using System.Collections.Concurrent;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Interfaces.Streaming;

namespace ErsatzTV.Core.Streaming;

public class DirectStreamSessionTracker : IDirectStreamSessionTracker
{
    private readonly ConcurrentDictionary<string, ConcurrentDictionary<Guid, DirectStreamSession>> _sessions = new();

    public IDisposable Register(string channelNumber, StreamingMode streamingMode)
    {
        var session = new DirectStreamSession(Guid.NewGuid(), channelNumber, streamingMode, DateTimeOffset.Now);

        ConcurrentDictionary<Guid, DirectStreamSession> channelSessions =
            _sessions.GetOrAdd(channelNumber, _ => new ConcurrentDictionary<Guid, DirectStreamSession>());

        OnRegisteringSession();

        channelSessions.TryAdd(session.Id, session);

        return new Registration(this, session);
    }

    protected virtual void OnRegisteringSession()
    {
    }

    public bool IsActive(string channelNumber) => GetViewerCount(channelNumber) > 0;

    public int GetViewerCount(string channelNumber) =>
        _sessions.TryGetValue(channelNumber, out ConcurrentDictionary<Guid, DirectStreamSession> channelSessions)
            ? channelSessions.Count
            : 0;

    public IReadOnlyCollection<DirectStreamSession> GetActiveSessions() =>
        _sessions.Values.SelectMany(s => s.Values).ToList();

    public IReadOnlyCollection<DirectStreamSession> GetActiveSessions(string channelNumber) =>
        _sessions.TryGetValue(channelNumber, out ConcurrentDictionary<Guid, DirectStreamSession> channelSessions)
            ? channelSessions.Values.ToList()
            : [];

    private void Remove(DirectStreamSession session)
    {
        if (!_sessions.TryGetValue(session.ChannelNumber, out ConcurrentDictionary<Guid, DirectStreamSession> channelSessions))
        {
            return;
        }

        channelSessions.TryRemove(session.Id, out _);
    }

    private sealed class Registration(DirectStreamSessionTracker tracker, DirectStreamSession session) : IDisposable
    {
        private int _disposed;

        public void Dispose()
        {
            if (Interlocked.Exchange(ref _disposed, 1) == 0)
            {
                tracker.Remove(session);
            }
        }
    }
}