Add catalog destination state schema

internal/state/shared_root.go

@@ -14,8 +14,14 @@ import (
 )
 
 type StateDocument struct {
-	SingleOwner *DistributorState
-	SharedRoot  *SharedRootState
+	SingleOwner      *DistributorState
+	SharedRoot       *SharedRootState
+	Catalog          *CatalogState
+	SupersededLegacy *SupersededLegacyState
+}
+
+type SupersededLegacyState struct {
+	SchemaVersion int
 }
 
 type SharedRootState struct {
@@ -103,18 +109,18 @@ func ParseDocument(data []byte) (StateDocument, error) {
 	if err != nil {
 		return StateDocument{}, err
 	}
-	if schemaVersion == SharedRootSchemaVersion {
-		sharedRoot, err := ParseSharedRoot(data)
+	switch schemaVersion {
+	case legacySchemaVersion, SchemaVersion, SharedRootSchemaVersion:
+		return StateDocument{SupersededLegacy: &SupersededLegacyState{SchemaVersion: schemaVersion}}, nil
+	case CatalogSchemaVersion:
+		catalog, err := ParseCatalog(data)
 		if err != nil {
 			return StateDocument{}, err
 		}
-		return StateDocument{SharedRoot: &sharedRoot}, nil
+		return StateDocument{Catalog: &catalog}, nil
+	default:
+		return StateDocument{}, fmt.Errorf("state schema_version %d is unsupported", schemaVersion)
 	}
-	singleOwner, err := Parse(data)
-	if err != nil {
-		return StateDocument{}, err
-	}
-	return StateDocument{SingleOwner: &singleOwner}, nil
 }
 
 func parseSchemaVersion(data []byte) (int, error) {
@@ -125,6 +131,10 @@ func parseSchemaVersion(data []byte) (int, error) {
 	if err := decoder.Decode(&raw); err != nil {
 		return 0, fmt.Errorf("parse distributor state: %w", err)
 	}
+	var extra any
+	if err := decoder.Decode(&extra); err != io.EOF {
+		return 0, fmt.Errorf("parse distributor state: trailing data")
+	}
 	if raw.SchemaVersion == nil {
 		return 0, fmt.Errorf("state schema_version is required")
 	}