Refactoring Design Patterns in Python

class CodeSmells:
    Duplicated_Code = [
        form_template_method,
        introduce_polymorphic_creation_with_factory_method,
        chain_constructors,
        replace_one__many_distinctions_with_composite,
        extract_composite,
        unify_interfaces_with_adapter,
        introduce_null_object,
    ]
    Long_Method = [
        compose_method,
        move_accumulation_to_collecting_parameter,
        replace_conditional_dispatcher_with_command,
        move_accumulation_to_visitor,
        replace_conditional_logic_with_strategy,
    ]
    Conditional_Complexity = [  # Complicated conditonal logic
        replace_conditional_logic_with_strategy,
        move_emblishment_to_decorator,
        replace_state_altering_conditionals_with_state,
        introduce_null_object,
    ]
    Primitive_Obssession = [
        replace_type_code_with_class,
        replace_state_altering_conditionals_with_state,
        replace_conditional_logic_with_strategy,
        replace_implict_tree_with_composite,
        replace_implicit_language_with_interpreter,
        move_emblishment_to_decorator,
        encapsulate_composite_with_builder,
    ]
    # Lack of "information hiding" [Parnas]
    Indecent_Exposure = [encapsulate_classes_with_factory]
    # The logic/responsibility is sprawled in multiple places
    # (classes, methods)
    Solution_Sprawl = [move_creation_knowledge_to_factory]
    # [Fowler and Beck] Interfaces of classes different,
    # but classes are similar
    Alternative_Classes_with_Different_Interfaces = unify_interfaces_with_adapter
    # [Fowler and Beck] A class the doesn't do enough to pay itself
    Lazy_Class = [inline_singleton]
    Large_Class = [
        replace_conditional_dispatcher_with_command,
        replace_state_altering_conditionals_with_state,
        replace_implict_tree_with_composite,
    ]
    Switch_Statements = [  # Complicated switches
        replace_conditional_dispatcher_with_command,
        move_accumulation_to_visitor,
    ]
    # Code that do the same with different types or quantity of data
    # (similar to duplication)
    Combination_Explostion = [replace_implicit_language_with_interpreter]
    # The same problem being solved in many ways in the system
    # (similar to duplication)
    Oddball_Solutions = [unify_interfaces_with_adapter]

# Original code
# It is not easy to understand the code
def add(element):
    readonly = False
    size = 0
    elements = []
    if not readonly:
        new_size = size + 1
        if new_size > len(elements):
            new_elements = []
            for i in range(size):
                new_elements[i] = elements[i]
            elements = new_elements
        size += 1
        elements[size] = element

# Code Refactored
# The new code has meaningfull names for blocks of code and is not nested.
# The Compose Method is a refactoring to simplificate the code
def at_capacity(new_size, elements):
    new_size > len(elements)


def grow(size):
    new_elements = []
    for i in range(size):
        new_elements[i] = elements[i]
    elements = new_elements


def add_elements(elements, element, size):
    size += 1
    elements[size] = element


def add_refac(element):
    readonly = False
    if readonly:
        return
    if at_capacity:
        grow()
    add_elements(element)

# Original code
# Similar methods differs from the object instantiation.
# All the rest is the same
class TestCase:
    pass


class DOMBuilder:
    def __init__(self, orders) -> None:
        pass

    def calc(self):
        return 42


class XMLBuilder:
    def __init__(self, orders) -> None:
        pass

    def calc(self):
        return 42


class DOMTest(TestCase):
    def run_dom_test(self):
        expected = 42
        builder = DOMBuilder("orders")  # different object created
        assert builder.calc() == expected


class XMLTest(TestCase):
    def run_xml_test(self):
        expected = 42
        builder = XMLBuilder("orders")  # different object created
        assert builder.calc() == expected


# Code refactored
# The instantiation of the DOMBuilder or XMLBuilder is the only difference
# in both tests.
# It was created an OutputBuilder like an interface for both classes
# (it is not necessary given that Python uses duck type).
# In TestCase a new method called "create_builder" was introduced to be
# implemented by the children classes.
# This is the step executed in runtime for each type of test. This is the
# polymorphism. When both tests (DOMTest and XMLTest) are executed,
# the instance returned from the "create_builder" depends on the
# implementation. Is can be DOMBuilder or XMLBuilder.
class OutputBuilder:
    def calc(self):
        raise NotImplementedError()


class DOMBuilderRefac(OutputBuilder):
    def calc(self):
        return 42


class XMLBuilderRefac(OutputBuilder):
    def calc(self):
        return 42


class TestCaseRefac:
    def create_builder(self):
        raise NotImplementedError()

    def run_test(self):
        expected = 42
        builder = self.create_builder()  # different object created
        assert builder.calc() == expected


class DOMTestRefac(TestCaseRefac):
    def create_builder(self) -> OutputBuilder:
        return DOMBuilderRefac()


class XMLTestRefac(TestCaseRefac):
    def create_builder(self):
        return XMLBuilderRefac()


def run():
    dom_tc = DOMTestRefac()
    dom_tc.run_test()

    xml_tc = XMLTestRefac()
    xml_tc.run_test()