Refactor/james

[JamesGai]

Why refactor?

1. Nested conditional statements (if)
2. Duplication (same logics for checking invoice types)
3. Lack of message indicators
4. Low readability and huge function

How to refactor?

1. Break the nested statements into separate helper functions so that function won't get too large
2. Replace duplicated invvoice checking logic with single conditional statement
3. Able to write individual test cases for these helper functions for long-term usage