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import { progress } from '../../progress'
import type { OnScrollCallback } from './index'
const SCROLL_KEYS = {
x: {
length: 'Width',
position: 'Left',
},
y: {
length: 'Height',
position: 'Top',
},
} as const
/**
* Whilst user's may not need the scrollLength, it's easier to return
* the whole state we're storing and let them pick what they want.
*/
export interface ScrollAxis {
current: number
progress: number
scrollLength: number
}
export interface ScrollInfo {
time: number
x: ScrollAxis
y: ScrollAxis
}
/**
* Why use a class? More extensible in the future.
*/
export class ScrollHandler {
protected callback: OnScrollCallback
protected container: HTMLElement
protected info: ScrollInfo
constructor(callback: OnScrollCallback, container: HTMLElement) {
this.callback = callback
this.container = container
this.info = {
time: 0,
x: this.createAxis(),
y: this.createAxis(),
}
}
private createAxis = (): ScrollAxis => ({
current: 0,
progress: 0,
scrollLength: 0,
})
private updateAxis = (axisName: keyof Pick<ScrollInfo, 'x' | 'y'>) => {
const axis = this.info[axisName]
const { length, position } = SCROLL_KEYS[axisName]
axis.current = this.container[`scroll${position}`]
axis.scrollLength =
this.container[`scroll${length}`] - this.container[`client${length}`]
axis.progress = progress(0, axis.scrollLength, axis.current)
}
private update = () => {
this.updateAxis('x')
this.updateAxis('y')
}
private sendEvent = () => {
this.callback(this.info)
}
advance = () => {
this.update()
this.sendEvent()
}
}
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