Implement pagination

Author: rasmusjp

src/Our.Umbraco.GraphQL/Types/ConnectionExtensions.cs

@@ -2,10 +2,9 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
-using System.Threading.Tasks;
 using GraphQL.Builders;
-using GraphQL.Types;
 using GraphQL.Types.Relay.DataObjects;
+using Umbraco.Core.Models;
 
 namespace Our.Umbraco.GraphQL.Types
 {
@@ -21,24 +20,64 @@ public static Connection<TSource> ToConnection<TSource, TParent>(this IEnumerabl
         public static Connection<TSource> ToConnection<TSource, TParent>(this IEnumerable<TSource> source,
             ResolveConnectionContext<TParent> context, int totalCount)
         {
-            // TODO: Implement paging logic
-            var items = source.Select(x => new Edge<TSource>
-            {
-                Node = x
-            }).ToList();
+            var items = source.ToList();
 
             var after = context.After;
             var before = context.Before;
             var first = context.First;
             var last = context.Last;
 
+            int startOffset = 0;
+            int endOffset = items.Count;
+
+            if (after != null)
+            {
+                // cursor starts at 0, so we need to add one to the offset to ensure we don't include the same item
+                startOffset = CursorToOffset(after) + 1;
+            }
+            if(before != null)
+            {
+                endOffset = CursorToOffset(before);
+            }
+            if (first.HasValue)
+            {
+                endOffset = startOffset + first.Value;
+            }
+            if (last.HasValue)
+            {
+                startOffset = endOffset - last.Value;
+            }
+
+            // Ensure startOffset is not negative
+            startOffset = Math.Max(0, startOffset);
+
+            var edges = source.Skip(startOffset).Take(endOffset - startOffset).Select((x, i) => new Edge<TSource>
+            {
+                Cursor = OffsetToCursor(startOffset + i),
+                Node = x
+            }).ToList();
+
             return new Connection<TSource>
             {
-                Edges = items,
+                Edges = edges,
                 PageInfo = new PageInfo
                 {
+                    EndCursor = edges.LastOrDefault()?.Cursor,
+                    HasNextPage = endOffset < items.Count,
+                    HasPreviousPage = startOffset > 0,
+                    StartCursor = edges.FirstOrDefault()?.Cursor
                 }
             };
         }
+
+        public static int CursorToOffset(string cursor)
+        {
+            return int.Parse(Encoding.UTF8.GetString(Convert.FromBase64String(cursor)).Substring("connection:".Length));
+        }
+
+        public static string OffsetToCursor(int offset)
+        {
+            return Convert.ToBase64String(Encoding.UTF8.GetBytes($"connection:{offset}"));
+        }
     }
 }