Trading System with Order Cancellation

Description

Company: Jane Street

Task Description

Implement a trading system with the ability to fulfill buy orders and support order cancellation and rollback.

Requirements

Class Item:

• buyer: String (optional/nullable)
• seller: String
• price: Integer
• item_name: String

Class Database:

• show_all_items(): Output all items in the market.

Trading Logic:

1. buy(item_name, buyer_name, max_price): Logic to sell items in the market starting with the cheapest available (that is <= max_price).
2. cancel_order(buyer_name): Cancel all orders from a specific buyer.
   • Rollback: This must "roll back" the records, making the items available for sale again.
   • Reprocessing: Handle the case where another buyer previously missed out on an item because this buyer took it. Ensure transactions are reprocessed or the state allows others to buy the freed items.

Data Scale

• Support up to 1000 items and users.

Test Cases

1. Add three items to the market and display their information.
2. Simulate buyers purchasing items at different prices and validate updates.
3. Simulate order cancellation and rollback, verifying that items become available or are taken by waitlisted buyers (if queueing is implemented).