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import { batch, createEffect } 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,
lastScrollTop: 0,
lastScrollHeight: 0,
lastContentWidth: 0,
autoScrolled: false,
userScrolled: false,
reflowing: false,
})
function scrollToBottom() {
if (!scrollRef || store.userScrolled || !options.working()) return
setStore("autoScrolled", true)
const targetHeight = scrollRef.scrollHeight
scrollRef.scrollTo({ top: targetHeight, behavior: "smooth" })
// Wait for scroll to complete before clearing autoScrolled
const checkScrollComplete = () => {
if (!scrollRef) {
setStore("autoScrolled", false)
return
}
const atBottom = scrollRef.scrollTop + scrollRef.clientHeight >= scrollRef.scrollHeight - 10
const reachedTarget = scrollRef.scrollTop >= targetHeight - scrollRef.clientHeight - 10
if (atBottom || reachedTarget) {
batch(() => {
setStore("lastScrollTop", scrollRef?.scrollTop ?? 0)
setStore("lastScrollHeight", scrollRef?.scrollHeight ?? 0)
setStore("autoScrolled", false)
})
} else {
requestAnimationFrame(checkScrollComplete)
}
}
requestAnimationFrame(checkScrollComplete)
}
function handleScroll() {
if (!scrollRef || store.autoScrolled) return
const scrollTop = scrollRef.scrollTop
const scrollHeight = scrollRef.scrollHeight
if (store.reflowing) {
batch(() => {
setStore("lastScrollTop", scrollTop)
setStore("lastScrollHeight", scrollHeight)
})
return
}
const scrollHeightChanged = Math.abs(scrollHeight - store.lastScrollHeight) > 10
const scrollTopDelta = scrollTop - store.lastScrollTop
// Handle reflow-caused scroll position changes
if (scrollHeightChanged && scrollTopDelta < 0) {
const heightRatio = store.lastScrollHeight > 0 ? scrollHeight / store.lastScrollHeight : 1
const expectedScrollTop = store.lastScrollTop * heightRatio
if (Math.abs(scrollTop - expectedScrollTop) < 100) {
batch(() => {
setStore("lastScrollTop", scrollTop)
setStore("lastScrollHeight", scrollHeight)
})
return
}
}
// Handle reset to top while working
const reset = scrollTop <= 0 && store.lastScrollTop > 0 && options.working() && !store.userScrolled
if (reset) {
batch(() => {
setStore("lastScrollTop", scrollTop)
setStore("lastScrollHeight", scrollHeight)
})
requestAnimationFrame(scrollToBottom)
return
}
// Detect intentional scroll up
const scrolledUp = scrollTop < store.lastScrollTop - 50 && !scrollHeightChanged
if (scrolledUp && options.working()) {
setStore("userScrolled", true)
options.onUserInteracted?.()
}
batch(() => {
setStore("lastScrollTop", scrollTop)
setStore("lastScrollHeight", scrollHeight)
})
}
function handleInteraction() {
if (options.working()) {
setStore("userScrolled", true)
options.onUserInteracted?.()
}
}
// Reset userScrolled when work completes
createEffect(() => {
if (!options.working()) setStore("userScrolled", false)
})
// Handle content resize
createResizeObserver(
() => store.contentRef,
({ width }) => {
const widthChanged = Math.abs(width - store.lastContentWidth) > 5
if (widthChanged && store.lastContentWidth > 0) {
setStore("reflowing", true)
requestAnimationFrame(() => {
requestAnimationFrame(() => {
setStore("reflowing", false)
if (options.working() && !store.userScrolled) {
scrollToBottom()
}
})
})
} else if (!store.reflowing) {
scrollToBottom()
}
setStore("lastContentWidth", width)
},
)
return {
scrollRef: (el: HTMLElement | undefined) => {
scrollRef = el
},
contentRef: (el: HTMLElement | undefined) => setStore("contentRef", el),
handleScroll,
handleInteraction,
scrollToBottom,
userScrolled: () => store.userScrolled,
}
}
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