feat(P8.3): milestone preflight endpoint for freeze/start button pre-condition checks

app/api/routers/milestone_actions.py

@@ -53,6 +53,90 @@ class CloseBody(BaseModel):
     reason: Optional[str] = None
 
 
+# ---------------------------------------------------------------------------
+# GET /preflight  — lightweight pre-condition check for UI button states
+# ---------------------------------------------------------------------------
+
+@router.get("/preflight", status_code=200)
+def preflight_milestone_actions(
+    project_id: int,
+    milestone_id: int,
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user_or_apikey),
+):
+    """Return pre-condition check results for freeze / start actions.
+
+    The frontend uses this to decide whether to *disable* buttons and what
+    hint text to show.  This endpoint never mutates data.
+    """
+    check_project_role(db, current_user.id, project_id, min_role="viewer")
+    ms = _get_milestone_or_404(db, project_id, milestone_id)
+    ms_status = _ms_status_value(ms)
+
+    result: dict = {"status": ms_status, "freeze": None, "start": None}
+
+    # --- freeze pre-check (only meaningful when status == open) ---
+    if ms_status == "open":
+        release_tasks = (
+            db.query(Task)
+            .filter(
+                Task.milestone_id == milestone_id,
+                Task.task_type == "maintenance",
+                Task.task_subtype == "release",
+            )
+            .all()
+        )
+        if len(release_tasks) == 0:
+            result["freeze"] = {
+                "allowed": False,
+                "reason": "No maintenance/release task found. Create one before freezing.",
+            }
+        elif len(release_tasks) > 1:
+            result["freeze"] = {
+                "allowed": False,
+                "reason": f"Found {len(release_tasks)} maintenance/release tasks — expected exactly 1.",
+            }
+        else:
+            result["freeze"] = {"allowed": True, "reason": None}
+
+    # --- start pre-check (only meaningful when status == freeze) ---
+    if ms_status == "freeze":
+        blockers: list[str] = []
+
+        # milestone dependencies
+        dep_ms_ids = []
+        if ms.depend_on_milestones:
+            try:
+                dep_ms_ids = json.loads(ms.depend_on_milestones)
+            except (json.JSONDecodeError, TypeError):
+                dep_ms_ids = []
+        if dep_ms_ids:
+            dep_milestones = db.query(Milestone).filter(Milestone.id.in_(dep_ms_ids)).all()
+            incomplete = [m.id for m in dep_milestones if _ms_status_value(m) != "completed"]
+            if incomplete:
+                blockers.append(f"Dependent milestones not completed: {incomplete}")
+
+        # task dependencies
+        dep_task_ids = []
+        if ms.depend_on_tasks:
+            try:
+                dep_task_ids = json.loads(ms.depend_on_tasks)
+            except (json.JSONDecodeError, TypeError):
+                dep_task_ids = []
+        if dep_task_ids:
+            dep_tasks = db.query(Task).filter(Task.id.in_(dep_task_ids)).all()
+            incomplete_tasks = [t.id for t in dep_tasks if (t.status.value if hasattr(t.status, "value") else t.status) != "completed"]
+            if incomplete_tasks:
+                blockers.append(f"Dependent tasks not completed: {incomplete_tasks}")
+
+        if blockers:
+            result["start"] = {"allowed": False, "reason": "; ".join(blockers)}
+        else:
+            result["start"] = {"allowed": True, "reason": None}
+
+    return result
+
+
 # ---------------------------------------------------------------------------
 # POST /freeze
 # ---------------------------------------------------------------------------