sharp-chat/SharpChat/EventStorage/VirtualEventStorage.cs

using SharpChat.Events;
using System;
using System.Collections.Generic;
using System.Linq;

namespace SharpChat.EventStorage {
    public class VirtualEventStorage : IEventStorage {
        private readonly Dictionary<long, IChatEvent> Events = new();

        public void AddEvent(IChatEvent evt) {
            if(evt == null)
                throw new ArgumentNullException(nameof(evt));
            Events.Add(evt.SequenceId, evt);
        }

        public IChatEvent GetEvent(long seqId) {
            return Events.TryGetValue(seqId, out IChatEvent evt) ? evt : null;
        }

        public void RemoveEvent(IChatEvent evt) {
            if(evt == null)
                throw new ArgumentNullException(nameof(evt));
            Events.Remove(evt.SequenceId);
        }

        public IEnumerable<IChatEvent> GetChannelEventLog(string channelName, int amount = 20, int offset = 0) {
            IEnumerable<IChatEvent> subset = Events.Values.Where(ev => ev.ChannelName == channelName);

            int start = subset.Count() - offset - amount;
            if(start < 0) {
                amount += start;
                start = 0;
            }

            return subset.Skip(start).Take(amount).ToArray();
        }
    }
}