Build complete SaaS invoicing application with FastAPI

Features: - JWT authentication with user registration and login - Customer management with full CRUD operations - Invoice management with automatic calculations - Multi-tenant data isolation by user - SQLite database with Alembic migrations - RESTful API with comprehensive documentation - Tax calculations and invoice status tracking - Code formatted with Ruff linting
2025-06-20 09:52:34 +00:00 · 2025-06-20 09:52:34 +00:00 · bad5cc0eba
commit bad5cc0eba
parent 0008f92434
29 changed files with 1461 additions and 2 deletions
--- a/README.md
+++ b/README.md
@ -1,3 +1,191 @@
-# FastAPI Application
+# SaaS Invoicing Application

-This is a FastAPI application bootstrapped by BackendIM, the AI-powered backend generation platform.
+A comprehensive SaaS invoicing solution built with FastAPI and SQLite for managing customers, invoices, and billing operations.
+
+## Features
+
+- **User Authentication**: JWT-based authentication with secure registration and login
+- **Customer Management**: Create, read, update, and delete customer records
+- **Invoice Management**: Full invoice lifecycle management with automatic calculations
+- **Invoice Items**: Line-item management with quantity, unit price, and total calculations
+- **Multiple Invoice Statuses**: Draft, Sent, Paid, Overdue, and Cancelled
+- **Tax Calculations**: Configurable tax rates with automatic tax amount calculations
+- **RESTful API**: Comprehensive REST API with FastAPI documentation
+
+## Technology Stack
+
+- **Backend**: FastAPI (Python)
+- **Database**: SQLite with SQLAlchemy ORM
+- **Authentication**: JWT tokens with passlib for password hashing
+- **API Documentation**: Automatic OpenAPI/Swagger documentation
+- **Database Migrations**: Alembic for database schema management
+- **Code Quality**: Ruff for linting and code formatting
+
+## Environment Variables
+
+The following environment variables should be set:
+
+- `SECRET_KEY` - Secret key for JWT token signing (required for production)
+
+## Project Structure
+
+```
+├── main.py                 # FastAPI application entry point
+├── requirements.txt        # Python dependencies
+├── alembic.ini            # Alembic configuration
+├── alembic/               # Database migrations
+├── app/
+│   ├── api/               # API route handlers
+│   │   ├── auth.py        # Authentication endpoints
+│   │   ├── users.py       # User management endpoints
+│   │   ├── customers.py   # Customer management endpoints
+│   │   ├── invoices.py    # Invoice management endpoints
+│   │   └── routes.py      # Main API router
+│   ├── core/              # Core functionality
+│   │   ├── config.py      # Application configuration
+│   │   ├── security.py    # Authentication and security
+│   │   └── deps.py        # Dependency injection
+│   ├── db/                # Database configuration
+│   │   ├── base.py        # SQLAlchemy base class
+│   │   └── session.py     # Database session management
+│   ├── models/            # SQLAlchemy models
+│   │   ├── user.py        # User model
+│   │   ├── customer.py    # Customer model
+│   │   └── invoice.py     # Invoice and InvoiceItem models
+│   ├── schemas/           # Pydantic schemas
+│   │   ├── user.py        # User schemas
+│   │   ├── customer.py    # Customer schemas
+│   │   └── invoice.py     # Invoice schemas
+│   └── services/          # Business logic
+│       ├── user_service.py      # User business logic
+│       ├── customer_service.py  # Customer business logic
+│       └── invoice_service.py   # Invoice business logic
+```
+
+## Installation & Setup
+
+1. Install dependencies:
+```bash
+pip install -r requirements.txt
+```
+
+2. Set environment variables:
+```bash
+export SECRET_KEY="your-secret-key-here"
+```
+
+3. Run database migrations:
+```bash
+alembic upgrade head
+```
+
+4. Start the application:
+```bash
+uvicorn main:app --reload
+```
+
+The application will be available at `http://localhost:8000`
+
+## API Documentation
+
+- **Interactive API Documentation**: http://localhost:8000/docs
+- **Alternative Documentation**: http://localhost:8000/redoc
+- **OpenAPI Schema**: http://localhost:8000/openapi.json
+- **Health Check**: http://localhost:8000/health
+
+## API Endpoints
+
+### Authentication
+- `POST /auth/register` - Register a new user
+- `POST /auth/login` - Login user
+- `POST /auth/token` - OAuth2 compatible token endpoint
+
+### Users
+- `GET /users/me` - Get current user information
+- `PUT /users/me` - Update current user information
+
+### Customers
+- `GET /customers/` - List all customers (paginated)
+- `POST /customers/` - Create a new customer
+- `GET /customers/{id}` - Get customer by ID
+- `PUT /customers/{id}` - Update customer
+- `DELETE /customers/{id}` - Delete customer
+
+### Invoices
+- `GET /invoices/` - List all invoices (paginated)
+- `POST /invoices/` - Create a new invoice
+- `GET /invoices/{id}` - Get invoice by ID
+- `PUT /invoices/{id}` - Update invoice
+- `DELETE /invoices/{id}` - Delete invoice
+- `PATCH /invoices/{id}/status` - Update invoice status
+
+## Data Models
+
+### User
+- ID, email, password, full name, company name
+- Active status and timestamps
+
+### Customer
+- ID, name, email, phone, address details
+- Associated with user (multi-tenant)
+
+### Invoice
+- ID, invoice number, customer, dates, status
+- Subtotal, tax rate, tax amount, total
+- Notes and timestamps
+
+### Invoice Items
+- ID, invoice, description, quantity, unit price, total price
+
+## Database Storage
+
+The application uses SQLite database stored at `/app/storage/db/db.sqlite` with automatic directory creation.
+
+## Security Features
+
+- JWT token-based authentication
+- Password hashing with bcrypt
+- User isolation (multi-tenant data access)
+- CORS enabled for cross-origin requests
+
+## Development
+
+### Code Quality
+Run Ruff for linting and formatting:
+```bash
+ruff check .
+ruff format .
+```
+
+### Database Operations
+Create new migration:
+```bash
+alembic revision --autogenerate -m "Description"
+```
+
+Apply migrations:
+```bash
+alembic upgrade head
+```
+
+## Health Check
+
+The application provides a health check endpoint at `/health` that returns:
+```json
+{
+  "status": "healthy",
+  "service": "invoicing-api"
+}
+```
+
+## Production Deployment
+
+1. Set a strong `SECRET_KEY` environment variable
+2. Configure proper database backups for `/app/storage/db/`
+3. Use a production WSGI server like Gunicorn
+4. Set up proper logging and monitoring
+5. Configure reverse proxy (nginx/Apache) if needed
+
+## License
+
+This project is available for use in SaaS applications and business purposes.
--- a/alembic.ini
+++ b/alembic.ini
@ -0,0 +1,41 @@
+[alembic]
+script_location = alembic
+prepend_sys_path = .
+version_path_separator = os
+sqlalchemy.url = sqlite:////app/storage/db/db.sqlite
+
+[post_write_hooks]
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S
--- a/alembic/env.py
+++ b/alembic/env.py
@ -0,0 +1,62 @@
+from logging.config import fileConfig
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+from alembic import context
+import sys
+import os
+
+# Add the parent directory to the path to import app modules
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from app.db.base import Base
+from app.core.config import settings
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Set the SQLAlchemy URL from our settings
+config.set_main_option("sqlalchemy.url", settings.SQLALCHEMY_DATABASE_URL)
+
+# Interpret the config file for Python logging.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode."""
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode."""
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(connection=connection, target_metadata=target_metadata)
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()
--- a/alembic/script.py.mako
+++ b/alembic/script.py.mako
@ -0,0 +1,24 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}
--- a/alembic/versions/001_initial_tables.py
+++ b/alembic/versions/001_initial_tables.py
@ -0,0 +1,148 @@
+"""Initial tables
+
+Revision ID: 001
+Revises:
+Create Date: 2024-01-01 00:00:00.000000
+
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "001"
+down_revision = None
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Create users table
+    op.create_table(
+        "users",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("email", sa.String(), nullable=False),
+        sa.Column("hashed_password", sa.String(), nullable=False),
+        sa.Column("full_name", sa.String(), nullable=False),
+        sa.Column("company_name", sa.String(), nullable=True),
+        sa.Column("is_active", sa.Boolean(), nullable=True),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("CURRENT_TIMESTAMP"),
+            nullable=True,
+        ),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=True),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(op.f("ix_users_id"), "users", ["id"], unique=False)
+    op.create_index(op.f("ix_users_email"), "users", ["email"], unique=True)
+
+    # Create customers table
+    op.create_table(
+        "customers",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("name", sa.String(), nullable=False),
+        sa.Column("email", sa.String(), nullable=False),
+        sa.Column("phone", sa.String(), nullable=True),
+        sa.Column("address", sa.Text(), nullable=True),
+        sa.Column("city", sa.String(), nullable=True),
+        sa.Column("state", sa.String(), nullable=True),
+        sa.Column("zip_code", sa.String(), nullable=True),
+        sa.Column("country", sa.String(), nullable=True),
+        sa.Column("user_id", sa.Integer(), nullable=False),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("CURRENT_TIMESTAMP"),
+            nullable=True,
+        ),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=True),
+        sa.ForeignKeyConstraint(
+            ["user_id"],
+            ["users.id"],
+        ),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(op.f("ix_customers_id"), "customers", ["id"], unique=False)
+
+    # Create invoices table
+    op.create_table(
+        "invoices",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("invoice_number", sa.String(), nullable=False),
+        sa.Column("customer_id", sa.Integer(), nullable=False),
+        sa.Column("user_id", sa.Integer(), nullable=False),
+        sa.Column(
+            "issue_date",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("CURRENT_TIMESTAMP"),
+            nullable=True,
+        ),
+        sa.Column("due_date", sa.DateTime(timezone=True), nullable=False),
+        sa.Column(
+            "status",
+            sa.Enum(
+                "DRAFT", "SENT", "PAID", "OVERDUE", "CANCELLED", name="invoicestatus"
+            ),
+            nullable=True,
+        ),
+        sa.Column("subtotal", sa.Numeric(precision=10, scale=2), nullable=True),
+        sa.Column("tax_rate", sa.Numeric(precision=5, scale=2), nullable=True),
+        sa.Column("tax_amount", sa.Numeric(precision=10, scale=2), nullable=True),
+        sa.Column("total", sa.Numeric(precision=10, scale=2), nullable=True),
+        sa.Column("notes", sa.Text(), nullable=True),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("CURRENT_TIMESTAMP"),
+            nullable=True,
+        ),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=True),
+        sa.ForeignKeyConstraint(
+            ["customer_id"],
+            ["customers.id"],
+        ),
+        sa.ForeignKeyConstraint(
+            ["user_id"],
+            ["users.id"],
+        ),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("invoice_number"),
+    )
+    op.create_index(op.f("ix_invoices_id"), "invoices", ["id"], unique=False)
+
+    # Create invoice_items table
+    op.create_table(
+        "invoice_items",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("invoice_id", sa.Integer(), nullable=False),
+        sa.Column("description", sa.String(), nullable=False),
+        sa.Column("quantity", sa.Numeric(precision=10, scale=2), nullable=False),
+        sa.Column("unit_price", sa.Numeric(precision=10, scale=2), nullable=False),
+        sa.Column("total_price", sa.Numeric(precision=10, scale=2), nullable=False),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("CURRENT_TIMESTAMP"),
+            nullable=True,
+        ),
+        sa.ForeignKeyConstraint(
+            ["invoice_id"],
+            ["invoices.id"],
+        ),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(op.f("ix_invoice_items_id"), "invoice_items", ["id"], unique=False)
+
+
+def downgrade() -> None:
+    op.drop_index(op.f("ix_invoice_items_id"), table_name="invoice_items")
+    op.drop_table("invoice_items")
+    op.drop_index(op.f("ix_invoices_id"), table_name="invoices")
+    op.drop_table("invoices")
+    op.drop_index(op.f("ix_customers_id"), table_name="customers")
+    op.drop_table("customers")
+    op.drop_index(op.f("ix_users_email"), table_name="users")
+    op.drop_index(op.f("ix_users_id"), table_name="users")
+    op.drop_table("users")
--- a/app/init.py
+++ b/app/init.py
--- a/app/api/init.py
+++ b/app/api/init.py
--- a/app/api/auth.py
+++ b/app/api/auth.py
@ -0,0 +1,67 @@
+from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi.security import OAuth2PasswordRequestForm
+from sqlalchemy.orm import Session
+from datetime import timedelta
+from app.db.session import get_db
+from app.services.user_service import UserService
+from app.schemas.user import UserCreate, User, Token, UserLogin
+from app.core.security import create_access_token
+from app.core.config import settings
+
+router = APIRouter()
+
+
+@router.post("/register", response_model=User, status_code=status.HTTP_201_CREATED)
+def register(user_data: UserCreate, db: Session = Depends(get_db)):
+    user_service = UserService(db)
+
+    existing_user = user_service.get_user_by_email(user_data.email)
+    if existing_user:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST, detail="Email already registered"
+        )
+
+    user = user_service.create_user(user_data)
+    return user
+
+
+@router.post("/login", response_model=Token)
+def login(user_data: UserLogin, db: Session = Depends(get_db)):
+    user_service = UserService(db)
+
+    user = user_service.authenticate_user(user_data.email, user_data.password)
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Incorrect email or password",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+
+    access_token_expires = timedelta(minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES)
+    access_token = create_access_token(
+        data={"sub": user.email}, expires_delta=access_token_expires
+    )
+
+    return {"access_token": access_token, "token_type": "bearer"}
+
+
+@router.post("/token", response_model=Token)
+def login_for_access_token(
+    form_data: OAuth2PasswordRequestForm = Depends(), db: Session = Depends(get_db)
+):
+    user_service = UserService(db)
+
+    user = user_service.authenticate_user(form_data.username, form_data.password)
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Incorrect email or password",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+
+    access_token_expires = timedelta(minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES)
+    access_token = create_access_token(
+        data={"sub": user.email}, expires_delta=access_token_expires
+    )
+
+    return {"access_token": access_token, "token_type": "bearer"}
--- a/app/api/customers.py
+++ b/app/api/customers.py
@ -0,0 +1,83 @@
+from fastapi import APIRouter, Depends, HTTPException, status, Query
+from sqlalchemy.orm import Session
+from typing import List
+from app.db.session import get_db
+from app.services.customer_service import CustomerService
+from app.schemas.customer import Customer, CustomerCreate, CustomerUpdate
+from app.core.deps import get_current_user
+from app.models.user import User
+
+router = APIRouter()
+
+
+@router.get("/", response_model=List[Customer])
+def get_customers(
+    skip: int = Query(0, ge=0),
+    limit: int = Query(100, ge=1, le=100),
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    customer_service = CustomerService(db)
+    return customer_service.get_customers(current_user.id, skip, limit)
+
+
+@router.post("/", response_model=Customer, status_code=status.HTTP_201_CREATED)
+def create_customer(
+    customer_data: CustomerCreate,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    customer_service = CustomerService(db)
+    return customer_service.create_customer(customer_data, current_user.id)
+
+
+@router.get("/{customer_id}", response_model=Customer)
+def get_customer(
+    customer_id: int,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    customer_service = CustomerService(db)
+    customer = customer_service.get_customer(customer_id, current_user.id)
+
+    if not customer:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Customer not found"
+        )
+
+    return customer
+
+
+@router.put("/{customer_id}", response_model=Customer)
+def update_customer(
+    customer_id: int,
+    customer_data: CustomerUpdate,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    customer_service = CustomerService(db)
+    customer = customer_service.update_customer(
+        customer_id, customer_data, current_user.id
+    )
+
+    if not customer:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Customer not found"
+        )
+
+    return customer
+
+
+@router.delete("/{customer_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_customer(
+    customer_id: int,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    customer_service = CustomerService(db)
+    success = customer_service.delete_customer(customer_id, current_user.id)
+
+    if not success:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Customer not found"
+        )
--- a/app/api/invoices.py
+++ b/app/api/invoices.py
@ -0,0 +1,100 @@
+from fastapi import APIRouter, Depends, HTTPException, status, Query
+from sqlalchemy.orm import Session
+from typing import List
+from app.db.session import get_db
+from app.services.invoice_service import InvoiceService
+from app.schemas.invoice import Invoice, InvoiceCreate, InvoiceUpdate
+from app.core.deps import get_current_user
+from app.models.user import User
+from app.models.invoice import InvoiceStatus
+
+router = APIRouter()
+
+
+@router.get("/", response_model=List[Invoice])
+def get_invoices(
+    skip: int = Query(0, ge=0),
+    limit: int = Query(100, ge=1, le=100),
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    invoice_service = InvoiceService(db)
+    return invoice_service.get_invoices(current_user.id, skip, limit)
+
+
+@router.post("/", response_model=Invoice, status_code=status.HTTP_201_CREATED)
+def create_invoice(
+    invoice_data: InvoiceCreate,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    invoice_service = InvoiceService(db)
+    return invoice_service.create_invoice(invoice_data, current_user.id)
+
+
+@router.get("/{invoice_id}", response_model=Invoice)
+def get_invoice(
+    invoice_id: int,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    invoice_service = InvoiceService(db)
+    invoice = invoice_service.get_invoice(invoice_id, current_user.id)
+
+    if not invoice:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Invoice not found"
+        )
+
+    return invoice
+
+
+@router.put("/{invoice_id}", response_model=Invoice)
+def update_invoice(
+    invoice_id: int,
+    invoice_data: InvoiceUpdate,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    invoice_service = InvoiceService(db)
+    invoice = invoice_service.update_invoice(invoice_id, invoice_data, current_user.id)
+
+    if not invoice:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Invoice not found"
+        )
+
+    return invoice
+
+
+@router.delete("/{invoice_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_invoice(
+    invoice_id: int,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    invoice_service = InvoiceService(db)
+    success = invoice_service.delete_invoice(invoice_id, current_user.id)
+
+    if not success:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Invoice not found"
+        )
+
+
+@router.patch("/{invoice_id}/status", response_model=Invoice)
+def update_invoice_status(
+    invoice_id: int,
+    status: InvoiceStatus,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    invoice_service = InvoiceService(db)
+    invoice = invoice_service.update_invoice_status(invoice_id, status, current_user.id)
+
+    if not invoice:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Invoice not found"
+        )
+
+    return invoice
--- a/app/api/routes.py
+++ b/app/api/routes.py
@ -0,0 +1,9 @@
+from fastapi import APIRouter
+from app.api import auth, users, customers, invoices
+
+api_router = APIRouter()
+
+api_router.include_router(auth.router, prefix="/auth", tags=["authentication"])
+api_router.include_router(users.router, prefix="/users", tags=["users"])
+api_router.include_router(customers.router, prefix="/customers", tags=["customers"])
+api_router.include_router(invoices.router, prefix="/invoices", tags=["invoices"])
--- a/app/api/users.py
+++ b/app/api/users.py
@ -0,0 +1,31 @@
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.orm import Session
+from app.db.session import get_db
+from app.services.user_service import UserService
+from app.schemas.user import User, UserUpdate
+from app.core.deps import get_current_user
+from app.models.user import User as UserModel
+
+router = APIRouter()
+
+
+@router.get("/me", response_model=User)
+def get_current_user_info(current_user: UserModel = Depends(get_current_user)):
+    return current_user
+
+
+@router.put("/me", response_model=User)
+def update_current_user(
+    user_data: UserUpdate,
+    current_user: UserModel = Depends(get_current_user),
+    db: Session = Depends(get_db),
+):
+    user_service = UserService(db)
+    updated_user = user_service.update_user(current_user.id, user_data)
+
+    if not updated_user:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="User not found"
+        )
+
+    return updated_user
--- a/app/core/config.py
+++ b/app/core/config.py
@ -0,0 +1,22 @@
+import os
+from pathlib import Path
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    SECRET_KEY: str = os.getenv("SECRET_KEY", "your-secret-key-change-in-production")
+    ALGORITHM: str = "HS256"
+    ACCESS_TOKEN_EXPIRE_MINUTES: int = 30
+
+    DB_DIR: Path = Path("/app/storage/db")
+
+    def __init__(self):
+        super().__init__()
+        self.DB_DIR.mkdir(parents=True, exist_ok=True)
+
+    @property
+    def SQLALCHEMY_DATABASE_URL(self) -> str:
+        return f"sqlite:///{self.DB_DIR}/db.sqlite"
+
+
+settings = Settings()
--- a/app/core/deps.py
+++ b/app/core/deps.py
@ -0,0 +1,46 @@
+from fastapi import Depends, HTTPException, status
+from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
+from sqlalchemy.orm import Session
+from app.db.session import get_db
+from app.models.user import User
+from app.core.security import verify_token
+
+security = HTTPBearer()
+
+
+def get_current_user(
+    db: Session = Depends(get_db),
+    credentials: HTTPAuthorizationCredentials = Depends(security),
+) -> User:
+    token = credentials.credentials
+    payload = verify_token(token)
+
+    if payload is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Could not validate credentials",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+
+    email: str = payload.get("sub")
+    if email is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Could not validate credentials",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+
+    user = db.query(User).filter(User.email == email).first()
+    if user is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="User not found",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+
+    if not user.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST, detail="Inactive user"
+        )
+
+    return user
--- a/app/core/security.py
+++ b/app/core/security.py
@ -0,0 +1,40 @@
+from datetime import datetime, timedelta
+from typing import Optional
+from jose import JWTError, jwt
+from passlib.context import CryptContext
+from app.core.config import settings
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+
+def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
+    to_encode = data.copy()
+    if expires_delta:
+        expire = datetime.utcnow() + expires_delta
+    else:
+        expire = datetime.utcnow() + timedelta(
+            minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES
+        )
+    to_encode.update({"exp": expire})
+    encoded_jwt = jwt.encode(
+        to_encode, settings.SECRET_KEY, algorithm=settings.ALGORITHM
+    )
+    return encoded_jwt
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def get_password_hash(password: str) -> str:
+    return pwd_context.hash(password)
+
+
+def verify_token(token: str) -> Optional[dict]:
+    try:
+        payload = jwt.decode(
+            token, settings.SECRET_KEY, algorithms=[settings.ALGORITHM]
+        )
+        return payload
+    except JWTError:
+        return None
--- a/app/db/base.py
+++ b/app/db/base.py
@ -0,0 +1,3 @@
+from sqlalchemy.ext.declarative import declarative_base
+
+Base = declarative_base()
--- a/app/db/session.py
+++ b/app/db/session.py
@ -0,0 +1,17 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from app.core.config import settings
+
+engine = create_engine(
+    settings.SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
+)
+
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
--- a/app/models/init.py
+++ b/app/models/init.py
@ -0,0 +1,12 @@
+from sqlalchemy.orm import relationship
+from .user import User
+from .customer import Customer as Customer
+from .invoice import (
+    Invoice as Invoice,
+    InvoiceItem as InvoiceItem,
+    InvoiceStatus as InvoiceStatus,
+)
+
+# Update relationships after all models are imported
+User.customers = relationship("Customer", back_populates="owner")
+User.invoices = relationship("Invoice", back_populates="user")
--- a/app/models/customer.py
+++ b/app/models/customer.py
@ -0,0 +1,24 @@
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, Text
+from sqlalchemy.sql import func
+from sqlalchemy.orm import relationship
+from app.db.base import Base
+
+
+class Customer(Base):
+    __tablename__ = "customers"
+
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String, nullable=False)
+    email = Column(String, nullable=False)
+    phone = Column(String, nullable=True)
+    address = Column(Text, nullable=True)
+    city = Column(String, nullable=True)
+    state = Column(String, nullable=True)
+    zip_code = Column(String, nullable=True)
+    country = Column(String, nullable=True)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+    owner = relationship("User", back_populates="customers")
+    invoices = relationship("Invoice", back_populates="customer")
--- a/app/models/invoice.py
+++ b/app/models/invoice.py
@ -0,0 +1,61 @@
+from sqlalchemy import (
+    Column,
+    Integer,
+    String,
+    DateTime,
+    ForeignKey,
+    Numeric,
+    Text,
+    Enum,
+)
+from sqlalchemy.sql import func
+from sqlalchemy.orm import relationship
+from app.db.base import Base
+import enum
+
+
+class InvoiceStatus(enum.Enum):
+    DRAFT = "draft"
+    SENT = "sent"
+    PAID = "paid"
+    OVERDUE = "overdue"
+    CANCELLED = "cancelled"
+
+
+class Invoice(Base):
+    __tablename__ = "invoices"
+
+    id = Column(Integer, primary_key=True, index=True)
+    invoice_number = Column(String, unique=True, nullable=False)
+    customer_id = Column(Integer, ForeignKey("customers.id"), nullable=False)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    issue_date = Column(DateTime(timezone=True), server_default=func.now())
+    due_date = Column(DateTime(timezone=True), nullable=False)
+    status = Column(Enum(InvoiceStatus), default=InvoiceStatus.DRAFT)
+    subtotal = Column(Numeric(10, 2), default=0)
+    tax_rate = Column(Numeric(5, 2), default=0)
+    tax_amount = Column(Numeric(10, 2), default=0)
+    total = Column(Numeric(10, 2), default=0)
+    notes = Column(Text, nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+    customer = relationship("Customer", back_populates="invoices")
+    user = relationship("User", back_populates="invoices")
+    items = relationship(
+        "InvoiceItem", back_populates="invoice", cascade="all, delete-orphan"
+    )
+
+
+class InvoiceItem(Base):
+    __tablename__ = "invoice_items"
+
+    id = Column(Integer, primary_key=True, index=True)
+    invoice_id = Column(Integer, ForeignKey("invoices.id"), nullable=False)
+    description = Column(String, nullable=False)
+    quantity = Column(Numeric(10, 2), nullable=False)
+    unit_price = Column(Numeric(10, 2), nullable=False)
+    total_price = Column(Numeric(10, 2), nullable=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    invoice = relationship("Invoice", back_populates="items")
--- a/app/models/user.py
+++ b/app/models/user.py
@ -0,0 +1,16 @@
+from sqlalchemy import Column, Integer, String, Boolean, DateTime
+from sqlalchemy.sql import func
+from app.db.base import Base
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(Integer, primary_key=True, index=True)
+    email = Column(String, unique=True, index=True, nullable=False)
+    hashed_password = Column(String, nullable=False)
+    full_name = Column(String, nullable=False)
+    company_name = Column(String, nullable=True)
+    is_active = Column(Boolean, default=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
--- a/app/schemas/customer.py
+++ b/app/schemas/customer.py
@ -0,0 +1,43 @@
+from pydantic import BaseModel, EmailStr
+from typing import Optional
+from datetime import datetime
+
+
+class CustomerBase(BaseModel):
+    name: str
+    email: EmailStr
+    phone: Optional[str] = None
+    address: Optional[str] = None
+    city: Optional[str] = None
+    state: Optional[str] = None
+    zip_code: Optional[str] = None
+    country: Optional[str] = None
+
+
+class CustomerCreate(CustomerBase):
+    pass
+
+
+class CustomerUpdate(BaseModel):
+    name: Optional[str] = None
+    email: Optional[EmailStr] = None
+    phone: Optional[str] = None
+    address: Optional[str] = None
+    city: Optional[str] = None
+    state: Optional[str] = None
+    zip_code: Optional[str] = None
+    country: Optional[str] = None
+
+
+class CustomerInDB(CustomerBase):
+    id: int
+    user_id: int
+    created_at: datetime
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class Customer(CustomerInDB):
+    pass
--- a/app/schemas/invoice.py
+++ b/app/schemas/invoice.py
@ -0,0 +1,79 @@
+from pydantic import BaseModel
+from typing import Optional, List
+from datetime import datetime
+from decimal import Decimal
+from app.models.invoice import InvoiceStatus
+
+
+class InvoiceItemBase(BaseModel):
+    description: str
+    quantity: Decimal
+    unit_price: Decimal
+
+
+class InvoiceItemCreate(InvoiceItemBase):
+    pass
+
+
+class InvoiceItemUpdate(BaseModel):
+    description: Optional[str] = None
+    quantity: Optional[Decimal] = None
+    unit_price: Optional[Decimal] = None
+
+
+class InvoiceItemInDB(InvoiceItemBase):
+    id: int
+    invoice_id: int
+    total_price: Decimal
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class InvoiceItem(InvoiceItemInDB):
+    pass
+
+
+class InvoiceBase(BaseModel):
+    customer_id: int
+    due_date: datetime
+    tax_rate: Optional[Decimal] = Decimal("0")
+    notes: Optional[str] = None
+
+
+class InvoiceCreate(InvoiceBase):
+    items: List[InvoiceItemCreate]
+
+
+class InvoiceUpdate(BaseModel):
+    customer_id: Optional[int] = None
+    due_date: Optional[datetime] = None
+    status: Optional[InvoiceStatus] = None
+    tax_rate: Optional[Decimal] = None
+    notes: Optional[str] = None
+    items: Optional[List[InvoiceItemCreate]] = None
+
+
+class InvoiceInDB(InvoiceBase):
+    id: int
+    invoice_number: str
+    user_id: int
+    issue_date: datetime
+    status: InvoiceStatus
+    subtotal: Decimal
+    tax_amount: Decimal
+    total: Decimal
+    created_at: datetime
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class Invoice(InvoiceInDB):
+    items: List[InvoiceItem] = []
+
+
+class InvoiceWithCustomer(Invoice):
+    customer: Optional[dict] = None
--- a/app/schemas/user.py
+++ b/app/schemas/user.py
@ -0,0 +1,47 @@
+from pydantic import BaseModel, EmailStr
+from typing import Optional
+from datetime import datetime
+
+
+class UserBase(BaseModel):
+    email: EmailStr
+    full_name: str
+    company_name: Optional[str] = None
+
+
+class UserCreate(UserBase):
+    password: str
+
+
+class UserUpdate(BaseModel):
+    full_name: Optional[str] = None
+    company_name: Optional[str] = None
+    is_active: Optional[bool] = None
+
+
+class UserInDB(UserBase):
+    id: int
+    is_active: bool
+    created_at: datetime
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class User(UserInDB):
+    pass
+
+
+class UserLogin(BaseModel):
+    email: EmailStr
+    password: str
+
+
+class Token(BaseModel):
+    access_token: str
+    token_type: str
+
+
+class TokenData(BaseModel):
+    email: Optional[str] = None
--- a/app/services/customer_service.py
+++ b/app/services/customer_service.py
@ -0,0 +1,58 @@
+from sqlalchemy.orm import Session
+from app.models.customer import Customer
+from app.schemas.customer import CustomerCreate, CustomerUpdate
+from typing import List, Optional
+
+
+class CustomerService:
+    def __init__(self, db: Session):
+        self.db = db
+
+    def get_customers(
+        self, user_id: int, skip: int = 0, limit: int = 100
+    ) -> List[Customer]:
+        return (
+            self.db.query(Customer)
+            .filter(Customer.user_id == user_id)
+            .offset(skip)
+            .limit(limit)
+            .all()
+        )
+
+    def get_customer(self, customer_id: int, user_id: int) -> Optional[Customer]:
+        return (
+            self.db.query(Customer)
+            .filter(Customer.id == customer_id, Customer.user_id == user_id)
+            .first()
+        )
+
+    def create_customer(self, customer_data: CustomerCreate, user_id: int) -> Customer:
+        customer = Customer(**customer_data.dict(), user_id=user_id)
+        self.db.add(customer)
+        self.db.commit()
+        self.db.refresh(customer)
+        return customer
+
+    def update_customer(
+        self, customer_id: int, customer_data: CustomerUpdate, user_id: int
+    ) -> Optional[Customer]:
+        customer = self.get_customer(customer_id, user_id)
+        if not customer:
+            return None
+
+        update_data = customer_data.dict(exclude_unset=True)
+        for field, value in update_data.items():
+            setattr(customer, field, value)
+
+        self.db.commit()
+        self.db.refresh(customer)
+        return customer
+
+    def delete_customer(self, customer_id: int, user_id: int) -> bool:
+        customer = self.get_customer(customer_id, user_id)
+        if not customer:
+            return False
+
+        self.db.delete(customer)
+        self.db.commit()
+        return True
--- a/app/services/invoice_service.py
+++ b/app/services/invoice_service.py
@ -0,0 +1,142 @@
+from sqlalchemy.orm import Session
+from app.models.invoice import Invoice, InvoiceItem, InvoiceStatus
+from app.schemas.invoice import InvoiceCreate, InvoiceUpdate
+from typing import List, Optional
+from decimal import Decimal
+import uuid
+
+
+class InvoiceService:
+    def __init__(self, db: Session):
+        self.db = db
+
+    def get_invoices(
+        self, user_id: int, skip: int = 0, limit: int = 100
+    ) -> List[Invoice]:
+        return (
+            self.db.query(Invoice)
+            .filter(Invoice.user_id == user_id)
+            .offset(skip)
+            .limit(limit)
+            .all()
+        )
+
+    def get_invoice(self, invoice_id: int, user_id: int) -> Optional[Invoice]:
+        return (
+            self.db.query(Invoice)
+            .filter(Invoice.id == invoice_id, Invoice.user_id == user_id)
+            .first()
+        )
+
+    def create_invoice(self, invoice_data: InvoiceCreate, user_id: int) -> Invoice:
+        # Generate unique invoice number
+        invoice_number = f"INV-{uuid.uuid4().hex[:8].upper()}"
+
+        # Calculate totals
+        subtotal = sum(item.quantity * item.unit_price for item in invoice_data.items)
+        tax_amount = (
+            subtotal * (invoice_data.tax_rate / 100)
+            if invoice_data.tax_rate
+            else Decimal("0")
+        )
+        total = subtotal + tax_amount
+
+        # Create invoice
+        invoice = Invoice(
+            invoice_number=invoice_number,
+            customer_id=invoice_data.customer_id,
+            user_id=user_id,
+            due_date=invoice_data.due_date,
+            tax_rate=invoice_data.tax_rate or Decimal("0"),
+            subtotal=subtotal,
+            tax_amount=tax_amount,
+            total=total,
+            notes=invoice_data.notes,
+        )
+
+        self.db.add(invoice)
+        self.db.flush()  # Get the invoice ID
+
+        # Create invoice items
+        for item_data in invoice_data.items:
+            item_total = item_data.quantity * item_data.unit_price
+            item = InvoiceItem(
+                invoice_id=invoice.id,
+                description=item_data.description,
+                quantity=item_data.quantity,
+                unit_price=item_data.unit_price,
+                total_price=item_total,
+            )
+            self.db.add(item)
+
+        self.db.commit()
+        self.db.refresh(invoice)
+        return invoice
+
+    def update_invoice(
+        self, invoice_id: int, invoice_data: InvoiceUpdate, user_id: int
+    ) -> Optional[Invoice]:
+        invoice = self.get_invoice(invoice_id, user_id)
+        if not invoice:
+            return None
+
+        # Update basic fields
+        update_data = invoice_data.dict(exclude_unset=True, exclude={"items"})
+        for field, value in update_data.items():
+            setattr(invoice, field, value)
+
+        # Update items if provided
+        if invoice_data.items is not None:
+            # Delete existing items
+            self.db.query(InvoiceItem).filter(
+                InvoiceItem.invoice_id == invoice_id
+            ).delete()
+
+            # Add new items
+            subtotal = Decimal("0")
+            for item_data in invoice_data.items:
+                item_total = item_data.quantity * item_data.unit_price
+                subtotal += item_total
+                item = InvoiceItem(
+                    invoice_id=invoice.id,
+                    description=item_data.description,
+                    quantity=item_data.quantity,
+                    unit_price=item_data.unit_price,
+                    total_price=item_total,
+                )
+                self.db.add(item)
+
+            # Recalculate totals
+            tax_amount = (
+                subtotal * (invoice.tax_rate / 100)
+                if invoice.tax_rate
+                else Decimal("0")
+            )
+            invoice.subtotal = subtotal
+            invoice.tax_amount = tax_amount
+            invoice.total = subtotal + tax_amount
+
+        self.db.commit()
+        self.db.refresh(invoice)
+        return invoice
+
+    def delete_invoice(self, invoice_id: int, user_id: int) -> bool:
+        invoice = self.get_invoice(invoice_id, user_id)
+        if not invoice:
+            return False
+
+        self.db.delete(invoice)
+        self.db.commit()
+        return True
+
+    def update_invoice_status(
+        self, invoice_id: int, status: InvoiceStatus, user_id: int
+    ) -> Optional[Invoice]:
+        invoice = self.get_invoice(invoice_id, user_id)
+        if not invoice:
+            return None
+
+        invoice.status = status
+        self.db.commit()
+        self.db.refresh(invoice)
+        return invoice
--- a/app/services/user_service.py
+++ b/app/services/user_service.py
@ -0,0 +1,48 @@
+from sqlalchemy.orm import Session
+from app.models.user import User
+from app.schemas.user import UserCreate, UserUpdate
+from app.core.security import get_password_hash, verify_password
+from typing import Optional
+
+
+class UserService:
+    def __init__(self, db: Session):
+        self.db = db
+
+    def get_user_by_email(self, email: str) -> Optional[User]:
+        return self.db.query(User).filter(User.email == email).first()
+
+    def get_user_by_id(self, user_id: int) -> Optional[User]:
+        return self.db.query(User).filter(User.id == user_id).first()
+
+    def create_user(self, user_data: UserCreate) -> User:
+        hashed_password = get_password_hash(user_data.password)
+        user = User(
+            email=user_data.email,
+            hashed_password=hashed_password,
+            full_name=user_data.full_name,
+            company_name=user_data.company_name,
+        )
+        self.db.add(user)
+        self.db.commit()
+        self.db.refresh(user)
+        return user
+
+    def authenticate_user(self, email: str, password: str) -> Optional[User]:
+        user = self.get_user_by_email(email)
+        if not user or not verify_password(password, user.hashed_password):
+            return None
+        return user
+
+    def update_user(self, user_id: int, user_data: UserUpdate) -> Optional[User]:
+        user = self.get_user_by_id(user_id)
+        if not user:
+            return None
+
+        update_data = user_data.dict(exclude_unset=True)
+        for field, value in update_data.items():
+            setattr(user, field, value)
+
+        self.db.commit()
+        self.db.refresh(user)
+        return user
--- a/main.py
+++ b/main.py
@ -0,0 +1,36 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from app.api.routes import api_router
+
+app = FastAPI(
+    title="SaaS Invoicing Application",
+    description="A comprehensive invoicing solution for SaaS businesses",
+    version="1.0.0",
+    openapi_url="/openapi.json",
+    docs_url="/docs",
+    redoc_url="/redoc",
+)
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+app.include_router(api_router)
+
+
+@app.get("/")
+async def root():
+    return {
+        "title": "SaaS Invoicing Application",
+        "documentation": "/docs",
+        "health": "/health",
+    }
+
+
+@app.get("/health")
+async def health_check():
+    return {"status": "healthy", "service": "invoicing-api"}
--- a/requirements.txt
+++ b/requirements.txt
@ -0,0 +1,12 @@
+fastapi==0.104.1
+uvicorn[standard]==0.24.0
+sqlalchemy==2.0.23
+alembic==1.12.1
+python-jose[cryptography]==3.3.0
+passlib[bcrypt]==1.7.4
+python-multipart==0.0.6
+pydantic==2.5.0
+pydantic-settings==2.1.0
+python-dotenv==1.0.0
+email-validator==2.1.0
+ruff==0.1.6