feat: add ai model alias configuration

apps/ai/aliases.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+from apps.ai.providers import ResolvedModel
+
+from .models import AiModel, ModelAlias
+
+
+class AliasResolutionError(RuntimeError):
+    """Base error for alias resolution failures."""
+
+
+class AliasNotFoundError(AliasResolutionError):
+    """Raised when an active alias cannot be found."""
+
+
+class ModelCapabilityError(AliasResolutionError):
+    """Raised when an alias points to a model without the required capability."""
+
+
+REQUIRED_CAPABILITIES = {
+    ModelAlias.OperationType.TITLE: "text",
+    ModelAlias.OperationType.IMAGE: "image",
+}
+
+
+def resolve_alias(operation_type: str, alias: str | None = None) -> ResolvedModel:
+    """Resolve an external capability alias to a provider-ready model config."""
+    required_capability = REQUIRED_CAPABILITIES.get(operation_type)
+    if required_capability is None:
+        raise AliasResolutionError(f"unsupported operation_type: {operation_type}")
+
+    queryset = ModelAlias.objects.select_related("ai_model").filter(
+        operation_type=operation_type,
+        is_active=True,
+        ai_model__is_active=True,
+    )
+    if alias:
+        queryset = queryset.filter(alias=alias)
+    else:
+        queryset = queryset.filter(is_default=True)
+
+    model_alias = queryset.order_by("id").first()
+    if model_alias is None:
+        if alias:
+            raise AliasNotFoundError(f"alias not found: {operation_type}:{alias}")
+        raise AliasNotFoundError(f"default alias not found: {operation_type}")
+
+    ai_model: AiModel = model_alias.ai_model
+    capabilities = ai_model.capabilities_set()
+    if required_capability not in capabilities:
+        raise ModelCapabilityError(
+            f"alias {model_alias.alias} maps to model {ai_model.name} without "
+            f"{required_capability} capability"
+        )
+    return ai_model.to_resolved_model()