// products.php — Legacy monolithic controller
<?php
class ProductController {
    public function getProducts($category) {
        //  N+1 Query Problem
        $products = DB::query("SELECT * FROM products WHERE cat='$category'");
        foreach ($products as $p) {
            //  Query in loop = N+1
            $p->reviews = DB::query("SELECT * FROM reviews WHERE pid={$p->id}");
            $p->stock = DB::query("SELECT qty FROM inventory WHERE pid={$p->id}");
            //  No caching
            $p->recommendations = $this->getRecommendations($p->id);
        }
        //  No pagination, loads ALL products
        return view('products', ['products' => $products]);
    }

    private function getRecommendations($pid) {
        //  Hardcoded rules, no AI
        return DB::query("SELECT * FROM products WHERE cat=(SELECT cat FROM products WHERE id=$pid) LIMIT 4");
    }
}

// products_handler.go — Modern microservice with AI
package handlers

func (h *ProductHandler) GetProducts(c *fiber.Ctx) error {
    category := c.Params("category")
    page, limit := c.QueryInt("page", 1), c.QueryInt("limit", 20)

    //  Single optimized query with JOINs + pagination
    products, err := h.repo.GetProductsWithDetails(category, page, limit)

    //  Redis cache layer (TTL: 5 min)
    cached := h.cache.GetOrSet(cacheKey, 5*time.Minute, func() interface{} {
        return products
    })

    //  AI-powered recommendations (replaces hardcoded SQL)
    userID := c.Locals("userID").(string)
    recommendations := h.aiService.GetPersonalizedRecs(userID, category)

    return c.JSON(fiber.Map{
        "products":        cached,
        "recommendations": recommendations,
        "pagination":      fiber.Map{"page": page, "limit": limit},
    })
}