[#176] localstore: Draft storage engine structure and ops

Implement the primary structure and operation of the local object
storage engine.

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

pkg/local_object_storage/engine/engine.go

@@ -0,0 +1,53 @@
+package engine
+
+import (
+	"sync"
+
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/shard"
+	"github.com/nspcc-dev/neofs-node/pkg/util/logger"
+	"go.uber.org/zap"
+)
+
+// StorageEngine represents NeoFS local storage engine.
+type StorageEngine struct {
+	*cfg
+
+	mtx *sync.RWMutex
+
+	shards map[string]*shard.Shard
+}
+
+// Option represents StorageEngine's constructor option.
+type Option func(*cfg)
+
+type cfg struct {
+	log *logger.Logger
+}
+
+func defaultCfg() *cfg {
+	return &cfg{
+		log: zap.L(),
+	}
+}
+
+// New creates, initializes and returns new StorageEngine instance.
+func New(opts ...Option) *StorageEngine {
+	c := defaultCfg()
+
+	for i := range opts {
+		opts[i](c)
+	}
+
+	return &StorageEngine{
+		cfg:    c,
+		mtx:    new(sync.RWMutex),
+		shards: make(map[string]*shard.Shard),
+	}
+}
+
+// WithLogger returns option to set StorageEngine's logger.
+func WithLogger(l *logger.Logger) Option {
+	return func(c *cfg) {
+		c.log = l
+	}
+}