import { describe, test, expect } from "vitest";
import { resolveBulkDiscount, getNextBulkDiscountTier } from "./bulk-discount-calc";

const tiers = [
  { code: "MENGE10", minQuantity: 3, percent: 10 },
  { code: "MENGE15", minQuantity: 6, percent: 15 },
];

describe("resolveBulkDiscount", () => {
  test("returns null when no tier is configured", () => {
    expect(resolveBulkDiscount([], 5)).toBeNull();
  });

  test("returns null below the lowest threshold", () => {
    expect(resolveBulkDiscount(tiers, 2)).toBeNull();
  });

  test("picks the lowest tier at its boundary", () => {
    expect(resolveBulkDiscount(tiers, 3)).toEqual({ code: "MENGE10", minQuantity: 3, percent: 10 });
  });

  test("picks the higher tier once its threshold is reached", () => {
    expect(resolveBulkDiscount(tiers, 6)).toEqual({ code: "MENGE15", minQuantity: 6, percent: 15 });
  });

  test("is unaffected by tier input order", () => {
    const shuffled = [...tiers].reverse();
    expect(resolveBulkDiscount(shuffled, 6)).toEqual({ code: "MENGE15", minQuantity: 6, percent: 15 });
  });
});

describe("getNextBulkDiscountTier", () => {
  test("returns null when no tier is configured", () => {
    expect(getNextBulkDiscountTier([], 1)).toBeNull();
  });

  test("returns null once the highest tier is reached", () => {
    expect(getNextBulkDiscountTier(tiers, 6)).toBeNull();
  });

  test("reports units and percent of the next tier", () => {
    expect(getNextBulkDiscountTier(tiers, 1)).toEqual({ unitsUntilNext: 2, percent: 10 });
  });

  test("reports the tier after the currently active one", () => {
    expect(getNextBulkDiscountTier(tiers, 3)).toEqual({ unitsUntilNext: 3, percent: 15 });
  });
});