import { describe, expect, it } from "vitest";

import "@edr/ui-common/display-timezone";

// The pin must hold on ANY machine timezone — these assertions are the bug:
// before the patch they only passed on a PC already set to UTC+3.
describe("display-timezone pin (EAT, UTC+3)", () => {
  const utcMidnight = new Date("2026-01-01T00:00:00Z");

  it("formats Date.toLocale* in EAT regardless of machine timezone", () => {
    expect(utcMidnight.toLocaleTimeString("en-GB", { hour12: false })).toBe(
      "03:00:00",
    );
    // 22:00 UTC is already the NEXT day in EAT.
    expect(new Date("2026-01-01T22:00:00Z").toLocaleDateString("en-CA")).toBe(
      "2026-01-02",
    );
  });

  it("formats Intl.DateTimeFormat in EAT and keeps instanceof/statics", () => {
    const fmt = new Intl.DateTimeFormat("en-GB", {
      hour: "2-digit",
      minute: "2-digit",
      hour12: false,
    });
    expect(fmt.format(utcMidnight)).toBe("03:00");
    expect(fmt).toBeInstanceOf(Intl.DateTimeFormat);
    expect(Intl.DateTimeFormat.supportedLocalesOf(["en-GB"])).toContain(
      "en-GB",
    );
  });

  it("respects an explicit timeZone option", () => {
    expect(
      utcMidnight.toLocaleTimeString("en-GB", {
        hour12: false,
        timeZone: "UTC",
      }),
    ).toBe("00:00:00");
  });
});