import { describe, it, expect } from "vitest";
import { previousMonth, defaultReferencePeriod, comparisonMeta } from "./useCompare";

describe("useCompare helpers", () => {
  describe("previousMonth", () => {
    it("goes back one month within the same year", () => {
      expect(previousMonth(2026, 3)).toEqual({ year: 2026, month: 2 });
      expect(previousMonth(2026, 12)).toEqual({ year: 2026, month: 11 });
    });

    it("wraps around January to December of previous year", () => {
      expect(previousMonth(2026, 1)).toEqual({ year: 2025, month: 12 });
    });
  });

  describe("defaultReferencePeriod", () => {
    it("returns the month before the given date", () => {
      expect(defaultReferencePeriod(new Date(2026, 3, 15))).toEqual({ year: 2026, month: 3 });
    });

    it("wraps around when today is in January", () => {
      expect(defaultReferencePeriod(new Date(2026, 0, 10))).toEqual({ year: 2025, month: 12 });
    });

    it("handles the last day of a month", () => {
      expect(defaultReferencePeriod(new Date(2026, 6, 31))).toEqual({ year: 2026, month: 6 });
    });
  });

  describe("comparisonMeta", () => {
    it("MoM returns the previous month", () => {
      expect(comparisonMeta("mom", 2026, 3)).toEqual({ previousYear: 2026, previousMonth: 2 });
    });

    it("MoM wraps around January", () => {
      expect(comparisonMeta("mom", 2026, 1)).toEqual({ previousYear: 2025, previousMonth: 12 });
    });

    it("YoY returns the same month in the previous year", () => {
      expect(comparisonMeta("yoy", 2026, 3)).toEqual({ previousYear: 2025, previousMonth: 3 });
    });

    it("YoY for January stays on January of previous year", () => {
      expect(comparisonMeta("yoy", 2026, 1)).toEqual({ previousYear: 2025, previousMonth: 1 });
    });
  });
});