Started core API route work

app/Api/ListingResponseBuilder.php

@@ -0,0 +1,82 @@
+<?php namespace BookStack\Api;
+
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Collection;
+
+class ListingResponseBuilder
+{
+
+    protected $query;
+    protected $fields;
+
+    /**
+     * ListingResponseBuilder constructor.
+     */
+    public function __construct(Builder $query, array $fields)
+    {
+        $this->query = $query;
+        $this->fields = $fields;
+    }
+
+    /**
+     * Get the response from this builder.
+     */
+    public function toResponse()
+    {
+        $total = $this->query->count();
+        $data = $this->fetchData();
+
+        return response()->json([
+            'data' => $data,
+            'total' => $total,
+        ]);
+    }
+
+    /**
+     * Fetch the data to return in the response.
+     */
+    protected function fetchData(): Collection
+    {
+        $this->applyCountAndOffset($this->query);
+        $this->applySorting($this->query);
+        // TODO - Apply filtering
+
+        return $this->query->get($this->fields);
+    }
+
+    /**
+     * Apply sorting operations to the query from given parameters
+     * otherwise falling back to the first given field, ascending.
+     */
+    protected function applySorting(Builder $query)
+    {
+        $defaultSortName = $this->fields[0];
+        $direction = 'asc';
+
+        $sort = request()->get('sort', '');
+        if (strpos($sort, '-') === 0) {
+            $direction = 'desc';
+        }
+
+        $sortName = ltrim($sort, '+- ');
+        if (!in_array($sortName, $this->fields)) {
+            $sortName = $defaultSortName;
+        }
+
+        $query->orderBy($sortName, $direction);
+    }
+
+    /**
+     * Apply count and offset for paging, based on params from the request while falling
+     * back to system defined default, taking the max limit into account.
+     */
+    protected function applyCountAndOffset(Builder $query)
+    {
+        $offset = max(0, request()->get('offset', 0));
+        $maxCount = config('api.max_item_count');
+        $count = request()->get('count', config('api.default_item_count'));
+        $count = max(min($maxCount, $count), 1);
+
+        $query->skip($offset)->take($count);
+    }
+}