Restructured project

src/assets/javascripts/components/header/offset/index.ts

@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2016-2019 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 } from "rxjs"
+import {
+  distinctUntilChanged,
+  map,
+  shareReplay,
+  switchMapTo
+} from "rxjs/operators"
+
+import { ViewportOffset, ViewportSize } from "../../../utilities"
+import { Header } from "../_"
+
+/* ----------------------------------------------------------------------------
+ * Function types
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Options
+ */
+interface Options {
+  size$: Observable<ViewportSize>      /* Viewport size observable */
+  offset$: Observable<ViewportOffset>  /* Viewport offset observable */
+  header$: Observable<Header>          /* Header observable */
+}
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Watch viewport offset relative to an element's top
+ *
+ * This function returns an observable that computes the relative offset to the
+ * top of the given element based on the current viewport offset.
+ *
+ * @param el - Element
+ * @param options - Options
+ *
+ * @return Viewport offset observable
+ */
+export function watchTopOffset(
+  el: HTMLElement, { size$, offset$, header$ }: Options
+): Observable<ViewportOffset> {
+
+  /* Compute necessary adjustment for offset */
+  const adjust$ = size$
+    .pipe(
+      switchMapTo(header$),
+      map(({ height }) => el.offsetTop - height),
+      distinctUntilChanged()
+    )
+
+  /* Compute relative offset and return as hot observable */
+  return combineLatest([offset$, adjust$])
+    .pipe(
+      map(([{ x, y }, adjust]) => ({ x, y: y - adjust })),
+      shareReplay(1)
+    )
+}
+
+/**
+ * Watch viewport offset relative to an element's bottom
+ *
+ * This function returns an observable that computes the relative offset to the
+ * bottom of the given element based on the current viewport offset.
+ *
+ * @param el - Element
+ * @param options - Options
+ *
+ * @return Viewport offset observable
+ */
+export function watchBottomOffset(
+  el: HTMLElement, { size$, offset$, header$ }: Options
+): Observable<ViewportOffset> {
+
+  /* Compute necessary adjustment for offset */
+  const adjust$ = size$
+    .pipe(
+      switchMapTo(header$),
+      map(({ height }) => el.offsetTop + el.offsetHeight - height),
+      distinctUntilChanged()
+    )
+
+  /* Compute relative offset and return as hot observable */
+  return combineLatest([offset$, adjust$])
+    .pipe(
+      map(([{ x, y }, adjust]) => ({ x, y: y - adjust })),
+      shareReplay(1)
+    )
+}