Search by Name in Go

A search box sends what the user typed as a query parameter, often named q (for query): /products?q=no. The shop answers the products whose name contains that text, anywhere in the name.

In Go, strings.Contains(s, part) checks whether part is somewhere inside s. It is case-sensitive, so a capital letter doesn't match a small one. Turn both sides to lowercase with strings.ToLower and the case stops mattering:

city := "Paris"
fmt.Println(strings.Contains(city, "ar"))   // true
fmt.Println(strings.Contains(city, "PA"))   // false: "PA" is not "Pa"
fmt.Println(strings.Contains(strings.ToLower(city), strings.ToLower("PA")))   // true: "pa" is in "paris"

The search is a third optional filter in GET /products, next to max_price and category. When the URL has no q, Get gives the empty string "", and then every product must pass. A product is added only when it passes all three filters, and sort still orders what is left. Finding nothing is not an error: the answer is an empty list. The lists below show product names only.

GET /products?q=no  →  200  [Notebook]
GET /products?q=NO  →  200  [Notebook]
GET /products?q=m  →  200  [Mug, Lamp]
GET /products?q=e&sort=price  →  200  [Pen, Notebook]
GET /products?q=p&category=office  →  200  [Pen]
GET /products?q=chair  →  200  []
GET /products  →  200  [Mug, Notebook, Lamp, Pen]

Your task: in GET /products, read q and keep only the products whose name contains it, ignoring case.

Assignment
Follow the Coding Tutorial to add a search filter to GET /products.

Hint
Put the new if inside the category check and type result = append(result, product) again inside it. When q is "", the check must let every product through.