using System.Diagnostics;

namespace Salmon.Core.Depth;

public class EventManager
{
    public long MaxBufferedEvents { get; set; } = 2000;
    Queue<string> _EventIds = new ();
    Dictionary<string, Event> _LastEvents = new ();
    public Persistence? History { get; set; }
    object Mutex = new();

    public EventManager()
    {

    }

    void Trim()
    {
        List<string> toDelete = new();

        lock(Mutex)
            while(_LastEvents.Count > MaxBufferedEvents)
                _LastEvents.Remove(_EventIds.Dequeue());
    }

    [Obsolete]
    void Set(Event e)
    {
        ArgumentNullException.ThrowIfNull(e, "e");

        lock (Mutex)
        {
            Debug.Assert(_LastEvents.ContainsKey(e.UniqueId));
            _LastEvents[e.UniqueId] = e;
        }
    }

    void Add(Event e)
    {
        ArgumentNullException.ThrowIfNull (e, "e");
        

        lock (Mutex)
        {
            Debug.Assert(!_LastEvents.ContainsKey(e.UniqueId));

            _EventIds.Enqueue(e.UniqueId);
            _LastEvents.Add(e.UniqueId, e);
        }
        if(History is not null)
            History.RegisterEvent(e);

        Trim();
    }

    public void Push(Event e)
    {
        ArgumentNullException.ThrowIfNull(e, "e");

        Add(e);
    }

    public IEnumerable<Event> GetLastEvents(int maxCount = 200)
    {
        return _LastEvents.Values.OrderByDescending(x => x.When).Take(maxCount).ToList();
    }

    public async IAsyncEnumerable<Event> GetEvents(string? subject = null,
        DateTime? from = null,
        DateTime? to = null,
        int? limit = null,
        int? offset = null,
        Dictionary<string, object>? filters = null)
    {
        if(History is null)
        {
            IEnumerable<Event> ret;
            lock (Mutex)
            {
                ret = _LastEvents
                .Values
                .OrderByDescending(x => x.When);
            }            

            if(subject is not null)
                ret = ret.Where(x => x.ThrowerId == subject);

            if (from is not null)
                ret = ret.Where(x => x.When >= from);           
            
            if (to is not null)
                ret = ret.Where(x => x.When <= to);

            if (offset is not null)
                ret = ret.Skip(offset.Value);

            if (limit is not null)
                ret = ret.Take(limit.Value);

            foreach (var i in ret)
                yield return i;

            //TODO: Implement filters

            yield break;
        }

        await foreach (var i in History.GetEvents(subject, from, to, limit, offset, filters))
            yield return i;
    }
}