/**
 * @file keepIfSame.test.ts
 * @description Covers the identity contract `keepIfSame` exists for: a polled
 * payload that is value-identical must keep the PREVIOUS reference (so React
 * bails out of the re-render), and any real change must yield the new one.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

import { describe, it, expect } from "vitest";
import { keepIfSame } from "../keepIfSame";

describe("keepIfSame", () => {
  it("keeps the previous reference when the fetched payload is value-identical", () => {
    const prev = [{ id: 1, stage: "implement" }];
    const fetched = [{ id: 1, stage: "implement" }];

    expect(keepIfSame(fetched)(prev)).toBe(prev);
  });

  it("yields the new value when anything actually changed", () => {
    const prev = [{ id: 1, stage: "implement" }];
    const fetched = [{ id: 1, stage: "review" }];

    expect(keepIfSame(fetched)(prev)).toBe(fetched);
  });

  it("yields the new value out of the null a poller starts from", () => {
    const fetched = { available: false };

    expect(keepIfSame(fetched)(null)).toBe(fetched);
  });

  it("keeps null when the payload is still null", () => {
    expect(keepIfSame(null)(null)).toBeNull();
  });
});