Build an AI Image Generator with Usage-Based Billing

import 'dotenv/config';
import OpenAI from 'openai';
import * as readline from 'readline';
import { randomUUID } from 'crypto';
import { writeFileSync } from 'fs';

// Initialize OpenAI client
const openai = new OpenAI({
  apiKey: process.env.OPENAI_API_KEY,
});

// Dodo Payments configuration
const DODO_PAYMENTS_CONFIG = {
  apiKey: process.env.DODO_PAYMENTS_API_KEY,
  baseUrl: 'https://test.dodopayments.com',
  customerId: 'cus_FX5FAB43aShGyiHJGIqjB', // Replace with your actual customer ID from Step 3
};

// OpenAI image model used by the sample
const IMAGE_MODEL = 'gpt-image-2.5-flare';

interface ImageGenerationOptions {
  prompt: string;
  quality?: 'medium' | 'high';
  size?: '1024x1024' | '1536x1024' | '1024x1536';
}

interface UsageEvent {
  event_id: string;
  customer_id: string;
  event_name: string;
  timestamp: string;
  metadata: {
    quality: string;
  };
}

/**
 * Send usage event to Dodo Payments for billing tracking
 */
async function sendUsageEvent(event: UsageEvent): Promise<void> {
  try {
    console.log('Sending usage event to Dodo Payments...');
    console.log(`URL: ${DODO_PAYMENTS_CONFIG.baseUrl}/events/ingest`);
    console.log(`API Key present: ${!!DODO_PAYMENTS_CONFIG.apiKey}`);
    console.log(`API Key length: ${DODO_PAYMENTS_CONFIG.apiKey?.length || 0}`);
    console.log(`Customer ID: ${DODO_PAYMENTS_CONFIG.customerId}`);
    
    const requestBody = {
      events: [event]
    };
    console.log('Request body:', JSON.stringify(requestBody, null, 2));
    
    const headers = {
      'Authorization': `Bearer ${DODO_PAYMENTS_CONFIG.apiKey}`,
      'Content-Type': 'application/json',
    }
    const response = await fetch(`${DODO_PAYMENTS_CONFIG.baseUrl}/events/ingest`, {
      method: 'POST',
      headers: headers,
      body: JSON.stringify(requestBody),
    });

    console.log(`Response status: ${response.status}`);
    console.log(`Response headers:`, Object.fromEntries(response.headers.entries()));

    if (!response.ok) {
      const errorData = await response.text();
      console.log(`Error response body: ${errorData}`);
      throw new Error(`HTTP ${response.status}: ${errorData}`);
    }

    const result = await response.json();
    console.log('Usage event sent successfully');
    console.log(`   • Event ID: ${event.event_id}`);
    console.log(`   • Customer: ${event.customer_id}`);
    console.log(`   • Quality: ${event.metadata.quality}`);
    
  } catch (error) {
    console.error('Failed to send usage event:', error);
    // In production, you might want to queue failed events for retry
    throw error;
  }
}

async function generateImage(options: ImageGenerationOptions) {
  const startTime = Date.now();
  const eventId = randomUUID();
  
  try {
    console.log('Generating image...');
    console.log(`Prompt: "${options.prompt}"`);
    console.log(`Quality: ${options.quality || 'medium'}`);
    console.log(`Size: ${options.size || '1024x1024'}`);
    
    const response = await openai.images.generate({
      model: IMAGE_MODEL,
      prompt: options.prompt,
      n: 1,
      size: options.size || '1024x1024',
      quality: options.quality || 'medium',
    });

    const endTime = Date.now();
    const duration = (endTime - startTime) / 1000;

    // The Image API returns base64-encoded image data, so save it as a PNG file
    const imageBase64 = response.data?.[0]?.b64_json;
    if (!imageBase64) {
      throw new Error('OpenAI returned no image data');
    }
    const imagePath = `image-${eventId}.png`;
    writeFileSync(imagePath, Buffer.from(imageBase64, 'base64'));
    
    // Create usage event for Dodo Payments
    const usageEvent: UsageEvent = {
      event_id: eventId,
      customer_id: DODO_PAYMENTS_CONFIG.customerId!,
      event_name: 'image.generated',
      timestamp: new Date().toISOString(),
      metadata: {
        quality: options.quality || 'medium',
      }
    };

    // Send usage event to Dodo Payments for billing
    await sendUsageEvent(usageEvent);
    
    console.log('\nImage generated successfully!');
    console.log(`Generation Stats:`);
    console.log(`   • Duration: ${duration.toFixed(2)} seconds`);
    console.log(`   • Quality: ${options.quality || 'medium'}`);
    console.log(`   • Image file: ${imagePath}`);

    return {
      imagePath: imagePath,
      duration: duration,
      eventId: eventId,
    };

  } catch (error) {
    console.error('Error generating image:', error);
    
    // Send failure event for monitoring (optional)
    try {
      const failureEvent: UsageEvent = {
        event_id: eventId,
        customer_id: DODO_PAYMENTS_CONFIG.customerId!,
        event_name: 'image.generation.failed',
        timestamp: new Date().toISOString(),
        metadata: {
          quality: options.quality || 'medium',
        }
      };
      
      // Note: You might want to create a separate meter for failed attempts
      // await sendUsageEvent(failureEvent);
    } catch (eventError) {
      console.error('Failed to send failure event:', eventError);
    }
    
    throw error;
  }
}

async function getUserInput(): Promise<string> {
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
  });

  return new Promise((resolve) => {
    rl.question('Enter your image prompt: ', (answer) => {
      rl.close();
      resolve(answer);
    });
  });
}

async function main() {
  console.log('PixelGen AI - Image Generator with Usage Billing\n');
  
  // Validate environment variables
  const requiredEnvVars = [
    'OPENAI_API_KEY',
    'DODO_PAYMENTS_API_KEY'
  ];
  
  for (const envVar of requiredEnvVars) {
    if (!process.env[envVar]) {
      console.error(`Error: ${envVar} environment variable is not set.`);
      console.log('Please set all required environment variables:');
      console.log('export OPENAI_API_KEY="your-openai-key"');
      console.log('export DODO_PAYMENTS_API_KEY="your-dodo-api-key"');
      console.log('Note: Customer ID is hardcoded in the application');
      process.exit(1);
    }
  }

  try {
    const prompt = await getUserInput();
    
    if (!prompt.trim()) {
      console.log('No prompt provided. Exiting...');
      return;
    }

    const result = await generateImage({
      prompt: prompt.trim(),
      quality: 'medium', // Change to 'high' for higher quality
      size: '1024x1024',
    });

    console.log('\nProcess completed successfully!');
    console.log(`Billing Information:`);
    console.log(`   • Event ID: ${result.eventId}`);
    console.log(`   • Billing will be processed automatically via Dodo Payments`);
    
  } catch (error) {
    console.error('Application error:', error);
    process.exit(1);
  }
}

// Run the application
if (require.main === module) {
  main().catch(console.error);
}