learning_ai_clock/backend/src/modules/webhooks/dispatcher.ts

import { createHmac } from 'node:crypto';
import type { WebhookEventType, WebhookSubscriptionDoc, WebhookEventDoc } from './types.js';
import * as repo from './repository.js';

// ── HMAC Signing ──────────────────────────────────────────────

export function signPayload(payload: string, secret: string): string {
  return createHmac('sha256', secret).update(payload).digest('hex');
}

export function buildSignatureHeader(payload: string, secret: string): string {
  const timestamp = Math.floor(Date.now() / 1000);
  const signature = createHmac('sha256', secret).update(`${timestamp}.${payload}`).digest('hex');
  return `t=${timestamp},v1=${signature}`;
}

// ── Delivery ──────────────────────────────────────────────────

export interface DeliveryResult {
  subscriptionId: string;
  eventId: string;
  success: boolean;
  statusCode?: number;
  error?: string;
}

/**
 * Dispatch a webhook event to all matching subscriptions for a user.
 * Returns delivery results for each subscription.
 */
export async function dispatchEvent(
  userId: string,
  productId: string,
  eventType: WebhookEventType,
  payload: Record<string, unknown>,
  log?: { info: (...args: unknown[]) => void; error: (...args: unknown[]) => void }
): Promise<DeliveryResult[]> {
  const subscriptions = await repo.findSubscriptionsForEvent(userId, productId, eventType);

  if (subscriptions.length === 0) {
    return [];
  }

  const results: DeliveryResult[] = [];

  for (const sub of subscriptions) {
    const result = await deliverToSubscription(sub, eventType, payload, log);
    results.push(result);
  }

  return results;
}

/**
 * Deliver a single event to a single subscription.
 * Creates an event log entry and handles retries.
 */
async function deliverToSubscription(
  sub: WebhookSubscriptionDoc,
  eventType: WebhookEventType,
  payload: Record<string, unknown>,
  log?: { info: (...args: unknown[]) => void; error: (...args: unknown[]) => void }
): Promise<DeliveryResult> {
  const eventId = crypto.randomUUID();
  const now = new Date().toISOString();

  // Create event log entry
  const eventDoc: WebhookEventDoc = {
    id: eventId,
    subscriptionId: sub.id,
    userId: sub.userId,
    productId: sub.productId,
    eventType,
    payload,
    createdAt: now,
    attempts: 0,
    maxRetries: sub.maxRetries,
  };

  await repo.createEvent(eventDoc);

  // Attempt delivery with retries
  const maxAttempts = (sub.maxRetries || 3) + 1;
  let lastError: string | undefined;
  let statusCode: number | undefined;

  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      const bodyJson = JSON.stringify({
        id: eventId,
        type: eventType,
        timestamp: now,
        data: payload,
      });

      const signatureHeader = buildSignatureHeader(bodyJson, sub.secret);

      const controller = new globalThis.AbortController();
      const timeout = globalThis.setTimeout(() => controller.abort(), 10_000);

      const response = await fetch(sub.url, {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
          'X-Webhook-Signature': signatureHeader,
          'X-Webhook-Id': eventId,
          'X-Webhook-Event': eventType,
          'User-Agent': 'ChronoMind-Webhooks/1.0',
        },
        body: bodyJson,
        signal: controller.signal,
      });

      globalThis.clearTimeout(timeout);
      statusCode = response.status;

      if (response.ok) {
        // Success — update event log
        await repo.updateEvent({
          ...eventDoc,
          deliveredAt: new Date().toISOString(),
          statusCode,
          attempts: attempt,
        });
        await repo.resetFailureCount(sub.id, sub.userId);

        log?.info({ subscriptionId: sub.id, eventType, attempt, statusCode }, 'webhook delivered');

        return {
          subscriptionId: sub.id,
          eventId,
          success: true,
          statusCode,
        };
      }

      lastError = `HTTP ${statusCode}`;
    } catch (err: unknown) {
      lastError = err instanceof Error ? err.message : String(err);
    }

    // Exponential backoff between retries (100ms, 200ms, 400ms, ...)
    if (attempt < maxAttempts) {
      const delay = Math.min(100 * Math.pow(2, attempt - 1), 5000);
      await new Promise<void>(resolve => globalThis.setTimeout(resolve, delay));
    }
  }

  // All attempts failed
  await repo.updateEvent({
    ...eventDoc,
    attempts: maxAttempts,
    error: lastError,
    statusCode,
  });
  await repo.incrementFailureCount(sub.id, sub.userId);

  log?.error({ subscriptionId: sub.id, eventType, error: lastError }, 'webhook delivery failed');

  return {
    subscriptionId: sub.id,
    eventId,
    success: false,
    statusCode,
    error: lastError,
  };
}

// ── Verify Signature (for consumers) ──────────────────────────

export function verifySignature(
  signatureHeader: string,
  body: string,
  secret: string,
  toleranceSeconds = 300
): boolean {
  const parts = signatureHeader.split(',');
  const timestampPart = parts.find(p => p.startsWith('t='));
  const signaturePart = parts.find(p => p.startsWith('v1='));

  if (!timestampPart || !signaturePart) return false;

  const timestamp = parseInt(timestampPart.slice(2), 10);
  const signature = signaturePart.slice(3);

  // Check timestamp tolerance
  const now = Math.floor(Date.now() / 1000);
  if (Math.abs(now - timestamp) > toleranceSeconds) return false;

  // Verify HMAC
  const expected = createHmac('sha256', secret).update(`${timestamp}.${body}`).digest('hex');

  // Constant-time comparison
  if (expected.length !== signature.length) return false;
  let diff = 0;
  for (let i = 0; i < expected.length; i++) {
    diff |= expected.charCodeAt(i) ^ signature.charCodeAt(i);
  }
  return diff === 0;
}