feat(cart): add session cart service

src/Services/Cart.php

@@ -0,0 +1,175 @@
+<?php
+
+namespace Bazaar\Services;
+
+use Bazaar\Core\Session;
+use Bazaar\Repositories\ProductRepository;
+use Bazaar\Repositories\VariantRepository;
+
+final class Cart
+{
+    private const KEY = 'cart';
+
+    public function __construct(
+        private readonly Session $session,
+        private readonly ProductRepository $products,
+        private readonly ?VariantRepository $variants = null
+    ) {
+    }
+
+    public function add(int $productId, int $quantity, ?int $variantId = null): void
+    {
+        if ($quantity < 1) {
+            return;
+        }
+        $resolved = $this->resolve($productId, $variantId);
+        if ($resolved === null) {
+            return;
+        }
+
+        $lines = $this->raw();
+        $key = $this->lineKey($productId, $variantId);
+        $desired = ($lines[$key]['quantity'] ?? 0) + $quantity;
+        $quantity = min($desired, $resolved['availableStock']);
+        if ($quantity < 1) {
+            unset($lines[$key]);
+        } else {
+            $lines[$key] = ['productId' => $productId, 'variantId' => $variantId, 'quantity' => $quantity];
+        }
+        $this->persist($lines);
+    }
+
+    public function update(int $productId, int $quantity, ?int $variantId = null): void
+    {
+        $lines = $this->raw();
+        $key = $this->lineKey($productId, $variantId);
+        if ($quantity < 1) {
+            unset($lines[$key]);
+            $this->persist($lines);
+            return;
+        }
+        $resolved = $this->resolve($productId, $variantId);
+        if ($resolved === null) {
+            unset($lines[$key]);
+            $this->persist($lines);
+            return;
+        }
+        $lines[$key] = [
+            'productId' => $productId,
+            'variantId' => $variantId,
+            'quantity' => min($quantity, $resolved['availableStock']),
+        ];
+        $this->persist($lines);
+    }
+
+    public function remove(int $productId, ?int $variantId = null): void
+    {
+        $lines = $this->raw();
+        unset($lines[$this->lineKey($productId, $variantId)]);
+        $this->persist($lines);
+    }
+
+    public function clear(): void
+    {
+        $this->session->forget(self::KEY);
+    }
+
+    public function raw(): array
+    {
+        $lines = $this->session->get(self::KEY, []);
+        return is_array($lines) ? $lines : [];
+    }
+
+    public function isEmpty(): bool
+    {
+        return $this->raw() === [];
+    }
+
+    public function count(): int
+    {
+        $total = 0;
+        foreach ($this->raw() as $line) {
+            $total += (int) $line['quantity'];
+        }
+        return $total;
+    }
+
+    public function lines(): array
+    {
+        $lines = [];
+        foreach ($this->raw() as $line) {
+            $resolved = $this->resolve((int) $line['productId'], $line['variantId']);
+            if ($resolved === null) {
+                continue;
+            }
+            $quantity = (int) $line['quantity'];
+            $lines[] = [
+                'productId' => (int) $line['productId'],
+                'variantId' => $line['variantId'],
+                'product' => $resolved['product'],
+                'variant' => $resolved['variant'],
+                'name' => $resolved['product']['name'],
+                'variantLabel' => $resolved['variantLabel'],
+                'unitPriceCents' => $resolved['unitPriceCents'],
+                'availableStock' => $resolved['availableStock'],
+                'quantity' => $quantity,
+                'lineTotalCents' => $resolved['unitPriceCents'] * $quantity,
+            ];
+        }
+        return $lines;
+    }
+
+    public function totalCents(): int
+    {
+        $total = 0;
+        foreach ($this->lines() as $line) {
+            $total += $line['lineTotalCents'];
+        }
+        return $total;
+    }
+
+    private function resolve(int $productId, ?int $variantId): ?array
+    {
+        $product = $this->products->findActive($productId);
+        if ($product === null) {
+            return null;
+        }
+
+        if ($variantId !== null && $this->variants !== null) {
+            $variant = $this->variants->findActive($variantId);
+            if ($variant === null || (int) $variant['productId'] !== $productId) {
+                return null;
+            }
+            $options = $this->variants->options($variantId);
+            return [
+                'product' => $product,
+                'variant' => $variant,
+                'variantLabel' => $this->variants->label($options),
+                'unitPriceCents' => (int) $variant['priceCents'],
+                'availableStock' => (int) $variant['stockQuantity'],
+            ];
+        }
+
+        return [
+            'product' => $product,
+            'variant' => null,
+            'variantLabel' => '',
+            'unitPriceCents' => (int) $product['priceCents'],
+            'availableStock' => (int) $product['stockQuantity'],
+        ];
+    }
+
+    private function lineKey(int $productId, ?int $variantId): string
+    {
+        return $variantId !== null ? 'v' . $variantId : 'p' . $productId;
+    }
+
+    private function persist(array $lines): void
+    {
+        if ($lines === []) {
+            $this->session->forget(self::KEY);
+            return;
+        }
+        $this->session->put(self::KEY, $lines);
+    }
+}