Add Message.withInheritedSchemaVersion

js/modules/types/message.js

@@ -1,9 +1,12 @@
 const Attachment = require('./attachment');
+const SchemaVersion = require('./schema_version');
 
 
 const GROUP = 'group';
 const PRIVATE = 'private';
 
+const INITIAL_SCHEMA_VERSION = 0;
+
 // Public API
 exports.GROUP = GROUP;
 exports.PRIVATE = PRIVATE;
@@ -15,3 +18,39 @@ exports.upgradeSchema = async message =>
     attachments:
       await Promise.all(message.attachments.map(Attachment.upgradeSchema)),
   });
+
+// Inherits existing schema from attachments:
+exports.withInheritedSchemaVersion = (message) => {
+  const isInitialized = SchemaVersion.isValid(message.schemaVersion) &&
+    message.schemaVersion >= 1;
+  if (isInitialized) {
+    return message;
+  }
+
+  const numAttachments = Array.isArray(message.attachments)
+    ? message.attachments.length : 0;
+  const hasAttachments = numAttachments > 0;
+  if (!hasAttachments) {
+    return Object.assign(
+      {},
+      message,
+      { schemaVersion: INITIAL_SCHEMA_VERSION }
+    );
+  }
+
+  // All attachments should have the same schema version, so we just pick
+  // the first one:
+  const firstAttachment = message.attachments[0];
+  const inheritedSchemaVersion = SchemaVersion.isValid(firstAttachment.schemaVersion)
+    ? firstAttachment.schemaVersion : INITIAL_SCHEMA_VERSION;
+  const messageWithInitialSchema = Object.assign(
+    {},
+    message,
+    {
+      schemaVersion: inheritedSchemaVersion,
+      attachments: message.attachments.map(Attachment.removeSchemaVersion),
+    }
+  );
+
+  return messageWithInitialSchema;
+};