From ee003c416c9af62a11e890e9183abbc33f81d39a Mon Sep 17 00:00:00 2001
From: Ben Thomson <bennothommo@users.noreply.github.com>
Date: Mon, 31 Dec 2018 02:49:42 +0800
Subject: [PATCH] Redirect user to last available page in list widget if
 current page is unavailable (#4020)

Credit to @bennothommo. Fixes #4008.
---
 modules/backend/widgets/Lists.php | 37 ++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/modules/backend/widgets/Lists.php b/modules/backend/widgets/Lists.php
index fd656a8ff..102ab2eea 100644
--- a/modules/backend/widgets/Lists.php
+++ b/modules/backend/widgets/Lists.php
@@ -585,11 +585,7 @@ class Lists extends WidgetBase
         }
         elseif ($this->showPagination) {
             $method            = $this->showPageNumbers ? 'paginate' : 'simplePaginate';
-            $currentPageNumber = $this->currentPageNumber;
-            if (!$currentPageNumber && empty($this->searchTerm)) {
-                // Restore the last visited page from the session if available.
-                $currentPageNumber = $this->getSession('lastVisitedPage');
-            }
+            $currentPageNumber = $this->getCurrentPageNumber($query);
             $records = $query->{$method}($this->recordsPerPage, $currentPageNumber);
         }
         else {
@@ -622,6 +618,37 @@ class Lists extends WidgetBase
         return $this->records = $records;
     }
 
+    /**
+     * Returns the current page number for the list.
+     *
+     * This will override the current page number provided by the user if it is past the last page of available records.
+     *
+     * @param object $query
+     * @return int
+     */
+    protected function getCurrentPageNumber($query)
+    {
+        $currentPageNumber = $this->currentPageNumber;
+
+        if (!$currentPageNumber && empty($this->searchTerm)) {
+            // Restore the last visited page from the session if available.
+            $currentPageNumber = $this->getSession('lastVisitedPage');
+        }
+
+        $currentPageNumber = intval($currentPageNumber);
+
+        if ($currentPageNumber > 1) {
+            $count = $query->count();
+
+            // If the current page number is higher than the amount of available pages, go to the last available page
+            if ($count <= (($currentPageNumber - 1) * $this->recordsPerPage)) {
+                $currentPageNumber = ceil($count / $this->recordsPerPage);
+            }
+        }
+
+        return $currentPageNumber;
+    }
+
     /**
      * Returns the record URL address for a list row.
      * @param  Model $record