test(miner-ui): cover chat-scroll stick-to-bottom boundary and clamp (#7793)

apps/loopover-miner-ui/src/lib/chat-scroll.test.ts

@@ -0,0 +1,63 @@
+import { describe, expect, it } from "vitest";
+import { CHAT_NEAR_BOTTOM_PX, isChatViewportNearBottom, scrollChatViewportToBottom } from "./chat-scroll";
+
+/** A minimal stand-in for the scroll viewport: jsdom can't set scrollHeight/clientHeight on a real element. */
+function viewport(scrollHeight: number, clientHeight: number, scrollTop = 0): HTMLElement {
+  return { scrollTop, scrollHeight, clientHeight } as unknown as HTMLElement;
+}
+
+describe("isChatViewportNearBottom (#7229)", () => {
+  it("treats a distance of exactly CHAT_NEAR_BOTTOM_PX as still pinned (the <= boundary)", () => {
+    // scrollHeight - scrollTop - clientHeight === 80
+    expect(isChatViewportNearBottom(viewport(1000, 400, 520))).toBe(true);
+  });
+
+  it("treats one pixel past the threshold as scrolled away", () => {
+    // ...=== 81
+    expect(isChatViewportNearBottom(viewport(1000, 400, 519))).toBe(false);
+  });
+
+  it("is true when the viewport sits exactly at the bottom", () => {
+    expect(isChatViewportNearBottom(viewport(1000, 400, 600))).toBe(true);
+  });
+
+  it("is true for content shorter than the viewport (negative distance, nothing to scroll)", () => {
+    expect(isChatViewportNearBottom(viewport(200, 400, 0))).toBe(true);
+  });
+
+  it("is false when scrolled far up", () => {
+    expect(isChatViewportNearBottom(viewport(5000, 400, 0))).toBe(false);
+  });
+
+  it("honors an explicit thresholdPx instead of the default", () => {
+    // distance === 10: outside a 0px threshold, inside the 80px default.
+    expect(isChatViewportNearBottom(viewport(1000, 400, 590), 0)).toBe(false);
+    expect(isChatViewportNearBottom(viewport(1000, 400, 590))).toBe(true);
+    // distance === 0 still counts at a 0px threshold (<=, not <).
+    expect(isChatViewportNearBottom(viewport(1000, 400, 600), 0)).toBe(true);
+  });
+
+  it("exposes the documented 80px threshold", () => {
+    expect(CHAT_NEAR_BOTTOM_PX).toBe(80);
+  });
+});
+
+describe("scrollChatViewportToBottom (#7229)", () => {
+  it("scrolls to the maximum scrollable offset", () => {
+    const el = viewport(1000, 400, 0);
+    scrollChatViewportToBottom(el);
+    expect(el.scrollTop).toBe(600);
+  });
+
+  it("clamps to 0 when the content is shorter than the viewport", () => {
+    const el = viewport(200, 400, 25);
+    scrollChatViewportToBottom(el);
+    expect(el.scrollTop).toBe(0);
+  });
+
+  it("leaves an already-bottomed viewport at the same offset (idempotent)", () => {
+    const el = viewport(1000, 400, 600);
+    scrollChatViewportToBottom(el);
+    expect(el.scrollTop).toBe(600);
+  });
+});