src/main.py

import os
import logging
import secrets
import requests
from typing import Annotated, Generator
from fastapi import (
    FastAPI,
    Request,
    HTTPException,
    Security,
    Depends
)
from fastapi.background import BackgroundTasks
from fastapi.responses import RedirectResponse, JSONResponse
from fastapi.security.api_key import APIKeyHeader
from psycopg.errors import UniqueViolation
from sqlalchemy.exc import IntegrityError
from starlette.status import (
    HTTP_200_OK,
    HTTP_403_FORBIDDEN,
    HTTP_422_UNPROCESSABLE_ENTITY,
    HTTP_500_INTERNAL_SERVER_ERROR,
    HTTP_503_SERVICE_UNAVAILABLE)
from dotenv import load_dotenv
from sqlalchemy import text
from sqlalchemy.orm import Session

from src.entity.api.transaction_api import TransactionApi, TransactionProcessingOutput
from src.service.fraud_service import check_for_fraud_api
from src.service.logging_service import setup_logging
from src.service.notification_service import send_notification
from src.repository.common import get_session
from src.repository.fraud_details_repo import insert_fraud
from src.repository.transaction_repo import insert_transaction, fetch_transaction_by_number

# ------------------------------------------------------------------------------
# Configure logging
setup_logging()
logger = logging.getLogger(__name__)

# ------------------------------------------------------------------------------
def provide_connection() -> Generator[Session, None, None]:
    with get_session() as conn:
        yield conn

# ------------------------------------------------------------------------------
# Load environment variables
load_dotenv()
FASTAPI_API_KEY = os.getenv("FASTAPI_API_KEY")
FRAUD_ML_API_KEY = os.getenv("FRAUD_ML_API_KEY")
FRAUD_ML_HEALTHCHECK_ENDPOINT = os.getenv("FRAUD_ML_HEALTHCHECK_ENDPOINT")
safe_clients = ['127.0.0.1']

api_key_header = APIKeyHeader(name='Authorization', auto_error=False)

async def validate_api_key(request: Request, key: str = Security(api_key_header)):
    '''
    Check if the API key is valid

    Args:
        key (str): The API key to check
    
    Raises:
        HTTPException: If the API key is invalid
    '''
    if request.client.host not in safe_clients and not secrets.compare_digest(str(key), str(FASTAPI_API_KEY)):
        raise HTTPException(
            status_code=HTTP_403_FORBIDDEN, detail="Unauthorized - API Key is wrong"
        )
    return None

app = FastAPI(dependencies=[Depends(validate_api_key)] if FASTAPI_API_KEY else None,
              title="Fraud Detection Service API")


# ------------------------------------------------------------------------------
@app.get("/", include_in_schema=False)
def redirect_to_docs():
    '''
    Redirect to the API documentation.
    '''
    return RedirectResponse(url='/docs')
    
@app.get("/transaction/get_fraud_status/{transaction_number}",
          tags=["transaction"],
          description="Get the fraud status of a transaction",
          response_model=TransactionProcessingOutput,
          )
async def get_fraud_status(
    transaction_number: str,
    db: Annotated[Session, Depends(provide_connection)]
):
    """
    Get the fraud status of a transaction
    """
    # Check if the transaction exists in the database
    try:
        transaction = fetch_transaction_by_number(
            db=db,
            transaction_number=transaction_number
        )
    except ValueError as e:
        logger.error(e)
        raise HTTPException(
            status_code=HTTP_422_UNPROCESSABLE_ENTITY,
            detail=f"Transaction {transaction_number} does not exist"
        )
    except Exception as e:
        logger.error(e)
        raise HTTPException(
            status_code=HTTP_500_INTERNAL_SERVER_ERROR,
            detail="An error occurred while fetching the transaction. See logs for details."
        )

    # Check if the transaction is fraudulent
    is_fraud = transaction.is_fraud is True
    fraud_score = transaction.fraud_details.fraud_score if transaction.fraud_details else -1

    return {
        'is_fraud': is_fraud,
        'fraud_score': fraud_score
    }

# ------------------------------------------------------------------------------
@app.post("/transaction/process",
          tags=["transaction"],
          description="Process a transaction",
          response_model=TransactionProcessingOutput,
          )
async def process_transaction(
    background_tasks: BackgroundTasks,
    transactionApi: TransactionApi,
    db: Annotated[Session, Depends(provide_connection)]
):
    """
    Process a transaction
    """
    # Check the transaction
    if not transactionApi.is_valid():
        raise HTTPException(
            status_code=HTTP_422_UNPROCESSABLE_ENTITY,
            detail="Transaction is not valid. Check input values."
        )
    
    # Convert the API object to a Transaction object
    transaction = transactionApi.to_transaction()

    # Process the transaction
    try:
        # Insert every single transaction into the database
        transaction = insert_transaction(db, transaction)
    except (UniqueViolation, IntegrityError):
        logger.warning("Transaction cannot be inserted in the database - checking existence...")
        db.rollback()
        return await get_fraud_status(
            transaction_number=transaction.transaction_number,
            db=db
        )
    except Exception as e:
        logger.error(e)
        raise HTTPException(
            status_code=HTTP_500_INTERNAL_SERVER_ERROR,
            detail="An error occurred while processing the transaction. See logs for details."
        )
    
    # Call the fraud detection API
    fraud_output = check_for_fraud_api(transaction)
    is_fraud = fraud_output.result == 1

    if is_fraud:
        insert_fraud(
            db=db,
            transaction=transaction,
            fraud_score=fraud_output.fraud_probability,
            model_version=fraud_output.model_metadata['version'] if 'version' in fraud_output.model_metadata else 'unknown'
        )

        # Send notification to the user
        background_tasks.add_task(
            func=send_notification,
            transaction_id=transaction.id)

    # Return the result
    output = {
        'is_fraud': fraud_output.result,
        'fraud_score': fraud_output.fraud_probability
    }

    return output

# ------------------------------------------------------------------------------
@app.get("/check_health", tags=["general"], description="Check the health of the API")
async def check_health(session: Annotated[Session, Depends(provide_connection)]):
    """
    Check all the services in the infrastructure are working
    """
    # Check if the database is alive
    try:
        session.execute(text("SELECT 1"))
    except Exception as e:
        logger.error(f"DB check failed: {e}")
        return JSONResponse(content={"status": "unhealthy"}, status_code=HTTP_503_SERVICE_UNAVAILABLE)
    
    # Check if the fraud detection API is alive
    response = requests.get(FRAUD_ML_HEALTHCHECK_ENDPOINT,
                            headers={
                                'Content-Type': 'application/json',
                                'Authorization': FRAUD_ML_API_KEY,
                            })
    
    if response.status_code != HTTP_200_OK:
        logger.error(f"Fraud detection API check failed: {response.status_code} - {response.text}")
        return JSONResponse(content={"status": "unhealthy"}, status_code=HTTP_503_SERVICE_UNAVAILABLE)
    
    return JSONResponse(content={"status": "healthy"}, status_code=HTTP_200_OK)