1 files changed, 118 insertions, 0 deletions
diff --git a/packages/app/src/context/layout-scroll.ts b/packages/app/src/context/layout-scroll.ts
new file mode 100644
index 000000000..30b0f6904
--- /dev/null
+++ b/packages/app/src/context/layout-scroll.ts
@@ -0,0 +1,118 @@
+import { createStore, produce } from "solid-js/store"
+
+export type SessionScroll = {
+  x: number
+  y: number
+}
+
+type ScrollMap = Record<string, SessionScroll>
+
+type Options = {
+  debounceMs?: number
+  getSnapshot: (sessionKey: string) => ScrollMap | undefined
+  onFlush: (sessionKey: string, scroll: ScrollMap) => void
+}
+
+export function createScrollPersistence(opts: Options) {
+  const wait = opts.debounceMs ?? 200
+  const [cache, setCache] = createStore<Record<string, ScrollMap>>({})
+  const dirty = new Set<string>()
+  const timers = new Map<string, ReturnType<typeof setTimeout>>()
+
+  function clone(input?: ScrollMap) {
+    const out: ScrollMap = {}
+    if (!input) return out
+
+    for (const key of Object.keys(input)) {
+      const pos = input[key]
+      if (!pos) continue
+      out[key] = { x: pos.x, y: pos.y }
+    }
+
+    return out
+  }
+
+  function seed(sessionKey: string) {
+    if (cache[sessionKey]) return
+    setCache(sessionKey, clone(opts.getSnapshot(sessionKey)))
+  }
+
+  function scroll(sessionKey: string, tab: string) {
+    seed(sessionKey)
+    return cache[sessionKey]?.[tab] ?? opts.getSnapshot(sessionKey)?.[tab]
+  }
+
+  function schedule(sessionKey: string) {
+    const prev = timers.get(sessionKey)
+    if (prev) clearTimeout(prev)
+    timers.set(
+      sessionKey,
+      setTimeout(() => flush(sessionKey), wait),
+    )
+  }
+
+  function setScroll(sessionKey: string, tab: string, pos: SessionScroll) {
+    seed(sessionKey)
+
+    const prev = cache[sessionKey]?.[tab]
+    if (prev?.x === pos.x && prev?.y === pos.y) return
+
+    setCache(sessionKey, tab, { x: pos.x, y: pos.y })
+    dirty.add(sessionKey)
+    schedule(sessionKey)
+  }
+
+  function flush(sessionKey: string) {
+    const timer = timers.get(sessionKey)
+    if (timer) clearTimeout(timer)
+    timers.delete(sessionKey)
+
+    if (!dirty.has(sessionKey)) return
+    dirty.delete(sessionKey)
+
+    opts.onFlush(sessionKey, clone(cache[sessionKey]))
+  }
+
+  function flushAll() {
+    const keys = Array.from(dirty)
+    if (keys.length === 0) return
+
+    for (const key of keys) {
+      flush(key)
+    }
+  }
+
+  function drop(keys: string[]) {
+    if (keys.length === 0) return
+
+    for (const key of keys) {
+      const timer = timers.get(key)
+      if (timer) clearTimeout(timer)
+      timers.delete(key)
+      dirty.delete(key)
+    }
+
+    setCache(
+      produce((draft) => {
+        for (const key of keys) {
+          delete draft[key]
+        }
+      }),
+    )
+  }
+
+  function dispose() {
+    drop(Array.from(timers.keys()))
+  }
+
+  return {
+    cache,
+    drop,
+    flush,
+    flushAll,
+    scroll,
+    seed,
+    setScroll,
+    dispose,
+  }
+}