I GEAR GEEK : Vending Machine Problem

Please follow these conditions before code!

Unlimited products.
Unlimited changes.
User can insert only coin : 1 baht, 2 baht, 5 baht and 10 baht.
API calling for get product listing.
Design User Interface (UI) of vending machine based on good user experience (UX).
Focus on good code quality.
- Readability, consistency — how easy it is to read and understand sections of the code; this includes code clarity, simplicity, and documentation.
- Predictability, reliability, and robustness — software behavior should be predictable, and not prone to hidden bugs.
- Maintainability and extensibility — fixing, updating and improving software should be as simple as possible, not inherently complex.
Do you have any idea? Let's make more cool features. (Bonus point)

Example

	Story	Insert	Total	Selected	Got item?	Change
1	User insert 10 baht and 5 baht coins and select Pepsi Max	10, 5	15	Pepsi Max	true	-
2	User insert 10 baht, 5 baht, 2 baht and 1 baht coins and select Pepsi Max	10, 5, 2, 1	18	Pepsi Max	true	2, 1
3	User insert 10 baht and 2 baht coins and select Pepsi Max but can't select it because user don't have enough money	10, 2	12	Pepsi Max	false	-
4	User insert 10 baht and 2 baht coins and select Coke Vanilla (S) but can't select it because this product isn't available	10, 2	12	Coke Vanilla (S)	false	-
6	User insert 10 baht (2 coins) and 2 baht (1 coin) but user would like to refund	10, 10, 2	22	-	false	10, 10, 2

Product listing

API	Endpoint	Method
Product listing	http://www.mocky.io/v2/5af11f8c3100004d0096c7ed	GET

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