1 files changed, 85 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..f5bc6bf9ce
--- /dev/null
+++ b/packages/frontend/src/scripts/scroll.ts
@@ -0,0 +1,85 @@
+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 getScrollPosition(el: Element | null): number {
+	const container = getScrollContainer(el);
+	return container == null ? window.scrollY : container.scrollTop;
+}
+
+export function isTopVisible(el: Element | null): boolean {
+	const scrollTop = getScrollPosition(el);
+	const topPosition = el.offsetTop; // TODO: container内でのelの相対位置を取得できればより正確になる
+
+	return scrollTop <= topPosition;
+}
+
+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;
+}
+
+export function onScrollTop(el: Element, cb) {
+	const container = getScrollContainer(el) || window;
+	const onScroll = ev => {
+		if (!document.body.contains(el)) return;
+		if (isTopVisible(el)) {
+			cb();
+			container.removeEventListener('scroll', onScroll);
+		}
+	};
+	container.addEventListener('scroll', onScroll, { passive: true });
+}
+
+export function onScrollBottom(el: Element, cb) {
+	const container = getScrollContainer(el) || window;
+	const onScroll = ev => {
+		if (!document.body.contains(el)) return;
+		const pos = getScrollPosition(el);
+		if (pos + el.clientHeight > el.scrollHeight - 1) {
+			cb();
+			container.removeEventListener('scroll', onScroll);
+		}
+	};
+	container.addEventListener('scroll', onScroll, { passive: true });
+}
+
+export function scroll(el: Element, options: {
+	top?: number;
+	left?: number;
+	behavior?: ScrollBehavior;
+}) {
+	const container = getScrollContainer(el);
+	if (container == null) {
+		window.scroll(options);
+	} else {
+		container.scroll(options);
+	}
+}
+
+export function scrollToTop(el: Element, options: { behavior?: ScrollBehavior; } = {}) {
+	scroll(el, { top: 0, ...options });
+}
+
+export function scrollToBottom(el: Element, options: { behavior?: ScrollBehavior; } = {}) {
+	scroll(el, { top: 99999, ...options }); // TODO: ちゃんと計算する
+}
+
+export function isBottom(el: Element, asobi = 0) {
+	const container = getScrollContainer(el);
+	const current = container
+		? el.scrollTop + el.offsetHeight
+		: window.scrollY + window.innerHeight;
+	const max = container
+		? el.scrollHeight
+		: document.body.offsetHeight;
+	return current >= (max - asobi);
+}