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

@@ -20,6 +20,7 @@ import (
 
 	"git.eeqj.de/sneak/routewatch/internal/config"
 	"git.eeqj.de/sneak/routewatch/internal/logger"
+	"git.eeqj.de/sneak/routewatch/internal/ristypes"
 	"git.eeqj.de/sneak/routewatch/pkg/asinfo"
 	"github.com/mattn/go-sqlite3"
 )
@@ -1960,6 +1961,130 @@ func TestUpdatePeerBatchStoresTheEarliestAndLatestTimesOfANewPeer(
 	}
 }
 
+// backlogAge is how much older the second write is than the first in the tests
+// of first_seen and last_seen, as when a collector catches up on a backlog.
+const backlogAge = 24 * 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.
+func TestOlderWriteKeepsLastSeenAndLowersFirstSeen(t *testing.T) {
+	t.Parallel()
+
+	db, err := New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("failed to create database: %v", err)
+	}
+	defer func() { _ = db.Close() }()
+
+	const (
+		batchASN, singleASN = 64500, 64501
+		peerASN             = 64502
+		asnQuery            = "SELECT first_seen, last_seen FROM asns WHERE asn = ?"
+		peeringQuery        = "SELECT first_seen, last_seen FROM peerings " +
+			"WHERE as_a = ? AND as_b = ?"
+		peerQuery = "SELECT first_seen, last_seen FROM bgp_peers " +
+			"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(at time.Time) error {
+		_, err := db.GetOrCreateASN(singleASN, at)
+
+		return err
+	}, 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(at time.Time) error {
+		return db.UpdatePeerBatch(map[string]PeerUpdate{
+			testV4PeerIP: {
+				PeerIP: testV4PeerIP, PeerASN: peerASN,
+				MessageType: ristypes.MessageTypeUpdate,
+				Seen:        SeenTimes{First: at, Last: at},
+			},
+		})
+	}, peerQuery, testV4PeerIP)
+
+	checkOlderWrite(t, db, func(at time.Time) error {
+		return db.UpdatePeer(testPeerIP, peerASN, ristypes.MessageTypeUpdate, at)
+	}, 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.
+func checkOlderWrite(
+	t *testing.T, db *Database, write func(at time.Time) error,
+	query string, args ...any,
+) {
+	t.Helper()
+
+	newer := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+	older := newer.Add(-backlogAge)
+
+	for _, at := range []time.Time{newer, older} {
+		err := write(at)
+		if err != nil {
+			t.Fatalf("writing at %s: %v", at, err)
+		}
+	}
+
+	var firstSeen, lastSeen time.Time
+
+	err := db.db.QueryRowContext(t.Context(), query, args...).
+		Scan(&firstSeen, &lastSeen)
+	if err != nil {
+		t.Fatalf("reading the row: %v", err)
+	}
+
+	if !firstSeen.Equal(older) || !lastSeen.Equal(newer) {
+		t.Errorf("first seen %s, last seen %s; want %s, %s",
+			firstSeen, lastSeen, older, newer)
+	}
+}
+
+// TestGetOrCreateASNReturnsStoredSeenTimes stores an AS at a newer time, then
+// at an older one. The second call returns the times the row now holds: the
+// older first_seen and the newer last_seen.
+func TestGetOrCreateASNReturnsStoredSeenTimes(t *testing.T) {
+	t.Parallel()
+
+	db, err := New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("failed to create database: %v", err)
+	}
+	defer func() { _ = db.Close() }()
+
+	const asn = 64500
+
+	newer := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
+	older := newer.Add(-backlogAge)
+
+	_, err = db.GetOrCreateASN(asn, newer)
+	if err != nil {
+		t.Fatalf("GetOrCreateASN at %s: %v", newer, err)
+	}
+
+	got, err := db.GetOrCreateASN(asn, older)
+	if err != nil {
+		t.Fatalf("GetOrCreateASN at %s: %v", older, err)
+	}
+
+	if !got.FirstSeen.Equal(older) || !got.LastSeen.Equal(newer) {
+		t.Errorf("first seen %s, last seen %s; want %s, %s",
+			got.FirstSeen, got.LastSeen, older, newer)
+	}
+}
+
 // TestUpsertLiveRouteBatchWritesInKeyOrder writes new routes of two peers out
 // of key order, the last one a second announcement of the first, and checks
 // that the rows were inserted in key order, peer then prefix (each new row's id