Move getPageIndex to utils, add tests

src/store.js

@@ -1,5 +1,9 @@
 import { writable } from 'svelte/store';
-import { getNextPageIndexFn, getPrevPageIndexFn } from './utils/page'
+import {
+  getNextPageIndexFn,
+  getPrevPageIndexFn,
+  getPageIndex
+} from './utils/page'
 
 const initState = {
   currentPageIndex: 0,
@@ -26,7 +30,7 @@ function createStore() {
     update(store => {
       return {
         ...store,
-        currentPageIndex: pageIndex < 0 ? 0 : Math.min(pageIndex, pagesCount - 1),
+        currentPageIndex: getPageIndex(pageIndex, pagesCount),
       }
     })
   }

src/utils/page.js

@@ -23,3 +23,7 @@ export function getPrevPageIndexInfinte(currentPageIndex, pagesCount) {
 export function getPrevPageIndexFn(infinite) {
   return infinite ? getPrevPageIndexInfinte : getPrevPageIndexLimited
 }
+
+export function getPageIndex(pageIndex, pagesCount) {
+  return pageIndex < 0 ? 0 : Math.min(pageIndex, pagesCount - 1)
+}

src/utils/page.test.js

@@ -2,7 +2,8 @@ import {
   getNextPageIndexLimited,
   getNextPageIndexInfinte,
   getPrevPageIndexLimited,
-  getPrevPageIndexInfinte
+  getPrevPageIndexInfinte,
+  getPageIndex
 } from './page.js';
 
 describe('getNextPageIndexLimited', () => {
@@ -64,3 +65,18 @@ describe('getPrevPageIndexInfinte', () => {
     });
   });
 });
+
+describe('getPageIndex', () => {
+  it('returns normalized page index as expected', () => {
+    const testCases = [
+      { pageIndex: -5, pagesCount: 3, expected: 0 },
+      { pageIndex: 0, pagesCount: 3, expected: 0 },
+      { pageIndex: 1, pagesCount: 3, expected: 1 },
+      { pageIndex: 2, pagesCount: 3, expected: 2 },
+      { pageIndex: 7, pagesCount: 3, expected: 2 },
+    ]
+    testCases.forEach(({ pageIndex, pagesCount, expected }) => {
+      expect(getPageIndex(pageIndex, pagesCount)).toBe(expected);
+    });
+  });
+});