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import { createEffect, onCleanup } from "solid-js"
import { createStore } from "solid-js/store"
import { createResizeObserver } from "@solid-primitives/resize-observer"
export interface AutoScrollOptions {
working: () => boolean
onUserInteracted?: () => void
}
export function createAutoScroll(options: AutoScrollOptions) {
let scrollRef: HTMLElement | undefined
const [store, setStore] = createStore({
contentRef: undefined as HTMLElement | undefined,
userScrolled: false,
})
let lastScrollTop = 0
let isAutoScrolling = false
let autoScrollTimeout: ReturnType<typeof setTimeout> | undefined
let isMouseDown = false
let cleanupListeners: (() => void) | undefined
let scheduledScroll = false
let scheduledForce = false
function distanceFromBottom() {
if (!scrollRef) return 0
return scrollRef.scrollHeight - scrollRef.clientHeight - scrollRef.scrollTop
}
function startAutoScroll() {
isAutoScrolling = true
if (autoScrollTimeout) clearTimeout(autoScrollTimeout)
autoScrollTimeout = setTimeout(() => {
isAutoScrolling = false
}, 1000)
}
function scrollToBottomNow() {
if (!scrollRef || store.userScrolled || !options.working()) return
const distance = distanceFromBottom()
if (distance < 2) return
const behavior = distance > 96 ? "auto" : "smooth"
startAutoScroll()
scrollRef.scrollTo({
top: scrollRef.scrollHeight,
behavior,
})
}
function forceScrollToBottomNow() {
if (!scrollRef) return
if (store.userScrolled) setStore("userScrolled", false)
const distance = distanceFromBottom()
if (distance < 2) return
startAutoScroll()
scrollRef.scrollTo({
top: scrollRef.scrollHeight,
behavior: "auto",
})
}
function scheduleScrollToBottom(force = false) {
if (typeof requestAnimationFrame === "undefined") {
if (force) {
forceScrollToBottomNow()
return
}
scrollToBottomNow()
return
}
if (force) scheduledForce = true
if (scheduledScroll) return
scheduledScroll = true
requestAnimationFrame(() => {
scheduledScroll = false
const shouldForce = scheduledForce
scheduledForce = false
if (shouldForce) {
forceScrollToBottomNow()
return
}
scrollToBottomNow()
})
}
function scrollToBottom() {
scheduleScrollToBottom(false)
}
function forceScrollToBottom() {
scheduleScrollToBottom(true)
}
function handleScroll() {
if (!scrollRef) return
const { scrollTop, scrollHeight, clientHeight } = scrollRef
const atBottom = Math.abs(scrollHeight - clientHeight - scrollTop) < 10
if (isAutoScrolling) {
if (atBottom) {
isAutoScrolling = false
if (autoScrollTimeout) clearTimeout(autoScrollTimeout)
}
lastScrollTop = scrollTop
return
}
if (atBottom) {
if (store.userScrolled) {
setStore("userScrolled", false)
}
lastScrollTop = scrollTop
return
}
const delta = scrollTop - lastScrollTop
if (delta < 0) {
if (isMouseDown && !store.userScrolled && options.working()) {
setStore("userScrolled", true)
options.onUserInteracted?.()
}
}
lastScrollTop = scrollTop
}
function handleInteraction() {
if (options.working()) {
setStore("userScrolled", true)
options.onUserInteracted?.()
}
}
function handleWheel(e: WheelEvent) {
if (e.deltaY < 0 && !store.userScrolled && options.working()) {
setStore("userScrolled", true)
options.onUserInteracted?.()
}
}
function handleTouchStart() {
if (!store.userScrolled && options.working()) {
setStore("userScrolled", true)
options.onUserInteracted?.()
}
}
function handleKeyDown(e: KeyboardEvent) {
if (["ArrowUp", "PageUp", "Home"].includes(e.key)) {
if (!store.userScrolled && options.working()) {
setStore("userScrolled", true)
options.onUserInteracted?.()
}
}
}
function handleMouseDown() {
isMouseDown = true
window.addEventListener("mouseup", handleMouseUp)
}
function handleMouseUp() {
isMouseDown = false
window.removeEventListener("mouseup", handleMouseUp)
}
// Reset userScrolled when work completes
createEffect(() => {
if (!options.working()) {
setStore("userScrolled", false)
}
})
// Ensure pinned-to-bottom stays pinned during heavy DOM updates
createEffect(() => {
const el = store.contentRef
if (!el) return
const observer = new MutationObserver(() => {
if (store.userScrolled) return
if (!options.working()) return
scheduleScrollToBottom(false)
})
observer.observe(el, { childList: true, subtree: true, characterData: true })
onCleanup(() => observer.disconnect())
})
// Handle content resize
createResizeObserver(
() => store.contentRef,
() => {
if (options.working() && !store.userScrolled) {
scrollToBottom()
}
},
)
onCleanup(() => {
if (autoScrollTimeout) clearTimeout(autoScrollTimeout)
if (cleanupListeners) cleanupListeners()
})
return {
scrollRef: (el: HTMLElement | undefined) => {
if (cleanupListeners) {
cleanupListeners()
cleanupListeners = undefined
}
scrollRef = el
if (el) {
lastScrollTop = el.scrollTop
el.style.overflowAnchor = "none"
el.addEventListener("wheel", handleWheel, { passive: true })
el.addEventListener("touchstart", handleTouchStart, { passive: true })
el.addEventListener("keydown", handleKeyDown)
el.addEventListener("mousedown", handleMouseDown)
cleanupListeners = () => {
el.removeEventListener("wheel", handleWheel)
el.removeEventListener("touchstart", handleTouchStart)
el.removeEventListener("keydown", handleKeyDown)
el.removeEventListener("mousedown", handleMouseDown)
window.removeEventListener("mouseup", handleMouseUp)
}
}
},
contentRef: (el: HTMLElement | undefined) => setStore("contentRef", el),
handleScroll,
handleInteraction,
scrollToBottom,
forceScrollToBottom,
userScrolled: () => store.userScrolled,
}
}
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