Bloomberg Software Engineer System Design Questions

Background: Bloomberg provides financial services and information, where managing stock portfolios is essential for users to track their investments and performance.
Requirements:
1. The class should allow adding, removing, and updating stocks in a user's portfolio.
2. It should provide methods to calculate the total value of the portfolio and the performance over time.
3. The service must handle multiple users.
4. It should support concurrency for simultaneous modifications.
5. The portfolio must store the historical prices of stocks for performance analysis.
Class API:

• add_stock(user_id: str, stock_symbol: str, quantity: int) -> None: Adds a stock for the user.


• remove_stock(user_id: str, stock_symbol: str) -> None: Removes a stock from the user's portfolio.


• update_stock(user_id: str, stock_symbol: str, quantity: int) -> None: Updates stock quantity in the portfolio.


• get_total_value(user_id: str) -> float: Returns the total value of the portfolio based on current stock prices.


• get_performance(user_id: str) -> dict: Returns performance metrics like returns over a specified period.

Example 1:
Input: add_stock('user123', 'AAPL', 10) → Output: None → Explanation: Adds 10 shares of AAPL to user 'user123's portfolio.Example 2:
Input: get_total_value('user123') → Output: 1500.00 → Explanation: Total value based on current stock prices of the user's portfolio.
Constraints:

• Max users: 10000


• Max stocks per user: 100


• Concurrent operations should not lead to data inconsistency.