Search by Name

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 C#, Contains checks whether one string is part of another. It is case-sensitive, so a capital letter doesn't match a small one. Turn both sides to lowercase with ToLower() and the case stops mattering:

var city = "Paris";
Console.WriteLine(city.Contains("ar"));                       // True
Console.WriteLine(city.Contains("PA"));                       // False: "PA" is not "Pa"
Console.WriteLine(city.ToLower().Contains("PA".ToLower()));   // True: "paris" contains "pa"

The search is a third optional filter in GET /products, next to max_price and category. The route already takes string? q, which is null when the URL has no q. 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, keep only the products whose name contains q, 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 add the product to result inside it. When q is null, the check must let every product through.