chore: import upstream snapshot with attribution

apps/sim/hooks/use-animated-placeholder.ts

@@ -0,0 +1,74 @@
+import { useEffect, useRef, useState } from 'react'
+
+const PLACEHOLDER_PREFIX = 'Ask Sim to '
+const PLACEHOLDER_SUFFIXES = [
+  'respond to my emails...',
+  'find and track leads...',
+  'DM me Linear updates on Slack...',
+  'track GitHub commits...',
+] as const
+
+const TYPE_SPEED_MS = 60
+const DELETE_SPEED_MS = 35
+const PAUSE_AFTER_TYPING_MS = 2000
+const PAUSE_AFTER_DELETING_MS = 400
+
+export function useAnimatedPlaceholder(enabled = true): string {
+  const [text, setText] = useState(PLACEHOLDER_PREFIX)
+  const stateRef = useRef({
+    suffixIndex: 0,
+    charIndex: 0,
+    phase: 'typing' as 'typing' | 'paused' | 'deleting' | 'waiting',
+  })
+
+  useEffect(() => {
+    if (!enabled) return
+
+    const tick = () => {
+      const s = stateRef.current
+      const suffix = PLACEHOLDER_SUFFIXES[s.suffixIndex]
+
+      switch (s.phase) {
+        case 'typing': {
+          s.charIndex++
+          setText(PLACEHOLDER_PREFIX + suffix.slice(0, s.charIndex))
+          if (s.charIndex >= suffix.length) {
+            s.phase = 'paused'
+            return PAUSE_AFTER_TYPING_MS
+          }
+          return TYPE_SPEED_MS
+        }
+        case 'paused': {
+          s.phase = 'deleting'
+          return DELETE_SPEED_MS
+        }
+        case 'deleting': {
+          s.charIndex--
+          setText(PLACEHOLDER_PREFIX + suffix.slice(0, s.charIndex))
+          if (s.charIndex <= 0) {
+            s.phase = 'waiting'
+            return PAUSE_AFTER_DELETING_MS
+          }
+          return DELETE_SPEED_MS
+        }
+        case 'waiting': {
+          s.suffixIndex = (s.suffixIndex + 1) % PLACEHOLDER_SUFFIXES.length
+          s.charIndex = 0
+          s.phase = 'typing'
+          return TYPE_SPEED_MS
+        }
+      }
+    }
+
+    let timer: ReturnType<typeof setTimeout>
+    const schedule = () => {
+      const delay = tick()
+      timer = setTimeout(schedule, delay)
+    }
+    timer = setTimeout(schedule, TYPE_SPEED_MS)
+
+    return () => clearTimeout(timer)
+  }, [enabled])
+
+  return enabled ? text : PLACEHOLDER_PREFIX
+}