Food ordering system
Time: 90mins

Description: Implement an online food ordering system.
Features:
This system has a tie-up with restaurants where each restaurant has a menu with all the items & their prices. Restaurants also have a rating out of 5.
Each restaurant has max #orders it can process at any given time. Beyond that, it shouldn’t be assigned any further orders until an ongoing order is completed.
Once an order is ACCEPTED, the restaurant can mark it as COMPLETED when the order is ready. This will free up the processing capacity of the restaurant. A restaurant can’t CANCEL an ACCEPTED order.
An order will be auto-assigned to a restaurant based on a selection strategy. Eg: Assign by lowest cost or best rating.
An order will be auto-assigned to a restaurant only if all the items in an order can be fulfilled by a single restaurant. Else the order will not be ACCEPTED.

Requirements:
Onboard a new restaurant.
A restaurant should be able to update its menu. For simplicity, a restaurant can't delete an item from the menu.
Restaurants can mark ACCEPTED orders as COMPLETED. Orders once ACCEPTED can’t be CANCELLED by a restaurant.
A customer should be able to place an order by giving items, respective quantities & selection strategy.
Order will be auto-assigned to a restaurant based on a selection strategy.
Implement at least one restaurant selection strategy.

Note: Do not use any database or NoSQL store, use an in-memory store.

Expectations:
Make sure that you have working and demoable & functionally correct code.
Use proper abstractions, separation of concerns, proper entity modeling
Use appropriate design patterns wherever required.
The code should be modular, extensible, readable and unit-testable.
Proper exception handling is required.
Restaurant selection strategy must be pluggable
Concurrency handling (BONUS / Good to have)

Sample test cases:
Onboard Restaurants
R1
“max_orders_that_can_be_processed_at_a_time” : 5,
“Menu”: [Veg Biryani : Rs.100, Chicken Biryani: Rs.150],
“rating”: 4.5/5
R2
“max_orders_that_can_be_processed_at_a_time”: 5,
menu: [Chicken Biryani : Rs.175, Idli : Rs.10, Dosa : Rs.50, Veg Biryani : Rs. 80],
rating: 4/5
R3
“max_orders_that_can_be_processed_at_a_time”: 1,
menu: [Gobi Manchurian : Rs.150, Idli : Rs.15, Chicken Biryani : Rs.175, Dosa: Rs.30 ],
rating: 4.9/5
2. Update restaurant menu
ADD: {Restaurant_1, add, Chicken65, Rs.250}
UPDATE: {Restaurant_2, update, Chicken Biryani, Rs.150}
3. Place Order
Order1.
Input: { user: Ashwin, items: [ 3Idli, 1Dosa ], selection: Lowest cost }
Output: Order assigned to R3
Order2.
Input: { user: Harish, items: [ 3Idli, 1Dosa ], selection: Lowest cost }
Output: 1) Order assigned to R2
(Not R3 since it has reached its full capacity from Order1)
Order3:
Input: { user: Shruthi, items: [3Veg Biryani], selection: ‘Highest rating’ }
Output: Order assigned to R1
Update Order Status:
R3 marks Order1 as COMPLETED
Order4:
Input: { user: Harish, items: [ 3Idli, 1Dosa ], selection: Lowest cost }
Output: Order assigned to R3
(since R3 had COMPLETED Order1)
Order5:
Input: {user: xyz, items: [1Paneer Tikka, 1*Idli], selection: ‘Lowest cost}
Output: Order can’t be fulfilled
(since none of the restaurants above serve Paneer Tikka)

4. Update Order Status
   Input: {R3, Order1, COMPLETED}