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using System;
using System.Collections.Generic;
namespace Discord
{
/// <summary>
/// Represents a collection of <see cref="IEqualityComparer{T}"/> for various Discord objects.
/// </summary>
public static class DiscordComparers
{
/// <summary>
/// Gets an <see cref="IEqualityComparer{T}"/> to be used to compare users.
/// </summary>
public static IEqualityComparer<IUser> UserComparer => _userComparer ??= new EntityEqualityComparer<IUser, ulong>();
/// <summary>
/// Gets an <see cref="IEqualityComparer{T}"/> to be used to compare guilds.
/// </summary>
public static IEqualityComparer<IGuild> GuildComparer => _guildComparer ??= new EntityEqualityComparer<IGuild, ulong>();
/// <summary>
/// Gets an <see cref="IEqualityComparer{T}"/> to be used to compare channels.
/// </summary>
public static IEqualityComparer<IChannel> ChannelComparer => _channelComparer ??= new EntityEqualityComparer<IChannel, ulong>();
/// <summary>
/// Gets an <see cref="IEqualityComparer{T}"/> to be used to compare roles.
/// </summary>
public static IEqualityComparer<IRole> RoleComparer => _roleComparer ??= new EntityEqualityComparer<IRole, ulong>();
/// <summary>
/// Gets an <see cref="IEqualityComparer{T}"/> to be used to compare messages.
/// </summary>
public static IEqualityComparer<IMessage> MessageComparer => _messageComparer ??= new EntityEqualityComparer<IMessage, ulong>();
private static IEqualityComparer<IUser> _userComparer;
private static IEqualityComparer<IGuild> _guildComparer;
private static IEqualityComparer<IChannel> _channelComparer;
private static IEqualityComparer<IRole> _roleComparer;
private static IEqualityComparer<IMessage> _messageComparer;
private sealed class EntityEqualityComparer<TEntity, TId> : EqualityComparer<TEntity>
where TEntity : IEntity<TId>
where TId : IEquatable<TId>
{
public override bool Equals(TEntity x, TEntity y)
{
return (x, y) switch
{
(null, null) => true,
(null, _) => false,
(_, null) => false,
var (l, r) => l.Id.Equals(r.Id)
};
}
public override int GetHashCode(TEntity obj)
{
return obj?.Id.GetHashCode() ?? 0;
}
}
}
}