using System.Buffers.Binary;
using System.Collections;

namespace Uwaa.Pleroma;

/// <summary>
/// Base class for ActivityStreams objects.
/// </summary>
public class ASObject
{
    public static UInt128 FromBase62(string id)
    {
        //TODO: Optimize
        const string table = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

        BitArray bits = new BitArray(id.Length * 6);
        for (int i = 0; i < id.Length; i++)
        {
            int index = table.IndexOf(id[^(i + 1)]);
            bits[i * 6] = (index & 1) != 0;
            bits[i * 6 + 1] = (index & 2) != 0;
            bits[i * 6 + 2] = (index & 4) != 0;
            bits[i * 6 + 3] = (index & 8) != 0;
            bits[i * 6 + 4] = (index & 16) != 0;
            bits[i * 6 + 5] = (index & 32) != 0;
        }

        byte[] bytes = new byte[16];
        bits.CopyTo(bytes, 0);

        return BinaryPrimitives.ReadUInt128LittleEndian(bytes);
    }
    
    /// <summary>
    /// Pleroma uses 128-bit ids as opposed to Mastodon's 64 bits. However just like Mastodon's ids they are lexically sortable strings
    /// </summary>
    [JsonPropertyName("id")]
    public string ID { get; set; } = null!;

    [JsonConstructor()]
    internal ASObject()
    {
    }

    public override string ToString() => ID;

    public override bool Equals(object? obj) => Equals(obj as ASObject);
    public bool Equals(ASObject? other) => other is not null && ID == other.ID;
    public static bool operator ==(ASObject? left, ASObject? right) => EqualityComparer<ASObject>.Default.Equals(left, right);
    public static bool operator !=(ASObject? left, ASObject? right) => !(left == right);
    public override int GetHashCode() => ID.GetHashCode();
}