init claude-code

ink/hooks/use-terminal-viewport.ts

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+import { useCallback, useContext, useLayoutEffect, useRef } from 'react'
+import { TerminalSizeContext } from '../components/TerminalSizeContext.js'
+import type { DOMElement } from '../dom.js'
+
+type ViewportEntry = {
+  /**
+   * Whether the element is currently within the terminal viewport
+   */
+  isVisible: boolean
+}
+
+/**
+ * Hook to detect if a component is within the terminal viewport.
+ *
+ * Returns a callback ref and a viewport entry object.
+ * Attach the ref to the component you want to track.
+ *
+ * The entry is updated during the layout phase (useLayoutEffect) so callers
+ * always read fresh values during render. Visibility changes do NOT trigger
+ * re-renders on their own — callers that re-render for other reasons (e.g.
+ * animation ticks, state changes) will pick up the latest value naturally.
+ * This avoids infinite update loops when combined with other layout effects
+ * that also call setState.
+ *
+ * @example
+ * const [ref, entry] = useTerminalViewport()
+ * return <Box ref={ref}><Animation enabled={entry.isVisible}>...</Animation></Box>
+ */
+export function useTerminalViewport(): [
+  ref: (element: DOMElement | null) => void,
+  entry: ViewportEntry,
+] {
+  const terminalSize = useContext(TerminalSizeContext)
+  const elementRef = useRef<DOMElement | null>(null)
+  const entryRef = useRef<ViewportEntry>({ isVisible: true })
+
+  const setElement = useCallback((el: DOMElement | null) => {
+    elementRef.current = el
+  }, [])
+
+  // Runs on every render because yoga layout values can change
+  // without React being aware. Only updates the ref — no setState
+  // to avoid cascading re-renders during the commit phase.
+  // Walks the DOM ancestor chain fresh each time to avoid holding stale
+  // references after yoga tree rebuilds.
+  useLayoutEffect(() => {
+    const element = elementRef.current
+    if (!element?.yogaNode || !terminalSize) {
+      return
+    }
+
+    const height = element.yogaNode.getComputedHeight()
+    const rows = terminalSize.rows
+
+    // Walk the DOM parent chain (not yoga.getParent()) so we can detect
+    // scroll containers and subtract their scrollTop. Yoga computes layout
+    // positions without scroll offset — scrollTop is applied at render time.
+    // Without this, an element inside a ScrollBox whose yoga position exceeds
+    // terminalRows would be considered offscreen even when scrolled into view
+    // (e.g., the spinner in fullscreen mode after enough messages accumulate).
+    let absoluteTop = element.yogaNode.getComputedTop()
+    let parent: DOMElement | undefined = element.parentNode
+    let root = element.yogaNode
+    while (parent) {
+      if (parent.yogaNode) {
+        absoluteTop += parent.yogaNode.getComputedTop()
+        root = parent.yogaNode
+      }
+      // scrollTop is only ever set on scroll containers (by ScrollBox + renderer).
+      // Non-scroll nodes have undefined scrollTop → falsy fast-path.
+      if (parent.scrollTop) absoluteTop -= parent.scrollTop
+      parent = parent.parentNode
+    }
+
+    // Only the root's height matters
+    const screenHeight = root.getComputedHeight()
+
+    const bottom = absoluteTop + height
+    // When content overflows the viewport (screenHeight > rows), the
+    // cursor-restore at frame end scrolls one extra row into scrollback.
+    // log-update.ts accounts for this with scrollbackRows = viewportY + 1.
+    // We must match, otherwise an element at the boundary is considered
+    // "visible" here (animation keeps ticking) but its row is treated as
+    // scrollback by log-update (content change → full reset → flicker).
+    const cursorRestoreScroll = screenHeight > rows ? 1 : 0
+    const viewportY = Math.max(0, screenHeight - rows) + cursorRestoreScroll
+    const viewportBottom = viewportY + rows
+    const visible = bottom > viewportY && absoluteTop < viewportBottom
+
+    if (visible !== entryRef.current.isVisible) {
+      entryRef.current = { isVisible: visible }
+    }
+  })
+
+  return [setElement, entryRef.current]
+}