import { describe, expect, it } from "vitest";
import { currentFyStartYear, fyLabel, fyRange, fyStartYear, monthOf, todayIst, FY_MONTHS } from "./fiscal";

describe("financial year", () => {
  it("starts on 1 April", () => {
    expect(fyStartYear("2026-03-31")).toBe(2025);
    expect(fyStartYear("2026-04-01")).toBe(2026);
    expect(fyStartYear("2026-12-31")).toBe(2026);
    expect(fyStartYear("2027-01-01")).toBe(2026);
  });

  it("rejects things that are not ISO dates", () => {
    expect(fyStartYear("")).toBeNull();
    expect(fyStartYear("01/04/2026")).toBeNull();
    expect(fyStartYear("2026-13-01")).toBeNull();
    expect(monthOf("2026-00-10")).toBeNull();
    expect(monthOf("2026-07-10")).toBe(7);
  });

  it("labels and ranges", () => {
    expect(fyLabel(2025)).toBe("FY 2025-26");
    expect(fyLabel(2099)).toBe("FY 2099-00");
    expect(fyRange(2025)).toEqual({ from: "2025-04-01", to: "2026-03-31" });
  });

  it("lists months April to March", () => {
    expect(FY_MONTHS.map((m) => m.month)).toEqual([4, 5, 6, 7, 8, 9, 10, 11, 12, 1, 2, 3]);
    expect(FY_MONTHS[0].label).toBe("April");
  });

  it("uses IST for now, not the machine time zone", () => {
    // 20:00 UTC on 31 March is already 01:30 on 1 April in India: a new financial year.
    const now = new Date("2026-03-31T20:00:00Z");
    expect(todayIst(now)).toBe("2026-04-01");
    expect(currentFyStartYear(now)).toBe(2026);
    // 18:29 UTC is still 23:59 on 31 March in India.
    expect(currentFyStartYear(new Date("2026-03-31T18:29:00Z"))).toBe(2025);
  });
});