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import React, {useCallback, useEffect} from 'react'
import EventEmitter from 'eventemitter3'
import {ScrollProvider} from '#/lib/ScrollContext'
import {NativeScrollEvent} from 'react-native'
import {useSetMinimalShellMode, useMinimalShellMode} from '#/state/shell'
import {useShellLayout} from '#/state/shell/shell-layout'
import {isNative, isWeb} from 'platform/detection'
import {useSharedValue, interpolate} from 'react-native-reanimated'
const WEB_HIDE_SHELL_THRESHOLD = 200
function clamp(num: number, min: number, max: number) {
'worklet'
return Math.min(Math.max(num, min), max)
}
export function MainScrollProvider({children}: {children: React.ReactNode}) {
const {headerHeight} = useShellLayout()
const mode = useMinimalShellMode()
const setMode = useSetMinimalShellMode()
const startDragOffset = useSharedValue<number | null>(null)
const startMode = useSharedValue<number | null>(null)
useEffect(() => {
if (isWeb) {
return listenToForcedWindowScroll(() => {
startDragOffset.value = null
startMode.value = null
})
}
})
const onBeginDrag = useCallback(
(e: NativeScrollEvent) => {
'worklet'
if (isNative) {
startDragOffset.value = e.contentOffset.y
startMode.value = mode.value
}
},
[mode, startDragOffset, startMode],
)
const onEndDrag = useCallback(
(e: NativeScrollEvent) => {
'worklet'
if (isNative) {
startDragOffset.value = null
startMode.value = null
if (e.contentOffset.y < headerHeight.value / 2) {
// If we're close to the top, show the shell.
setMode(false)
} else {
// Snap to whichever state is the closest.
setMode(Math.round(mode.value) === 1)
}
}
},
[startDragOffset, startMode, setMode, mode, headerHeight],
)
const onScroll = useCallback(
(e: NativeScrollEvent) => {
'worklet'
if (isNative) {
if (startDragOffset.value === null || startMode.value === null) {
if (mode.value !== 0 && e.contentOffset.y < headerHeight.value) {
// If we're close enough to the top, always show the shell.
// Even if we're not dragging.
setMode(false)
}
return
}
// The "mode" value is always between 0 and 1.
// Figure out how much to move it based on the current dragged distance.
const dy = e.contentOffset.y - startDragOffset.value
const dProgress = interpolate(
dy,
[-headerHeight.value, headerHeight.value],
[-1, 1],
)
const newValue = clamp(startMode.value + dProgress, 0, 1)
if (newValue !== mode.value) {
// Manually adjust the value. This won't be (and shouldn't be) animated.
mode.value = newValue
}
} else {
// On the web, we don't try to follow the drag because we don't know when it ends.
// Instead, show/hide immediately based on whether we're scrolling up or down.
const dy = e.contentOffset.y - (startDragOffset.value ?? 0)
startDragOffset.value = e.contentOffset.y
if (dy < 0 || e.contentOffset.y < WEB_HIDE_SHELL_THRESHOLD) {
setMode(false)
} else if (dy > 0) {
setMode(true)
}
}
},
[headerHeight, mode, setMode, startDragOffset, startMode],
)
return (
<ScrollProvider
onBeginDrag={onBeginDrag}
onEndDrag={onEndDrag}
onScroll={onScroll}>
{children}
</ScrollProvider>
)
}
const emitter = new EventEmitter()
if (isWeb) {
const originalScroll = window.scroll
window.scroll = function () {
emitter.emit('forced-scroll')
return originalScroll.apply(this, arguments as any)
}
const originalScrollTo = window.scrollTo
window.scrollTo = function () {
emitter.emit('forced-scroll')
return originalScrollTo.apply(this, arguments as any)
}
}
function listenToForcedWindowScroll(listener: () => void) {
emitter.addListener('forced-scroll', listener)
return () => {
emitter.removeListener('forced-scroll', listener)
}
}
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