Adapters

The Booking Kit uses the adapter pattern to abstract external dependencies. Each adapter is a TypeScript interface — implement it for your preferred provider.

Available adapters

AuthAdapter

interface AuthAdapter {
  getSession(request: Request): Promise<AuthSession | null>;
  getUser(userId: string): Promise<AuthUser | null>;
}

Default: NextAuth.js 5.x Alternatives: Supabase Auth, Clerk, Lucia, custom JWT

EmailAdapter

interface EmailAdapter {
  sendEmail(options: SendEmailOptions): Promise<EmailResult>;
}

interface SendEmailOptions {
  to: string;
  subject: string;
  html: string;
  text?: string;
  from?: string;
  replyTo?: string;
  attachments?: EmailAttachment[];
}

Default: Resend Alternatives: SendGrid, AWS SES, Postmark, Nodemailer

CalendarAdapter

interface CalendarAdapter {
  createEvent(options: CalendarEventOptions): Promise<CalendarEventResult>;
  updateEvent(eventId: string, options: CalendarEventOptions): Promise<CalendarEventResult>;
  deleteEvent(eventId: string): Promise<void>;
  getConflicts(start: Date, end: Date): Promise<CalendarConflict[]>;
}

Default: Google Calendar (OAuth) Alternatives: Microsoft Outlook, CalDAV

JobAdapter

interface JobAdapter {
  enqueue(jobName: string, payload: unknown, options?: { delay?: number }): Promise<void>;
  scheduleAt(jobName: string, payload: unknown, runAt: Date): Promise<void>;
}

Default: Inngest 3.x Alternatives: Trigger.dev, BullMQ, Vercel Cron, pg-boss

PaymentAdapter

interface PaymentAdapter {
  createPaymentIntent(options: CreatePaymentIntentOptions): Promise<CreatePaymentIntentResult>;
  createSetupIntent(options: CreateSetupIntentOptions): Promise<CreateSetupIntentResult>;
  capturePayment(paymentIntentId: string): Promise<CaptureResult>;
  refundPayment(paymentIntentId: string, amountCents?: number): Promise<RefundResult>;
}

Default: Stripe Alternatives: Implement for your payment provider

StorageAdapter

interface StorageAdapter {
  encrypt(plaintext: string): Promise<string>;
  decrypt(ciphertext: string): Promise<string>;
}

Default: Env var encryption key (AES-256) Alternatives: HashiCorp Vault, AWS KMS, Azure Key Vault

SmsAdapter

interface SmsAdapter {
  sendSms(options: SendSmsOptions): Promise<SmsResult>;
}

Default: Not implemented (optional) Alternatives: Twilio, MessageBird, Vonage

Database Adapters

While The Booking Kit is built for PostgreSQL, it provides specialized adapters for other database environments.

Cloudflare D1 / SQLite (@thebookingkit/d1)

Cloudflare D1 requires special handling for date storage and concurrency. This package provides:

• Canonical Date Encoding: SQLite has no native timestamp type. D1DateCodec ensures all dates are stored as sortable UTC-Z strings.
• Advisory Locking: Since SQLite lacks EXCLUDE constraints, D1BookingLock provides application-level mutexes to prevent double-booking.
• Schedule Adapters: Utilities to intersect personal and location schedules into RRULE windows.

import { D1DateCodec, D1BookingLock } from "@thebookingkit/d1";

// Ensure a slot is available and book it atomically
const lock = new D1BookingLock(db);
await lock.withLock(`provider:${id}`, async () => {
  // Read-check-write logic here
});

Implementing an adapter

// Example: Custom email adapter using SendGrid
import sgMail from "@sendgrid/mail";

const sendGridAdapter: EmailAdapter = {
  async sendEmail(options) {
    sgMail.setApiKey(process.env.SENDGRID_API_KEY!);

    const [response] = await sgMail.send({
      to: options.to,
      from: options.from || "noreply@example.com",
      subject: options.subject,
      html: options.html,
      text: options.text,
    });

    return {
      messageId: response.headers["x-message-id"],
      status: "sent" as const,
    };
  },
};

Using adapters

Pass adapters to the functions that need them:

import { sendConfirmationEmail } from "@thebookingkit/core";

await sendConfirmationEmail(bookingPayload, sendGridAdapter);

Adapters are injected at the call site, not globally configured. This makes testing easy — pass a mock adapter in tests.