master-zapier-plan-draft/packages/zappier/src/billing/stripe.ts

import { UsageEntry } from '../usage';

export const METER_EVENT_NAME = 'zappier.api_cents';

export interface MeterEventClient {
  createMeterEvent(params: {
    eventName: string;
    customerId: string;
    value: string;
    /** Stripe-side dedup key; events with the same identifier are dropped. */
    identifier?: string;
  }): Promise<void>;
}

export function computeBillableCents(entries: UsageEntry[], monthlyCreditCents: number): number {
  const totalCents = entries.reduce((sum, e) => sum + e.cents, 0);
  return Math.max(0, totalCents - monthlyCreditCents);
}

export function computeDelta(billableCents: number, previouslyReportedCents: number): number {
  return Math.max(0, billableCents - previouslyReportedCents);
}

// Public API: retained for API compatibility. The monthly billing job now uses
// the delta-based path in src/jobs/report-usage.ts (reportMonthlyUsage), which
// shares computeBillableCents with this function. Do not remove.
export async function reportUsage(
  client: MeterEventClient,
  stripeCustomerId: string,
  entries: UsageEntry[],
  monthlyCreditCents: number,
): Promise<number> {
  const billable = computeBillableCents(entries, monthlyCreditCents);
  if (billable <= 0) return 0;
  await client.createMeterEvent({
    eventName: METER_EVENT_NAME,
    customerId: stripeCustomerId,
    value: String(billable),
  });
  return billable;
}