Add partial import functionality (#812)

pkg/manager/import.go

@@ -0,0 +1,61 @@
+package manager
+
+import (
+	"fmt"
+
+	"github.com/stashapp/stash/pkg/logger"
+	"github.com/stashapp/stash/pkg/models"
+)
+
+type importer interface {
+	PreImport() error
+	PostImport(id int) error
+	Name() string
+	FindExistingID() (*int, error)
+	Create() (*int, error)
+	Update(id int) error
+}
+
+func performImport(i importer, duplicateBehaviour models.ImportDuplicateEnum) error {
+	if err := i.PreImport(); err != nil {
+		return err
+	}
+
+	// try to find an existing object with the same name
+	name := i.Name()
+	existing, err := i.FindExistingID()
+	if err != nil {
+		return fmt.Errorf("error finding existing objects: %s", err.Error())
+	}
+
+	var id int
+
+	if existing != nil {
+		if duplicateBehaviour == models.ImportDuplicateEnumFail {
+			return fmt.Errorf("existing object with name '%s'", name)
+		} else if duplicateBehaviour == models.ImportDuplicateEnumIgnore {
+			logger.Info("Skipping existing object")
+			return nil
+		}
+
+		// must be overwriting
+		id = *existing
+		if err := i.Update(id); err != nil {
+			return fmt.Errorf("error updating existing object: %s", err.Error())
+		}
+	} else {
+		// creating
+		createdID, err := i.Create()
+		if err != nil {
+			return fmt.Errorf("error creating object: %s", err.Error())
+		}
+
+		id = *createdID
+	}
+
+	if err := i.PostImport(id); err != nil {
+		return err
+	}
+
+	return nil
+}