spindle/db: add _jetstream and known_dids helpers

Signed-off-by: Anirudh Oppiliappan <[e-mail]>

spindle/db/db.go

···
 		pragma auto_vacuum = incremental;
 		pragma busy_timeout = 5000;
 
+		create table if not exists _jetstream (
+			id integer primary key autoincrement,
+			last_time_us integer not null
+		);
+
 		create table if not exists known_dids (
 			did text primary key
 		);

spindle/db/known_dids.go

···
+package db
+
+func (d *DB) AddDid(did string) error {
+	_, err := d.Exec(`insert or ignore into known_dids (did) values (?)`, did)
+	return err
+}
+
+func (d *DB) RemoveDid(did string) error {
+	_, err := d.Exec(`delete from known_dids where did = ?`, did)
+	return err
+}
+
+func (d *DB) GetAllDids() ([]string, error) {
+	var dids []string
+
+	rows, err := d.Query(`select did from known_dids`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var did string
+		if err := rows.Scan(&did); err != nil {
+			return nil, err
+		}
+		dids = append(dids, did)
+	}
+
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+
+	return dids, nil
+}
+
+func (d *DB) HasKnownDids() bool {
+	var count int
+	err := d.QueryRow(`select count(*) from known_dids`).Scan(&count)
+	if err != nil {
+		return false
+	}
+	return count > 0
+}