mkdocs-material/src/assets/javascripts/components/main/react/index.ts

/*
 * Copyright (c) 2016-2020 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 {
  MonoTypeOperatorFunction,
  Observable,
  animationFrameScheduler,
  combineLatest,
  pipe
} from "rxjs"
import {
  distinctUntilChanged,
  finalize,
  map,
  observeOn,
  pluck,
  shareReplay,
  tap
} from "rxjs/operators"

import { Viewport, watchElementSize } from "browser"

import { Header } from "../../header"
import { Main } from "../_"
import {
  resetHeaderShadow,
  setHeaderShadow
} from "../set"

/* ----------------------------------------------------------------------------
 * Helper types
 * ------------------------------------------------------------------------- */

/**
 * Watch options
 */
interface WatchOptions {
  header$: Observable<Header>          /* Header observable */
  viewport$: Observable<Viewport>      /* Viewport 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
 *
 * @return Main area observable
 */
export function watchMain(
  el: HTMLElement, { header$, viewport$ }: WatchOptions
): Observable<Main> {

  /* Compute necessary adjustment for header */
  const adjust$ = header$
    .pipe(
      pluck("height")
    )

  /* Compute the main area's top and bottom markers */
  const marker$ = watchElementSize(el)
    .pipe(
      map(({ height }) => [
        el.offsetTop,
        el.offsetTop + height
      ]),
      distinctUntilChanged(),
      shareReplay(1)
    )

  /* Compute the main area's visible height */
  const height$ = combineLatest([adjust$, marker$, viewport$])
    .pipe(
      map(([header, [top, bottom], { offset: { y }, size: { height } }]) => {
        return height
          - Math.max(0, top    - y,  header)
          - Math.max(0, height + y - bottom)
      }),
      map(height => Math.max(0, height)),
      distinctUntilChanged()
    )

  /* Compute whether the viewport offset is past the main area's top */
  const active$ = combineLatest([adjust$, marker$, viewport$])
    .pipe(
      map(([header, [top], { offset: { y } }]) => y >= top - header),
      distinctUntilChanged()
    )

  /* Combine into a single observable */
  return combineLatest([adjust$, marker$, height$, active$])
    .pipe(
      map(([header, [top], height, active]) => ({
        offset: top - header,
        height,
        active
      }))
    )
}

/* ------------------------------------------------------------------------- */

/**
 * Apply header shadow
 *
 * @param el - Header element
 *
 * @return Operator function
 */
export function applyHeaderShadow(
  el: HTMLElement
): MonoTypeOperatorFunction<Main> {
  return pipe(

    /* Defer repaint to next animation frame */
    observeOn(animationFrameScheduler),
    tap(({ active }) => {
      setHeaderShadow(el, active)
    }),

    /* Reset on complete or error */
    finalize(() => {
      resetHeaderShadow(el)
    })
  )
}