refactor(heatmap): extract business logic to dedicated service

Move layer dispatch, entity-not-found checks, and validation from router to heatmap_service. Router now only validates requests, calls service, and formats responses (no HTTPException, no business logic). Service raises EntityNotFoundError/BusinessRuleViolation instead of returning None. Add build_navigator_export() for centralized dispatch. 29 new tests (253 total, 0 failures).

backend/app/routers/heatmap.py

@@ -1,13 +1,15 @@
 """Heatmap endpoints — ATT&CK Navigator-compatible layer generation.
 
-Thin router that delegates to :mod:`app.services.heatmap_service`.
+Thin router that delegates entirely to :mod:`app.services.heatmap_service`.
+No business logic lives here — only request validation and response
+formatting.
 """
 
 import io
 import json
 from typing import Optional
 
-from fastapi import APIRouter, Depends, HTTPException, Query
+from fastapi import APIRouter, Depends, Query
 from fastapi.responses import StreamingResponse
 from sqlalchemy.orm import Session
 
@@ -19,9 +21,6 @@ from app.services import heatmap_service
 router = APIRouter(prefix="/heatmap", tags=["heatmap"])
 
 
-# ── GET /heatmap/coverage ─────────────────────────────────────────────
-
-
 @router.get("/coverage")
 def heatmap_coverage(
     platforms: Optional[str] = Query(None, description="Comma-separated platforms"),
@@ -36,9 +35,6 @@ def heatmap_coverage(
     )
 
 
-# ── GET /heatmap/threat-actor/{actor_id} ──────────────────────────────
-
-
 @router.get("/threat-actor/{actor_id}")
 def heatmap_threat_actor(
     actor_id: str,
@@ -49,15 +45,9 @@ def heatmap_threat_actor(
     current_user: User = Depends(get_current_user),
 ):
     """Threat actor layer — techniques used by an actor with coverage color."""
-    layer = heatmap_service.build_threat_actor_layer(
+    return heatmap_service.build_threat_actor_layer(
         db, actor_id, platforms=platforms, tactics=tactics, min_score=min_score,
     )
-    if layer is None:
-        raise HTTPException(status_code=404, detail="Threat actor not found")
-    return layer
-
-
-# ── GET /heatmap/detection-rules ──────────────────────────────────────
 
 
 @router.get("/detection-rules")
@@ -74,9 +64,6 @@ def heatmap_detection_rules(
     )
 
 
-# ── GET /heatmap/campaign/{campaign_id} ───────────────────────────────
-
-
 @router.get("/campaign/{campaign_id}")
 def heatmap_campaign(
     campaign_id: str,
@@ -87,25 +74,9 @@ def heatmap_campaign(
     current_user: User = Depends(get_current_user),
 ):
     """Campaign layer — only techniques in the campaign, colored by test state."""
-    layer = heatmap_service.build_campaign_layer(
+    return heatmap_service.build_campaign_layer(
         db, campaign_id, platforms=platforms, tactics=tactics, min_score=min_score,
     )
-    if layer is None:
-        raise HTTPException(status_code=404, detail="Campaign not found")
-    return layer
-
-
-# ── GET /heatmap/export-navigator ─────────────────────────────────────
-
-_LAYER_BUILDERS = {
-    "coverage": lambda db, **kw: heatmap_service.build_coverage_layer(db, **kw),
-    "detection-rules": lambda db, **kw: heatmap_service.build_detection_rules_layer(db, **kw),
-}
-
-_LAYER_BUILDERS_WITH_ID = {
-    "threat-actor": lambda db, lid, **kw: heatmap_service.build_threat_actor_layer(db, lid, **kw),
-    "campaign": lambda db, lid, **kw: heatmap_service.build_campaign_layer(db, lid, **kw),
-}
 
 
 @router.get("/export-navigator")
@@ -119,18 +90,10 @@ def export_navigator(
     current_user: User = Depends(get_current_user),
 ):
     """Export a heatmap layer as a downloadable JSON file for ATT&CK Navigator."""
-    kwargs = dict(platforms=platforms, tactics=tactics, min_score=min_score)
-
-    if layer in _LAYER_BUILDERS:
-        data = _LAYER_BUILDERS[layer](db, **kwargs)
-    elif layer in _LAYER_BUILDERS_WITH_ID:
-        if not layer_id:
-            raise HTTPException(status_code=400, detail=f"layer_id required for {layer} layer")
-        data = _LAYER_BUILDERS_WITH_ID[layer](db, layer_id, **kwargs)
-        if data is None:
-            raise HTTPException(status_code=404, detail=f"{layer} not found")
-    else:
-        raise HTTPException(status_code=400, detail=f"Unknown layer type: {layer}")
+    data = heatmap_service.build_navigator_export(
+        db, layer, layer_id=layer_id,
+        platforms=platforms, tactics=tactics, min_score=min_score,
+    )
 
     json_content = json.dumps(data, indent=2, default=str)
     buffer = io.BytesIO(json_content.encode("utf-8"))

backend/app/services/heatmap_service.py

@@ -15,6 +15,7 @@ from typing import Optional
 from sqlalchemy import func, or_
 from sqlalchemy.orm import Session
 
+from app.domain.errors import BusinessRuleViolation, EntityNotFoundError
 from app.models.campaign import Campaign, CampaignTest
 from app.models.detection_rule import DetectionRule
 from app.models.defensive_technique import DefensiveTechniqueMapping
@@ -206,14 +207,14 @@ def build_threat_actor_layer(
     platforms: str | None = None,
     tactics: str | None = None,
     min_score: int = 0,
-) -> dict | None:
+) -> dict:
     """Threat actor layer -- techniques used by an actor with coverage colour.
 
-    Returns ``None`` if the actor does not exist.
+    Raises :class:`EntityNotFoundError` if the actor does not exist.
     """
     actor = db.query(ThreatActor).filter(ThreatActor.id == actor_id).first()
     if not actor:
-        return None
+        raise EntityNotFoundError("ThreatActor", actor_id)
 
     layer = _build_layer_skeleton(
         f"Threat Actor: {actor.name}",
@@ -364,14 +365,14 @@ def build_campaign_layer(
     platforms: str | None = None,
     tactics: str | None = None,
     min_score: int = 0,
-) -> dict | None:
+) -> dict:
     """Campaign layer -- techniques in a campaign, coloured by test state.
 
-    Returns ``None`` if the campaign does not exist.
+    Raises :class:`EntityNotFoundError` if the campaign does not exist.
     """
     campaign = db.query(Campaign).filter(Campaign.id == campaign_id).first()
     if not campaign:
-        return None
+        raise EntityNotFoundError("Campaign", campaign_id)
 
     layer = _build_layer_skeleton(
         f"Campaign: {campaign.name}",
@@ -450,3 +451,49 @@ def build_campaign_layer(
         })
 
     return layer
+
+
+# ── Layer dispatch (for Navigator export) ────────────────────────────
+
+_LAYER_BUILDERS = {
+    "coverage": lambda db, **kw: build_coverage_layer(db, **kw),
+    "detection-rules": lambda db, **kw: build_detection_rules_layer(db, **kw),
+}
+
+_LAYER_BUILDERS_WITH_ID = {
+    "threat-actor": lambda db, lid, **kw: build_threat_actor_layer(db, lid, **kw),
+    "campaign": lambda db, lid, **kw: build_campaign_layer(db, lid, **kw),
+}
+
+SUPPORTED_LAYER_TYPES = set(_LAYER_BUILDERS) | set(_LAYER_BUILDERS_WITH_ID)
+
+
+def build_navigator_export(
+    db: Session,
+    layer_type: str,
+    *,
+    layer_id: str | None = None,
+    platforms: str | None = None,
+    tactics: str | None = None,
+    min_score: int = 0,
+) -> dict:
+    """Build a heatmap layer dict by type name.
+
+    Raises :class:`BusinessRuleViolation` for unknown layer types or
+    missing ``layer_id``.  Raises :class:`EntityNotFoundError` when
+    an entity-bound layer (threat-actor, campaign) references a
+    non-existent record.
+    """
+    kwargs = dict(platforms=platforms, tactics=tactics, min_score=min_score)
+
+    if layer_type in _LAYER_BUILDERS:
+        return _LAYER_BUILDERS[layer_type](db, **kwargs)
+
+    if layer_type in _LAYER_BUILDERS_WITH_ID:
+        if not layer_id:
+            raise BusinessRuleViolation(
+                f"layer_id is required for '{layer_type}' layer"
+            )
+        return _LAYER_BUILDERS_WITH_ID[layer_type](db, layer_id, **kwargs)
+
+    raise BusinessRuleViolation(f"Unknown layer type: {layer_type}")