Simulating Hopscotch in svcs

test_svcs.py

from dataclasses import dataclass
from pathlib import PurePath
from typing import Protocol, Callable, Any

import pytest
from svcs import Container, Registry


@dataclass
class Registration:
    # Wish I could say type[Protocol] here
    svc_type: Any
    factory: Callable[..., object]
    # Per-request overrides
    context: Callable[..., object] | None = None
    location: PurePath | None = None


@dataclass
class Registrations:
    # These two go in the registry
    system: list[Registration]
    site: list[Registration]


# ---- Different kinds of people we might talk to
class Context(Protocol):
    first_name: str


@dataclass
class CustomerContext:
    first_name: str


@dataclass
class EmployeeContext:
    first_name: str


# --- Different kinds of greetings we might give
class Greeting(Protocol):
    salutation: str


@dataclass
class DefaultGreeting:
    # The system default greeting
    salutation: str = "Good Day"


# The site has two other kinds of context
@dataclass
class CustomerGreeting:
    salutation: str = "Hello"


@dataclass
class EmployeeGreeting:
    salutation: str = "Wassup"


# The site has a special greeting in the garden aisle
@dataclass
class GardenGreeting:
    salutation: str = "Hot day outside"


@dataclass
class Request:
    context: Context
    location: PurePath


@dataclass
class RegistryRegistrations:
    """Registrations discovered at startup time from system and site."""
    site: list[Registration]
    system: list[Registration]


registry_registrations = RegistryRegistrations(
    system=[
        Registration(svc_type=Greeting, factory=DefaultGreeting),
    ],
    site=[
        Registration(svc_type=Greeting, factory=EmployeeGreeting, context=EmployeeContext),
        Registration(svc_type=Greeting, factory=GardenGreeting, location=PurePath("/garden")),
    ]
)


@pytest.fixture
def registry() -> Registry:
    registry = Registry()
    # Process the non-context, non-location registrations, starting with system,
    # then doing site (thus the latter has precedence.)
    registrations = registry_registrations.system + registry_registrations.site
    for r in registrations:
        if r.location is None and r.context is None:
            # Not request-dependent, so put it in the registry.
            registry.register_factory(r.svc_type, r.factory)
    return registry


def setup_container(registry: Registry, request: Request) -> Container:
    # The big idea:
    # 1. We've already collected all the "registrations" during a configuration 
    #    step, e.g. with venusian.
    # 2. We're processing a "request" which means creating a container.
    # 3. Find the "best" request-specific registration, if any, and register 
    #    locally in the container. But only if they match the request values.
    # 4. Thus we won't have multiple container-local registrations for the same 
    #    thing and then figure out which one is best.
    container = Container(registry)
    registrations = registry_registrations.system + registry_registrations.site
    for r in registrations:
        if (r.location is not None and request.location.is_relative_to(r.location)) or (
                r.context is not None and isinstance(request.context, r.context)):
            # This registration was EITHER location or context, and it matches the
            # request value, so register it in container.
            container.register_local_factory(r.svc_type, r.factory)
    # TODO There's a smarter way to "score" registrations, dumb way for now.
    for r in registrations:
        if (r.location and request.location.is_relative_to(r.location)) and (r.context is request.context):
            # This registration was for BOTH location and context, and it matches the
            # request values, so register it.
            container.register_local_factory(r.svc_type, r.factory)

    # Finally, put the request in the container.
    container.register_local_value(Request, request)
    return container


def test_defaults(registry: Registry):
    context = CustomerContext(first_name="Mary")
    location = PurePath("/entrance")
    request = Request(context=context, location=location)
    container = setup_container(registry, request)
    request: Request = container.get_abstract(Request)
    assert request.context is context
    assert request.location == location
    greeting: Greeting = container.get_abstract(Greeting)
    assert greeting.salutation == "Good Day"


def test_employee_context(registry: Registry):
    # This is a site-local registration which depends on a value in
    # the container.
    context = EmployeeContext(first_name="Fred")
    location = PurePath("/entrance")
    request = Request(context=context, location=location)
    container = setup_container(registry, request)
    greeting: Greeting = container.get_abstract(Greeting)
    assert greeting.salutation == "Wassup"


def test_employee_garden(registry: Registry):
    # Match on both employee and location
    context = EmployeeContext(first_name="Fred")
    location = PurePath("/garden/plans")
    request = Request(context=context, location=location)
    container = setup_container(registry, request)
    greeting: Greeting = container.get_abstract(Greeting)
    assert greeting.salutation == "Hot day outside"