WIP

FerretDB · AlekSi · May 18, 2023 · May 16, 2023 · May 16, 2023 · May 16, 2023
commit f801b753f240fbdb1b32caa3f9d2c4abd4c9f89c
diff --git a/internal/handlers/mdb/metadata.go b/internal/handlers/mdb/metadata.go
@@ -0,0 +1,94 @@
+package mdb
+
+import (
+	"errors"
+	"sync"
+
+	"github.com/FerretDB/FerretDB/internal/handlers/sjson"
+	"github.com/FerretDB/FerretDB/internal/types"
+)
+
+var (
+	ErrCollectionNotFound = errors.New("collection not found")
+	ErrDatabaseNotFound   = errors.New("database not found")
+	ErrMalformedMetadata  = errors.New("malformed metadata")
+)
+
+type MetadataStorage interface {
+	CreateCollection(name string) error
+
+	GetDatabasesList() ([]byte, error)
+
+	RemoveCollection(database, collection string) error
+	RemoveDatabase(database string) error
+}
+
+type Metadata struct {
+	storage MetadataStorage
+
+	mx  sync.Mutex
+	dbs *types.Document
+}
+
+func (m *Metadata) GetDatabasesList() ([]string, error) {
+	m.mx.Lock()
+	defer m.mx.Unlock()
+
+	// short path
+	if m.dbs != nil {
+		return m.dbs.Keys(), nil
+	}
+
+	list, err := m.storage.GetDatabasesList()
+	if err != nil {
+		return nil, err
+	}
+
+	dbs, err := sjson.Unmarshal(list)
+	if err != nil {
+		return nil, err
+	}
+
+	m.dbs = dbs
+
+	return m.dbs.Keys(), nil
+}
+
+func (m *Metadata) GetCollectionsList(database string) ([]string, error) {
+	m.mx.Lock()
+	defer m.mx.Unlock()
+
+	if !m.dbs.Has(database) {
+		return nil, ErrDatabaseNotFound
+	}
+
+	dbMetadataDoc, err := m.dbs.Get(database)
+	if err != nil {
+		return nil, err
+	}
+
+	dbMetadata, ok := dbMetadataDoc.(*types.Document)
+	if !ok {
+		return nil, ErrMalformedMetadata
+	}
+
+	collMetadataDoc, err := dbMetadata.Get("collections")
+	if err != nil {
+		return nil, err
+	}
+
+	collMetadata, ok := collMetadataDoc.(*types.Document)
+	if !ok {
+		return nil, ErrMalformedMetadata
+	}
+
+	return collMetadata.Keys(), nil
+}
+
+func (m *Metadata) RemoveCollection(database, collection string) error {
+	return nil
+}
+
+func (m *Metadata) RemoveDatabase(database string) error {
+	return nil
+}