feat(frontend): tail-store Zustand with FIFO cap 10k per slice

src/store/tail-store.test.ts

@@ -0,0 +1,131 @@
+// @vitest-environment node
+// `useTailStore` is a pure zustand store with no DOM / React dependencies,
+// so a node environment is fine. We import `getState()` and `setState`
+// from the store directly (no React render) and assert on the resulting
+// state shape.
+
+import { beforeEach, describe, expect, it } from "vitest";
+import type { Activity, Claim, Remittance } from "@/types";
+import { TAIL_CAP, useTailStore } from "./tail-store";
+
+function makeClaim(id: string, overrides: Partial<Claim> = {}): Claim {
+  return {
+    id,
+    patientName: `Patient ${id}`,
+    providerNpi: "1234567890",
+    payerName: "Medicaid",
+    cptCode: "99213",
+    billedAmount: 100,
+    receivedAmount: 0,
+    status: "submitted",
+    submissionDate: "2026-06-20T00:00:00Z",
+    ...overrides,
+  };
+}
+
+function makeRemittance(id: string, overrides: Partial<Remittance> = {}): Remittance {
+  return {
+    id,
+    claimId: `CLM-${id}`,
+    payerName: "Medicaid",
+    paidAmount: 100,
+    adjustmentAmount: 0,
+    receivedDate: "2026-06-20",
+    checkNumber: id,
+    status: "received",
+    ...overrides,
+  };
+}
+
+function makeActivity(id: string, overrides: Partial<Activity> = {}): Activity {
+  return {
+    id,
+    kind: "claim_submitted",
+    message: `Event ${id}`,
+    timestamp: "2026-06-20T00:00:00Z",
+    ...overrides,
+  };
+}
+
+describe("useTailStore", () => {
+  // Each test starts from a known-empty state. The store is module-level
+  // (singleton), so we use `reset()` to clear between cases — that's also
+  // what production code calls on stream open.
+  beforeEach(() => {
+    useTailStore.getState().reset("claims");
+    useTailStore.getState().reset("remittances");
+    useTailStore.getState().reset("activity");
+  });
+
+  it("test_add_claim_adds_new_claim_keyed_by_id", () => {
+    const { addClaim } = useTailStore.getState();
+    addClaim(makeClaim("CLM-1"));
+    addClaim(makeClaim("CLM-2"));
+    const { claims } = useTailStore.getState();
+    expect(Object.keys(claims)).toHaveLength(2);
+    expect(claims["CLM-1"]?.id).toBe("CLM-1");
+    expect(claims["CLM-2"]?.id).toBe("CLM-2");
+  });
+
+  it("test_add_claim_with_duplicate_id_is_noop", () => {
+    const { addClaim } = useTailStore.getState();
+    addClaim(makeClaim("CLM-1", { patientName: "Original" }));
+    addClaim(makeClaim("CLM-1", { patientName: "Updated" }));
+    const { claims } = useTailStore.getState();
+    expect(Object.keys(claims)).toHaveLength(1);
+    // First write wins; duplicates are silently dropped so the snapshot
+    // replay on reconnect doesn't trample the canonical row.
+    expect(claims["CLM-1"]?.patientName).toBe("Original");
+  });
+
+  it("test_reset_claims_clears_only_claims_slice", () => {
+    const { addClaim, addRemittance, addActivity, reset } = useTailStore.getState();
+    addClaim(makeClaim("CLM-1"));
+    addRemittance(makeRemittance("RMT-1"));
+    addActivity(makeActivity("ACT-1"));
+
+    reset("claims");
+    const s = useTailStore.getState();
+    expect(Object.keys(s.claims)).toHaveLength(0);
+    expect(Object.keys(s.remittances)).toHaveLength(1);
+    expect(s.activity).toHaveLength(1);
+  });
+
+  it("test_add_activity_appends", () => {
+    const { addActivity } = useTailStore.getState();
+    addActivity(makeActivity("ACT-1", { message: "first" }));
+    addActivity(makeActivity("ACT-2", { message: "second" }));
+    addActivity(makeActivity("ACT-3", { message: "third" }));
+    const { activity } = useTailStore.getState();
+    expect(activity).toHaveLength(3);
+    // Activity has no stable id; it lives in an array. Insertion order is
+    // the only ordering signal.
+    expect(activity.map((a) => a.message)).toEqual(["first", "second", "third"]);
+  });
+
+  it("test_fifo_cap_evicts_oldest_when_over_10000", () => {
+    // Insert 5 over the cap so the eviction policy must actually run.
+    // The plan calls for evicting the oldest 100 (or enough to be back at
+    // the cap) — we just assert: size == TAIL_CAP and the very-first
+    // items are gone.
+    //
+    // 10 005 individual `addClaim` calls is intentionally a stress test
+    // of the eviction path: each call rebuilds the dict + order array
+    // so the wall-clock cost is O(N^2) in the number of items ever
+    // inserted. Bump the per-test timeout from the default 5s to 60s
+    // so this case can complete in CI on slow runners.
+    const N = TAIL_CAP + 5;
+    const { addClaim } = useTailStore.getState();
+    for (let i = 0; i < N; i++) {
+      addClaim(makeClaim(`CLM-${i.toString().padStart(6, "0")}`));
+    }
+    const { claims } = useTailStore.getState();
+    expect(Object.keys(claims)).toHaveLength(TAIL_CAP);
+    // The five oldest (CLM-000000 .. CLM-000004) must be gone.
+    expect(claims["CLM-000000"]).toBeUndefined();
+    expect(claims["CLM-000004"]).toBeUndefined();
+    // The most recent (CLM-0010004) must be present.
+    const lastKey = `CLM-${(N - 1).toString().padStart(6, "0")}`;
+    expect(claims[lastKey]).toBeDefined();
+  }, 60_000);
+});