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/*
* Copyright (c) 2016-2023 Martin Donath <martin.donath@squidfunk.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
import {
Observable,
combineLatest,
distinctUntilChanged,
distinctUntilKeyChanged,
map,
switchMap
} from "rxjs"
import {
Viewport,
watchElementSize
} from "~/browser"
import { Header } from "../header"
/* ----------------------------------------------------------------------------
* Types
* ------------------------------------------------------------------------- */
/**
* Main area
*/
export interface Main {
offset: number /* Main area top offset */
height: number /* Main area visible height */
active: boolean /* Main area is active */
}
/* ----------------------------------------------------------------------------
* Helper types
* ------------------------------------------------------------------------- */
/**
* Watch options
*/
interface WatchOptions {
viewport$: Observable<Viewport> /* Viewport observable */
header$: Observable<Header> /* Header observable */
}
/* ----------------------------------------------------------------------------
* Functions
* ------------------------------------------------------------------------- */
/**
* Watch main area
*
* This function returns an observable that computes the visual parameters of
* the main area which depends on the viewport vertical offset and height, as
* well as the height of the header element, if the header is fixed.
*
* @param el - Main area element
* @param options - Options
*
* @returns Main area observable
*/
export function watchMain(
el: HTMLElement, { viewport$, header$ }: WatchOptions
): Observable<Main> {
/* Compute necessary adjustment for header */
const adjust$ = header$
.pipe(
map(({ height }) => height),
distinctUntilChanged()
)
/* Compute the main area's top and bottom borders */
const border$ = adjust$
.pipe(
switchMap(() => watchElementSize(el)
.pipe(
map(({ height }) => ({
top: el.offsetTop,
bottom: el.offsetTop + height
})),
distinctUntilKeyChanged("bottom")
)
)
)
/* Compute the main area's offset, visible height and if we scrolled past */
return combineLatest([adjust$, border$, viewport$])
.pipe(
map(([header, { top, bottom }, { offset: { y }, size: { height } }]) => {
height = Math.max(0, height
- Math.max(0, top - y, header)
- Math.max(0, height + y - bottom)
)
return {
offset: top - header,
height,
active: top - header <= y
}
}),
distinctUntilChanged((a, b) => (
a.offset === b.offset &&
a.height === b.height &&
a.active === b.active
))
)
}
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