fix: behave properly when pageProvider returns fewer items than pageSize

Author: rocwang

src/pipeline.test.ts

@@ -179,7 +179,7 @@ describe("accumulateAllItems", () => {
   it("can extend allItems", () => {
     const allItems = accumulateAllItems(
       [0, 1, 2, 3, 4, 5],
-      [{ pageNumber: 1, items: ["a", "b", "c"] }, 10]
+      [{ pageNumber: 1, items: ["a", "b", "c"] }, 10, 3]
     );
 
     expect(allItems).toEqual([
@@ -199,11 +199,29 @@ describe("accumulateAllItems", () => {
   it("can shrink allItems", () => {
     const allItems = accumulateAllItems(
       [0, 1, 2, 3, 4, 5, 6],
-      [{ pageNumber: 0, items: ["a", "b", "c"] }, 5]
+      [{ pageNumber: 0, items: ["a", "b", "c"] }, 5, 3]
     );
 
     expect(allItems).toEqual(["a", "b", "c", 3, 4]);
   });
+
+  it("behave properly when pageProvider returns fewer items than pageSize", () => {
+    const allItems = accumulateAllItems(
+      [0, 1, 2, 3, 4, 5],
+      [{ pageNumber: 0, items: ["a", "b"] }, 6, 3]
+    );
+
+    expect(allItems).toEqual(["a", "b", undefined, 3, 4, 5]);
+  });
+
+  it("behave properly when pageProvider returns more items than pageSize", () => {
+    const allItems = accumulateAllItems(
+      [0, 1, 2, 3, 4, 5],
+      [{ pageNumber: 0, items: ["a", "b", "c", "d"] }, 6, 3]
+    );
+
+    expect(allItems).toEqual(["a", "b", "c", 3, 4, 5]);
+  });
 });
 
 describe("getVisibleItems", () => {

src/pipeline.ts

@@ -146,15 +146,22 @@ export function callPageProvider(
 
 export function accumulateAllItems(
   allItems: unknown[],
-  [{ pageNumber, items }, length]: [ItemsByPage, number]
+  [{ pageNumber, items }, length, pageSize]: [ItemsByPage, number, number]
 ): unknown[] {
+  const allItemsFill = new Array(Math.max(length - allItems.length, 0)).fill(
+    undefined
+  );
+
+  const pageFill = new Array(Math.max(pageSize - items.length, 0)).fill(
+    undefined
+  );
+
+  const normalizedItems = concat(slice(0, pageSize, items), pageFill);
+
   return pipe<unknown[][], unknown[], unknown[], unknown[], unknown[]>(
-    concat(
-      __,
-      new Array(Math.max(length - allItems.length, 0)).fill(undefined)
-    ),
-    remove(pageNumber * items.length, items.length),
-    insertAll(pageNumber * items.length, items),
+    concat(__, allItemsFill),
+    remove(pageNumber * pageSize, pageSize),
+    insertAll(pageNumber * pageSize, normalizedItems),
     slice(0, length)
   )(allItems);
 }
@@ -335,7 +342,7 @@ export function pipeline({
   const replayLength$ = length$.pipe(shareReplay(1));
 
   const allItems$: Observable<unknown[]> = pageProvider$.pipe(
-    switchMap(() => combineLatest([itemsByPage$, replayLength$])),
+    switchMap(() => combineLatest([itemsByPage$, replayLength$, pageSize$])),
     scan(accumulateAllItems, [])
   );