feat: define policy impact subject contract

src/govoplan_core/core/policy.py

@@ -7,6 +7,12 @@ from urllib.parse import quote, unquote
 from govoplan_core.core.access import PrincipalRef
 
 PolicyScopeType = Literal["system", "tenant", "user", "group", "campaign"]
+PolicyImpactPopulationState = Literal[
+    "complete",
+    "sampled",
+    "truncated",
+    "unavailable",
+]
 CampaignArchiveEncryptionMethod = Literal["aes", "zip_standard"]
 CampaignArchivePasswordDeliveryChannel = Literal[
     "separate_mail",
@@ -54,6 +60,7 @@ CAPABILITY_POLICY_DEFINITION_GOVERNANCE = "policy.definitionGovernance"
 CAPABILITY_POLICY_VIEW_GOVERNANCE = "policy.viewGovernance"
 CAPABILITY_POLICY_FUNCTION_ASSIGNMENT_GOVERNANCE = "policy.functionAssignmentGovernance"
 CAPABILITY_POLICY_CAMPAIGN_ARCHIVE_ENCRYPTION = "policy.campaignArchiveEncryption"
+CAPABILITY_POLICY_IMPACT_SUBJECT_PREFIX = "policy.impactSubjects."
 
 POLICY_SCOPE_TYPES: tuple[PolicyScopeType, ...] = (
     "system",
@@ -191,6 +198,146 @@ class PolicyDecision:
         }
 
 
+@dataclass(frozen=True, slots=True)
+class PolicyImpactPopulationRequest:
+    """One explicit, bounded request to an optional impact-subject provider."""
+
+    tenant_id: str
+    policy_family: str
+    selector: Mapping[str, Any] = field(default_factory=dict)
+    limit: int = 200
+    actor_scopes: tuple[str, ...] = ()
+    allow_sensitive_details: bool = False
+
+    def __post_init__(self) -> None:
+        if not self.tenant_id.strip():
+            raise ValueError("Policy impact population requires a tenant ID")
+        if not self.policy_family.strip() or len(self.policy_family) > 120:
+            raise ValueError(
+                "Policy impact population family must contain 1 to 120 characters"
+            )
+        if self.limit < 1 or self.limit > 500:
+            raise ValueError("Policy impact population limit must be between 1 and 500")
+
+
+@dataclass(frozen=True, slots=True)
+class PolicyImpactSubject:
+    """Provider-owned reference safe for Policy to compare without domain imports."""
+
+    module_id: str
+    resource_type: str
+    resource_id: str
+    action: str
+    label: str | None = None
+    scope_type: PolicyScopeType | None = None
+    scope_id: str | None = None
+    attributes: Mapping[str, Any] = field(default_factory=dict)
+
+    def __post_init__(self) -> None:
+        for label, value, maximum in (
+            ("module ID", self.module_id, 80),
+            ("resource type", self.resource_type, 80),
+            ("resource ID", self.resource_id, 240),
+            ("action", self.action, 120),
+        ):
+            if not value.strip() or len(value) > maximum:
+                raise ValueError(
+                    f"Policy impact subject {label} must contain 1 to {maximum} characters"
+                )
+
+    @property
+    def key(self) -> tuple[str, str, str, str]:
+        return (
+            self.module_id,
+            self.resource_type,
+            self.resource_id,
+            self.action,
+        )
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "module_id": self.module_id,
+            "resource_type": self.resource_type,
+            "resource_id": self.resource_id,
+            "action": self.action,
+            "label": self.label,
+            "scope_type": self.scope_type,
+            "scope_id": self.scope_id,
+            "attributes": dict(self.attributes),
+        }
+
+
+@dataclass(frozen=True, slots=True)
+class PolicyImpactSubjectBatch:
+    provider_id: str
+    subjects: tuple[PolicyImpactSubject, ...] = ()
+    state: PolicyImpactPopulationState = "complete"
+    total_available: int | None = None
+    explanation: str | None = None
+
+    def __post_init__(self) -> None:
+        if not self.provider_id.strip() or len(self.provider_id) > 120:
+            raise ValueError(
+                "Policy impact provider ID must contain 1 to 120 characters"
+            )
+        if len(self.subjects) > 500:
+            raise ValueError("Policy impact providers may return at most 500 subjects")
+        if len({subject.key for subject in self.subjects}) != len(self.subjects):
+            raise ValueError("Policy impact provider returned duplicate subjects")
+        if self.total_available is not None and self.total_available < len(self.subjects):
+            raise ValueError(
+                "Policy impact population total cannot be smaller than its subjects"
+            )
+        if self.state == "unavailable" and not self.explanation:
+            raise ValueError("Unavailable policy impact populations need an explanation")
+
+    def to_dict(self, *, include_subjects: bool = True) -> dict[str, Any]:
+        return {
+            "provider_id": self.provider_id,
+            "state": self.state,
+            "returned": len(self.subjects),
+            "total_available": self.total_available,
+            "explanation": self.explanation,
+            "subjects": (
+                [subject.to_dict() for subject in self.subjects]
+                if include_subjects
+                else []
+            ),
+        }
+
+
+@runtime_checkable
+class PolicyImpactSubjectProvider(Protocol):
+    provider_id: str
+    supported_policy_families: tuple[str, ...]
+
+    def collect_policy_impact_subjects(
+        self,
+        session: object | None = None,
+        *,
+        request: PolicyImpactPopulationRequest,
+    ) -> PolicyImpactSubjectBatch: ...
+
+
+def policy_impact_subject_provider(
+    registry: object | None,
+    provider_id: str,
+) -> PolicyImpactSubjectProvider | None:
+    clean_provider_id = provider_id.strip()
+    if not clean_provider_id or registry is None:
+        return None
+    capability_name = f"{CAPABILITY_POLICY_IMPACT_SUBJECT_PREFIX}{clean_provider_id}"
+    if (
+        not hasattr(registry, "has_capability")
+        or not registry.has_capability(capability_name)
+    ):
+        return None
+    capability = registry.capability(capability_name)
+    if not isinstance(capability, PolicyImpactSubjectProvider):
+        return None
+    return capability
+
+
 @dataclass(frozen=True, slots=True)
 class CampaignArchiveEncryptionRequest:
     """Context required to resolve one Campaign archive-encryption ceiling.