Running tests

pip install -r requirements_test.txt
pytest --mypy --cov --black

Problem Statement

An online order contains line items. Each line item is identified by a product SKU and its quantity.

E.g. Order-1 has products SKU1, SKU1, SKU2 (repeating SKUs means same products in more than one quantity in an order). The line items would be:

• SKU1, quantity 2
• SKU2, quantity 1

Products inside an order can be shipped in more than one shipment. A shipment is uniquely identified with a tracking number.

E.g. Order-1 with the above SKUs could be shipped in two shipments:

• Shipment with tracking tracking-1 ships SKU1, SKU2
• Shipment with tracking tracking-2 ships SKU1

Updates for a Shipment can arrive in multiple parts. For example:

# update 1 at timestamp-1

• Order-1 got SKU1 shipped with tracking-1

# update 2 at timestamp-2

• Order-1 got SKU1 shipped with tracking-2

# update 3 at timestamp-3

• Order-1 got SKU2 shipped with tracking-1

One shipment update contains all or part of SKUs for one tracking code. (i.e assume one tracking per shipment update)

After the above three updates, all SKUs in Order-1 have shipment information. These will be the shipments for Order-1:

• Shipment with tracking-1 shipped SKU1, SKU2
• Shipment with tracking-2 shipped SKU1

Shipment information can be repeated in a later update. For example, consider this alternative version of update 3:

# update 3, alternative 1 at timestamp-3

• Order-1 got SKU1 shipped with tracking-1
• Order-1 got SKU2 shipped with tracking-1

After update 2 only one quantity of SKU2 needs an update, whereas the update provides for SKU1 also. When such a shipment update comes with shipment information for more SKUs than there is room for to update, such updates should not be applied.

Therefore following alternatives cannot be accepted either:

# update 3 alternative2 at timestamp-3

• Order-1 got SKU1 shipped with tracking-2
  • There are no SKU1s left that need shipment update
• Order-1 got SKU2 shipped with tracking-2
  • This part is valid, but since the update itself has an invalid part, the update needs to be rejected

# update 3 alternative 3 at timestamp-3

• Order-1 got SKU3 shipped with tracking-1
  • There is no such SKU 'SKU3' in the original order, so this update is invalid.

Programming Task

Write a service that allows the following operations:

• add an order with line items
• accept shipment updates for an order
  • follow the rules for rejecting updates as specified above
• return current known shipments for an order
• write unit tests covering all update scenarios described above to verify the solution meets the requirement

You might be provided with a partial solution for the problem. In that case, the task will be following:

• extend the provided code so that it can accept shipment updates for an order
• follow the rules for rejecting updates as specified above
• write unit tests covering all update scenarios described above to verify the solution meets the requirement

Assume no interaction with network or database for the solution. A solution that keeps everything in memory is sufficient. All the above operations should be runnable and testable.