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import { createEffect, on, 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 scroll: HTMLElement | undefined
let settling = false
let settleTimer: ReturnType<typeof setTimeout> | undefined
let down = false
let cleanup: (() => void) | undefined
const [store, setStore] = createStore({
contentRef: undefined as HTMLElement | undefined,
userScrolled: false,
})
const active = () => options.working() || settling
const distanceFromBottom = () => {
const el = scroll
if (!el) return 0
return el.scrollHeight - el.clientHeight - el.scrollTop
}
const scrollToBottomNow = (behavior: ScrollBehavior) => {
const el = scroll
if (!el) return
el.scrollTo({ top: el.scrollHeight, behavior })
}
const scrollToBottom = (force: boolean) => {
if (!force && !active()) return
if (!scroll) return
if (!force && store.userScrolled) return
if (force && store.userScrolled) setStore("userScrolled", false)
const distance = distanceFromBottom()
if (distance < 2) return
const behavior: ScrollBehavior = force || distance > 96 ? "auto" : "smooth"
scrollToBottomNow(behavior)
}
const stop = () => {
if (!active()) return
if (store.userScrolled) return
setStore("userScrolled", true)
options.onUserInteracted?.()
}
const handleWheel = (e: WheelEvent) => {
if (e.deltaY >= 0) return
stop()
}
const handlePointerUp = () => {
down = false
window.removeEventListener("pointerup", handlePointerUp)
}
const handlePointerDown = () => {
if (down) return
down = true
window.addEventListener("pointerup", handlePointerUp)
}
const handleTouchEnd = () => {
down = false
window.removeEventListener("touchend", handleTouchEnd)
}
const handleTouchStart = () => {
if (down) return
down = true
window.addEventListener("touchend", handleTouchEnd)
}
const handleScroll = () => {
if (!active()) return
if (!scroll) return
if (distanceFromBottom() < 10) {
if (store.userScrolled) setStore("userScrolled", false)
return
}
if (down) stop()
}
const handleInteraction = () => {
stop()
}
createResizeObserver(
() => store.contentRef,
() => {
if (!active()) return
if (store.userScrolled) return
scrollToBottom(false)
},
)
createEffect(
on(options.working, (working) => {
settling = false
if (settleTimer) clearTimeout(settleTimer)
settleTimer = undefined
setStore("userScrolled", false)
if (working) {
scrollToBottom(true)
return
}
settling = true
settleTimer = setTimeout(() => {
settling = false
}, 300)
}),
)
onCleanup(() => {
if (settleTimer) clearTimeout(settleTimer)
if (cleanup) cleanup()
})
return {
scrollRef: (el: HTMLElement | undefined) => {
if (cleanup) {
cleanup()
cleanup = undefined
}
scroll = el
down = false
if (!el) return
el.style.overflowAnchor = "none"
el.addEventListener("wheel", handleWheel, { passive: true })
el.addEventListener("pointerdown", handlePointerDown)
el.addEventListener("touchstart", handleTouchStart, { passive: true })
cleanup = () => {
el.removeEventListener("wheel", handleWheel)
el.removeEventListener("pointerdown", handlePointerDown)
el.removeEventListener("touchstart", handleTouchStart)
window.removeEventListener("pointerup", handlePointerUp)
window.removeEventListener("touchend", handleTouchEnd)
}
},
contentRef: (el: HTMLElement | undefined) => setStore("contentRef", el),
handleScroll,
handleInteraction,
scrollToBottom: () => scrollToBottom(false),
forceScrollToBottom: () => scrollToBottom(true),
userScrolled: () => store.userScrolled,
}
}
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