using System.Collections.Concurrent;
using System.Diagnostics.CodeAnalysis;
using Remora.Discord.API.Abstractions.Objects;
using Remora.Rest.Core;

namespace Catalogger.Backend.Cache.InMemoryCache;

public class ChannelCache
{
    private readonly ConcurrentDictionary<Snowflake, IChannel> _channels = new();
    private readonly ConcurrentDictionary<Snowflake, HashSet<Snowflake>> _guildChannels = new();

    public int Size => _channels.Count;

    public void Set(IChannel channel, Snowflake? guildId = null)
    {
        _channels[channel.ID] = channel;
        if (guildId == null)
        {
            if (!channel.GuildID.TryGet(out var snowflake)) return;
            guildId = snowflake;
        }

        // Add to set of guild channels
        _guildChannels.AddOrUpdate(guildId.Value,
            _ => [channel.ID],
            (_, l) =>
            {
                l.Add(channel.ID);
                return l;
            });
    }

    public bool TryGet(Snowflake id, [NotNullWhen(true)] out IChannel? channel) =>
        _channels.TryGetValue(id, out channel);

    public void Remove(Snowflake? guildId, Snowflake id, out IChannel? channel)
    {
        _channels.Remove(id, out channel);
        if (guildId == null) return;
        // Remove from set of guild channels
        _guildChannels.AddOrUpdate(guildId.Value, _ => [], (_, s) =>
        {
            s.Remove(id);
            return s;
        });
    }

    /// <summary>
    /// Gets all of a guild's cached channels.
    /// </summary>
    /// <param name="guildId">The guild to get the channels of</param>
    /// <returns>A list of cached channels</returns>
    public IEnumerable<IChannel> GuildChannels(Snowflake guildId) =>
        !_guildChannels.TryGetValue(guildId, out var channelIds)
            ? []
            : channelIds.Select(id => _channels.GetValueOrDefault(id))
                .Where(c => c != null).Select(c => c!);
}