Add FilterPager and refresh filter support for blocking channels

Grayjay.Engine/Pagers/FilterPager.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Grayjay.Engine.Pagers
+{
+    public class FilterPager<T> : INestedPager<T>, IPager<T>
+    {
+        private readonly IPager<T> _pager;
+        private readonly Func<T, bool> _filter;
+
+        public string ID { get { return _pager.ID; } set { _pager.ID = value; } }
+
+        public FilterPager(IPager<T> pager, Func<T, bool> filter)
+        {
+            _pager = pager ?? throw new ArgumentNullException(nameof(pager));
+            _filter = filter ?? throw new ArgumentNullException(nameof(filter));
+        }
+
+        public IPager<T> FindPager(Func<IPager<T>, bool> query)
+        {
+            if (query(_pager))
+                return _pager;
+            else if (_pager is INestedPager<T>)
+                return ((_pager as INestedPager<T>) ?? throw new InvalidOperationException()).FindPager(query);
+            return null;
+        }
+
+        public T[] GetResults()
+        {
+            return _pager.GetResults().Where(_filter).ToArray();
+        }
+
+        public bool HasMorePages()
+        {
+            return _pager.HasMorePages();
+        }
+
+        public void NextPage()
+        {
+            _pager.NextPage();
+        }
+    }
+}

Grayjay.Engine/Pagers/RefreshDistributionContentPager.cs

@@ -9,12 +9,19 @@ namespace Grayjay.Engine.Pagers
 {
     public class RefreshDistributionContentPager<T> : MultiRefreshPager<T>
     {
-        public RefreshDistributionContentPager(IEnumerable<IPager<T>> pagers, IEnumerable<Task<IPager<T>>> pendingPagers, IEnumerable<IPager<T>> placeholderPager, Action<IPager<T>> onChanged = null, int pageSize = 20) : base(pagers, pendingPagers, placeholderPager, onChanged, pageSize)
+        private readonly Func<T, bool>? _filter;
+
+        public RefreshDistributionContentPager(IEnumerable<IPager<T>> pagers, IEnumerable<Task<IPager<T>>> pendingPagers, IEnumerable<IPager<T>> placeholderPager, Action<IPager<T>> onChanged = null, int pageSize = 20, Func<T, bool>? filter = null) : base(pagers, pendingPagers, placeholderPager, onChanged, pageSize)
         {
+            _filter = filter;
         }
 
         protected override IPager<T> RecreatePager(List<IPager<T>> pagers)
         {
+            if (_filter != null)
+            {
+                pagers = pagers.Select(x => x is FilterPager<T> ? x : (IPager<T>)new FilterPager<T>(x, _filter)).ToList();
+            }
             return new MultiDistributionPager<T>(pagers.ToDictionary(x => x, y => 1f), false, _pageSize);
         }
     }