resolved endpoint
        return selected.GetEndpoint();
    }

    public IObservable<ServiceEndpoint> ObserveEndpoint(ServiceQuery query)
    {
        return Observable.Create<ServiceEndpoint>(async observer =>
        {
            // Initial resolution
            var endpoint = await ResolveEndpointAsync(query);
            observer.OnNext(endpoint);

            // Subscribe to changes
            var subscription = _discovery
                .ObserveServices(query)
                .Select(async services =>
                {
                    var selected = await _loadBalancer
                        .SelectServiceAsync(services);
                    return selected.GetEndpoint();
                })
                .Subscribe(observer);

            return subscription;
        });
    }
}