Restructured folders and project names, ci should be fixed

src/NadekoBot/Services/Common/GreetGrouper.cs

@@ -0,0 +1,77 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace NadekoBot.Core.Services
+{
+    public class GreetGrouper<T>
+    {
+        private readonly Dictionary<ulong, HashSet<T>> group;
+        private readonly object locker = new object();
+
+        public GreetGrouper()
+        {
+            group = new Dictionary<ulong, HashSet<T>>();
+        }
+
+
+        /// <summary>
+        /// Creates a group, if group already exists, adds the specified user
+        /// </summary>
+        /// <param name="guildId">Id of the server for which to create group for</param>
+        /// <param name="toAddIfExists">User to add if group already exists</param>
+        /// <returns></returns>
+        public bool CreateOrAdd(ulong guildId, T toAddIfExists)
+        {
+            lock (locker)
+            {
+                if (group.TryGetValue(guildId, out var list))
+                {
+                    list.Add(toAddIfExists);
+                    return false;
+                }
+
+                group[guildId] = new HashSet<T>();
+                return true;
+            }
+        }
+
+        /// <summary>
+        /// Remove the specified amount of items from the group. If all items are removed, group will be removed.
+        /// </summary>
+        /// <param name="guildId">Id of the group</param>
+        /// <param name="count">Maximum number of items to retrieve</param>
+        /// <param name="items">Items retrieved</param>
+        /// <returns>Whether the group has no more items left and is deleted</returns>
+        public bool ClearGroup(ulong guildId, int count, out IEnumerable<T> items)
+        {
+            lock (locker)
+            {
+                if (group.TryGetValue(guildId, out var set))
+                {
+                    // if we want more than there are, return everything
+                    if (count >= set.Count)
+                    {
+                        items = set;
+                        group.Remove(guildId);
+                        return true;
+                    }
+
+                    // if there are more in the group than what's needed
+                    // take the requested number, remove them from the set
+                    // and return them
+                    var toReturn = set.TakeWhile(item => count-- != 0).ToList();
+                    foreach (var item in toReturn)
+                        set.Remove(item);
+
+                    items = toReturn;
+                    // returning falsemeans group is not yet deleted
+                    // because there are items left
+                    return false;
+                }
+
+                items = Enumerable.Empty<T>();
+                return true;
+            }
+        }
+    }
+}