Requirements

Functional Requirements:

• Users can browse available products on a display or interface, select one, and complete a purchase.
• The system supports various payment methods including cash, coins, credit/debit cards, and mobile payments.
• The system tracks product stock levels in real time, updates inventory after each transaction, and generates alerts when stock falls below a minimum threshold.
• The system issues a refund for the payment amount if a transaction fails or the user cancels it.
• Authorized service personnel can access the machine in a maintenance mode for restocking products, performing repairs, updating configuration, and viewing diagnostic information.

Non-Functional Requirements:

1. Availability: The System should be highly available
2. Latency: The user request should have very low latency.
3. Durability
   1. Once comment is created, needs to ensure that the data never lost

API Design

• Add to cart - Add a product to the cart.
  • HTTP GET: api/v1/add-to-cart/{product-id}/{vending-id}
• Remove from cart - Remove a product from cart.
  • HTTP DELETE: api/v1/remove-from-cart/{product-id}/{vending-id}
• Select and Purchase Product
  • HTTP POST: api/v1/purchase-product
  • Request: {

"product-id":"",

"user-id":"",

"payment-option":"",

"quantity":""

"vending-id":""

}

• Update Product Inventory
  • HTTP POST: api/v1/update-product/
  • Request: {

"product-id":"",

"quantity":""

"vending-id":""

}

• Get Products:
  • HTTP GET: api/v1/products/{vending-id}
  • Response { "products":

[{"id":"","name":"","description":"","price":"","quantity":"","image-path":""},

{"id":"","name":"","description":"","price":"","quantity":"","image-path":""},

{"id":"","name":"","description":"","price":"","quantity":"","image-path":""}

]

}

• Get Product:
  • HTTP GET: api/v1/product/{vending-id}/{product-id}
  • Response {

"id":"",

"name":"",

"description":"",

"price":"",

"quantity":"",

"image-path":""

}

High-Level Design

• On the start of then Vending Machine it loads the product details form the backend services and maintain into the local cache.
• The Local Cache With the TTL of 1 hour.
• Once the Purchase it make a call to the backend service (product-mgmt-service). and update the product inventory for the vending machine.
• The product-mgmt-service generate the notification if the product quantity goes below threshold.
• User Will get the product details on the Vending machine interface from the local cache. User Can add the product into cart, update the product quantity, delete product quantity from the local cache only.
• Once User click on the purchase option it call to the backend product-purchase-service it calls the third party services to complete the payment process and update the inventory details for a vending machine.
• If user selects the Payment by cash/coins then it there will be no backend service call happen for this it will be process within the Vendin Machine locally only and the data will be maintain in the local machine and on the TTL time it gets synch to the backend service.
• Vending Machine sends the Heart beats for every 3 seconds interval to the backend service. This will help to track the health status of the vending machine.
• There will be a admin section where from where Admin user can refill the vending machine set the product, quantity and all details of the product which will be added locally and then synch with the backed service to update the inventory details.   

Detailed Component Design

Deep dive into 2-3 key components. Explain how they work, how they scale, discuss tradeoffs, capacity, and any relevant algorithms or data structures.