using System.Text;
namespace GuestOps.Web;

public sealed record ConversationPage(IReadOnlyList<Conversation> Items,string? NextCursor);
public static class ConversationPaging
{
    public static string Encode(Conversation item)=>Convert.ToBase64String(Encoding.UTF8.GetBytes(item.ReceivedAt.Ticks+"|"+item.Id)).TrimEnd('=').Replace('+','-').Replace('/','_');
    public static bool TryDecode(string? value,out DateTime at,out string id)
    {
        at=default;id="";if(string.IsNullOrEmpty(value))return true;
        try
        {
            if(value.Length>160)return false;var raw=value.Replace('-','+').Replace('_','/');raw=raw.PadRight((raw.Length+3)/4*4,'=');
            var parts=Encoding.UTF8.GetString(Convert.FromBase64String(raw)).Split('|');
            return parts.Length==2&&long.TryParse(parts[0],out var ticks)&&ticks>=DateTime.MinValue.Ticks&&ticks<=DateTime.MaxValue.Ticks&&System.Text.RegularExpressions.Regex.IsMatch(parts[1],"^[a-f0-9]{32}$")&&(at=new DateTime(ticks,DateTimeKind.Utc))!=default&&(id=parts[1]).Length>0;
        }
        catch{return false;}
    }
}