[#188] shard: Define the enumeration of shard modes

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/shard/mode.go

@@ -0,0 +1,42 @@
+package shard
+
+// Mode represents enumeration of Shard work modes.
+type Mode uint32
+
+// TODO: more detailed description of shard modes.
+
+const (
+	_ Mode = iota
+
+	// ModeActive is a Mode value for active shard.
+	ModeActive
+
+	// ModeInactive is a Mode value for inactive shard.
+	ModeInactive
+
+	// ModeReadOnly is a Mode value for read-only shard.
+	ModeReadOnly
+
+	// ModeFault is a Mode value for faulty shard.
+	ModeFault
+
+	// ModeEvacuate is a Mode value for evacuating shard.
+	ModeEvacuate
+)
+
+func (m Mode) String() string {
+	switch m {
+	default:
+		return "UNDEFINED"
+	case ModeActive:
+		return "ACTIVE"
+	case ModeInactive:
+		return "INACTIVE"
+	case ModeReadOnly:
+		return "READ_ONLY"
+	case ModeFault:
+		return "FAULT"
+	case ModeEvacuate:
+		return "EVACUATE"
+	}
+}