refactor: move capacity_forecast_service from billing to monitoring

Resolves the billing (core) → monitoring (optional) architecture violation
by moving CapacityForecastService to the monitoring module where it belongs.

- Create BillingMetricsProvider to expose subscription counts via stats_aggregator
- Move CapacitySnapshot model from billing to monitoring
- Replace direct MerchantSubscription queries with stats_aggregator calls
- Fix middleware test mocks to cover StoreDomain/MerchantDomain fallback chains

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/billing/definition.py

@@ -89,6 +89,13 @@ def _get_store_router():
     return store_router
 
 
+def _get_metrics_provider():
+    """Lazy import of metrics provider to avoid circular imports."""
+    from app.modules.billing.services.billing_metrics import billing_metrics_provider
+
+    return billing_metrics_provider
+
+
 def _get_feature_provider():
     """Lazy import of feature provider to avoid circular imports."""
     from app.modules.billing.services.billing_features import billing_feature_provider
@@ -271,6 +278,8 @@ billing_module = ModuleDefinition(
     ],
     # Feature provider for feature flags
     feature_provider=_get_feature_provider,
+    # Metrics provider for subscription metrics
+    metrics_provider=_get_metrics_provider,
 )
 
 

app/modules/billing/models/__init__.py

@@ -22,7 +22,6 @@ from app.modules.billing.models.subscription import (
     AddOnProduct,
     BillingHistory,
     BillingPeriod,
-    CapacitySnapshot,
     StoreAddOn,
     StripeWebhookEvent,
     SubscriptionStatus,
@@ -46,7 +45,6 @@ __all__ = [
     "StoreAddOn",
     "StripeWebhookEvent",
     "BillingHistory",
-    "CapacitySnapshot",
     # Merchant Subscription
     "MerchantSubscription",
     # Feature Limits

app/modules/billing/models/subscription.py

@@ -345,61 +345,3 @@ class BillingHistory(Base, TimestampMixin):
 
     def __repr__(self):
         return f"<BillingHistory(store_id={self.store_id}, invoice='{self.invoice_number}', status='{self.status}')>"
-
-
-# ============================================================================
-# Capacity Planning
-# ============================================================================
-
-
-class CapacitySnapshot(Base, TimestampMixin):
-    """
-    Daily snapshot of platform capacity metrics.
-
-    Used for growth trending and capacity forecasting.
-    Captured daily by background job.
-    """
-
-    __tablename__ = "capacity_snapshots"
-
-    id = Column(Integer, primary_key=True, index=True)
-    snapshot_date = Column(DateTime(timezone=True), nullable=False, unique=True, index=True)
-
-    # Store metrics
-    total_stores = Column(Integer, default=0, nullable=False)
-    active_stores = Column(Integer, default=0, nullable=False)
-    trial_stores = Column(Integer, default=0, nullable=False)
-
-    # Subscription metrics
-    total_subscriptions = Column(Integer, default=0, nullable=False)
-    active_subscriptions = Column(Integer, default=0, nullable=False)
-
-    # Resource metrics
-    total_products = Column(Integer, default=0, nullable=False)
-    total_orders_month = Column(Integer, default=0, nullable=False)
-    total_team_members = Column(Integer, default=0, nullable=False)
-
-    # Storage metrics
-    storage_used_gb = Column(Numeric(10, 2), default=0, nullable=False)
-    db_size_mb = Column(Numeric(10, 2), default=0, nullable=False)
-
-    # Capacity metrics (theoretical limits from subscriptions)
-    theoretical_products_limit = Column(Integer, nullable=True)
-    theoretical_orders_limit = Column(Integer, nullable=True)
-    theoretical_team_limit = Column(Integer, nullable=True)
-
-    # Tier distribution (JSON: {"essential": 10, "professional": 5, ...})
-    tier_distribution = Column(JSON, nullable=True)
-
-    # Performance metrics
-    avg_response_ms = Column(Integer, nullable=True)
-    peak_cpu_percent = Column(Numeric(5, 2), nullable=True)
-    peak_memory_percent = Column(Numeric(5, 2), nullable=True)
-
-    # Indexes
-    __table_args__ = (
-        Index("ix_capacity_snapshots_date", "snapshot_date"),
-    )
-
-    def __repr__(self) -> str:
-        return f"<CapacitySnapshot(date={self.snapshot_date}, stores={self.total_stores})>"

app/modules/billing/services/__init__.py

@@ -21,10 +21,6 @@ from app.modules.billing.services.billing_service import (
     BillingService,
     billing_service,
 )
-from app.modules.billing.services.capacity_forecast_service import (
-    CapacityForecastService,
-    capacity_forecast_service,
-)
 from app.modules.billing.services.feature_service import (
     FeatureService,
     feature_service,
@@ -68,8 +64,6 @@ __all__ = [
     "SubscriptionNotCancelledError",
     "FeatureService",
     "feature_service",
-    "CapacityForecastService",
-    "capacity_forecast_service",
     "PlatformPricingService",
     "platform_pricing_service",
     "UsageService",

app/modules/billing/services/billing_metrics.py

@@ -0,0 +1,115 @@
+# app/modules/billing/services/billing_metrics.py
+"""
+Metrics provider for the billing module.
+
+Provides metrics for:
+- Subscription counts (total, active, trial)
+"""
+
+import logging
+
+from sqlalchemy import func
+from sqlalchemy.orm import Session
+
+from app.modules.contracts.metrics import (
+    MetricsContext,
+    MetricValue,
+)
+
+logger = logging.getLogger(__name__)
+
+
+class BillingMetricsProvider:
+    """
+    Metrics provider for billing module.
+
+    Provides subscription metrics at the platform level.
+    """
+
+    @property
+    def metrics_category(self) -> str:
+        return "billing"
+
+    def get_store_metrics(
+        self,
+        db: Session,
+        store_id: int,
+        context: MetricsContext | None = None,
+    ) -> list[MetricValue]:
+        """
+        Get metrics for a specific store.
+
+        Subscriptions are merchant-level, not store-level, so no store metrics.
+        """
+        return []
+
+    def get_platform_metrics(
+        self,
+        db: Session,
+        platform_id: int,
+        context: MetricsContext | None = None,
+    ) -> list[MetricValue]:
+        """
+        Get subscription metrics aggregated for a platform.
+
+        Provides:
+        - Total subscriptions
+        - Active subscriptions (active + trial)
+        - Trial subscriptions
+        """
+        from app.modules.billing.models import MerchantSubscription, SubscriptionStatus
+
+        try:
+            total_subs = (
+                db.query(func.count(MerchantSubscription.id)).scalar() or 0
+            )
+
+            active_subs = (
+                db.query(func.count(MerchantSubscription.id))
+                .filter(MerchantSubscription.status.in_(["active", "trial"]))
+                .scalar()
+                or 0
+            )
+
+            trial_subs = (
+                db.query(func.count(MerchantSubscription.id))
+                .filter(MerchantSubscription.status == SubscriptionStatus.TRIAL.value)
+                .scalar()
+                or 0
+            )
+
+            return [
+                MetricValue(
+                    key="billing.total_subscriptions",
+                    value=total_subs,
+                    label="Total Subscriptions",
+                    category="billing",
+                    icon="credit-card",
+                    description="Total number of merchant subscriptions",
+                ),
+                MetricValue(
+                    key="billing.active_subscriptions",
+                    value=active_subs,
+                    label="Active Subscriptions",
+                    category="billing",
+                    icon="check-circle",
+                    description="Subscriptions with active or trial status",
+                ),
+                MetricValue(
+                    key="billing.trial_subscriptions",
+                    value=trial_subs,
+                    label="Trial Subscriptions",
+                    category="billing",
+                    icon="clock",
+                    description="Subscriptions currently in trial period",
+                ),
+            ]
+        except Exception as e:
+            logger.warning(f"Failed to get billing platform metrics: {e}")
+            return []
+
+
+# Singleton instance
+billing_metrics_provider = BillingMetricsProvider()
+
+__all__ = ["BillingMetricsProvider", "billing_metrics_provider"]

app/modules/monitoring/models/__init__.py

@@ -2,11 +2,10 @@
 """
 Monitoring module database models.
 
-Re-exports monitoring-related models from their source locations.
+Provides monitoring-related models including capacity snapshots.
 """
 
-# CapacitySnapshot is in billing module (tracks system capacity over time)
+from app.modules.monitoring.models.capacity_snapshot import CapacitySnapshot
-from app.modules.billing.models import CapacitySnapshot
 
 # Admin notification and logging models
 from app.modules.messaging.models import AdminNotification

app/modules/monitoring/models/capacity_snapshot.py

@@ -0,0 +1,71 @@
+# app/modules/monitoring/models/capacity_snapshot.py
+"""
+Capacity snapshot model for platform capacity monitoring.
+
+Stores daily snapshots of platform metrics for growth trending and capacity forecasting.
+"""
+
+from sqlalchemy import (
+    Column,
+    DateTime,
+    Index,
+    Integer,
+    Numeric,
+)
+from sqlalchemy.dialects.sqlite import JSON
+
+from app.core.database import Base
+from models.database.base import TimestampMixin
+
+
+class CapacitySnapshot(Base, TimestampMixin):
+    """
+    Daily snapshot of platform capacity metrics.
+
+    Used for growth trending and capacity forecasting.
+    Captured daily by background job.
+    """
+
+    __tablename__ = "capacity_snapshots"
+
+    id = Column(Integer, primary_key=True, index=True)
+    snapshot_date = Column(DateTime(timezone=True), nullable=False, unique=True, index=True)
+
+    # Store metrics
+    total_stores = Column(Integer, default=0, nullable=False)
+    active_stores = Column(Integer, default=0, nullable=False)
+    trial_stores = Column(Integer, default=0, nullable=False)
+
+    # Subscription metrics
+    total_subscriptions = Column(Integer, default=0, nullable=False)
+    active_subscriptions = Column(Integer, default=0, nullable=False)
+
+    # Resource metrics
+    total_products = Column(Integer, default=0, nullable=False)
+    total_orders_month = Column(Integer, default=0, nullable=False)
+    total_team_members = Column(Integer, default=0, nullable=False)
+
+    # Storage metrics
+    storage_used_gb = Column(Numeric(10, 2), default=0, nullable=False)
+    db_size_mb = Column(Numeric(10, 2), default=0, nullable=False)
+
+    # Capacity metrics (theoretical limits from subscriptions)
+    theoretical_products_limit = Column(Integer, nullable=True)
+    theoretical_orders_limit = Column(Integer, nullable=True)
+    theoretical_team_limit = Column(Integer, nullable=True)
+
+    # Tier distribution (JSON: {"essential": 10, "professional": 5, ...})
+    tier_distribution = Column(JSON, nullable=True)
+
+    # Performance metrics
+    avg_response_ms = Column(Integer, nullable=True)
+    peak_cpu_percent = Column(Numeric(5, 2), nullable=True)
+    peak_memory_percent = Column(Numeric(5, 2), nullable=True)
+
+    # Indexes
+    __table_args__ = (
+        Index("ix_capacity_snapshots_date", "snapshot_date"),
+    )
+
+    def __repr__(self) -> str:
+        return f"<CapacitySnapshot(date={self.snapshot_date}, stores={self.total_stores})>"

app/modules/monitoring/routes/api/admin_platform_health.py

@@ -172,7 +172,7 @@ async def get_growth_trends(
 
     Returns growth rates and projections for key metrics.
     """
-    from app.modules.billing.services.capacity_forecast_service import (
+    from app.modules.monitoring.services.capacity_forecast_service import (
         capacity_forecast_service,
     )
 
@@ -189,7 +189,7 @@ async def get_scaling_recommendations(
 
     Returns prioritized list of recommendations.
     """
-    from app.modules.billing.services.capacity_forecast_service import (
+    from app.modules.monitoring.services.capacity_forecast_service import (
         capacity_forecast_service,
     )
 
@@ -206,7 +206,7 @@ async def capture_snapshot(
 
     Normally run automatically by daily background job.
     """
-    from app.modules.billing.services.capacity_forecast_service import (
+    from app.modules.monitoring.services.capacity_forecast_service import (
         capacity_forecast_service,
     )
 

app/modules/monitoring/services/__init__.py

@@ -9,6 +9,10 @@ from app.modules.monitoring.services.admin_audit_service import (
     AdminAuditService,
     admin_audit_service,
 )
+from app.modules.monitoring.services.capacity_forecast_service import (
+    CapacityForecastService,
+    capacity_forecast_service,
+)
 from app.modules.monitoring.services.background_tasks_service import (
     BackgroundTasksService,
     background_tasks_service,
@@ -25,6 +29,8 @@ from app.modules.monitoring.services.platform_health_service import (
 __all__ = [
     "admin_audit_service",
     "AdminAuditService",
+    "capacity_forecast_service",
+    "CapacityForecastService",
     "background_tasks_service",
     "BackgroundTasksService",
     "log_service",

app/modules/monitoring/services/capacity_forecast_service.py

@@ -1,4 +1,4 @@
-# app/modules/billing/services/capacity_forecast_service.py
+# app/modules/monitoring/services/capacity_forecast_service.py
 """
 Capacity forecasting service for growth trends and scaling recommendations.
 
@@ -16,13 +16,9 @@ from decimal import Decimal
 from sqlalchemy import func
 from sqlalchemy.orm import Session
 
-from app.modules.billing.models import (
-    CapacitySnapshot,
-    MerchantSubscription,
-    SubscriptionStatus,
-)
 from app.modules.contracts.metrics import MetricsContext
 from app.modules.core.services.stats_aggregator import stats_aggregator
+from app.modules.monitoring.models.capacity_snapshot import CapacitySnapshot
 from app.modules.tenancy.models import Platform, Store, StoreUser
 
 logger = logging.getLogger(__name__)
@@ -75,22 +71,7 @@ class CapacityForecastService:
             or 0
         )
 
-        # Subscription metrics
+        # Resource metrics via provider pattern (avoids cross-module imports)
-        total_subs = db.query(func.count(MerchantSubscription.id)).scalar() or 0
-        active_subs = (
-            db.query(func.count(MerchantSubscription.id))
-            .filter(MerchantSubscription.status.in_(["active", "trial"]))
-            .scalar()
-            or 0
-        )
-        trial_stores = (
-            db.query(func.count(MerchantSubscription.id))
-            .filter(MerchantSubscription.status == SubscriptionStatus.TRIAL.value)
-            .scalar()
-            or 0
-        )
-
-        # Resource metrics via provider pattern (avoids direct catalog/orders imports)
         start_of_month = now.replace(day=1, hour=0, minute=0, second=0, microsecond=0)
         platform = db.query(Platform).first()
         platform_id = platform.id if platform else 1
@@ -100,6 +81,11 @@ class CapacityForecastService:
             context=MetricsContext(date_from=start_of_month),
         )
 
+        # Subscription metrics via stats aggregator (avoids billing → monitoring violation)
+        total_subs = stats.get("billing.total_subscriptions", 0)
+        active_subs = stats.get("billing.active_subscriptions", 0)
+        trial_stores = stats.get("billing.trial_subscriptions", 0)
+
         total_products = stats.get("catalog.total_products", 0)
         total_team = (
             db.query(func.count(StoreUser.id))

app/modules/monitoring/tasks/capacity.py

@@ -27,7 +27,7 @@ def capture_capacity_snapshot(self):
     Returns:
         dict: Snapshot summary with store and product counts.
     """
-    from app.modules.billing.services.capacity_forecast_service import (
+    from app.modules.monitoring.services.capacity_forecast_service import (
         capacity_forecast_service,
     )
 

app/modules/monitoring/tests/unit/test_capacity_forecast_service.py

@@ -1,4 +1,4 @@
-# tests/unit/services/test_capacity_forecast_service.py
+# app/modules/monitoring/tests/unit/test_capacity_forecast_service.py
 """
 Unit tests for CapacityForecastService.
 
@@ -14,8 +14,8 @@ from decimal import Decimal
 
 import pytest
 
-from app.modules.billing.models import CapacitySnapshot
+from app.modules.monitoring.models import CapacitySnapshot
-from app.modules.billing.services.capacity_forecast_service import (
+from app.modules.monitoring.services.capacity_forecast_service import (
     INFRASTRUCTURE_SCALING,
     CapacityForecastService,
     capacity_forecast_service,

tests/unit/middleware/test_platform_context.py

@@ -312,7 +312,10 @@ class TestPlatformContextManager:
     def test_get_platform_from_domain_not_found(self):
         """Test domain lookup when platform not found."""
         mock_db = Mock(spec=Session)
-        mock_db.query.return_value.filter.return_value.filter.return_value.first.return_value = None
+        # Ensure all query chain variants return None for .first()
+        query_mock = mock_db.query.return_value
+        query_mock.filter.return_value.first.return_value = None
+        query_mock.filter.return_value.filter.return_value.first.return_value = None
 
         context = {"detection_method": "domain", "domain": "unknown.lu"}
 
@@ -367,8 +370,11 @@ class TestPlatformContextManager:
     def test_get_platform_inactive_not_returned(self):
         """Test that inactive platforms are not returned."""
         mock_db = Mock(spec=Session)
-        # First call returns None (is_active filter excludes it)
+        # Ensure all query chain variants return None for .first()
-        mock_db.query.return_value.filter.return_value.filter.return_value.first.return_value = None
+        # (primary Platform lookup and StoreDomain/MerchantDomain fallbacks)
+        query_mock = mock_db.query.return_value
+        query_mock.filter.return_value.first.return_value = None
+        query_mock.filter.return_value.filter.return_value.first.return_value = None
 
         context = {"detection_method": "domain", "domain": "inactive.lu"}
 

tests/unit/middleware/test_store_context.py

@@ -245,7 +245,13 @@ class TestStoreContextManager:
     def test_get_store_from_custom_domain_not_found(self):
         """Test custom domain not found in database."""
         mock_db = Mock(spec=Session)
-        mock_db.query.return_value.filter.return_value.filter.return_value.filter.return_value.first.return_value = None
+        # Ensure all query chain variants return None for .first()
+        # (primary StoreDomain lookup and MerchantDomain fallback)
+        query_mock = mock_db.query.return_value
+        query_mock.filter.return_value.first.return_value = None
+        query_mock.filter.return_value.filter.return_value.first.return_value = None
+        query_mock.filter.return_value.filter.return_value.filter.return_value.first.return_value = None
+        query_mock.filter.return_value.order_by.return_value.first.return_value = None
 
         context = {"detection_method": "custom_domain", "domain": "nonexistent.com"}