Fix pagination behavior when page # exceeds search results (#4817)

# What this PR does
Change pagination to return last available page if the page number
exceeds the pages available instead of returning 404. This came up from
if the user is on a page other than the first and they enter a search
and the number of search results are smaller than what would be needed
to reach the current page number it would give a blank page and 404.

## Which issue(s) this PR closes

Related to [issue link here]

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## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

---------

Co-authored-by: Rares Mardare <rares.mardare@grafana.com>

engine/apps/public_api/tests/test_alert_groups.py

@@ -447,10 +447,9 @@ def test_pagination(settings, alert_group_public_api_setup):
     token, alert_groups, _, _ = alert_group_public_api_setup
     client = APIClient()
 
-    url = reverse("api-public:alert_groups-list")
+    url = "{}?perpage=1".format(reverse("api-public:alert_groups-list"))
 
-    with patch("common.api_helpers.paginators.PathPrefixedPagePagination.get_page_size", return_value=1):
-        response = client.get(url, HTTP_AUTHORIZATION=token)
+    response = client.get(url, HTTP_AUTHORIZATION=token)
 
     assert response.status_code == status.HTTP_200_OK
     result = response.json()

engine/common/api_helpers/paginators.py

@@ -1,5 +1,6 @@
 import typing
 
+from django.core.paginator import EmptyPage
 from rest_framework.pagination import BasePagination, CursorPagination, PageNumberPagination
 from rest_framework.response import Response
 
@@ -54,6 +55,44 @@ class PathPrefixedPagePagination(BasePathPrefixedPagination, PageNumberPaginatio
         )
         return paginated_schema
 
+    def paginate_queryset(self, queryset, request, view=None):
+        request.build_absolute_uri = lambda: create_engine_url(request.get_full_path())
+        per_page = request.query_params.get(self.page_size_query_param, self.page_size)
+        try:
+            per_page = int(per_page)
+        except ValueError:
+            per_page = self.page_size
+
+        if per_page < 1:
+            per_page = self.page_size
+
+        paginator = self.django_paginator_class(queryset, per_page)
+        page_number = request.query_params.get(self.page_query_param, 1)
+        try:
+            page_number = int(page_number)
+        except ValueError:
+            page_number = 1
+
+        if page_number < 1:
+            page_number = 1
+
+        try:
+            self.page = self.get_page(page_number, paginator)
+        except EmptyPage:
+            self.page = paginator.page(paginator.num_pages)
+
+        if paginator.num_pages > 1 and self.template is not None:
+            self.display_page_controls = True
+
+        self.request = request
+        return list(self.page)
+
+    def get_page(self, page_number, paginator):
+        try:
+            return paginator.page(page_number)
+        except EmptyPage:
+            return paginator.page(paginator.num_pages)
+
 
 class PathPrefixedCursorPagination(BasePathPrefixedPagination, CursorPagination):
     def get_paginated_response(self, data: PaginatedData) -> Response:

grafana-plugin/src/pages/integrations/Integrations.tsx

@@ -660,6 +660,7 @@ class _IntegrationsPage extends React.Component<IntegrationsProps, IntegrationsS
 
   invalidateRequestFn = (requestedPage: number) => {
     const { store } = this.props;
+
     return requestedPage !== store.filtersStore.currentTablePageNum[PAGE.Integrations];
   };
 
@@ -696,6 +697,10 @@ class _IntegrationsPage extends React.Component<IntegrationsProps, IntegrationsS
     const { alertReceiveChannelStore } = store;
     const newPage = isOnMount ? store.filtersStore.currentTablePageNum[PAGE.Integrations] : 1;
 
+    runInAction(() => {
+      store.filtersStore.currentTablePageNum[PAGE.Integrations] = newPage;
+    });
+
     await alertReceiveChannelStore.fetchPaginatedItems({
       filters: this.getFiltersBasedOnCurrentTab(),
       page: newPage,
@@ -703,9 +708,6 @@ class _IntegrationsPage extends React.Component<IntegrationsProps, IntegrationsS
       invalidateFn: () => this.invalidateRequestFn(newPage),
     });
 
-    runInAction(() => {
-      store.filtersStore.currentTablePageNum[PAGE.Integrations] = newPage;
-    });
     LocationHelper.update({ p: newPage }, 'partial');
   };