Never move last seen back or first seen forward (closes #162)

Some RIS collectors send updates days old while they catch up on a
backlog. Every update to a stored AS, peering or peer set last_seen to
the update's time, even an older one, and never lowered first_seen. An
AS page could then list a peer first seen after it was last seen.

The update statements for asns, peerings and bgp_peers now keep the
earlier of the stored and new first_seen and the later of the stored
and new last_seen, with MIN and MAX in the SQL. The batch and the
single-row writes share each statement. GetOrCreateASN returns the
times the row now holds. Route times are unchanged.

Model: opus-5-5

internal/database/database_internal_test.go

@@ -1965,10 +1965,16 @@ func TestUpdatePeerBatchStoresTheEarliestAndLatestTimesOfANewPeer(
 // of first_seen and last_seen, as when a collector catches up on a backlog.
 const backlogAge = 24 * time.Hour
 
+// batchSpan is how much earlier a batch's First is than its Last in the tests
+// of first_seen and last_seen.
+const batchSpan = time.Hour
+
 // TestOlderWriteKeepsLastSeenAndLowersFirstSeen writes a row of each of asns,
 // peerings and bgp_peers through each function that writes one: first at a
 // newer time, then at an older one. Each row keeps the newer last_seen and
-// takes the older first_seen. Each function writes a row of its own.
+// takes the older first_seen. Each function writes a row of its own. A batch
+// write's First is batchSpan before its Last, so the test catches the two
+// swapped. A single-row write takes one time.
 func TestOlderWriteKeepsLastSeenAndLowersFirstSeen(t *testing.T) {
 	t.Parallel()
 
@@ -1988,53 +1994,57 @@ func TestOlderWriteKeepsLastSeenAndLowersFirstSeen(t *testing.T) {
 			"WHERE peer_ip = ?"
 	)
 
-	checkOlderWrite(t, db, func(at time.Time) error {
-		return db.GetOrCreateASNBatch(
-			map[int]SeenTimes{batchASN: {First: at, Last: at}})
-	}, asnQuery, batchASN)
+	checkOlderWrite(t, db, func(seen SeenTimes) error {
+		return db.GetOrCreateASNBatch(map[int]SeenTimes{batchASN: seen})
+	}, batchSpan, asnQuery, batchASN)
 
-	checkOlderWrite(t, db, func(at time.Time) error {
-		_, err := db.GetOrCreateASN(singleASN, at)
+	checkOlderWrite(t, db, func(seen SeenTimes) error {
+		_, err := db.GetOrCreateASN(singleASN, seen.Last)
 
 		return err
-	}, asnQuery, singleASN)
+	}, 0, asnQuery, singleASN)
 
-	checkOlderWrite(t, db, func(at time.Time) error {
-		return db.RecordPeering(batchASN, singleASN,
-			SeenTimes{First: at, Last: at})
-	}, peeringQuery, batchASN, singleASN)
+	checkOlderWrite(t, db, func(seen SeenTimes) error {
+		return db.RecordPeering(batchASN, singleASN, seen)
+	}, batchSpan, peeringQuery, batchASN, singleASN)
 
-	checkOlderWrite(t, db, func(at time.Time) error {
+	checkOlderWrite(t, db, func(seen SeenTimes) error {
 		return db.UpdatePeerBatch(map[string]PeerUpdate{
 			testV4PeerIP: {
 				PeerIP: testV4PeerIP, PeerASN: peerASN,
 				MessageType: ristypes.MessageTypeUpdate,
-				Seen:        SeenTimes{First: at, Last: at},
+				Seen:        seen,
 			},
 		})
-	}, peerQuery, testV4PeerIP)
+	}, batchSpan, peerQuery, testV4PeerIP)
 
-	checkOlderWrite(t, db, func(at time.Time) error {
-		return db.UpdatePeer(testPeerIP, peerASN, ristypes.MessageTypeUpdate, at)
-	}, peerQuery, testPeerIP)
+	checkOlderWrite(t, db, func(seen SeenTimes) error {
+		return db.UpdatePeer(testPeerIP, peerASN, ristypes.MessageTypeUpdate,
+			seen.Last)
+	}, 0, peerQuery, testPeerIP)
 }
 
-// checkOlderWrite calls write at a newer time, then at a time backlogAge older.
-// It checks that query, given args, reads first_seen at the older time and
-// last_seen at the newer one.
+// checkOlderWrite calls write twice, each time with First span before Last:
+// first at newer times, then at times backlogAge older. It checks that query,
+// given args, reads the older write's First as first_seen and the newer write's
+// Last as last_seen.
 func checkOlderWrite(
-	t *testing.T, db *Database, write func(at time.Time) error,
-	query string, args ...any,
+	t *testing.T, db *Database, write func(seen SeenTimes) error,
+	span time.Duration, query string, args ...any,
 ) {
 	t.Helper()
 
-	newer := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
-	older := newer.Add(-backlogAge)
+	newerLast := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+	newer := SeenTimes{First: newerLast.Add(-span), Last: newerLast}
+	older := SeenTimes{
+		First: newer.First.Add(-backlogAge),
+		Last:  newer.Last.Add(-backlogAge),
+	}
 
-	for _, at := range []time.Time{newer, older} {
-		err := write(at)
+	for _, seen := range []SeenTimes{newer, older} {
+		err := write(seen)
 		if err != nil {
-			t.Fatalf("writing at %s: %v", at, err)
+			t.Fatalf("writing first %s, last %s: %v", seen.First, seen.Last, err)
 		}
 	}
 
@@ -2046,9 +2056,9 @@ func checkOlderWrite(
 		t.Fatalf("reading the row: %v", err)
 	}
 
-	if !firstSeen.Equal(older) || !lastSeen.Equal(newer) {
+	if !firstSeen.Equal(older.First) || !lastSeen.Equal(newer.Last) {
 		t.Errorf("first seen %s, last seen %s; want %s, %s",
-			firstSeen, lastSeen, older, newer)
+			firstSeen, lastSeen, older.First, newer.Last)
 	}
 }