Return empty series instead of an HTTP 500 when compute_node_series has no observations

api/requirements-dev.txt

@@ -2,3 +2,4 @@ isort==5.13.2
 black==24.4.2
 debugpy==1.8.2
 epdb
+pytest==8.2.2

api/swotvis/app/routers/data/router.py

@@ -36,9 +36,17 @@ async def compute_node_series(data: List[List[SwotNodeDataModel]]):
     # from HydroCron.
     series = SwotNodeDataSeriesModel(all_series=data)
 
+    df = series.as_dataframe()
+
+    # With no observations to summarize, the dataframe has no node-variable
+    # columns and the selection below raises a KeyError -> HTTP 500. Return
+    # empty series in that case instead.
+    if df.empty:
+        return {"median": [], "q0.25": [], "q0.75": []}
+
     # group all data by p_dist_out and remove all columns except
     # those corresponding to node variables
-    grouped = series.as_dataframe()[NodeVariables.list()].groupby("p_dist_out")
+    grouped = df[NodeVariables.list()].groupby("p_dist_out")
 
     # Compute node-level statistics. Replace np.nan with None because np.nan
     # is not JSON serializable. Convert all pandas dataframes to dictionaries

api/swotvis/tests/test_compute_node_series.py

@@ -0,0 +1,80 @@
+"""Tests for the /data/compute_node_series statistics endpoint.
+
+Run with the repo's `make test` target (docker compose exec api pytest tests),
+or directly from the api/swotvis directory with `PYTHONPATH=. pytest tests`.
+"""
+
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+from app.routers.data import router as data_router
+
+
+def _client():
+    app = FastAPI()
+    app.include_router(data_router, prefix="/data")
+    return TestClient(app, raise_server_exceptions=False)
+
+
+def _observation(p_dist_out, wse, width, area_total, time_str):
+    return {
+        "time_str": time_str,
+        "node_q": 1,
+        "p_dist_out": p_dist_out,
+        "wse": wse,
+        "width": width,
+        "area_total": area_total,
+        "wse_units": "m",
+        "width_units": "m",
+        "area_total_units": "m^2",
+        "p_dist_out_units": "m",
+        "datetime": time_str,
+    }
+
+
+def test_compute_node_series_summarizes_observations_by_distance():
+    client = _client()
+    # Two observations at p_dist_out=100 (wse 10 and 20) and one at 200.
+    data = [
+        [
+            _observation(100.0, 10.0, 50.0, 500.0, "2024-01-01T00:00:00Z"),
+            _observation(100.0, 20.0, 60.0, 600.0, "2024-01-08T00:00:00Z"),
+            _observation(200.0, 30.0, 70.0, 700.0, "2024-01-01T00:00:00Z"),
+        ]
+    ]
+
+    response = client.post("/data/compute_node_series", json=data)
+
+    assert response.status_code == 200
+    body = response.json()
+    assert set(body.keys()) == {"median", "q0.25", "q0.75"}
+
+    median = {row["p_dist_out"]: row for row in body["median"]}
+    assert median[100.0]["wse"] == 15.0
+    assert median[100.0]["width"] == 55.0
+    assert median[200.0]["wse"] == 30.0
+
+    q25 = {row["p_dist_out"]: row for row in body["q0.25"]}
+    q75 = {row["p_dist_out"]: row for row in body["q0.75"]}
+    assert q25[100.0]["wse"] == 12.5
+    assert q75[100.0]["wse"] == 17.5
+
+
+def test_compute_node_series_empty_body_returns_empty_series():
+    # Regression: an empty request body used to raise a KeyError -> HTTP 500.
+    client = _client()
+
+    response = client.post("/data/compute_node_series", json=[])
+
+    assert response.status_code == 200
+    assert response.json() == {"median": [], "q0.25": [], "q0.75": []}
+
+
+def test_compute_node_series_series_without_observations_returns_empty_series():
+    # Regression: a series carrying no observations used to raise a 500 too.
+    client = _client()
+
+    response = client.post("/data/compute_node_series", json=[[]])
+
+    assert response.status_code == 200
+    assert response.json() == {"median": [], "q0.25": [], "q0.75": []}