feat: add DatabaseDriver

Implements CartDriver for Eloquent-backed persistence using firstOrNew
pattern. Includes 9 unit tests covering CRUD, flush, clearItems, and
model retrieval.

src/Drivers/DatabaseDriver.php

@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wearepixel\Cart\Drivers;
+
+use Illuminate\Database\Eloquent\Model;
+use Wearepixel\Cart\Drivers\Contracts\CartDriver;
+
+class DatabaseDriver implements CartDriver
+{
+    private Model $model;
+
+    public function __construct(
+        private string $modelClass,
+        private string $idColumn,
+        private string $itemsColumn,
+        private string $conditionsColumn,
+        private string $sessionKey,
+    ) {
+        $this->model = (new $modelClass)->firstOrNew([$idColumn => $sessionKey]);
+        $this->model[$itemsColumn] ??= [];
+        $this->model[$conditionsColumn] ??= [];
+    }
+
+    public function getSessionKey(): string
+    {
+        return $this->sessionKey;
+    }
+
+    public function setSessionKey(string $sessionKey): void
+    {
+        $this->sessionKey = $sessionKey;
+        $this->model[$this->idColumn] = $sessionKey;
+        $this->model->save();
+    }
+
+    public function getDriverName(): string
+    {
+        return 'database';
+    }
+
+    public function getItems(): array
+    {
+        return $this->model[$this->itemsColumn] ?? [];
+    }
+
+    public function putItems(array $items): void
+    {
+        $this->model[$this->itemsColumn] = $items;
+        $this->model->save();
+    }
+
+    public function getConditions(): array
+    {
+        return $this->model[$this->conditionsColumn] ?? [];
+    }
+
+    public function putConditions(array $conditions): void
+    {
+        $this->model[$this->conditionsColumn] = $conditions;
+        $this->model->save();
+    }
+
+    public function clearItems(): void
+    {
+        $this->model[$this->itemsColumn] = [];
+        $this->model->save();
+    }
+
+    public function flush(): void
+    {
+        $this->model->delete();
+        $this->model[$this->itemsColumn] = [];
+        $this->model[$this->conditionsColumn] = [];
+    }
+
+    public function getSessionModel(): mixed
+    {
+        return $this->model;
+    }
+}