Don't use original filenames when saving multi-attachment messages

ts/test-node/types/Attachment_test.ts

@@ -62,7 +62,7 @@ describe('Attachment', () => {
       });
     });
     context('for attachment with index', () => {
-      it('should use filename if provided', () => {
+      it('should use filename if it is provided', () => {
         const attachment: Attachment.AttachmentType = fakeAttachment({
           fileName: 'funny-cat.mov',
           data: Bytes.fromString('foo'),
@@ -74,12 +74,47 @@ describe('Attachment', () => {
         const actual = Attachment.getSuggestedFilename({
           attachment,
           timestamp,
-          index: 3,
         });
         const expected = 'funny-cat.mov';
         assert.strictEqual(actual, expected);
       });
 
+      it('should use filename if it is provided and index is 1', () => {
+        const attachment: Attachment.AttachmentType = fakeAttachment({
+          fileName: 'funny-cat.mov',
+          data: Bytes.fromString('foo'),
+          contentType: MIME.VIDEO_QUICKTIME,
+        });
+        const timestamp = new Date(
+          DAY + new Date(DAY).getTimezoneOffset() * 60 * 1000
+        );
+        const actual = Attachment.getSuggestedFilename({
+          attachment,
+          timestamp,
+          index: 1,
+        });
+        const expected = 'funny-cat.mov';
+        assert.strictEqual(actual, expected);
+      });
+
+      it('should use filename if it is provided and index is >1', () => {
+        const attachment: Attachment.AttachmentType = fakeAttachment({
+          fileName: 'funny-cat.mov',
+          data: Bytes.fromString('foo'),
+          contentType: MIME.VIDEO_QUICKTIME,
+        });
+        const timestamp = new Date(
+          DAY + new Date(DAY).getTimezoneOffset() * 60 * 1000
+        );
+        const actual = Attachment.getSuggestedFilename({
+          attachment,
+          timestamp,
+          index: 2,
+        });
+        const expected = 'signal-1970-01-02-000000_002.mov';
+        assert.strictEqual(actual, expected);
+      });
+
       it('should use provided index if > 1 and filename not provided', () => {
         const attachment: Attachment.AttachmentType = fakeAttachment({
           data: Bytes.fromString('foo'),

ts/types/Attachment.ts

@@ -1001,7 +1001,7 @@ export const getSuggestedFilename = ({
   index?: number;
 }): string => {
   const { fileName } = attachment;
-  if (fileName) {
+  if (fileName && (!isNumber(index) || index === 1)) {
     return fileName;
   }