Initial import of NousResearch/hermes-agent

ui-tui/src/app/scroll.ts

@@ -0,0 +1,71 @@
+import type { ScrollBoxHandle } from '@hermes/ink'
+
+import type { SelectionApi } from './interfaces.js'
+
+export interface SelectionSnap {
+  anchor?: { row: number } | null
+  focus?: { row: number } | null
+  isDragging?: boolean
+}
+
+export interface ScrollWithSelectionOptions {
+  readonly scrollRef: { readonly current: ScrollBoxHandle | null }
+  readonly selection: SelectionApi
+}
+
+function scrollBoundsForDelta(s: ScrollBoxHandle, cur: number, delta: number) {
+  const viewport = Math.max(0, s.getViewportHeight())
+  const cachedHeight = Math.max(viewport, s.getScrollHeight())
+  let max = Math.max(0, cachedHeight - viewport)
+
+  // getScrollHeight() is render-time cached. After the streaming tail is
+  // committed into virtual history, the Yoga height can be fresher than the
+  // cached value; if we clamp only against the cached fake bottom, wheel-down
+  // becomes a no-op and no render is scheduled to reveal the real tail.
+  if (delta > 0 && cur + delta >= max - 1) {
+    const freshHeight = Math.max(viewport, s.getFreshScrollHeight())
+    max = Math.max(0, freshHeight - viewport)
+  }
+
+  return { max, viewport }
+}
+
+export function scrollWithSelectionBy(delta: number, { scrollRef, selection }: ScrollWithSelectionOptions): void {
+  const s = scrollRef.current
+
+  if (!s) {
+    return
+  }
+
+  const cur = s.getScrollTop() + s.getPendingDelta()
+  const { max, viewport } = scrollBoundsForDelta(s, cur, delta)
+  const actual = Math.max(0, Math.min(max, cur + delta)) - cur
+
+  if (actual === 0) {
+    return
+  }
+
+  const sel = selection.getState() as null | SelectionSnap
+  const top = s.getViewportTop()
+  const bottom = top + viewport - 1
+
+  if (
+    sel?.anchor &&
+    sel.focus &&
+    sel.anchor.row >= top &&
+    sel.anchor.row <= bottom &&
+    (sel.isDragging || (sel.focus.row >= top && sel.focus.row <= bottom))
+  ) {
+    const shift = sel.isDragging ? selection.shiftAnchor : selection.shiftSelection
+
+    if (actual > 0) {
+      selection.captureScrolledRows(top, top + actual - 1, 'above')
+    } else {
+      selection.captureScrolledRows(bottom + actual + 1, bottom, 'below')
+    }
+
+    shift(-actual, top, bottom)
+  }
+
+  s.scrollBy(actual)
+}