1 files changed, 120 insertions, 0 deletions
diff --git a/src/features/layout/logic/collapse.test.ts b/src/features/layout/logic/collapse.test.ts
new file mode 100644
index 0000000..77e9f3c
--- /dev/null
+++ b/src/features/layout/logic/collapse.test.ts
@@ -0,0 +1,120 @@
+import { describe, expect, it } from "vitest";
+import {
+  bootDefaultOpen,
+  createCollapseStore,
+  parsePersistedOpen,
+  SIDEBAR_OPEN_KEY,
+  WIDE_BREAKPOINT,
+} from "./collapse";
+
+function fakeStorage(): { storage: Storage; raw(key: string): string | null } {
+  const map = new Map<string, string>();
+  const storage: Storage = {
+    get length() {
+      return map.size;
+    },
+    clear: () => map.clear(),
+    getItem: (key) => map.get(key) ?? null,
+    key: () => null,
+    removeItem: (key) => map.delete(key),
+    setItem: (key, value) => void map.set(key, value),
+  };
+  return { storage, raw: (key) => map.get(key) ?? null };
+}
+
+describe("bootDefaultOpen", () => {
+  it("defaults to open on wide screens (>= 1024px) and closed on narrow ones", () => {
+    expect(bootDefaultOpen(WIDE_BREAKPOINT)).toBe(true);
+    expect(bootDefaultOpen(1440)).toBe(true);
+    expect(bootDefaultOpen(1023)).toBe(false);
+    expect(bootDefaultOpen(0)).toBe(false);
+  });
+
+  it("defaults to open when the viewport is unknown (SSR/tests)", () => {
+    expect(bootDefaultOpen(undefined)).toBe(true);
+  });
+});
+
+describe("parsePersistedOpen", () => {
+  it("accepts today's bare JSON boolean format", () => {
+    expect(parsePersistedOpen("true")).toBe(true);
+    expect(parsePersistedOpen("false")).toBe(false);
+  });
+
+  it("ignores null, malformed JSON, and non-boolean values", () => {
+    expect(parsePersistedOpen(null)).toBeNull();
+    expect(parsePersistedOpen("{")).toBeNull();
+    expect(parsePersistedOpen('"true"')).toBeNull();
+    expect(parsePersistedOpen("{}")).toBeNull();
+  });
+});
+
+describe("createCollapseStore", () => {
+  it("uses the viewport default when nothing is persisted", () => {
+    const store = createCollapseStore({ viewportWidth: 1024 });
+    expect(store.isOpen("side")).toBe(true);
+    const narrow = createCollapseStore({ viewportWidth: 800 });
+    expect(narrow.isOpen("side")).toBe(false);
+  });
+
+  it("restores the persisted boolean over the viewport default", () => {
+    const { storage } = fakeStorage();
+    storage.setItem(SIDEBAR_OPEN_KEY, "false");
+    const store = createCollapseStore({ storage, viewportWidth: 1440 });
+    expect(store.isOpen("side")).toBe(false);
+  });
+
+  it("persists toggles as today's bare JSON boolean (same key, same bytes)", () => {
+    const { storage, raw } = fakeStorage();
+    const store = createCollapseStore({ storage, viewportWidth: 1024 });
+    store.toggle("side");
+    expect(raw(SIDEBAR_OPEN_KEY)).toBe("false");
+    store.toggle("side");
+    expect(raw(SIDEBAR_OPEN_KEY)).toBe("true");
+  });
+
+  it("tracks per-node state reactively", () => {
+    const store = createCollapseStore({ viewportWidth: 1024 });
+    const seen: boolean[] = [];
+    const unsubscribe = store.subscribe((state) =>
+      seen.push(state.openByNode.side ?? state.defaultOpen),
+    );
+    try {
+      store.setOpen("side", false);
+      store.setOpen("side", true);
+    } finally {
+      unsubscribe();
+    }
+    expect(seen).toEqual([true, false, true]);
+    expect(store.isOpen("side")).toBe(true);
+  });
+
+  it("an untracked node falls back to the default", () => {
+    const store = createCollapseStore({ viewportWidth: 800 });
+    expect(store.isOpen("other")).toBe(false);
+  });
+
+  it("survives storage failures (quota errors are swallowed)", () => {
+    const broken: Storage = {
+      get length() {
+        return 0;
+      },
+      clear: () => undefined,
+      getItem: () => null,
+      key: () => null,
+      removeItem: () => undefined,
+      setItem: () => {
+        throw new Error("quota exceeded");
+      },
+    };
+    const store = createCollapseStore({ storage: broken, viewportWidth: 1024 });
+    expect(() => store.toggle("side")).not.toThrow();
+    expect(store.isOpen("side")).toBe(false);
+  });
+
+  it("works without storage (session-only chrome state)", () => {
+    const store = createCollapseStore({ viewportWidth: 1024 });
+    store.toggle("side");
+    expect(store.isOpen("side")).toBe(false);
+  });
+});