Simplified and aligned handling of mixed entity endpoints

Fixes #4444

app/Entities/Tools/MixedEntityRequestHelper.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace BookStack\Entities\Tools;
+
+use BookStack\Entities\EntityProvider;
+use BookStack\Entities\Models\Entity;
+
+class MixedEntityRequestHelper
+{
+    public function __construct(
+        protected EntityProvider $entities,
+    ) {
+    }
+
+    /**
+     * Query out an entity, visible to the current user, for the given
+     * entity request details (this provided in a request validated by
+     * this classes' validationRules method).
+     * @param array{type: string, id: string} $requestData
+     */
+    public function getVisibleEntityFromRequestData(array $requestData): Entity
+    {
+        $entityType = $this->entities->get($requestData['type']);
+
+        return $entityType->newQuery()->scopes(['visible'])->findOrFail($requestData['id']);
+    }
+
+    /**
+     * Get the validation rules for an abstract entity request.
+     * @return array{type: string[], id: string[]}
+     */
+    public function validationRules(): array
+    {
+        return [
+                'type' => ['required', 'string'],
+                'id'   => ['required', 'integer'],
+        ];
+    }
+}