From d154937ac2fdf5877095c4a0f1076cba04d7c3d1 Mon Sep 17 00:00:00 2001
From: Maze Winther <mazewinther@gmail.com>
Date: Sat, 26 Jul 2025 22:25:57 +0200
Subject: feat: lock playhead to frame (instead of floating) and add autoscroll
 to timeline

---
 apps/web/src/components/editor/timeline/index.tsx  |  5 +-
 .../editor/timeline/timeline-playhead.tsx          | 75 +++++++++++++++++++---
 2 files changed, 70 insertions(+), 10 deletions(-)

(limited to 'apps/web/src/components/editor/timeline')

diff --git a/apps/web/src/components/editor/timeline/index.tsx b/apps/web/src/components/editor/timeline/index.tsx
index bcaece89..bdb4433c 100644
--- a/apps/web/src/components/editor/timeline/index.tsx
+++ b/apps/web/src/components/editor/timeline/index.tsx
@@ -537,12 +537,13 @@ export function Timeline() {
           tracks={tracks}
           timelineRef={timelineRef}
           trackLabelsRef={trackLabelsRef}
+          tracksScrollRef={tracksScrollRef}
           isVisible={showSnapIndicator}
         />
         {/* Timeline Header with Ruler */}
         <div className="flex bg-panel sticky top-0 z-10">
           {/* Track Labels Header */}
-          <div className="w-48 flex-shrink-0 bg-muted/30 border-r flex items-center justify-between px-3 py-2">
+          <div className="w-48 flex-shrink-0 bg-panel border-r flex items-center justify-between px-3 py-2">
             {/* Empty space */}
             <span className="text-sm font-medium text-muted-foreground opacity-0">
               .
@@ -651,7 +652,7 @@ export function Timeline() {
           {tracks.length > 0 && (
             <div
               ref={trackLabelsRef}
-              className="w-48 flex-shrink-0 border-r border-black overflow-y-auto"
+              className="w-48 flex-shrink-0 border-r border-black overflow-y-auto z-[200] bg-panel"
               data-track-labels
             >
               <ScrollArea className="w-full h-full" ref={trackLabelsScrollRef}>
diff --git a/apps/web/src/components/editor/timeline/timeline-playhead.tsx b/apps/web/src/components/editor/timeline/timeline-playhead.tsx
index d0aea7fa..b33166c0 100644
--- a/apps/web/src/components/editor/timeline/timeline-playhead.tsx
+++ b/apps/web/src/components/editor/timeline/timeline-playhead.tsx
@@ -1,11 +1,8 @@
 "use client";
 
-import { useRef } from "react";
+import { useRef, useState, useEffect } from "react";
 import { TimelineTrack } from "@/types/timeline";
-import {
-  TIMELINE_CONSTANTS,
-  getTotalTracksHeight,
-} from "@/constants/timeline-constants";
+import { TIMELINE_CONSTANTS } from "@/constants/timeline-constants";
 import { useTimelinePlayhead } from "@/hooks/use-timeline-playhead";
 
 interface TimelinePlayheadProps {
@@ -39,6 +36,8 @@ export function TimelinePlayhead({
 }: TimelinePlayheadProps) {
   const internalPlayheadRef = useRef<HTMLDivElement>(null);
   const playheadRef = externalPlayheadRef || internalPlayheadRef;
+  const [scrollLeft, setScrollLeft] = useState(0);
+
   const { playheadPosition, handlePlayheadMouseDown } = useTimelinePlayhead({
     currentTime,
     duration,
@@ -50,6 +49,25 @@ export function TimelinePlayhead({
     playheadRef,
   });
 
+  // Track scroll position to lock playhead to frame
+  useEffect(() => {
+    const tracksViewport = tracksScrollRef.current?.querySelector(
+      "[data-radix-scroll-area-viewport]"
+    ) as HTMLElement;
+
+    if (!tracksViewport) return;
+
+    const handleScroll = () => {
+      setScrollLeft(tracksViewport.scrollLeft);
+    };
+
+    // Set initial scroll position
+    setScrollLeft(tracksViewport.scrollLeft);
+
+    tracksViewport.addEventListener("scroll", handleScroll);
+    return () => tracksViewport.removeEventListener("scroll", handleScroll);
+  }, [tracksScrollRef]);
+
   // Use timeline container height minus a few pixels for breathing room
   const timelineContainerHeight = timelineRef.current?.offsetHeight || 400;
   const totalHeight = timelineContainerHeight - 8; // 8px padding from edges
@@ -59,9 +77,51 @@ export function TimelinePlayhead({
     tracks.length > 0 && trackLabelsRef?.current
       ? trackLabelsRef.current.offsetWidth
       : 0;
-  const leftPosition =
-    trackLabelsWidth +
+
+  // Calculate position locked to timeline content (accounting for scroll)
+  const timelinePosition =
     playheadPosition * TIMELINE_CONSTANTS.PIXELS_PER_SECOND * zoomLevel;
+  const rawLeftPosition = trackLabelsWidth + timelinePosition - scrollLeft;
+
+  // Get the timeline content width and viewport width for right boundary
+  const timelineContentWidth =
+    duration * TIMELINE_CONSTANTS.PIXELS_PER_SECOND * zoomLevel;
+  const tracksViewport = tracksScrollRef.current?.querySelector(
+    "[data-radix-scroll-area-viewport]"
+  ) as HTMLElement;
+  const viewportWidth = tracksViewport?.clientWidth || 1000;
+
+  // Constrain playhead to never appear outside the timeline area
+  const leftBoundary = trackLabelsWidth;
+  const rightBoundary = Math.min(
+    trackLabelsWidth + timelineContentWidth - scrollLeft, // Don't go beyond timeline content
+    trackLabelsWidth + viewportWidth // Don't go beyond viewport
+  );
+
+  const leftPosition = Math.max(
+    leftBoundary,
+    Math.min(rightBoundary, rawLeftPosition)
+  );
+
+  // Debug logging when playhead might go outside
+  if (rawLeftPosition < leftBoundary || rawLeftPosition > rightBoundary) {
+    console.log(
+      "PLAYHEAD VISUAL DEBUG:",
+      JSON.stringify({
+        playheadPosition,
+        timelinePosition,
+        trackLabelsWidth,
+        scrollLeft,
+        rawLeftPosition,
+        constrainedLeftPosition: leftPosition,
+        leftBoundary,
+        rightBoundary,
+        timelineContentWidth,
+        viewportWidth,
+        zoomLevel,
+      })
+    );
+  }
 
   return (
     <div
@@ -72,7 +132,6 @@ export function TimelinePlayhead({
         top: 0,
         height: `${totalHeight}px`,
         width: "2px", // Slightly wider for better click target
-        zIndex: 100,
       }}
       onMouseDown={handlePlayheadMouseDown}
     >
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