Restructured project

src/assets/javascripts/components/main/index.ts

@@ -0,0 +1,117 @@
+/*
+ * 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,
+  pluck,
+  shareReplay
+} from "rxjs/operators"
+
+import { ViewportOffset, ViewportSize } from "../../utilities"
+import { Header } from "../header"
+
+/* ----------------------------------------------------------------------------
+ * Types
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Main area
+ */
+export interface Main {
+  offset: number                       /* Main area top offset */
+  height: number                       /* Main area visible height */
+  active: boolean                      /* Scrolled past top offset */
+}
+
+/* ----------------------------------------------------------------------------
+ * Function types
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Options
+ */
+interface Options {
+  size$: Observable<ViewportSize>      /* Viewport size observable */
+  offset$: Observable<ViewportOffset>  /* Viewport offset observable */
+  header$: Observable<Header>          /* Header observable */
+}
+
+/* ----------------------------------------------------------------------------
+ * Functions
+ * ------------------------------------------------------------------------- */
+
+/**
+ * Watch main area
+ *
+ * This function returns an observable that computes the visual parameters of
+ * the main area from the viewport height and vertical offset, as well as the
+ * height of the header element. The height of the main area is corrected by
+ * the height of the header (if fixed) and footer element.
+ *
+ * @param el - Main area element
+ * @param options - Options
+ *
+ * @return Main area observable
+ */
+export function watchMain(
+  el: HTMLElement, { size$, offset$, header$ }: Options
+): Observable<Main> {
+
+  /* Compute necessary adjustment for header */
+  const adjust$ = header$
+    .pipe(
+      pluck("height")
+    )
+
+  /* Compute the main area's visible height */
+  const height$ = combineLatest([offset$, size$, adjust$])
+    .pipe(
+      map(([{ y }, { height }, adjust]) => {
+        const top    = el.offsetTop
+        const bottom = el.offsetHeight + top
+        return height
+          - Math.max(0, top    - y,  adjust)
+          - Math.max(0, height + y - bottom)
+      }),
+      distinctUntilChanged()
+    )
+
+  /* Compute whether the viewport offset is past the main area's top */
+  const active$ = combineLatest([offset$, adjust$])
+    .pipe(
+      map(([{ y }, adjust]) => y >= el.offsetTop - adjust),
+      distinctUntilChanged()
+    )
+
+  /* Combine into a single hot observable */
+  return combineLatest([height$, adjust$, active$])
+    .pipe(
+      map(([height, adjust, active]) => ({
+        offset: el.offsetTop - adjust,
+        height,
+        active
+      })),
+      shareReplay(1)
+    )
+}