Add backend names listing service

Author: shinaji

src/schnee/services/__init__.py

@@ -1,3 +1,9 @@
 """Application services."""
 
+from .backend import (
+    ListBackendNamesBackendError,
+    ListBackendNamesReaderError,
+    ListBackendNamesService,
+    ListBackendNamesServiceError,
+)
 from .base import ServiceError

src/schnee/services/backend.py

@@ -0,0 +1,43 @@
+"""Services for backend selection."""
+
+from __future__ import annotations
+
+from typing import ClassVar
+
+from schnee.adapters.backend.core import Backend
+from schnee.adapters.backend.pcsc import PcscReaderProvider
+from schnee.services.base import Service, ServiceError
+
+
+class ListBackendNamesServiceError(ServiceError):
+    """Base exception for list backend names service errors."""
+
+    msg: ClassVar[str] = "List backend names service error"
+
+
+class ListBackendNamesBackendError(ListBackendNamesServiceError):
+    """Raised when backend name discovery fails."""
+
+    msg: ClassVar[str] = "List backend names backend operation failed"
+
+
+class ListBackendNamesReaderError(ListBackendNamesServiceError):
+    """Raised when PC/SC reader discovery fails."""
+
+    msg: ClassVar[str] = "List backend names reader discovery failed"
+
+
+class ListBackendNamesService(Service[list[str]]):
+    """List selectable backend names."""
+
+    class Request(Service.Request):
+        """Request for listing selectable backend names."""
+
+    def process(self) -> list[str]:
+        """Return selectable backend names."""
+        try:
+            return Backend.backend_names()
+        except PcscReaderProvider.PcscReaderProviderError as exc:
+            raise ListBackendNamesReaderError from exc
+        except Backend.BackendError as exc:
+            raise ListBackendNamesBackendError from exc

tests/schnee/services/test_backend.py

@@ -0,0 +1,75 @@
+"""Tests for backend selection services."""
+
+import pytest
+
+from schnee.adapters.backend.core import Backend
+from schnee.adapters.backend.pcsc import PcscReaderProvider
+from schnee.services.backend import (
+    ListBackendNamesBackendError,
+    ListBackendNamesReaderError,
+    ListBackendNamesService,
+)
+
+
+def test_list_backend_names_service_returns_selectable_backend_names(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Selectable backend names are available through the service layer."""
+    monkeypatch.setattr(
+        "schnee.services.backend.Backend.backend_names",
+        lambda: ["pcsc", "pcsc:Reader A"],
+    )
+
+    names = ListBackendNamesService.call(ListBackendNamesService.Request())
+
+    assert names == ["pcsc", "pcsc:Reader A"]
+
+
+def test_list_backend_names_service_translates_reader_errors(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Reader discovery failures are exposed through service-level errors."""
+
+    def backend_names() -> list[str]:
+        raise PcscReaderProvider.PcscReaderProviderError
+
+    monkeypatch.setattr(
+        "schnee.services.backend.Backend.backend_names",
+        backend_names,
+    )
+
+    with pytest.raises(
+        ListBackendNamesReaderError,
+        match=ListBackendNamesReaderError.msg,
+    ) as exc_info:
+        ListBackendNamesService.call(ListBackendNamesService.Request())
+
+    assert isinstance(
+        exc_info.value.__cause__,
+        PcscReaderProvider.PcscReaderProviderError,
+    ), "service error should preserve the reader failure as its cause"
+
+
+def test_list_backend_names_service_translates_backend_errors(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Backend selector failures are exposed through service-level errors."""
+
+    def backend_names() -> list[str]:
+        raise Backend.BackendError
+
+    monkeypatch.setattr(
+        "schnee.services.backend.Backend.backend_names",
+        backend_names,
+    )
+
+    with pytest.raises(
+        ListBackendNamesBackendError,
+        match=ListBackendNamesBackendError.msg,
+    ) as exc_info:
+        ListBackendNamesService.call(ListBackendNamesService.Request())
+
+    assert isinstance(
+        exc_info.value.__cause__,
+        Backend.BackendError,
+    ), "service error should preserve the backend failure as its cause"