This backend provides a speech synthesis API with usage tracking and authentication.

• index.ts - Main Hono app with route definitions
• middleware/auth.ts - Authentication middleware (RevenueCat + admin key)
• middleware/usage.ts - Usage tracking and rate limiting middleware
• database/usage.ts - Database operations for usage tracking

• Admin access via ADMIN_ACCESS_KEY environment variable
• Customer authentication via RevenueCat subscription verification
• Authorization header format: Bearer {customer_id} or Customer {customer_id}

• Monthly character limit: 4,000,000 characters per customer
• Calendar month-based tracking (resets on 1st of each month)
• Automatic usage recording for successful requests
• Usage stats endpoint for customers to check their limits

The customer_usage_v1 table stores:

• id - Auto-incrementing primary key
• customer_id - Customer identifier from RevenueCat
• character_count - Number of characters in the request
• request_timestamp - ISO timestamp of the request
• created_at - Database insertion timestamp

Converts text to speech using LemonFox API.

Headers:

• Authorization: Bearer {customer_id} or Authorization: Bearer {admin_key}

Body:

{
  "voice": "voice_name",
  "input": "text to convert"
}

Response:

{
  "audio": "base64_encoded_audio",
  "word_timestamps": [
    {
      "word": "hello",
      "start": 0.0,
      "end": 0.5
    }
  ]
}

Get current month's usage statistics.

Headers:

• Authorization: Bearer {customer_id} or Authorization: Bearer {admin_key}

Query Parameters (admin only):

• customer_id - Check usage for specific customer

Response:

{
  "monthly_limit": 4000000,
  "current_usage": 150000,
  "remaining_characters": 3850000,
  "usage_percentage": 4
}

Free users might recieve something more like this: return c.json({ error: "Free tier character limit exceeded", details: { lifetime_limit: FREE_LIFETIME_USAGE, current_usage: currentUsage, requested_characters: characterCount, remaining_characters: remainingCharacters, user_tier: "free", message: "Upgrade to premium for monthly limits and unlimited usage", }, }, 429); // Too Many Requests

Health check endpoint.

Response:

{
  "status": "ok",
  "timestamp": "2024-01-01T00:00:00.000Z"
}

• ADMIN_ACCESS_KEY - Admin authentication key
• REVENUECAT_API_KEY - RevenueCat API key
• LEMONFOX_API_KEY - LemonFox API key

• 4,000,000 characters per calendar month per customer
• Admin users have unlimited usage
• Requests that would exceed the limit are rejected with HTTP 429
• Usage is tracked after successful requests only

• 401 - Missing or invalid authorization
• 403 - No active subscription or subscription verification failed
• 429 - Monthly character limit exceeded
• 500 - Internal server error