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backend/src/lib/lnbits.ts

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+/**
+ * LNbits API client for Lightning Network payments
+ * 
+ * Uses LNbits API to create and manage Lightning invoices with webhook support
+ * for payment detection.
+ */
+
+// Read environment variables dynamically to ensure dotenv has loaded
+function getConfig() {
+  return {
+    url: process.env.LNBITS_URL || '',
+    apiKey: process.env.LNBITS_API_KEY || '', // Invoice/read key
+    webhookSecret: process.env.LNBITS_WEBHOOK_SECRET || '',
+  };
+}
+
+export interface LNbitsInvoice {
+  paymentHash: string;
+  paymentRequest: string; // BOLT11 invoice string
+  checkingId: string;
+  amount: number; // Amount in satoshis (after conversion)
+  fiatAmount?: number; // Original fiat amount
+  fiatCurrency?: string; // Original fiat currency
+  memo: string;
+  expiry: string;
+  status: string;
+  extra?: Record<string, any>;
+}
+
+export interface CreateInvoiceParams {
+  amount: number; // Amount in the specified unit
+  unit?: string; // Currency unit: 'sat', 'USD', 'PYG', etc. (default: 'sat')
+  memo: string;
+  webhookUrl?: string;
+  expiry?: number; // Expiry in seconds (default 3600 = 1 hour)
+  extra?: Record<string, any>; // Additional metadata
+}
+
+/**
+ * Check if LNbits is configured
+ */
+export function isLNbitsConfigured(): boolean {
+  const config = getConfig();
+  return !!(config.url && config.apiKey);
+}
+
+
+/**
+ * Create a Lightning invoice using LNbits
+ * LNbits supports fiat currencies directly - it will convert to sats automatically
+ */
+export async function createInvoice(params: CreateInvoiceParams): Promise<LNbitsInvoice> {
+  const config = getConfig();
+  
+  if (!config.url || !config.apiKey) {
+    throw new Error('LNbits is not configured. Please set LNBITS_URL and LNBITS_API_KEY.');
+  }
+
+  const apiEndpoint = '/api/v1/payments';
+  
+  // LNbits supports fiat currencies via the 'unit' parameter
+  // It will automatically convert to sats using its exchange rate provider
+  const payload: any = {
+    out: false, // false = create invoice for receiving payment
+    amount: params.amount,
+    unit: params.unit || 'sat', // Support fiat currencies like 'USD', 'PYG', etc.
+    memo: params.memo,
+  };
+
+  if (params.webhookUrl) {
+    payload.webhook = params.webhookUrl;
+  }
+
+  if (params.expiry) {
+    payload.expiry = params.expiry;
+  }
+
+  if (params.extra) {
+    payload.extra = params.extra;
+  }
+
+  console.log('Creating LNbits invoice:', {
+    url: `${config.url}${apiEndpoint}`,
+    amount: params.amount,
+    unit: payload.unit,
+    memo: params.memo,
+    webhook: params.webhookUrl,
+  });
+
+  const response = await fetch(`${config.url}${apiEndpoint}`, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'X-Api-Key': config.apiKey,
+    },
+    body: JSON.stringify(payload),
+  });
+
+  if (!response.ok) {
+    const errorText = await response.text();
+    console.error('LNbits invoice creation failed:', {
+      status: response.status,
+      statusText: response.statusText,
+      error: errorText,
+    });
+    throw new Error(`Failed to create Lightning invoice: ${errorText}`);
+  }
+
+  const data = await response.json();
+  
+  // LNbits returns amount in millisatoshis for the actual invoice
+  // Convert to satoshis for display
+  const amountSats = data.amount ? Math.round(data.amount / 1000) : params.amount;
+  
+  console.log('LNbits invoice created successfully:', {
+    paymentHash: data.payment_hash,
+    amountMsats: data.amount,
+    amountSats,
+    hasPaymentRequest: !!data.payment_request,
+  });
+  
+  return {
+    paymentHash: data.payment_hash,
+    paymentRequest: data.payment_request || data.bolt11,
+    checkingId: data.checking_id,
+    amount: amountSats, // Amount in satoshis
+    fiatAmount: params.unit && params.unit !== 'sat' ? params.amount : undefined,
+    fiatCurrency: params.unit && params.unit !== 'sat' ? params.unit : undefined,
+    memo: params.memo,
+    expiry: data.expiry || '',
+    status: data.status || 'pending',
+    extra: params.extra,
+  };
+}
+
+/**
+ * Get invoice/payment status from LNbits
+ */
+export async function getPaymentStatus(paymentHash: string): Promise<{
+  paid: boolean;
+  status: string;
+  preimage?: string;
+} | null> {
+  const config = getConfig();
+  
+  if (!config.url || !config.apiKey) {
+    throw new Error('LNbits is not configured');
+  }
+
+  const apiEndpoint = `/api/v1/payments/${paymentHash}`;
+
+  const response = await fetch(`${config.url}${apiEndpoint}`, {
+    method: 'GET',
+    headers: {
+      'Content-Type': 'application/json',
+      'X-Api-Key': config.apiKey,
+    },
+  });
+
+  if (!response.ok) {
+    if (response.status === 404) {
+      return null;
+    }
+    throw new Error('Failed to get payment status from LNbits');
+  }
+
+  const data = await response.json();
+  
+  // LNbits payment status: "pending", "complete", "failed"
+  // For incoming payments, "complete" means paid
+  const isPaid = data.status === 'complete' || data.paid === true;
+  
+  return {
+    paid: isPaid,
+    status: data.status,
+    preimage: data.preimage,
+  };
+}
+
+/**
+ * Verify webhook payload from LNbits
+ * LNbits webhooks don't have signature verification by default,
+ * but we can verify the payment hash matches and check payment status
+ */
+export async function verifyWebhookPayment(paymentHash: string): Promise<boolean> {
+  try {
+    const status = await getPaymentStatus(paymentHash);
+    return status?.paid === true;
+  } catch (error) {
+    console.error('Error verifying webhook payment:', error);
+    return false;
+  }
+}
+
+/**
+ * Payment status types
+ */
+export type LNbitsPaymentStatus = 'pending' | 'complete' | 'failed' | 'expired';
+
+/**
+ * Check if payment is complete
+ */
+export function isPaymentComplete(status: string): boolean {
+  return status === 'complete';
+}
+
+/**
+ * Check if payment is still pending
+ */
+export function isPaymentPending(status: string): boolean {
+  return status === 'pending';
+}