[Feature] Bring in code from the Eloquent package

Author: lindyhopchris

composer.json

@@ -26,6 +26,7 @@
         "php": "^7.4|^8.0",
         "ext-json": "*",
         "illuminate/database": "^8.0",
+        "illuminate/pagination": "^8.0",
         "illuminate/support": "^8.0",
         "laravel-json-api/eloquent": "^1.0.0-stable"
     },

src/.gitkeep

@@ -0,0 +1,117 @@
+<?php
+/*
+ * Copyright 2021 Cloud Creativity Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+declare(strict_types=1);
+
+namespace LaravelJsonApi\CursorPagination\Cursor;
+
+use InvalidArgumentException;
+
+class Cursor
+{
+
+    /**
+     * @var string|null
+     */
+    private ?string $before;
+
+    /**
+     * @var string|null
+     */
+    private ?string $after;
+
+    /**
+     * @var int|null
+     */
+    private ?int $limit;
+
+    /**
+     * Cursor constructor.
+     *
+     * @param string|null $before
+     * @param string|null $after
+     * @param int|null $limit
+     */
+    public function __construct(string $before = null, string $after = null, int $limit = null)
+    {
+        if (is_int($limit) && 1 > $limit) {
+            throw new InvalidArgumentException('Expecting a limit that is 1 or greater.');
+        }
+
+        $this->before = $before ?: null;
+        $this->after = $after ?: null;
+        $this->limit = $limit;
+    }
+
+    /**
+     * @return bool
+     */
+    public function isBefore(): bool
+    {
+        return !is_null($this->before);
+    }
+
+    /**
+     * @return string|null
+     */
+    public function getBefore(): ?string
+    {
+        return $this->before;
+    }
+
+    /**
+     * @return bool
+     */
+    public function isAfter(): bool
+    {
+        return !is_null($this->after) && !$this->isBefore();
+    }
+
+    /**
+     * @return string|null
+     */
+    public function getAfter(): ?string
+    {
+        return $this->after;
+    }
+
+    /**
+     * Set a limit, if no limit is set on the cursor.
+     *
+     * @param int $limit
+     * @return Cursor
+     */
+    public function withDefaultLimit(int $limit): self
+    {
+        if (is_null($this->limit)) {
+            $copy = clone $this;
+            $copy->limit = $limit;
+            return $copy;
+        }
+
+        return $this;
+    }
+
+    /**
+     * @return int|null
+     */
+    public function getLimit(): ?int
+    {
+        return $this->limit;
+    }
+
+}