1 files changed, 129 insertions, 0 deletions
diff --git a/packages/frontend/src/scripts/scroll.ts b/packages/frontend/src/scripts/scroll.ts
new file mode 100644
index 0000000000..e3d9dc00c2
--- /dev/null
+++ b/packages/frontend/src/scripts/scroll.ts
@@ -0,0 +1,129 @@
+type ScrollBehavior = 'auto' | 'smooth' | 'instant';
+
+export function getScrollContainer(el: HTMLElement | null): HTMLElement | null {
+	if (el == null || el.tagName === 'HTML') return null;
+	const overflow = window.getComputedStyle(el).getPropertyValue('overflow-y');
+	if (overflow === 'scroll' || overflow === 'auto') {
+		return el;
+	} else {
+		return getScrollContainer(el.parentElement);
+	}
+}
+
+export function getStickyTop(el: HTMLElement, container: HTMLElement | null = null, top: number = 0) {
+	if (!el.parentElement) return top;
+	const data = el.dataset.stickyContainerHeaderHeight;
+	const newTop = data ? Number(data) + top : top;
+	if (el === container) return newTop;
+	return getStickyTop(el.parentElement, container, newTop);
+}
+
+export function getScrollPosition(el: HTMLElement | null): number {
+	const container = getScrollContainer(el);
+	return container == null ? window.scrollY : container.scrollTop;
+}
+
+export function onScrollTop(el: HTMLElement, cb: () => unknown, tolerance: number = 1, once: boolean = false) {
+	// とりあえず評価してみる
+	if (isTopVisible(el)) {
+		cb();
+		if (once) return null;
+	}
+
+	const container = getScrollContainer(el) || window;
+
+	const onScroll = ev => {
+		if (!document.body.contains(el)) return;
+		if (isTopVisible(el, tolerance)) {
+			cb();
+			if (once) removeListener();
+		}
+	};
+
+	function removeListener() { container.removeEventListener('scroll', onScroll); }
+	container.addEventListener('scroll', onScroll, { passive: true });
+	return removeListener;
+}
+
+export function onScrollBottom(el: HTMLElement, cb: () => unknown, tolerance: number = 1, once: boolean = false) {
+	const container = getScrollContainer(el);
+
+	// とりあえず評価してみる
+	if (isBottomVisible(el, tolerance, container)) {
+		cb();
+		if (once) return null;
+	}
+
+	const containerOrWindow = container || window;
+	const onScroll = ev => {
+		if (!document.body.contains(el)) return;
+		if (isBottomVisible(el, 1, container)) {
+			cb();
+			if (once) removeListener();
+		}
+	};
+
+	function removeListener() {
+		containerOrWindow.removeEventListener('scroll', onScroll);
+	}
+	containerOrWindow.addEventListener('scroll', onScroll, { passive: true });
+	return removeListener;
+}
+
+export function scroll(el: HTMLElement, options: ScrollToOptions | undefined) {
+	const container = getScrollContainer(el);
+	if (container == null) {
+		window.scroll(options);
+	} else {
+		container.scroll(options);
+	}
+}
+
+/**
+ * Scroll to Top
+ * @param el Scroll container element
+ * @param options Scroll options
+ */
+export function scrollToTop(el: HTMLElement, options: { behavior?: ScrollBehavior; } = {}) {
+	scroll(el, { top: 0, ...options });
+}
+
+/**
+ * Scroll to Bottom
+ * @param el Content element
+ * @param options Scroll options
+ * @param container Scroll container element
+ */
+export function scrollToBottom(
+	el: HTMLElement,
+	options: ScrollToOptions = {},
+	container = getScrollContainer(el),
+) {
+	if (container) {
+		container.scroll({ top: el.scrollHeight - container.clientHeight + getStickyTop(el, container) || 0, ...options });
+	} else {
+		window.scroll({
+			top: (el.scrollHeight - window.innerHeight + getStickyTop(el, container) + (window.innerWidth <= 500 ? 96 : 0)) || 0,
+			...options
+		});
+	}
+}
+
+export function isTopVisible(el: HTMLElement, tolerance: number = 1): boolean {
+	const scrollTop = getScrollPosition(el);
+	return scrollTop <= tolerance;
+}
+
+export function isBottomVisible(el: HTMLElement, tolerance = 1, container = getScrollContainer(el)) {
+	if (container) return el.scrollHeight <= container.clientHeight + Math.abs(container.scrollTop) + tolerance;
+	return el.scrollHeight <= window.innerHeight + window.scrollY + tolerance;
+}
+
+// https://ja.javascript.info/size-and-scroll-window#ref-932
+export function getBodyScrollHeight() {
+	return Math.max(
+		document.body.scrollHeight, document.documentElement.scrollHeight,
+		document.body.offsetHeight, document.documentElement.offsetHeight,
+		document.body.clientHeight, document.documentElement.clientHeight
+	);
+}