1 files changed, 184 insertions, 0 deletions
diff --git a/src/templates/assets/javascripts/components/top/index.ts b/src/templates/assets/javascripts/components/top/index.ts
new file mode 100644
index 00000000..82e88b61
--- /dev/null
+++ b/src/templates/assets/javascripts/components/top/index.ts
@@ -0,0 +1,184 @@
+/*
+ * 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,
+  Subject,
+  bufferCount,
+  combineLatest,
+  distinctUntilChanged,
+  distinctUntilKeyChanged,
+  endWith,
+  finalize,
+  fromEvent,
+  ignoreElements,
+  map,
+  repeat,
+  skip,
+  takeUntil,
+  tap
+} from "rxjs"
+
+import { Viewport } from "~/browser"
+
+import { Component } from "../_"
+import { Header } from "../header"
+import { Main } from "../main"
+
+/* ----------------------------------------------------------------------------
+ * Types
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Back-to-top button
+ */
+export interface BackToTop {
+  hidden: boolean                      /* Back-to-top button is hidden */
+}
+
+/* ----------------------------------------------------------------------------
+ * Helper types
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Watch options
+ */
+interface WatchOptions {
+  viewport$: Observable<Viewport>      /* Viewport observable */
+  main$: Observable<Main>              /* Main area observable */
+  target$: Observable<HTMLElement>     /* Location target observable */
+}
+
+/**
+ * Mount options
+ */
+interface MountOptions {
+  viewport$: Observable<Viewport>      /* Viewport observable */
+  header$: Observable<Header>          /* Header observable */
+  main$: Observable<Main>              /* Main area observable */
+  target$: Observable<HTMLElement>     /* Location target observable */
+}
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Watch back-to-top
+ *
+ * @param _el - Back-to-top element
+ * @param options - Options
+ *
+ * @returns Back-to-top observable
+ */
+export function watchBackToTop(
+  _el: HTMLElement, { viewport$, main$, target$ }: WatchOptions
+): Observable<BackToTop> {
+
+  /* Compute direction */
+  const direction$ = viewport$
+    .pipe(
+      map(({ offset: { y } }) => y),
+      bufferCount(2, 1),
+      map(([a, b]) => a > b && b > 0),
+      distinctUntilChanged()
+    )
+
+  /* Compute whether main area is active */
+  const active$ = main$
+    .pipe(
+      map(({ active }) => active)
+    )
+
+  /* Compute threshold for hiding */
+  return combineLatest([active$, direction$])
+    .pipe(
+      map(([active, direction]) => !(active && direction)),
+      distinctUntilChanged(),
+      takeUntil(target$.pipe(skip(1))),
+      endWith(true),
+      repeat({ delay: 250 }),
+      map(hidden => ({ hidden }))
+    )
+}
+
+/* ------------------------------------------------------------------------- */
+
+/**
+ * Mount back-to-top
+ *
+ * @param el - Back-to-top element
+ * @param options - Options
+ *
+ * @returns Back-to-top component observable
+ */
+export function mountBackToTop(
+  el: HTMLElement, { viewport$, header$, main$, target$ }: MountOptions
+): Observable<Component<BackToTop>> {
+  const push$ = new Subject<BackToTop>()
+  const done$ = push$.pipe(ignoreElements(), endWith(true))
+  push$.subscribe({
+
+    /* Handle emission */
+    next({ hidden }) {
+      el.hidden = hidden
+      if (hidden) {
+        el.setAttribute("tabindex", "-1")
+        el.blur()
+      } else {
+        el.removeAttribute("tabindex")
+      }
+    },
+
+    /* Handle complete */
+    complete() {
+      el.style.top = ""
+      el.hidden = true
+      el.removeAttribute("tabindex")
+    }
+  })
+
+  /* Watch header height */
+  header$
+    .pipe(
+      takeUntil(done$),
+      distinctUntilKeyChanged("height")
+    )
+      .subscribe(({ height }) => {
+        el.style.top = `${height + 16}px`
+      })
+
+  /* Go back to top */
+  fromEvent(el, "click")
+    .subscribe(ev => {
+      ev.preventDefault()
+      window.scrollTo({ top: 0 })
+    })
+
+  /* Create and return component */
+  return watchBackToTop(el, { viewport$, main$, target$ })
+    .pipe(
+      tap(state => push$.next(state)),
+      finalize(() => push$.complete()),
+      map(state => ({ ref: el, ...state }))
+    )
+}