fix: Add modality input validation and replace DSC hardcoded string with proper dict

[Devguru-codes]

Fixes two related modality processing issues that degrade API reliability. Fixes #35

Fix 1: Modality Input Validation (reports.py)

+    try:
+        parsed_modality = ModalityTypeValues(modality) if modality else ModalityTypeValues.ASL
+    except ValueError:
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+            detail=f"Invalid modality '{modality}'. Accepted values: {[m.value for m in ModalityTypeValues]}"
+        )
+
     data = {
-        "modality": ModalityTypeValues(modality) if modality else ModalityTypeValues.ASL,
+        "modality": parsed_modality,

Applied to both BIDS and DICOM endpoints. DICOM endpoint reordered to validate modality before file check.

Fix 2: DSCProcessor Placeholder (processor.py)

-    def process(self) -> str:
-        print("Processing DSC data...")
-        return "dsc data"
+    def process(self) -> dict:
+        return {
+            "status": "not_implemented",
+            "message": "DSC processing is not yet implemented.",
+            "modality": "DSC",
+            "asl_parameters": [],
+            "report": []
+        }

Files Changed

• apps/backend/app/routers/reports.py
• package/src/pyaslreport/modalities/testdsc/processor.py

---

API Endpoint Responses Comparison

main branch (before fix)

POST /api/report/process/bids modality=xyz   → Status: 500 (unhandled ValueError)
POST /api/report/process/dicom modality=INVALID → Status: 400 (file check ran first, modality never validated)
DSCProcessor.process() → 'dsc data' (string)

Modality_Validation branch (after fix)

POST /api/report/process/bids modality=xyz   → Status: 422, Body: {"detail": "Invalid modality 'xyz'. Accepted values: ['ASL', 'DCE', 'DSC']"}
POST /api/report/process/dicom modality=INVALID → Status: 422, Body: {"detail": "Invalid modality 'INVALID'. Accepted values: ['ASL', 'DCE', 'DSC']"}
DSCProcessor.process() → {"status": "not_implemented", "message": "DSC processing is not yet implemented.", ...}

---

Python Test Suite Results

main branch (before fix)

#	Test	Status	Detail
T1	Valid modality 'ASL' accepted	PASS
T2	Invalid modality 'xyz' → 422	FAIL	Status=500
T3	Invalid modality 'INVALID' on /dicom → 422	FAIL	Status=400
T4	No modality defaults to ASL	PASS
T5	DSCProcessor returns dict	FAIL	Got string

Summary: PASSED=2 FAILED=3

Modality_Validation branch (after fix)

#	Test	Status	Detail
T1	Valid modality 'ASL' accepted	PASS
T2	Invalid modality 'xyz' → 422	PASS
T3	Invalid modality 'INVALID' on /dicom → 422	PASS
T4	No modality defaults to ASL	PASS
T5	DSCProcessor returns dict	PASS

Summary: PASSED=5 FAILED=0