import crypto from 'crypto';

const WEBHOOK_SECRET = process.env.WEBHOOK_SECRET || 'test_secret_for_webhooks';
const WEBHOOK_URL = process.env.WEBHOOK_URL || 'http://localhost:8081/webhooks/pharmacy';
const MAX_RETRIES = 3;

export class WebhookService {
  /**
   * Fire-and-forget: dispatches the webhook in the background.
   * Dispensing will NEVER fail because of a webhook issue.
   */
  dispatchEvent(event: string, idempotencyKey: string, payload: any) {
    // Run in background — no await, no blocking
    this._sendWithRetry(event, idempotencyKey, payload).catch((err) => {
      console.error(`[WEBHOOK] All retries failed for ${event}: ${err.message}`);
    });
  }

  /**
   * Internal: send webhook with exponential backoff retry.
   */
  private async _sendWithRetry(event: string, idempotencyKey: string, payload: any) {
    const timestamp = Math.floor(Date.now() / 1000);
    const bodyString = JSON.stringify(payload);
    const dataToSign = `${timestamp}.${bodyString}`;

    const signature = crypto
      .createHmac('sha256', WEBHOOK_SECRET)
      .update(dataToSign)
      .digest('hex');

    const signatureHeader = `t=${timestamp},v1=${signature}`;

    for (let attempt = 1; attempt <= MAX_RETRIES; attempt++) {
      try {
        console.log(`[WEBHOOK] Attempt ${attempt}/${MAX_RETRIES} — ${event} (${idempotencyKey})`);

        const response = await fetch(WEBHOOK_URL, {
          method: 'POST',
          headers: {
            'Content-Type': 'application/json',
            'X-Pharmacy-Event': event,
            'X-Pharmacy-Signature': signatureHeader,
            'Idempotency-Key': idempotencyKey,
          },
          body: bodyString,
        });

        if (response.ok) {
          console.log(`[WEBHOOK] ✓ Delivered: ${event}`);
          return; // Success — stop retrying
        }

        console.warn(`[WEBHOOK] Server responded ${response.status} for ${event}`);
      } catch (error: any) {
        console.error(`[WEBHOOK] Attempt ${attempt} failed: ${error.message}`);
      }

      // Exponential backoff: 1s, 2s, 4s
      if (attempt < MAX_RETRIES) {
        const delay = Math.pow(2, attempt - 1) * 1000;
        await new Promise((resolve) => setTimeout(resolve, delay));
      }
    }

    console.error(`[WEBHOOK] ✗ Failed after ${MAX_RETRIES} attempts: ${event}`);
  }
}

export const webhookService = new WebhookService();