Create standalone browser port of LTX Athena with authenticated native API transport

frontend/lib/keyframe-controls.ts

@@ -0,0 +1,52 @@
+import {
+  findNearestFreeFrameIndex,
+  parseKeyframeTimecode,
+} from './keyframe-timeline.ts'
+
+type PositionedKeyframe = {
+  id: string
+  frameIndex: number
+}
+
+function placementContext(
+  keyframes: readonly PositionedKeyframe[],
+  id: string,
+): { current: PositionedKeyframe; others: PositionedKeyframe[] } | null {
+  const current = keyframes.find((keyframe) => keyframe.id === id)
+  if (!current) return null
+
+  return {
+    current,
+    others: keyframes.filter((keyframe) => keyframe.id !== id),
+  }
+}
+
+export function nudgeKeyframe(
+  keyframes: readonly PositionedKeyframe[],
+  id: string,
+  delta: -1 | 1,
+  lastFrame: number,
+): number | null {
+  const context = placementContext(keyframes, id)
+  if (!context) return null
+
+  return findNearestFreeFrameIndex(
+    context.others,
+    context.current.frameIndex + delta,
+    lastFrame,
+  )
+}
+
+export function applyTimecode(
+  keyframes: readonly PositionedKeyframe[],
+  id: string,
+  value: string,
+  fps: number,
+  lastFrame: number,
+): number | null {
+  const context = placementContext(keyframes, id)
+  const parsedFrame = parseKeyframeTimecode(value, fps)
+  if (!context || parsedFrame === null) return null
+
+  return findNearestFreeFrameIndex(context.others, parsedFrame, lastFrame)
+}