From 77b485d619e79fa59994a07909c78de4ff023590 Mon Sep 17 00:00:00 2001
From: Sameh Khamis <sameh@halfpixel.ai>
Date: Sat, 24 Oct 2026 21:10:12 -0700
Subject: [PATCH] fix(ais): refresh changed static metadata without advancing
 position

---
 changelog.d/1351-ais-static-keeps-motion.md |   3 +
 docs/CURRENT-STATE.md                       |   8 +
 server/providers/vessels/ais-store.js       |  60 ++++++--
 src/data/aisStreamSentinels.test.mjs        | 159 ++++++++++++++++++++
 4 files changed, 220 insertions(+), 10 deletions(-)

diff --git a/changelog.d/1351-ais-static-keeps-motion.md b/changelog.d/1351-ais-static-keeps-motion.md
index 78b0804f7..52dd9bede 100644
--- a/changelog.d/1351-ais-static-keeps-motion.md
+++ b/changelog.d/1351-ais-static-keeps-motion.md
@@ -1,3 +1,6 @@
 - Keep a tracked vessel's speed, course, heading and fix time when AISStream
   static data arrives; the static message only merges name, type, destination
   and IMO (rudycelekli, #1351).
+- Apply changed static metadata immediately, retaining known fields when a
+  later static report omits them, without refreshing the vessel's position
+  (samehkhamis, #1351).
diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index ede889fdc..282181df3 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -459,6 +459,14 @@ than a reading. Heading keeps its existing separate check for its own sentinel.
 Genuine readings are unchanged, including a stopped vessel's zero and the
 highest speed and course the fields can encode.
 
+For an already tracked vessel, AISStream static messages update name, type,
+destination and IMO without changing its position, motion, fix timestamps,
+position freshness or trail. Non-empty static values replace earlier values;
+omitted, empty or unavailable fields retain known metadata across Class B's
+separate reports and in the cache used by the next position update. Position
+reports still prefer their own metadata name. Invalid Class B parts are ignored;
+absent fields prefer the latest live value over the static cache.
+
 Native `<select>` controls declare a dark colour scheme and explicit option
 colours, so the browser-painted option list matches the panel it drops out of.
 The scheme is declared on the controls rather than on the document root, so
diff --git a/server/providers/vessels/ais-store.js b/server/providers/vessels/ais-store.js
index a456e19f4..71cefceed 100644
--- a/server/providers/vessels/ais-store.js
+++ b/server/providers/vessels/ais-store.js
@@ -43,11 +43,47 @@ export function ingestAisStreamEnvelope(envelope) {
   if (!mmsi) return false;
 
   if (messageType === 'ShipStaticData' || messageType === 'StaticDataReport') {
+    const previous = _aisStreamStatic.get(mmsi) || {};
+    const live = _aisStreamVessels.get(mmsi);
+    const liveName = live?.name === `MMSI ${mmsi}` ? '' : live?.name;
+    const fields =
+      messageType === 'StaticDataReport'
+        ? {
+            Name:
+              message.ReportA?.Valid === false
+                ? undefined
+                : message.ReportA?.Name,
+            Type:
+              message.ReportB?.Valid === false
+                ? undefined
+                : message.ReportB?.ShipType,
+          }
+        : message;
+    // Static reports may be partial (including Class B's separate A/B parts).
+    // Keep known values in the cache as well as in the current live row.
     const staticData = {
-      name: vesselNameFromAis(metadata, message, _aisStreamStatic.get(mmsi)),
-      type: vesselTypeFromAis(message, _aisStreamStatic.get(mmsi)),
-      destination: stringValue(message.Destination),
-      imo: stringValue(message.ImoNumber ?? message.IMO),
+      // The envelope repeats a cached name even on Class B's type-only part.
+      // Only an actual static name report replaces a known live name.
+      name:
+        stringValue(fields.Name ?? fields.ShipName) ||
+        liveName ||
+        previous.name ||
+        stringValue(metadata.ShipName),
+      type:
+        staticCode(fields.Type ?? fields.ShipType) ||
+        staticCode(live?.type) ||
+        staticCode(previous.type) ||
+        '',
+      destination:
+        stringValue(fields.Destination) ||
+        live?.destination ||
+        previous.destination ||
+        '',
+      imo:
+        staticCode(fields.ImoNumber ?? fields.IMO) ||
+        staticCode(live?.imo) ||
+        staticCode(previous.imo) ||
+        '',
     };
     _aisStreamStatic.set(mmsi, staticData);
     mergeAisStaticIntoLiveVessel(mmsi, staticData);
@@ -196,12 +232,10 @@ function approxMetersBetween(lat1, lon1, lat2, lon2) {
 function mergeAisStaticIntoLiveVessel(mmsi, staticData) {
   const existing = _aisStreamVessels.get(mmsi);
   if (!existing) return;
-  if (staticData.name && (!existing.name || existing.name === `MMSI ${mmsi}`))
-    existing.name = staticData.name;
-  if (staticData.type && !existing.type) existing.type = staticData.type;
-  if (staticData.destination && !existing.destination)
-    existing.destination = staticData.destination;
-  if (staticData.imo && !existing.imo) existing.imo = staticData.imo;
+  if (staticData.name) existing.name = staticData.name;
+  if (staticData.type) existing.type = staticData.type;
+  if (staticData.destination) existing.destination = staticData.destination;
+  if (staticData.imo) existing.imo = staticData.imo;
 }
 
 function vesselNameFromAis(metadata, message, staticData = {}) {
@@ -271,6 +305,12 @@ function stringValue(value) {
   return String(value).trim();
 }
 
+// AIS uses zero for unavailable ship type and IMO, not as a replacement value.
+function staticCode(value) {
+  const number = numberValue(value);
+  return Number.isInteger(number) && number > 0 ? String(number) : '';
+}
+
 function numberValue(value) {
   if (value === null || value === undefined || value === '') return null;
   const number = Number(value);
diff --git a/src/data/aisStreamSentinels.test.mjs b/src/data/aisStreamSentinels.test.mjs
index 49572c05d..5ca3375f7 100644
--- a/src/data/aisStreamSentinels.test.mjs
+++ b/src/data/aisStreamSentinels.test.mjs
@@ -1,8 +1,10 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import {
+  AISSTREAM_STALE_MS,
   aisStreamRows,
   ingestAisStreamEnvelope,
+  readAisTrack,
 } from '../../server/providers/vessels/ais-store.js';
 
 // ITU-R M.1371 encodes speed over ground in 0.1-knot units and course over
@@ -99,3 +101,160 @@ test('a static data report keeps the motion and fix time of a tracked vessel', (
   assert.equal(row.destination, 'ROTTERDAM');
   assert.equal(row.imo, '9876543');
 });
+
+// AISStream carries both Class B parts; the unused part has Valid: false.
+const classBStatic = (part, value) => ({
+  MessageID: 24,
+  RepeatIndicator: 0,
+  Valid: true,
+  Reserved: 0,
+  PartNumber: part === 'B',
+  ReportA: { Valid: part === 'A', Name: part === 'A' ? value : '' },
+  ReportB: {
+    Valid: part === 'B',
+    ShipType: part === 'B' ? value : 0,
+    VendorIDName: '',
+    VenderIDModel: 0,
+    VenderIDSerial: 0,
+    CallSign: '',
+    Dimension: { A: 0, B: 0, C: 0, D: 0 },
+    FixType: 0,
+    Spare: 0,
+  },
+});
+
+for (const [index, scenario] of [
+  {
+    type: 'ShipStaticData',
+    initial: [
+      {
+        Name: 'OLD VESSEL',
+        Type: 70,
+        Destination: 'ROTTERDAM',
+        ImoNumber: 9876543,
+      },
+    ],
+    updates: [
+      {
+        Name: 'NEW VESSEL',
+        Type: 80,
+        Destination: 'HAMBURG',
+        ImoNumber: 9876544,
+      },
+    ],
+    empty: { Name: ' ', Type: 0, Destination: '', ImoNumber: 0 },
+    expected: {
+      name: 'NEW VESSEL',
+      type: '80',
+      destination: 'HAMBURG',
+      imo: '9876544',
+    },
+  },
+  {
+    type: 'StaticDataReport',
+    initial: [classBStatic('A', 'OLD VESSEL'), classBStatic('B', 36)],
+    updates: [classBStatic('A', 'NEW VESSEL'), classBStatic('B', 37)],
+    empty: classBStatic('A', ''),
+    expected: { name: 'NEW VESSEL', type: '37', destination: '', imo: '' },
+  },
+].entries()) {
+  test(`${scenario.type} replaces static fields without inventing a position fix`, (t) => {
+    const mmsi = String(244690100 + index);
+    const start = Date.parse('2026-09-17T20:00:00Z');
+    let now = start;
+    t.mock.method(Date, 'now', () => now);
+    const position = (
+      lat,
+      body = { Sog: 12.4, Cog: 86.7, TrueHeading: 87 },
+    ) => {
+      const envelope = positionReport(mmsi, body);
+      Object.assign(envelope.MetaData, {
+        latitude: lat,
+        time_utc: new Date(now).toISOString(),
+      });
+      return ingestAisStreamEnvelope(envelope);
+    };
+    const sendStatic = (body) =>
+      ingestAisStreamEnvelope({
+        MessageType: scenario.type,
+        Message: { [scenario.type]: { UserID: Number(mmsi), ...body } },
+        MetaData: {
+          MMSI: mmsi,
+          ShipName: 'STALE HEADER',
+          latitude: 54,
+          longitude: 7,
+          time_utc: new Date(now).toISOString(),
+        },
+      });
+    position(53.40879);
+    for (const body of scenario.initial) assert.equal(sendStatic(body), true);
+    now += 60_000;
+    position(53.41879);
+    const before = rowFor(mmsi);
+    const track = readAisTrack(mmsi);
+    assert.equal(track.length, 2);
+
+    now += 5 * 60_000;
+    for (const body of scenario.updates) assert.equal(sendStatic(body), true);
+    assert.deepEqual(rowFor(mmsi), { ...before, ...scenario.expected });
+    assert.deepEqual(readAisTrack(mmsi), track);
+
+    // Empty or omitted static fields must not erase known metadata, including
+    // the cached values used when the next actual position arrives.
+    assert.equal(sendStatic(scenario.empty), true);
+    assert.deepEqual(rowFor(mmsi), { ...before, ...scenario.expected });
+    assert.deepEqual(readAisTrack(mmsi), track);
+    if (scenario.type === 'StaticDataReport') {
+      sendStatic({
+        ...classBStatic('A', ''),
+        ReportA: { Valid: false, Name: 'INVALID NAME' },
+        ReportB: { ...classBStatic('B', 99).ReportB, Valid: false },
+      });
+      assert.deepEqual(rowFor(mmsi), { ...before, ...scenario.expected });
+    }
+    now = start + 60_000 + AISSTREAM_STALE_MS + 1;
+    assert.equal(
+      rowFor(mmsi),
+      undefined,
+      'static traffic must not renew position freshness',
+    );
+    position(53.42879, { Sog: 0, Cog: 0, TrueHeading: 0 });
+    const next = rowFor(mmsi);
+    for (const [key, value] of Object.entries(scenario.expected))
+      assert.equal(next[key], value, key);
+    assert.equal(next.speed, 0);
+    assert.equal(next.course, 0);
+    assert.equal(next.heading, 0);
+    assert.equal(next.last_position_epoch, Math.floor(now / 1000));
+    assert.equal(readAisTrack(mmsi).length, 3);
+  });
+}
+
+test('partial static data keeps newer live metadata ahead of the old static cache', () => {
+  const mmsi = '244690200';
+  const staticReport = (body) => ({
+    MessageType: 'ShipStaticData',
+    Message: { ShipStaticData: { UserID: Number(mmsi), ...body } },
+    MetaData: { MMSI: mmsi },
+  });
+  ingestAisStreamEnvelope(staticReport({ Name: 'OLD VESSEL', Type: 70 }));
+  const extended = positionReport(mmsi, {});
+  extended.MessageType = 'ExtendedClassBPositionReport';
+  extended.Message = {
+    ExtendedClassBPositionReport: {
+      UserID: Number(mmsi),
+      Type: 80,
+      Sog: 12,
+      Cog: 86,
+    },
+  };
+  extended.MetaData.ShipName = 'NEW VESSEL';
+  ingestAisStreamEnvelope(extended);
+  const before = rowFor(mmsi);
+  ingestAisStreamEnvelope(staticReport({ Destination: 'HAMBURG' }));
+  assert.deepEqual(rowFor(mmsi), { ...before, destination: 'HAMBURG' });
+  ingestAisStreamEnvelope(positionReport(mmsi, { Sog: 12, Cog: 86 }));
+  assert.equal(rowFor(mmsi).name, 'NEW VESSEL');
+  assert.equal(rowFor(mmsi).type, '80');
+  assert.equal(rowFor(mmsi).destination, 'HAMBURG');
+});