1 files changed, 50 insertions, 0 deletions
diff --git a/packages/frontend/src/scripts/sticky-sidebar.ts b/packages/frontend/src/scripts/sticky-sidebar.ts
new file mode 100644
index 0000000000..c67b8f37ac
--- /dev/null
+++ b/packages/frontend/src/scripts/sticky-sidebar.ts
@@ -0,0 +1,50 @@
+export class StickySidebar {
+	private lastScrollTop = 0;
+	private container: HTMLElement;
+	private el: HTMLElement;
+	private spacer: HTMLElement;
+	private marginTop: number;
+	private isTop = false;
+	private isBottom = false;
+	private offsetTop: number;
+	private globalHeaderHeight: number = 59;
+
+	constructor(container: StickySidebar['container'], marginTop = 0, globalHeaderHeight = 0) {
+		this.container = container;
+		this.el = this.container.children[0] as HTMLElement;
+		this.el.style.position = 'sticky';
+		this.spacer = document.createElement('div');
+		this.container.prepend(this.spacer);
+		this.marginTop = marginTop;
+		this.offsetTop = this.container.getBoundingClientRect().top;
+		this.globalHeaderHeight = globalHeaderHeight;
+	}
+
+	public calc(scrollTop: number) {
+		if (scrollTop > this.lastScrollTop) { // downscroll
+			const overflow = Math.max(0, this.globalHeaderHeight + (this.el.clientHeight + this.marginTop) - window.innerHeight);
+			this.el.style.bottom = null;
+			this.el.style.top = `${-overflow + this.marginTop + this.globalHeaderHeight}px`;
+
+			this.isBottom = (scrollTop + window.innerHeight) >= (this.el.offsetTop + this.el.clientHeight);
+
+			if (this.isTop) {
+				this.isTop = false;
+				this.spacer.style.marginTop = `${Math.max(0, this.globalHeaderHeight + this.lastScrollTop + this.marginTop - this.offsetTop)}px`;
+			}
+		} else { // upscroll
+			const overflow = this.globalHeaderHeight + (this.el.clientHeight + this.marginTop) - window.innerHeight;
+			this.el.style.top = null;
+			this.el.style.bottom = `${-overflow}px`;
+
+			this.isTop = scrollTop + this.marginTop + this.globalHeaderHeight <= this.el.offsetTop;
+
+			if (this.isBottom) {
+				this.isBottom = false;
+				this.spacer.style.marginTop = `${this.globalHeaderHeight + this.lastScrollTop + this.marginTop - this.offsetTop - overflow}px`;
+			}
+		}
+
+		this.lastScrollTop = scrollTop <= 0 ? 0 : scrollTop;
+	}
+}