Add special case for first+last during inwards merge (#102)

src/extras/relayPagination.ts

@@ -131,6 +131,27 @@ export const relayPagination = (params: PaginationParams = {}): Resolver => {
       const page = getPage(cache, linkKey);
       if (page === null) {
         continue;
+      } else if (
+        mergeMode === 'inwards' &&
+        typeof args.last === 'number' &&
+        typeof args.first === 'number'
+      ) {
+        // This is a special but rare case for simultaneously merging first and last edges
+        if (page.edges.length < args.first + args.last) {
+          startEdges = concatEdges(cache, startEdges, page.edges);
+          pageInfo.hasNextPage = false;
+          pageInfo.hasPreviousPage = false;
+          pageInfo.startCursor = null;
+          pageInfo.endCursor = null;
+          break;
+        } else {
+          const firstEdges = page.edges.slice(0, args.first);
+          const lastEdges = page.edges.slice(-args.last);
+          startEdges = concatEdges(cache, startEdges, firstEdges);
+          endEdges = concatEdges(cache, lastEdges, endEdges);
+        }
+
+        pageInfo = page.pageInfo;
       } else if (args.after) {
         startEdges = concatEdges(cache, startEdges, page.edges);
         pageInfo.endCursor = page.pageInfo.endCursor;