Lenda Finance

Full StackLive on Vercel

A full-stack lending platform where users deposit real-world collateral (property, crypto, vehicles), borrow credit against it, and track their financial position in real time. Built with a FastAPI backend on PostgreSQL/AWS RDS and a Next.js 16 dashboard with TanStack Query and NextAuth.js.

FastAPI Next.js 16 TypeScript PostgreSQL / AWS RDS TanStack Query NextAuth.js License: MIT

Core Features

Real-World Collateral

Users deposit property, crypto, or vehicles as collateral. Each asset type carries its own depreciation rate: property 1%, crypto 5%, car 10%.

Credit Against Collateral

Available credit equals total deposited assets minus outstanding loans. Users can only borrow up to their available credit. Default interest rate: 5%.

Financial Position Tracking

Real-time dashboard tracks each user's position : collateral value, outstanding debt, available credit, and repayment history across all loans.

Loan Lifecycle Management

Full loan lifecycle: pending → approved → repaid. Supports partial and full repayments, plus batch repayment across multiple loans in a single request.

Layered Architecture

Clean separation of concerns: Controller (endpoints) → Service (business logic) → Repository (DB queries). Pydantic schemas enforce request/response validation throughout.

Secure Authentication

NextAuth.js v4 with Credentials provider and JWT sessions. Passwords hashed with Passlib + bcrypt. Auth-protected dashboard route group via Next.js middleware.

Architecture

The system is split into two independently deployable services: a FastAPI REST API handling all business logic and persistence, and a Next.js 16 dashboard that consumes the API via an Axios service layer and TanStack Query for server state management.

Backend: FastAPI

main.py: Controller layer (all endpoints)
service.py: Business logic
repository.py: Database queries
models.py: SQLAlchemy ORM models
schemas.py: Pydantic request/response schemas
rules.py: Business rules (asset types, statuses)
Alembic for database migrations
Pytest test suite

Frontend: Next.js 16

Auth-protected (dashboard) route group
Pages: Overview, Users, Assets, Loans, Settings
TanStack Query hooks for server state
Axios service layer for all API calls
Recharts for data visualizations
Tailwind CSS v4 + Solar icons (Iconify)
Sonner toast notifications
NextAuth middleware proxy for route protection

Tech Stack

Layer	Technology
API Framework	FastAPI
ORM	SQLAlchemy + Alembic migrations
Validation	Pydantic (request/response + settings)
Database	PostgreSQL on AWS RDS
Auth (backend)	Passlib + bcrypt (password hashing)
Frontend Framework	Next.js 16: App Router
Language	TypeScript
Styling	Tailwind CSS v4
State Management	TanStack Query (server state)
Auth (frontend)	NextAuth.js v4: Credentials + JWT
Charts	Recharts
HTTP Client	Axios
Deployment	Vercel (frontend)

API Reference

All endpoints are defined in the FastAPI backend. Authentication uses a POST to /auth/login which returns a token used for protected routes.

Method	Endpoint	Description
POST	/auth/login	Authenticate user (email + password)
POST	/users	Register a new user
GET	/users	List all users
GET	/users/{user_id}	Get user by ID
POST	/assets	Deposit a new asset
GET	/assets	List all assets
POST	/borrow	Request a loan against available credit
GET	/loans	List all loans
POST	/repay/{loan_id}	Repay a loan (partial or full)
POST	/repay/batch	Batch repay multiple loans
GET	/positions/{user_id}	Get user's full financial position

Data Model

Three core tables managed by SQLAlchemy ORM with Alembic migrations. All relationships are enforced at the database level with foreign key constraints.

users

id: Primary key
name: Full name
email: Unique identifier
password_hash: bcrypt hash

assets

id: Primary key
user_id: FK → users
type: property | crypto | car
value: Deposited value
created_at: Timestamp

loans

id: Primary key
user_id: FK → users
amount: Loan principal
amount_repaid: Running repayment
interest_rate: Default 5%
status: pending | approved | repaid
created_at: Timestamp

Business Rules

Rule	Detail
Allowed asset types	property, crypto, car
Depreciation: property	1% per period
Depreciation: crypto	5% per period
Depreciation: car	10% per period
Default interest rate	5%
Available credit formula	Total deposited assets − total outstanding loans
Borrow limit	Users cannot borrow beyond their available credit