""" STEP 0: original code --------------------------------------------------- """

def get_cached_user(user_id=None, username=None):
   """
    Returns a user object either by their user_id or by their username.
    Hits the database if no cached version is available.
    """
    user = cache.get_user_by_id(user_id)
    if not user:
        user = cache.get_user_by_username(username)
        if not user:
            user = db.get_user_by_id(user_id)
            if not user:
                user = db.get_user_by_username(username)
                if not user:
                    raise ValueError('User not found')
            cache.set_user(user)
    return user



""" STEP 1: group responsabilities -------------------------------------------- """

def get_cached_user(user_id=None, username=None):
   """
    Returns a user object either by their user_id or by their username.
    Hits the database if no cached version is available.
    """
    user = cache.get_user_by_id(user_id) or cache.get_user_by_username(username)
    if not user:
       user = db.get_user_by_id(user_id) or db.get_user_by_username(username)
         if not user:
            raise ValueError('User not found')
       cache.set_user(user)
    return user



""" STEP 2: move responsabilities to independent objects ----------------------- """

def get_cached_user(user_id=None, username=None):
   """
    Returns a user object either by their user_id or by their username.
    Hits the database if no cached version is available.
    """
    return cache.get_user(user_id, username)

class cache:
  def  get_user(user_id, username):
    user = get_user_from_cache(user_id, username)
    if not user:
      user = database.get_user(user_id, username)
      cache.set_user(user)
    return user

  def get_user_from_cache(user_id, username):
    return get_user_by_id(user_id) or get_user_by_username(username)

class database:
  def get_user(user_id, username):
    user = get_user_by_id(user_id) or db.get_user_by_username(username)
    if not user:
      raise ValueError('User not found')
    return user


""" STEP 3: generalize conditions --------------------------------------------- """

def get_cached_user(user_id=None, username=None):
   """
    Returns a user object either by their user_id or by their username.
    Hits the database if no cached version is available.
    """
    return get_cached_user_v2({"user_id" : user_id, "username" : username})


def get_cached_user_v2(conditions):
   """
     Require a dictionary with the conditions to match (all!)
     and returns a user object. Es: {"user_id" : "1234"} or
    {"username" : "login", "password" : "1234"}
    Hits the database if no cached version is available.
    """
    return cache.get_user(conditions)

class cache:
  def  get_user(conditions):
    user = get_user_from_cache(conditions)
    if not user:
      user = database.get_user(conditions)
      cache.set_user(user)
    return user

  def get_user_from_cache(conditions):
    """ some come to dynamically adapt query througt conditions"""

class database:
  def get_user(user_id, username):
    user = """ some come to dynamically adapt query througt conditions"""
    if not user:
      raise ValueError('User not found')
    return user

""" What I like about this result is the extraction of the 'Repository' interface
    that lets us define a generic kind of recursive cache/db.
    Whenever the dynamic conditions parsing it's not the best, OO speacking, it seems
    a pragmatic and fast solution. """