Credits handler

Credits Handler

This skill guides you through the entire credit system, from backend configuration to frontend UI implementation.

1. Configuration

All credit configuration lives in src/lib/credits/config.ts.

Adding a New Credit Type

1. Define the Type: Add the new type to creditTypeSchema enum.

   export const creditTypeSchema = z.enum([
     "image_generation",
     "video_generation",
     "your_new_credit_type" // Add this
   ]);
   

2. Configure Pricing & Metadata: Add an entry to creditsConfig.

   your_new_credit_type: {
     name: "New Credit Name",
     currency: "USD",
     minimumAmount: 10,
     // Option A: Fixed Slabs
     slabs: [
       { from: 1, to: 100, pricePerUnit: 0.10 },
       { from: 101, to: 1000, pricePerUnit: 0.08 },
     ],
     // Option B: Dynamic Calculator (e.g., based on user plan)
     priceCalculator: (amount, userPlan) => {
        // Logic here
        return amount * 0.1;
     }
   }
   

3. Plan Allocations (Optional): Define how many credits are given when subscribing to a plan in onPlanChangeCredits.

2. UI Implementation: Buying Credits

To let users purchase credits, use the useBuyCredits hook. This hook handles price calculation (factoring in plan discounts) and generating checkout URLs.

Key Hook: useBuyCredits

Location: src/lib/credits/useBuyCredits.ts

Usage

import useBuyCredits from "@/lib/credits/useBuyCredits";
import { PlanProvider } from "@/lib/plans/getSubscribeUrl";

const { 
  price,            // Calculated total price (number | undefined)
  isLoading,        // Price calculation in progress
  error,            // Error state
  getBuyCreditsUrl  // Function to generate payment URL
} = useBuyCredits(creditType, amount);

Example: Building a Pricing Card

Here is a pattern for creating a credit purchase UI, similar to src/components/website/website-credits-section.tsx.

"use client";

import { useState } from "react";
import useBuyCredits from "@/lib/credits/useBuyCredits";
import { PlanProvider } from "@/lib/plans/getSubscribeUrl";
import { Button } from "@/components/ui/button";
import { Loader2 } from "lucide-react";

// 1. Define your packages
const PACKAGE = {
  credits: 100,
  name: "Starter Pack",
};

export function BuyCreditsCard({ creditType }: { creditType: "image_generation" }) {
  const [provider] = useState(PlanProvider.STRIPE); // or LEMONSQUEEZY

  // 2. Call the hook
  const { price, isLoading, error, getBuyCreditsUrl } = useBuyCredits(
    creditType,
    PACKAGE.credits
  );

  // 3. Handle Purchase
  const handleBuy = () => {
    const url = getBuyCreditsUrl(provider);
    window.location.href = url;
  };

  // 4. Render UI
  return (
    <div className="border p-4 rounded-lg">
      <h3>{PACKAGE.name}</h3>
      <div className="text-2xl font-bold">
        {isLoading ? (
          <Loader2 className="animate-spin" />
        ) : (
          `$${price?.toFixed(2) || "0.00"}`
        )}
      </div>
      
      <Button 
        onClick={handleBuy}
        disabled={isLoading || !price}
        className="w-full mt-4"
      >
        Buy {PACKAGE.credits} Credits
      </Button>
      
      {error && <p className="text-red-500 text-sm">{error.message}</p>}
    </div>
  );
}

3. UI Implementation: Displaying Credits

To show the user's current balance, use the useCredits hook.

Key Hook: useCredits

Location: src/lib/users/useCredits.ts

Return Data Structure

const { 
  credits,    // Record<string, number> | undefined
              // e.g. { "image_generation": 100, "video_generation": 50 }
  isLoading,  // boolean
  error,      // any
  mutate      // SWR mutate function to refresh data
} = useCredits();

Usage Example

import useCredits from "@/lib/users/useCredits";

export function CreditBalance() {
  const { credits, isLoading } = useCredits();

  if (isLoading) return <div>Loading...</div>;

  return (
    <div>
      Image Credits: {credits?.image_generation || 0}
    </div>
  );
}

4. Core Operations (Backend)

These functions are used in API routes and webhooks.

Allocating Credits (e.g., on Plan Change)

Use allocatePlanCredits to give users credits when they subscribe/upgrade.

• File: src/lib/credits/allocatePlanCredits.ts
• Input: userId, planId, paymentId (for idempotency).
• Behavior: Checks onPlanChangeCredits config and adds credits if applicable.

Adding/Deducting Credits

To manually manipulate balances, use helpers from src/lib/credits/recalculate.ts (e.g., addCredits, deductCredits). Note: Always ensure you have a unique paymentId or transaction reference when adding credits to prevent duplicates.

5. Checking Balance (Backend/Common)

Use canDeductCredits before performing an action.

import { canDeductCredits } from "@/lib/credits/credits";

// Check if user has enough credits
const hasBalance = canDeductCredits(
  "image_generation", 
  1, 
  user // Must contain { credits: { ... } }
);

if (!hasBalance) {
  throw new Error("Insufficient credits");
}

6. Reference

For deep dives into database schema and architecture, see reference.md.