Implement FastAPI cart and checkout system

- Created FastAPI application with SQLite database
- Implemented cart management (create, get, add items, remove items, clear)
- Added checkout functionality with payment processing simulation
- Set up database models using SQLAlchemy with Cart and CartItem tables
- Configured Alembic for database migrations
- Added comprehensive API documentation and examples
- Included health endpoint and CORS support
- Formatted code with ruff linting

README.md

@@ -1,3 +1,152 @@
-# FastAPI Application
+# Cart and Checkout System
 
-This is a FastAPI application bootstrapped by BackendIM, the AI-powered backend generation platform.
+A FastAPI-based REST API for managing shopping carts and processing checkouts.
+
+## Features
+
+- Create and manage shopping carts
+- Add, update, and remove items from carts
+- Checkout functionality with payment processing simulation
+- SQLite database with SQLAlchemy ORM
+- Alembic database migrations
+- Automatic API documentation with FastAPI
+- CORS support for cross-origin requests
+
+## Installation
+
+1. Install dependencies:
+```bash
+pip install -r requirements.txt
+```
+
+2. Run database migrations:
+```bash
+alembic upgrade head
+```
+
+3. Start the application:
+```bash
+uvicorn main:app --reload
+```
+
+The application will be available at `http://localhost:8000`.
+
+## API Documentation
+
+Once the application is running, you can access:
+- Interactive API documentation: `http://localhost:8000/docs`
+- Alternative documentation: `http://localhost:8000/redoc`
+- OpenAPI JSON schema: `http://localhost:8000/openapi.json`
+
+## API Endpoints
+
+### Cart Management
+
+- `POST /api/v1/carts/` - Create a new cart
+- `GET /api/v1/carts/{cart_id}` - Get cart by ID
+- `GET /api/v1/carts/user/{user_id}` - Get all carts for a user
+- `DELETE /api/v1/carts/{cart_id}` - Clear all items from a cart
+
+### Cart Items
+
+- `POST /api/v1/carts/{cart_id}/items/` - Add item to cart
+- `PUT /api/v1/carts/{cart_id}/items/{item_id}` - Update item quantity
+- `DELETE /api/v1/carts/{cart_id}/items/{item_id}` - Remove item from cart
+
+### Checkout
+
+- `POST /api/v1/checkout/` - Process checkout
+
+### System
+
+- `GET /` - Service information
+- `GET /health` - Health check endpoint
+
+## Example Usage
+
+### Create a Cart
+```bash
+curl -X POST "http://localhost:8000/api/v1/carts/" \
+     -H "Content-Type: application/json" \
+     -d '{"user_id": "user123"}'
+```
+
+### Add Item to Cart
+```bash
+curl -X POST "http://localhost:8000/api/v1/carts/1/items/" \
+     -H "Content-Type: application/json" \
+     -d '{
+       "product_id": "prod123",
+       "product_name": "Example Product",
+       "price": 29.99,
+       "quantity": 2
+     }'
+```
+
+### Checkout
+```bash
+curl -X POST "http://localhost:8000/api/v1/checkout/" \
+     -H "Content-Type: application/json" \
+     -d '{
+       "cart_id": 1,
+       "payment_method": "credit_card",
+       "billing_address": {
+         "street": "123 Main St",
+         "city": "Anytown",
+         "state": "ST",
+         "zip": "12345"
+       }
+     }'
+```
+
+## Database Schema
+
+### Carts Table
+- `id` - Primary key
+- `user_id` - User identifier
+- `status` - Cart status (active, checked_out, abandoned)
+- `created_at` - Creation timestamp
+- `updated_at` - Last update timestamp
+
+### Cart Items Table
+- `id` - Primary key
+- `cart_id` - Foreign key to carts table
+- `product_id` - Product identifier
+- `product_name` - Product name
+- `price` - Item price
+- `quantity` - Item quantity
+
+## Development
+
+### Database Migrations
+
+To create a new migration:
+```bash
+alembic revision -m "Description of changes"
+```
+
+To apply migrations:
+```bash
+alembic upgrade head
+```
+
+To rollback migrations:
+```bash
+alembic downgrade -1
+```
+
+### Code Linting
+
+The project uses Ruff for code formatting and linting:
+```bash
+ruff check .
+ruff format .
+```
+
+## Architecture
+
+- **FastAPI** - Modern Python web framework
+- **SQLAlchemy** - SQL toolkit and ORM
+- **SQLite** - Lightweight database
+- **Alembic** - Database migration tool
+- **Pydantic** - Data validation and serialization

alembic.ini

@@ -0,0 +1,98 @@
+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+script_location = alembic
+
+# template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
+# Uncomment the line below if you want the files to be prepended with date and time
+# file_template = %%(year)d_%%(month).2d_%%(day).2d_%%(hour).2d%%(minute).2d-%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.
+prepend_sys_path = .
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the python-dateutil library that can be
+# installed by adding `alembic[tz]` to the pip requirements
+# string value is passed to dateutil.tz.gettz()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the
+# "slug" field
+# truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version path separator; As mentioned above, this is the character used to split
+# version_locations. The default within new alembic.ini files is "os", which uses
+# os.pathsep. If this key is omitted entirely, it falls back to the legacy
+# behavior of splitting on spaces and/or commas.
+# Valid values for version_path_separator are:
+#
+# version_path_separator = :
+# version_path_separator = ;
+# version_path_separator = space
+version_path_separator = os
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+sqlalchemy.url = sqlite:////app/storage/db/db.sqlite
+
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME
+
+# Logging configuration
+[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

alembic/env.py

@@ -0,0 +1,82 @@
+from logging.config import fileConfig
+import sys
+from pathlib import Path
+
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+
+# Add the project root to the path
+sys.path.append(str(Path(__file__).parent.parent))
+
+# Import the Base from your models
+from app.db.base import Base
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+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
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    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.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    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()

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"}

alembic/versions/001_initial_migration.py

@@ -0,0 +1,70 @@
+"""Initial migration
+
+Revision ID: 001
+Revises:
+Create Date: 2025-07-21 10:00:00.000000
+
+"""
+
+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 carts table
+    op.create_table(
+        "carts",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("user_id", sa.String(), nullable=True),
+        sa.Column("status", sa.String(), 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),
+            server_default=sa.text("(CURRENT_TIMESTAMP)"),
+            nullable=True,
+        ),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(op.f("ix_carts_id"), "carts", ["id"], unique=False)
+    op.create_index(op.f("ix_carts_user_id"), "carts", ["user_id"], unique=False)
+
+    # Create cart_items table
+    op.create_table(
+        "cart_items",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("cart_id", sa.Integer(), nullable=True),
+        sa.Column("product_id", sa.String(), nullable=True),
+        sa.Column("product_name", sa.String(), nullable=True),
+        sa.Column("price", sa.Float(), nullable=True),
+        sa.Column("quantity", sa.Integer(), nullable=True),
+        sa.ForeignKeyConstraint(
+            ["cart_id"],
+            ["carts.id"],
+        ),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index(op.f("ix_cart_items_id"), "cart_items", ["id"], unique=False)
+    op.create_index(
+        op.f("ix_cart_items_product_id"), "cart_items", ["product_id"], unique=False
+    )
+
+
+def downgrade() -> None:
+    op.drop_index(op.f("ix_cart_items_product_id"), table_name="cart_items")
+    op.drop_index(op.f("ix_cart_items_id"), table_name="cart_items")
+    op.drop_table("cart_items")
+    op.drop_index(op.f("ix_carts_user_id"), table_name="carts")
+    op.drop_index(op.f("ix_carts_id"), table_name="carts")
+    op.drop_table("carts")

app/api/cart.py

@@ -0,0 +1,203 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.orm import Session
+from typing import List
+import uuid
+
+from app.db.session import get_db
+from app.models.cart import Cart, CartItem
+from app.schemas import (
+    CartCreate,
+    CartResponse,
+    CartItemCreate,
+    CartItemResponse,
+    CheckoutRequest,
+    CheckoutResponse,
+)
+
+router = APIRouter()
+
+
+@router.post("/carts/", response_model=CartResponse)
+def create_cart(cart: CartCreate, db: Session = Depends(get_db)):
+    db_cart = Cart(user_id=cart.user_id)
+    db.add(db_cart)
+    db.commit()
+    db.refresh(db_cart)
+
+    # Calculate total
+    total = sum(item.price * item.quantity for item in db_cart.items)
+
+    response = CartResponse.model_validate(db_cart)
+    response.total = total
+    return response
+
+
+@router.get("/carts/{cart_id}", response_model=CartResponse)
+def get_cart(cart_id: int, db: Session = Depends(get_db)):
+    cart = db.query(Cart).filter(Cart.id == cart_id).first()
+    if cart is None:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    # Calculate total
+    total = sum(item.price * item.quantity for item in cart.items)
+
+    response = CartResponse.model_validate(cart)
+    response.total = total
+    return response
+
+
+@router.get("/carts/user/{user_id}", response_model=List[CartResponse])
+def get_user_carts(user_id: str, db: Session = Depends(get_db)):
+    carts = db.query(Cart).filter(Cart.user_id == user_id).all()
+
+    response_carts = []
+    for cart in carts:
+        total = sum(item.price * item.quantity for item in cart.items)
+        cart_response = CartResponse.model_validate(cart)
+        cart_response.total = total
+        response_carts.append(cart_response)
+
+    return response_carts
+
+
+@router.post("/carts/{cart_id}/items/", response_model=CartItemResponse)
+def add_item_to_cart(cart_id: int, item: CartItemCreate, db: Session = Depends(get_db)):
+    cart = db.query(Cart).filter(Cart.id == cart_id).first()
+    if cart is None:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    if cart.status != "active":
+        raise HTTPException(status_code=400, detail="Cannot add items to inactive cart")
+
+    # Check if item already exists in cart
+    existing_item = (
+        db.query(CartItem)
+        .filter(CartItem.cart_id == cart_id, CartItem.product_id == item.product_id)
+        .first()
+    )
+
+    if existing_item:
+        # Update quantity if item exists
+        existing_item.quantity += item.quantity
+        db.commit()
+        db.refresh(existing_item)
+        return CartItemResponse.model_validate(existing_item)
+    else:
+        # Create new item if it doesn't exist
+        db_item = CartItem(
+            cart_id=cart_id,
+            product_id=item.product_id,
+            product_name=item.product_name,
+            price=item.price,
+            quantity=item.quantity,
+        )
+        db.add(db_item)
+        db.commit()
+        db.refresh(db_item)
+        return CartItemResponse.model_validate(db_item)
+
+
+@router.put("/carts/{cart_id}/items/{item_id}", response_model=CartItemResponse)
+def update_cart_item(
+    cart_id: int, item_id: int, quantity: int, db: Session = Depends(get_db)
+):
+    cart = db.query(Cart).filter(Cart.id == cart_id).first()
+    if cart is None:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    if cart.status != "active":
+        raise HTTPException(
+            status_code=400, detail="Cannot modify items in inactive cart"
+        )
+
+    item = (
+        db.query(CartItem)
+        .filter(CartItem.id == item_id, CartItem.cart_id == cart_id)
+        .first()
+    )
+
+    if item is None:
+        raise HTTPException(status_code=404, detail="Cart item not found")
+
+    if quantity <= 0:
+        db.delete(item)
+        db.commit()
+        return {"message": "Item removed from cart"}
+    else:
+        item.quantity = quantity
+        db.commit()
+        db.refresh(item)
+        return CartItemResponse.model_validate(item)
+
+
+@router.delete("/carts/{cart_id}/items/{item_id}")
+def remove_item_from_cart(cart_id: int, item_id: int, db: Session = Depends(get_db)):
+    cart = db.query(Cart).filter(Cart.id == cart_id).first()
+    if cart is None:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    if cart.status != "active":
+        raise HTTPException(
+            status_code=400, detail="Cannot remove items from inactive cart"
+        )
+
+    item = (
+        db.query(CartItem)
+        .filter(CartItem.id == item_id, CartItem.cart_id == cart_id)
+        .first()
+    )
+
+    if item is None:
+        raise HTTPException(status_code=404, detail="Cart item not found")
+
+    db.delete(item)
+    db.commit()
+    return {"message": "Item removed from cart"}
+
+
+@router.delete("/carts/{cart_id}")
+def clear_cart(cart_id: int, db: Session = Depends(get_db)):
+    cart = db.query(Cart).filter(Cart.id == cart_id).first()
+    if cart is None:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    if cart.status != "active":
+        raise HTTPException(status_code=400, detail="Cannot clear inactive cart")
+
+    # Delete all items in the cart
+    db.query(CartItem).filter(CartItem.cart_id == cart_id).delete()
+    db.commit()
+    return {"message": "Cart cleared successfully"}
+
+
+@router.post("/checkout/", response_model=CheckoutResponse)
+def checkout(checkout_request: CheckoutRequest, db: Session = Depends(get_db)):
+    cart = db.query(Cart).filter(Cart.id == checkout_request.cart_id).first()
+    if cart is None:
+        raise HTTPException(status_code=404, detail="Cart not found")
+
+    if cart.status != "active":
+        raise HTTPException(status_code=400, detail="Cart is not active")
+
+    if not cart.items:
+        raise HTTPException(status_code=400, detail="Cart is empty")
+
+    # Calculate total
+    total_amount = sum(item.price * item.quantity for item in cart.items)
+
+    # In a real system, you would process payment here
+    # For now, we'll simulate a successful payment
+
+    # Generate order ID
+    order_id = str(uuid.uuid4())
+
+    # Update cart status to checked_out
+    cart.status = "checked_out"
+    db.commit()
+
+    return CheckoutResponse(
+        success=True,
+        order_id=order_id,
+        total_amount=total_amount,
+        message="Checkout completed successfully",
+    )

app/db/base.py

@@ -0,0 +1,3 @@
+from sqlalchemy.ext.declarative import declarative_base
+
+Base = declarative_base()

app/db/session.py

@@ -0,0 +1,22 @@
+from pathlib import Path
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+DB_DIR = Path("/app") / "storage" / "db"
+DB_DIR.mkdir(parents=True, exist_ok=True)
+
+SQLALCHEMY_DATABASE_URL = f"sqlite:///{DB_DIR}/db.sqlite"
+
+engine = create_engine(
+    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()

app/models/cart.py

@@ -0,0 +1,33 @@
+from sqlalchemy import Column, Integer, String, Float, DateTime, ForeignKey
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+from app.db.base import Base
+
+
+class Cart(Base):
+    __tablename__ = "carts"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(String, index=True)
+    status = Column(String, default="active")  # active, checked_out, abandoned
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+
+    items = relationship(
+        "CartItem", back_populates="cart", cascade="all, delete-orphan"
+    )
+
+
+class CartItem(Base):
+    __tablename__ = "cart_items"
+
+    id = Column(Integer, primary_key=True, index=True)
+    cart_id = Column(Integer, ForeignKey("carts.id"))
+    product_id = Column(String, index=True)
+    product_name = Column(String)
+    price = Column(Float)
+    quantity = Column(Integer)
+
+    cart = relationship("Cart", back_populates="items")

app/schemas.py

@@ -0,0 +1,51 @@
+from typing import List, Optional
+from pydantic import BaseModel
+from datetime import datetime
+
+
+class CartItemCreate(BaseModel):
+    product_id: str
+    product_name: str
+    price: float
+    quantity: int
+
+
+class CartItemResponse(BaseModel):
+    id: int
+    product_id: str
+    product_name: str
+    price: float
+    quantity: int
+
+    class Config:
+        from_attributes = True
+
+
+class CartCreate(BaseModel):
+    user_id: str
+
+
+class CartResponse(BaseModel):
+    id: int
+    user_id: Optional[str]
+    status: str
+    created_at: datetime
+    updated_at: datetime
+    items: List[CartItemResponse] = []
+    total: Optional[float] = None
+
+    class Config:
+        from_attributes = True
+
+
+class CheckoutRequest(BaseModel):
+    cart_id: int
+    payment_method: str
+    billing_address: dict
+
+
+class CheckoutResponse(BaseModel):
+    success: bool
+    order_id: Optional[str] = None
+    total_amount: float
+    message: str

main.py

@@ -0,0 +1,42 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.api.cart import router as cart_router
+from app.db.session import engine
+from app.db.base import Base
+
+# Create database tables
+Base.metadata.create_all(bind=engine)
+
+app = FastAPI(
+    title="Cart and Checkout System",
+    description="A simple cart and checkout system API",
+    version="1.0.0",
+    openapi_url="/openapi.json",
+)
+
+# CORS middleware
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# Include routers
+app.include_router(cart_router, prefix="/api/v1", tags=["Cart"])
+
+
+@app.get("/")
+async def root():
+    return {
+        "title": "Cart and Checkout System",
+        "documentation": "/docs",
+        "health": "/health",
+    }
+
+
+@app.get("/health")
+async def health_check():
+    return {"status": "healthy", "service": "cart-checkout-system"}

requirements.txt

@@ -0,0 +1,6 @@
+fastapi==0.104.1
+uvicorn==0.24.0
+sqlalchemy==2.0.23
+alembic==1.12.1
+pydantic==2.5.0
+ruff==0.1.6