Domain.cs

using System;
using System.Collections.Generic;
using System.Linq;

using Orleankka;
using Orleankka.Meta;

namespace Example
{
    [Interleave(typeof(GetDetails))]
    public class InventoryItem : EventSourcedActor
    {
        int total;
        string name;
        bool active;

        void On(InventoryItemCreated e)
        {
            name = e.Name;
            active = true;
        }

        void On(InventoryItemRenamed e)     => name = e.NewName;
        void On(InventoryItemCheckedIn e)   => total += e.Quantity;
        void On(InventoryItemCheckedOut e)  => total -= e.Quantity;
        void On(InventoryItemDeactivated e) => active = false;

        IEnumerable<Event> Handle(Create cmd)
        {
            if (string.IsNullOrEmpty(cmd.Name))
                throw new ArgumentException("Inventory item name cannot be null or empty");

            if (name != null)
                throw new InvalidOperationException(
                    $"Inventory item with id {Id} has been already created");

            yield return new InventoryItemCreated(cmd.Name);
        }

        IEnumerable<Event> Handle(Rename cmd)
        {
            CheckIsActive();

            if (string.IsNullOrEmpty(cmd.NewName))
                throw new ArgumentException("Inventory item name cannot be null or empty");

            yield return new InventoryItemRenamed(name, cmd.NewName);
        }

        IEnumerable<Event> Handle(CheckIn cmd)
        {
            CheckIsActive();

            if (cmd.Quantity <= 0)
                throw new InvalidOperationException("must have a qty greater than 0 to add to inventory");

            yield return new InventoryItemCheckedIn(cmd.Quantity);
        }

        IEnumerable<Event> Handle(CheckOut cmd)
        {
            CheckIsActive();

            if (cmd.Quantity <= 0)
                throw new InvalidOperationException("can't remove negative qty from inventory");

            yield return new InventoryItemCheckedOut(cmd.Quantity);
        }

        IEnumerable<Event> Handle(Deactivate cmd)
        {
            CheckIsActive();

            yield return new InventoryItemDeactivated();
        }

        InventoryItemDetails Handle(GetDetails query)
        {
            return new InventoryItemDetails(name, total, active);
        }

        void CheckIsActive()
        {
            if (!active)
                throw new InvalidOperationException(Id + " item is deactivated");
        }
    }

    [StreamSubscription(Source = "sms:/InventoryItem-.*/", Target = "#")]
    public class Inventory : Actor
    {
        readonly Dictionary<string, InventoryItemDetails> items =
             new Dictionary<string, InventoryItemDetails>();

        void On(EventEnvelope<InventoryItemCreated> e)     => items[e.Stream] = new InventoryItemDetails(e.Event.Name, 0, true);
        void On(EventEnvelope<InventoryItemCheckedIn> e)   => items[e.Stream].Total += e.Event.Quantity;
        void On(EventEnvelope<InventoryItemCheckedOut> e)  => items[e.Stream].Total -= e.Event.Quantity;
        void On(EventEnvelope<InventoryItemDeactivated> e) => items[e.Stream].Active = false;
        void On(EventEnvelope<InventoryItemRenamed> e)     => items[e.Stream].Name   = e.Event.NewName;

        InventoryItemDetails[] Answer(GetInventoryItems _) => items.Values.ToArray();
        int Answer(GetInventoryItemsTotal _)               => items.Values.Sum(x => x.Total);
    }
}