code scaffold:

from $\_\_$future$\_\_$ import annotations

from dataclasses import dataclass

from computer import Computer

from typing import TYPE$\_$CHECKING, Union

# Avoid circular imports for typing.

if TYPE$\_$CHECKING:

from virus import VirusType

@dataclass

class RouteSplit:

$"""$

A split in the route.

$\_\_\_\_\_$top$\_\_\_\_\_\_$

$/\backslash$

following$-$

$\backslash \_\_\_\_$bottom$\_\_\_\_/$

$"""$

top: Route

bottom: Route

following: Route

def remove$\_$branch$($self$)->$ RouteStore:

$"""$Removes the branch, should just leave the remaining following route."""

raise NotImplementedError$()$

@dataclass

class RouteSeries:

$"""$

A computer, followed by the rest of the route

$--$computer$--$following$--$

$"""$

computer: Computer

following: Route

def remove$\_$computer$($self$)->$ RouteStore:

$"""$

Returns a route store which would be the result of:

Removing the computer at the beginning of this series.

$"""$

raise NotImplementedError$()$

def add$\_$computer$\_$before$($self$,$ computer: Computer$)->$ RouteStore:

$"""$

Returns a route store which would be the result of:

Adding a computer in series before the current one.

$"""$

raise NotImplementedError$()$

def add$\_$computer$\_$after$($self$,$ computer: Computer$)->$ RouteStore:

$"""$

Returns a route store which would be the result of:

Adding a computer after the current computer, but before the following route.

$"""$

raise NotImplementedError$()$

def add$\_$empty$\_$branch$\_$before$($self$)->$ RouteStore:

$"""$Returns a route store which would be the result of:

Adding an empty branch, where the current routestore is now the following path.

$"""$

raise NotImplementedError$()$

def add$\_$empty$\_$branch$\_$after$($self$)->$ RouteStore:

$"""$

Returns a route store which would be the result of:

Adding an empty branch after the current computer, but before the following route.

$"""$

raise NotImplementedError$()$

RouteStore $=$ Union$[$RouteSplit$,$ RouteSeries, None$]$

@dataclass

class Route:

store: RouteStore $=$ None

def add$\_$computer$\_$before$($self$,$ computer: Computer$)->$ Route:

$"""$

Returns a $*$new$*$ route which would be the result of:

Adding a computer before everything currently in the route.

$"""$

raise NotImplementedError$()$

def add$\_$empty$\_$branch$\_$before$($self$)->$ Route:

$"""$

Returns a $*$new$*$ route which would be the result of:

Adding an empty branch before everything currently in the route.

$"""$

raise NotImplementedError$()$

def follow$\_$path$($self$,$ virus$\_$type: VirusType$)->$ None:

$"""$Follow a path and add computers according to a virus$\_$type."""

raise NotImplementedError$()$

def add$\_$all$\_$computers$($self$)->$ list$[$Computer$]$:

$"""$Returns a list of all computers on the route."""

raise NotImplementedError$()$