fixed add clip at zero bug

Author: k9p5

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@diffusionstudio/core",
   "private": false,
-  "version": "1.1.2",
+  "version": "1.1.3",
   "type": "module",
   "description": "Build bleeding edge video processing applications",
   "files": [

src/tracks/track/track.spec.ts

@@ -94,6 +94,15 @@ describe('The Track Object', () => {
 
 		expect(track.clips[1].start.frames).toBe(5);
 		expect(track.clips[1].stop.frames).toBe(10);
+
+		await track.add(new Clip({ stop: 17, start: 3, name: 'abc' }), 0);
+
+		expect(track.clips[0].start.frames).toBe(0);
+		expect(track.clips[0].stop.frames).toBe(14);
+		expect(track.clips[0].name).toBe('abc');
+
+		expect(track.clips[1].start.frames).toBe(14);
+		expect(track.clips[1].stop.frames).toBe(19);
 	});
 
 	it('should snap the clip when it overlaps with the end of another clip', async () => {

src/tracks/track/track.strategies.ts

@@ -62,14 +62,16 @@ export class DefaultInsertStrategy implements InsertStrategy<'DEFAULT'> {
 export class StackInsertStrategy implements InsertStrategy<'STACK'> {
 	public mode = insertModes[1];
 
-	public add(clip: Clip, track: Track<Clip>, index: number = 0): void {
-		// fallback is -1 because one frame will be added
-		const stop = track.clips.at(index - 1)?.stop.millis ?? -1;
-		const offset = stop - clip.start.millis + 1;
+	public add(clip: Clip, track: Track<Clip>, index: number | undefined = undefined): void {
+		let stop = -1;
 
-		clip.offsetBy(new Timestamp(offset));
+		if (index != undefined && index > 0 || index == undefined) {
+			stop = track.clips.at((index ?? 0) - 1)?.stop.millis ?? -1;
+		}
+
+		clip.offsetBy(new Timestamp(stop - clip.start.millis + 1));
 
-		if (index == 0) {
+		if (index == undefined) {
 			track.clips.push(clip);
 		} else {
 			track.clips.splice(index, 0, clip);