feat: implement IndexerService for InvoiceMinted events

.env.example

@@ -0,0 +1,10 @@
+# Stellar Configuration
+STELLAR_HORIZON_URL=https://horizon-testnet.stellar.org
+CONTRACT_ID=CCYU3LOQI34VHVN3ZOSEBHHKL4YK36FMTOEGLRYDUDRGS7JOLLRKCEQM
+
+# Database Configuration (existing)
+DB_HOST=localhost
+DB_PORT=5432
+DB_USERNAME=postgres
+DB_PASSWORD=password
+DB_DATABASE=tradeflow

src/app.module.ts

@@ -2,10 +2,11 @@ import { Module } from '@nestjs/common';
 import { AppController } from './app.controller';
 import { AppService } from './app.service';
 import { HealthModule } from './health/health.module';
+import { IndexerService } from './indexer.service';
 
 @Module({
   imports: [HealthModule],
   controllers: [AppController],
-  providers: [AppService],
+  providers: [AppService, IndexerService],
 })
 export class AppModule {}

src/indexer.service.ts

@@ -0,0 +1,82 @@
+import { Injectable, OnModuleInit } from '@nestjs/common';
+import { Server } from '@stellar/stellar-sdk';
+
+@Injectable()
+export class IndexerService implements OnModuleInit {
+  private server: Server;
+  private readonly POLLING_INTERVAL = 5000; // 5 seconds
+  private readonly CONTRACT_ID = process.env.CONTRACT_ID || '';
+  private readonly INVOICE_MINTED_TOPIC = 'InvoiceMinted';
+
+  constructor() {
+    // Initialize Stellar server (using testnet by default, can be configured via env)
+    this.server = new Server(
+      process.env.STELLAR_HORIZON_URL || 'https://horizon-testnet.stellar.org'
+    );
+  }
+
+  async onModuleInit() {
+    console.log('IndexerService starting...');
+
+    if (!this.CONTRACT_ID) {
+      console.warn('CONTRACT_ID not set in environment variables');
+      return;
+    }
+
+    // Start polling for events
+    this.startPolling();
+  }
+
+  private startPolling() {
+    console.log(`Starting to poll for ${this.INVOICE_MINTED_TOPIC} events from contract ${this.CONTRACT_ID}`);
+
+    setInterval(async () => {
+      try {
+        await this.pollForEvents();
+      } catch (error) {
+        console.error('Error polling for events:', error);
+      }
+    }, this.POLLING_INTERVAL);
+  }
+
+  private async pollForEvents() {
+    try {
+      // Get events from the Stellar server
+      const events = await this.server.getEvents({
+        contract: this.CONTRACT_ID,
+        topics: [[this.INVOICE_MINTED_TOPIC]],
+      });
+
+      if (events.records.length > 0) {
+        console.log(`Found ${events.records.length} events`);
+
+        for (const event of events.records) {
+          this.processInvoiceMintedEvent(event);
+        }
+      }
+    } catch (error) {
+      console.error('Error fetching events:', error);
+    }
+  }
+
+  private processInvoiceMintedEvent(event: any) {
+    try {
+      // Extract event data
+      const eventData = event.value;
+
+      // Assuming the event structure contains invoice_id and amount
+      // This may need adjustment based on actual event structure
+      const invoiceId = eventData.invoice_id || eventData.invoiceId || 'N/A';
+      const amount = eventData.amount || 'N/A';
+
+      console.log(`InvoiceMinted Event Detected:`);
+      console.log(`  - Invoice ID: ${invoiceId}`);
+      console.log(`  - Amount: ${amount}`);
+      console.log(`  - Transaction Hash: ${event.transaction_hash}`);
+      console.log(`  - Timestamp: ${event.created_at}`);
+      console.log('---');
+    } catch (error) {
+      console.error('Error processing InvoiceMinted event:', error);
+    }
+  }
+}