chore: refactoring and tests, splitting up files (#12495)

packages/app/src/pages/session/file-tab-scroll.ts

@@ -0,0 +1,67 @@
+type Input = {
+  prevScrollWidth: number
+  scrollWidth: number
+  clientWidth: number
+  prevContextOpen: boolean
+  contextOpen: boolean
+}
+
+export const nextTabListScrollLeft = (input: Input) => {
+  if (input.scrollWidth <= input.prevScrollWidth) return
+  if (!input.prevContextOpen && input.contextOpen) return 0
+  if (input.scrollWidth <= input.clientWidth) return
+  return input.scrollWidth - input.clientWidth
+}
+
+export const createFileTabListSync = (input: { el: HTMLDivElement; contextOpen: () => boolean }) => {
+  let frame: number | undefined
+  let prevScrollWidth = input.el.scrollWidth
+  let prevContextOpen = input.contextOpen()
+
+  const update = () => {
+    const scrollWidth = input.el.scrollWidth
+    const clientWidth = input.el.clientWidth
+    const contextOpen = input.contextOpen()
+    const left = nextTabListScrollLeft({
+      prevScrollWidth,
+      scrollWidth,
+      clientWidth,
+      prevContextOpen,
+      contextOpen,
+    })
+
+    if (left !== undefined) {
+      input.el.scrollTo({
+        left,
+        behavior: "smooth",
+      })
+    }
+
+    prevScrollWidth = scrollWidth
+    prevContextOpen = contextOpen
+  }
+
+  const schedule = () => {
+    if (frame !== undefined) cancelAnimationFrame(frame)
+    frame = requestAnimationFrame(() => {
+      frame = undefined
+      update()
+    })
+  }
+
+  const onWheel = (e: WheelEvent) => {
+    if (Math.abs(e.deltaY) <= Math.abs(e.deltaX)) return
+    input.el.scrollLeft += e.deltaY > 0 ? 50 : -50
+    e.preventDefault()
+  }
+
+  input.el.addEventListener("wheel", onWheel, { passive: false })
+  const observer = new MutationObserver(schedule)
+  observer.observe(input.el, { childList: true })
+
+  return () => {
+    input.el.removeEventListener("wheel", onWheel)
+    observer.disconnect()
+    if (frame !== undefined) cancelAnimationFrame(frame)
+  }
+}