chaosbot/ChaosBot/WebServer/Services/CheckPermissions.cs

using System;
using System.Linq;
using ChaosBot.Discord;
using Discord.WebSocket;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace ChaosBot.WebServer.Services
{
    public static class CheckPermissions
    {
        private static readonly AccessTokenCache Cache = WebServer.Cache;
        
        public static bool GetResult(HttpRequest request, ulong guildId, out IActionResult result)
        {
            result = null;
            
            if (!request.Cookies.TryGetValue("access_token", out string accessToken))
                result = new UnauthorizedObjectResult("No access_token cookie sent");

            SocketGuild guild = DiscordConnect._client.GetGuild(guildId);
            if (guild == null)
            {
                result = new NotFoundObjectResult("Bot is not part of that guild");
            }
            else
            {
                if (!Cache.HasKey(accessToken))
                {
                    result = new NotFoundObjectResult("Could not find your access token in cache, please logout and log back in.");
                }
                else
                {
                    SocketGuildUser user = guild.GetUser(Convert.ToUInt64(Cache.Get(accessToken)));
                    if (user == null)
                        result = new NotFoundObjectResult("Bot could not find you in that guild");
                    else if (!user.GuildPermissions.Administrator && !user.GuildPermissions.ManageGuild)
                        result = new UnauthorizedObjectResult("You have invalid permissions on the guild. Need at least ManageGuild");   
                }   
            }

            return result == null;
        }
    }
}