using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.Json;

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

        public long AddEvent(string type, ChatUser user, ChatChannel channel, object data = null, StoredEventFlags flags = StoredEventFlags.None) {
            if(type == null)
                throw new ArgumentNullException(nameof(type));

            // VES is meant as an emergency fallback but this is something else
            JsonDocument hack = JsonDocument.Parse(data == null ? "{}" : JsonSerializer.Serialize(data));

            long id = SharpId.Next();
            Events.Add(id, new(id, type, user, DateTimeOffset.Now, null, channel?.Name ?? null, hack, flags));

            return id;
        }

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

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

        public IEnumerable<StoredEventInfo> GetChannelEventLog(string channelName, int amount = 20, int offset = 0) {
            IEnumerable<StoredEventInfo> 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();
        }
    }
}