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Open Source Credit Management

PyPI version Python License: MIT Downloads FastAPI FastAPI

Production-ready credit management system for AI/LLM applications. Automatic credit deduction, Razorpay payment integration, subscription plans, promo codes, and multi-provider webhooks.

✨ Why Credit Management?

Building a credit system for your AI application shouldn't mean reinventing billing, payments, and usage tracking. This library gives you:

  • 🪙 Credit Reservations & Deductions — Reserve credits before API calls, deduct actual usage after. Prevents overcharging on failures.
  • 💳 Payment Integration — Razorpay payment links with atomic credit updates.
  • 📊 Subscription Plans — Daily, monthly, yearly plans with auto-renew and credit allocation.
  • 🎫 Promo Codes — Targeted promos with usage limits, expiry dates, and claim tracking.
  • 🔒 Request-Scoped Context — Automatic credit tracking via Python contextvars. Add LLM usage in your handlers, middleware handles the rest.
  • 🗄️ Database Agnostic — MongoDB or in-memory backend. Extensible to any database via BaseDBManager interface.
  • 📋 Dual-Write Ledger — Database + append-only file for audit trails and debugging.
  • 🔔 Notifications — Low credits, expiring credits, transaction errors — pluggable notification queue.

💡 Framework-agnostic, database-agnostic. Works with FastAPI, Flask, Django, or any async framework. Swap MongoDB for PostgreSQL, SQLite, or implement BaseDBManager for your database.

🚀 Quick Start

Installation

pip install credit-management

Basic Setup (3 Lines)

from fastapi import FastAPI
from credit_management.api.frontend_router import router as frontend_router
from credit_management.api.middleware import CreditDeductionMiddleware, _credit_service

app = FastAPI()
app.include_router(frontend_router)

# Automatic credit reservation → deduction on every request
app.add_middleware(
    CreditDeductionMiddleware,
    credit_service=_credit_service,
    path_prefix="/api",
    user_id_header="X-User-Id",
    default_estimated_tokens=100,
    skip_paths=("/api/health",),
)

Track LLM Usage in Your Handlers

from credit_management.context.creditContext import addLlmUsage

# After your LLM call
addLlmUsage(
    model="gpt-4o",
    provider="openai",
    cost=0.05,
    metadata={"prompt_tokens": 100, "completion_tokens": 50},
)
from credit_management.context.creditContext import addLlmUsage

# After your LLM call
addLlmUsage(
    model="gpt-4o",
    provider="openai",
    cost=0.05,
    metadata={"prompt_tokens": 100, "completion_tokens": 50},
)

The middleware automatically reserves credits before the request and deducts actual usage after. If the request fails, credits are unreserved — no overcharging.

Accept Payments via Razorpay

from credit_management.api.router import _payment_service, setup_razorpay_provider

# Initialize (auto-loaded from env vars)
setup_razorpay_provider(
    key_id="rzp_live_xxx",
    key_secret="xxx",
    webhook_secret="whsec_xxx",
    app_base_url="https://yourapp.com",
)

# Create payment link
response = await _payment_service.create_payment_link(
    user_id="user-123",
    amount_inr=500.0,
    provider_name="razorpay",
)

🏗️ Architecture

┌─────────────────────────────────────────────────────────────┐
│                     Your FastAPI App                         │
│  ┌──────────────────┐     ┌──────────────────────────────┐ │
│  │ CreditDeduction  │────▶│  ContextVar (LLM Usage)      │ │
│  │ Middleware       │     │  addLlmUsage(model, cost)    │ │
│  └────────┬─────────┘     └──────────────┬───────────────┘ │
│           │                              │                  │
│           ▼                              ▼                  │
│  ┌─────────────────────────────────────────────────────┐   │
│  │              CreditService (Core)                   │   │
│  │  reserve → execute → deduct / unreserve             │   │
│  └─────────────────────────┬───────────────────────────┘   │
└────────────────────────────┼───────────────────────────────┘
                             │
              ┌──────────────┼──────────────┐
              ▼              ▼              ▼
        ┌──────────┐  ┌──────────┐  ┌──────────────┐
        │ MongoDB  │  │ Ledger   │  │ Payment      │
        │ (or Mem) │  │ (DB+File)│  │ Providers    │
        └──────────┘  └──────────┘  └──────────────┘
                                    │ Razorpay │ Stripe │
                                    └──────────┴────────┘

Core Components

Component Purpose Key Feature
CreditService Core credit operations Cache-first reads, delta-based cache updates, transaction logging
PaymentService Payment processing Atomic updates, reference_id tracking, idempotent webhooks
SubscriptionService Plan management Daily/monthly/yearly plans, auto-renew, credit allocation
PromoService Promo code system Eligibility checks, usage limits, expiry tracking
CreditDeductionMiddleware Automatic credit deduction Reserve → execute → deduct/unreserve flow
LedgerLogger Audit logging Dual-write: database + append-only JSONL file
NotificationService User notifications Low credits, expiry warnings, transaction errors

📖 API Endpoints

User Endpoints (/credits/*)

Endpoint Method Description
/credits/balance/{user_id} GET Get available credit balance
/credits/payments/create POST Create Razorpay payment link
/credits/payments/history GET Payment history with pagination
/credits/payments/{payment_id} GET Get specific payment record
/credits/promo/eligibility?promo_code=X GET Check promo eligibility
/credits/promo/claim POST Claim promo code

Admin Endpoints (/admin/credits/*)

Endpoint Method Description
/admin/credits/add POST Add credits to a user
/admin/credits/deduct POST Deduct credits from a user
/admin/credits/plans POST Create subscription plan
/admin/credits/promos POST/GET Manage promo codes

Webhook Endpoint

Endpoint Method Description
/webhooks/{provider_name} POST Unified webhook handler (Razorpay, Stripe, etc.)

🔐 Security Features

  • Atomic Credit Updates — MongoDB conditional updates prevent double-crediting on concurrent webhooks
  • HMAC-SHA256 Webhook Verification — Timing-safe signature verification for all payment webhooks
  • State Machine Enforcement — Payment status only moves forward (prevents status rollback attacks)
  • Immutable Field Validation — Validates user_id, amount consistency across webhook events
  • Request-Scoped Isolation — Python contextvars ensure credit tracking is per-request, thread-safe

🗄️ Database Backends

MongoDB (Production)

export CREDIT_MONGO_URI="mongodb://localhost:27017"
export CREDIT_MONGO_DB="credit_management"

In-Memory (Testing)

from credit_management.db.memory import InMemoryDBManager
db = InMemoryDBManager()

Custom Backend

Implement BaseDBManager interface for any database (SQL, NoSQL, in-memory). Use schema_generator.py for automatic SQL DDL or MongoDB validators.

python -m schema_generator --backend sql --dialect postgres
python -m schema_generator --backend nosql

⚙️ Configuration

Environment Variable Default Description
CREDIT_MONGO_URI — MongoDB connection string
CREDIT_MONGO_DB credit_management Database name
RAZORPAY_KEY_ID — Razorpay API key ID
RAZORPAY_KEY_SECRET — Razorpay API key secret
RAZORPAY_WEBHOOK_SECRET — Webhook signing secret
APP_BASE_URL http://localhost:8000 Your application base URL

🔧 Manual HTTP API Usage

Prefer curl or HTTP clients? The library exposes REST endpoints you can call directly:

Credits

# Add credits (admin)
curl -X POST http://localhost:8000/admin/credits/add \
  -H "Content-Type: application/json" \
  -d '{"user_id": "user-1", "amount": 100, "description": "Welcome bonus"}'

# Get balance
curl http://localhost:8000/credits/balance/user-1

# Check promo eligibility
curl "http://localhost:8000/credits/promo/eligibility?promo_code=LAUNCH100"

# Claim promo
curl -X POST http://localhost:8000/credits/promo/claim \
  -H "Content-Type: application/json" \
  -d '{"user_id": "user-1", "promo_code": "LAUNCH100"}'

# Manual credit deduction (e.g., for non-API costs)
curl -X POST http://localhost:8000/admin/credits/deduct \
  -H "Content-Type: application/json" \
  -d '{"user_id": "user-1", "amount": 10, "description": "Storage overage"}'

# Create subscription plan (admin)
curl -X POST http://localhost:8000/admin/credits/plans \
  -H "Content-Type: application/json" \
  -d '{"name": "Pro", "credit_limit": 10000, "price": 29.99, "billing_period": "MONTHLY"}'

Payments

# Create payment link
curl -X POST http://localhost:8000/credits/payments/create \
  -H "Content-Type: application/json" \
  -H "X-User-Id: user-1" \
  -d '{"amount_inr": 500, "provider": "razorpay"}'

# Payment history
curl "http://localhost:9000/credits/payments/history?limit=10" \
  -H "X-User-Id: user-1"

# Handle Razorpay webhook
curl -X POST http://localhost:8000/webhooks/razorpay \
  -H "Content-Type: application/json" \
  -H "X-Razorpay-Signature: <signature>" \
  -d '{"event": "payment_link.paid", "payload": {...}}'

🔄 Manual Credit Deduction Use Cases

The middleware handles automatic credit deduction for API calls, but you may need manual deduction for:

Non-API Costs

from credit_management.api.router import _credit_service

# Storage overage
await _credit_service.deduct_credits_after_service(
    user_id="user-1",
    amount=10,
    description="Storage overage for 5GB extra usage",
)

# Manual adjustment
await _credit_service.deduct_credits(
    user_id="user-1",
    amount=50,
    description="Manual credit adjustment for billing cycle",
)

Refunds

# Refund credits to user
await _credit_service.add_credits(
    user_id="user-1",
    amount=100,
    description="Refund for failed API call #12345",
)

Scheduled Credit Allocation

from credit_management.services.expiration_service import ExpirationService

expiration = ExpirationService(db=_db, ledger=_ledger, credit_service=_credit_service)

# Check and expire credits
expired = await expiration.check_credit_expiration(user_id="user-1")
print(f"Expired {expired} credits for user-1")

🧪 Testing

Use the in-memory backend for zero-dependency tests:

import asyncio
from credit_management.db.memory import InMemoryDBManager
from credit_management.services.credit_service import CreditService
from credit_management.logging.ledger_logger import LedgerLogger

async def test():
    db = InMemoryDBManager()
    ledger = LedgerLogger(db=db, file_path="/tmp/test_ledger.log")
    service = CreditService(db=db, ledger=ledger)
    
    await service.add_credits(user_id="test", amount=100)
    info = await service.get_user_credits_info("test")
    assert info.available == 100

asyncio.run(test())

📋 Full Example: AI API with Credit Deduction

from fastapi import FastAPI, Depends
from credit_management.api.router import (
    frontend_router, webhook_router, backend_router,
    _credit_service, setup_razorpay_provider,
)
from credit_management.api.middleware import CreditDeductionMiddleware
from credit_management.context.creditContext import addLlmUsage

app = FastAPI()

# Include all routers
app.include_router(frontend_router)
app.include_router(backend_router, prefix="/admin")
app.include_router(webhook_router)

# Automatic credit middleware
app.add_middleware(
    CreditDeductionMiddleware,
    credit_service=_credit_service,
    path_prefix="/api",
    user_id_header="X-User-Id",
    default_estimated_tokens=100,
    skip_paths=("/api/health",),
)

# Initialize payment provider
setup_razorpay_provider()

@app.post("/api/generate")
async def generate(request: Request):
    user_id = request.headers.get("X-User-Id")
    
    # Your LLM call here
    response = await call_llm("gpt-4o", prompt)
    
    # Track usage — middleware deducts automatically
    addLlmUsage(
        model="gpt-4o",
        provider="openai",
        cost=0.05,
        metadata={"tokens": response.usage.total_tokens},
    )
    return response

🚀 Ready for Production

  • ✅ MongoDB or in-memory backend
  • ✅ Razorpay payment integration
  • ✅ Atomic credit updates (race-condition safe)
  • ✅ Security with Webhook signature verification
  • 🧪 Subscription plans with auto-renew
  • ✅ Promo codes with usage limits
  • ✅ Dual-write ledger (DB + file)
  • 🧪 Notification system (low credits, expiry)
  • ✅ Cache with delta-based updates
  • ✅ Request-scoped context isolation
  • ✅ Database-agnostic interface
  • ✅ Schema generator (SQL + NoSQL)

✅ -> Battle Tested & Verified, 🧪- In Testing ,Implemented

📄 License

MIT License — see LICENSE for details.

🤝 Contributing

Contributions welcome! Please read CONTRIBUTING.md for guidelines.

📦 Package Links

About

An open source credit management system ( library or as server api with any framework]

pypi.org/project/Credit-Management/

Topics

opensource credit opensourceforgood credit-management-system llmops llm-agent llm-tools llm-agents

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