fade in prompt metadata transitions (#23037)

packages/opencode/src/cli/cmd/tui/util/signal.ts

@@ -1,7 +1,38 @@
-import { createSignal, type Accessor } from "solid-js"
+import { createEffect, createSignal, on, onCleanup, type Accessor } from "solid-js"
 import { debounce, type Scheduled } from "@solid-primitives/scheduled"
 
 export function createDebouncedSignal<T>(value: T, ms: number): [Accessor<T>, Scheduled<[value: T]>] {
   const [get, set] = createSignal(value)
   return [get, debounce((v: T) => set(() => v), ms)]
 }
+
+export function createFadeIn(show: Accessor<boolean>, enabled: Accessor<boolean>) {
+  const [alpha, setAlpha] = createSignal(show() ? 1 : 0)
+
+  createEffect(
+    on([show, enabled], ([visible, animate], previous) => {
+      if (!visible) {
+        setAlpha(0)
+        return
+      }
+
+      if (!animate || !previous) {
+        setAlpha(1)
+        return
+      }
+
+      const start = performance.now()
+      setAlpha(0)
+
+      const timer = setInterval(() => {
+        const progress = Math.min((performance.now() - start) / 160, 1)
+        setAlpha(progress * progress * (3 - 2 * progress))
+        if (progress >= 1) clearInterval(timer)
+      }, 16)
+
+      onCleanup(() => clearInterval(timer))
+    }),
+  )
+
+  return alpha
+}