AI Credits

The AI Credits system lets you monetize AI features with a token-based model. Users get a monthly credit allowance based on their subscription tier. Each AI operation (form generation, chat, code generation) costs a set number of credits. The system tracks usage, handles refills, and blocks operations when credits run out - all automatically.

The credit system uses two Prisma models: CreditBalance (one per user) and CreditTransaction (history of all credit changes).

model CreditBalance {
  id               String   @id @default(cuid())
  userId           String   @unique
  balance          Int      @default(0)
  monthlyAllowance Int      @default(100)
  lastRefill       DateTime @default(now())

  user         User                @relation(...)
  transactions CreditTransaction[]
}

model CreditTransaction {
  id          String                @id @default(cuid())
  balanceId   String
  amount      Int      // Positive = add, Negative = deduct
  type        CreditTransactionType
  description String?
  endpoint    String?
  metadata    Json?
  createdAt   DateTime @default(now())
}

enum CreditTransactionType {
  SUBSCRIPTION_REFILL
  PURCHASE
  USAGE
  REFUND
  BONUS
}

• Current balance with progress bar
• 30-day usage chart showing daily consumption
• Subscription tier and monthly allowance
• Days until next credit refill
• Recent transaction history table

Here's the complete pattern for integrating credits into an AI route:

// src/app/api/ai/your-feature/route.ts
import { NextResponse } from "next/server";
import { auth } from "@/lib/auth";
import { hasCredits, deductCredits, CREDIT_COSTS } from "@/lib/credits";

export async function POST(request: Request) {
  const session = await auth();
  const userId = session?.user?.id;

  // 1. Check credits (if authenticated)
  const creditCost = CREDIT_COSTS.CODE_GENERATION;
  if (userId) {
    const hasEnough = await hasCredits(userId, creditCost);
    if (!hasEnough) {
      return NextResponse.json(
        { error: "Insufficient credits", code: "INSUFFICIENT CREDITS" },
        { status: 402 }
      );
    }
  }

  // 2. Do the AI operation
  const result = await callYourAIService();

  // 3. Deduct credits on success
  if (userId) {
    await deductCredits(userId, creditCost, {
      description: "Code generation",
      endpoint: "/api/ai/your-feature",
    });
  }

  return NextResponse.json(result);
}