[#341] Add notifications controller

Signed-off-by: Angira Kekteeva <kira@nspcc.ru>

api/notifications/controller.go

@@ -0,0 +1,51 @@
+package notifications
+
+import (
+	"time"
+
+	"github.com/nats-io/nats.go"
+)
+
+const (
+	DefaultTimeout = 30 * time.Second
+)
+
+type Options struct {
+	URL                       string
+	TLSCertFilepath           string
+	TLSAuthPrivateKeyFilePath string
+	Timeout                   time.Duration
+	RootCAFiles               []string
+}
+
+type Controller struct {
+	taskQueueConnection *nats.Conn
+	jsClient            nats.JetStream
+}
+
+func NewController(p *Options) (*Controller, error) {
+	if p == nil {
+		return nil, nil
+	}
+
+	ncopts := []nats.Option{
+		nats.ClientCert(p.TLSCertFilepath, p.TLSAuthPrivateKeyFilePath),
+		nats.RootCAs(p.RootCAFiles...),
+		nats.Timeout(p.Timeout),
+	}
+
+	nc, err := nats.Connect(p.URL, ncopts...)
+	if err != nil {
+		return nil, err
+	}
+
+	js, err := nc.JetStream()
+	if err != nil {
+		return nil, err
+	}
+
+	return &Controller{
+		taskQueueConnection: nc,
+		jsClient:            js,
+	}, nil
+}