knotclient: introduce sqlite3 based cursor store

Signed-off-by: oppiliappan <[e-mail]>

knotclient/cursor/sqlite.go

···
+package cursor
+
+import (
+	"database/sql"
+	"fmt"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+type SqliteStore struct {
+	db        *sql.DB
+	tableName string
+}
+
+type SqliteStoreOpt func(*SqliteStore)
+
+func WithTableName(name string) SqliteStoreOpt {
+	return func(s *SqliteStore) {
+		s.tableName = name
+	}
+}
+
+func NewSQLiteStore(dbPath string, opts ...SqliteStoreOpt) (*SqliteStore, error) {
+	db, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open sqlite database: %w", err)
+	}
+
+	store := &SqliteStore{
+		db:        db,
+		tableName: "cursors",
+	}
+
+	for _, o := range opts {
+		o(store)
+	}
+
+	if err := store.init(); err != nil {
+		return nil, err
+	}
+
+	return store, nil
+}
+
+func (s *SqliteStore) init() error {
+	createTable := fmt.Sprintf(`
+	create table if not exists %s (
+		knot text primary key,
+		cursor text
+	);`, s.tableName)
+	_, err := s.db.Exec(createTable)
+	return err
+}
+
+func (s *SqliteStore) Set(knot string, cursor int64) {
+	query := fmt.Sprintf(`
+		insert into %s (knot, cursor)
+		values (?, ?)
+		on conflict(knot) do update set cursor=excluded.cursor;
+	`, s.tableName)
+
+	_, err := s.db.Exec(query, knot, cursor)
+
+	if err != nil {
+		// TODO: log here
+	}
+}
+
+func (s *SqliteStore) Get(knot string) (cursor int64) {
+	query := fmt.Sprintf(`
+		select cursor from %s where knot = ?;
+	`, s.tableName)
+	err := s.db.QueryRow(query, knot).Scan(&cursor)
+
+	if err != nil {
+		if err != sql.ErrNoRows {
+			// TODO: log here
+		}
+		return 0
+	}
+
+	return cursor
+}