Ultimate Beneficial Owner

"""
* Every company has a shareholding structure (a.k.a. beneficial owners).
* Beneficial owner can be either a individual person or another company.
* Beneficial owner is characterized by % percentage in ownership.
* Shareholding structures can be multi-layered (see examples below)
* Ownership is transitive, so if person X owns 100% of company A which
  owns 100% of company B, then, effectively, person X owns 100% of company B
* Your goal is to write code that finds all ultimate (direct & indirect)
  individual beneficial owners of a company & calculates their percentages of ownership.

---------------------------------------
Example 1:
- Input (beneficial owners):
           C
        /      \
     I1(40%)  I2(60%)

- Output (ultimate beneficial owners):
  I1 (40%), I2 (60%)
---------------------------------------
Example 2:
- Input (beneficial owners):
           C
        /      \
     C1(50%)  I1(50%)
     /    \
 I2(50%)  I3(50%)

- Output (ultimate beneficial owners):
  I1 (50%), I2 (25%), I3 (25%)
---------------------------------------
Example 3:
- Input (beneficial owners):
               C
            /      \
        C1(50%)  I1(50%)
        /    \
    C2(40%)  I1(60%)
    /     \
I2(10%) I3(90%)

- Output (ultimate beneficial owners):
  I1 (80%), I2 (2%), I3 (18%)
---------------------------------------
"""


# Direct beneficial owner (aka shareholder) of a company.
# In case of corporate owner, "registration_number" field contains company identifier.
# In case of individual owner, "registration_number" is None.
# Ownership is a float [0, 1]
BeneficialOwner = tuple[
    str, str | None, float
]  # (name, registration_number, ownership)


# Ultimate beneficial owner of a company. Always an individual.
# Ownership is a float [0, 1]
UltimateBeneficialOwner = tuple[str, float]  # (name, ownership)


class BusinessRegisterClient:
    """
    A client that contains business register integration implementation.
    It has a method "get_beneficial_owners()" that returns a list of direct owners
    of a given company based on its registration number.
    """

    def get_beneficial_owners(
        self, registration_number: str
    ) -> list[BeneficialOwner]:
        # 3rd party API call
        # ASSUME IT'S ALREADY IMPLEMENTED
        ...


class UBOCalculator:
    """
    A class that finds a set of ultimate beneficial owners of a given company.
    """

    def __init__(self, br_client: BusinessRegisterClient):
        self.br_client = br_client

    def get_ultimate_beneficial_owners(
        self, registration_number: str
    ) -> set[UltimateBeneficialOwner]:
        # YOUR CODE GOES HERE
        ...