graceful shutdown, CoreInterface changes, MongoDB official driver is the only DB backend

interfaces.go

@@ -1,9 +1,6 @@
 package main
 
-import (
-	"github.com/globalsign/mgo"
-	"github.com/jinzhu/gorm"
-)
+import "go.mongodb.org/mongo-driver/mongo"
 
 type CoreInterface interface {
 	Register() (string, error)
@@ -17,20 +14,9 @@ type CoreInterface interface {
 	LoadConfiguration() error
 	AfterLoadConfiguration() error
 
-	// connection string parameter e.g. "localhost"
-	ConnectMongoDB(string) (*mgo.Session, error)
-
-	// connection string parameter
-	ConnectGORM(string) (*gorm.DB, error)
-
-	// ConnectNeo4j
-	// ConnectArangoDB
-	// ConnectCassandra
-	// ConnectDGraph
-
-	BeforeConnectToDatabases() error
-	ConnectToDatabases() error
-	AfterConnectToDatabases() error
+	BeforeDatabaseInit() error
+	DatabaseInit() error
+	AfterDatabaseInit() error
 
 	BeforeSetupLogger() error
 	SetupLogger() error
@@ -43,6 +29,14 @@ type CoreInterface interface {
 	BeforeRun() error
 	Run() error
 	AfterRun() error
+
+	BeforeShutdown() error
+	Shutdown() error
+}
+
+type DatabaseInterface interface {
+	Client() *mongo.Client
+	Close() error
 }
 
 type HandlerInterface interface {