import { PlanPeriod } from './plan';
import { formatUSD } from './pricingModel';

/** A priced voucher the merchant applied on the pricing page, waiting for checkout. */
export type AppliedVoucher = {
  code: string;
  type: 'PERCENTAGE' | 'FIXED_AMOUNT';
  value: number;
  /** Plan keys it applies to; empty or "ALL" means every plan. */
  plans: string[];
  /** Billing cycles it discounts on the subscription; null is every cycle. */
  durationMonths: number | null;
};

/** Said when a priced code has no Stripe promotion code behind it. */
export const VOUCHER_NOT_HERE_MESSAGE =
  "This code can't be used on this checkout yet.";

/**
 * Whether the voucher takes money off a given plan.
 * @param {AppliedVoucher | null} voucher - The applied voucher, if any.
 * @param {string} planKey - The plan the merchant is looking at.
 * @return {boolean} True when the voucher names the plan, or every plan.
 */
export const voucherAppliesTo = (
  voucher: AppliedVoucher | null,
  planKey: string
): boolean =>
  !!voucher &&
  (voucher.plans.length === 0 ||
    voucher.plans.includes('ALL') ||
    voucher.plans.includes(planKey));

/**
 * The monthly figure a plan comes to with the voucher on it. A percentage
 * takes its share off the monthly figure; a fixed amount comes off each
 * charge, so on the annual plan it is spread over the twelve months.
 * @param {number} monthly - The plan's monthly figure before the voucher.
 * @param {PlanPeriod} period - The period the figure is billed on.
 * @param {AppliedVoucher} voucher - The voucher.
 * @return {number} The discounted monthly figure, never below zero.
 */
export const voucherMonthlyPrice = (
  monthly: number,
  period: PlanPeriod,
  voucher: AppliedVoucher
): number => {
  if (voucher.type === 'PERCENTAGE') {
    return Math.max(0, Math.round(monthly * (100 - voucher.value)) / 100);
  }
  const perMonth =
    period === PlanPeriod.YEARLY ? voucher.value / 12 : voucher.value;

  return Math.max(0, Math.round((monthly - perMonth) * 100) / 100);
};

/**
 * The voucher in a few words: what it takes off.
 * @param {AppliedVoucher} voucher - The voucher.
 * @return {string} "15% off" or "$38 off".
 */
export const voucherLabel = (voucher: AppliedVoucher): string =>
  voucher.type === 'PERCENTAGE'
    ? `${voucher.value}% off`
    : `${formatUSD(voucher.value)} off`;

/**
 * How long the voucher lasts, for the line under the price.
 * @param {AppliedVoucher} voucher - The voucher.
 * @return {string} "on every payment", "on your first payment" or "for your first N months".
 */
export const voucherDurationNote = (voucher: AppliedVoucher): string => {
  if (voucher.durationMonths === null) return 'on every payment';
  if (voucher.durationMonths <= 1) return 'on your first payment';

  return `for your first ${voucher.durationMonths} months`;
};