webshop/app/main.py

import logging
import os
from contextlib import asynccontextmanager
from pathlib import Path
from typing import Literal
from urllib.parse import urljoin, urlparse

import stripe
from asgi_csrf import asgi_csrf
from dotenv import load_dotenv
from fastapi import BackgroundTasks, FastAPI, Form, HTTPException, Request
from fastapi.encoders import jsonable_encoder
from fastapi.exceptions import RequestValidationError
from fastapi.responses import HTMLResponse, JSONResponse, RedirectResponse
from fastapi.staticfiles import StaticFiles
from fastapi.templating import Jinja2Templates
from starlette.exceptions import HTTPException as StarletteHTTPException
from starsessions import CookieStore, SessionAutoloadMiddleware, SessionMiddleware

from pydantic import ValidationError, EmailStr

import pycountry

from app.cart import (
    calculate_quantity_requested_by_user,
    clear_cart,
    initialize_cart,
    product_exist_in_cart,
    update_cart,
    update_cart_meta,
    create_product_list,
)
from app.db import (
    check_product_availability,
    export_order_to_xlsx,
    fetch_order_product_list,
    get_products_by_category,
    is_order_id_open,
    prepare_customer_order_data,
    save_shipping_info,
    update_product_inventory,
    update_status_order,
    write_variation_id,
    get_variation_id,
)
from app.email import send_email
from app.parser import md, read_dir, read_file
from app.payment import (
    calculate_shipping_cost,
    prepare_shipping_rate,
    generate_payment_link,
    ipn_signature_check,
    prepare_stripe_data,
)
from app.read_settings import read_settings
from app.schema import CartSession, CartUpdate, NowPaymentsInvoice, ShippingInfo, ProductShippingMeta
from app.template import (
    make_product_selected,
    prepare_checkout,
    prepare_email_order,
    prepare_product,
    prepare_related_products,
    prepare_sets_for_menu,
    to_srcset,
    assets_hashing,
    make_slugify
)

from app.form_validation import form_validation_checkout_session


load_dotenv(".env")


logging_level = logging.INFO
main_logger = logging.getLogger()
main_logger.setLevel(logging_level)
formatter = logging.Formatter("%(asctime)s %(levelname)s: %(name)s => %(message)s")

# Set up a stream handler to log to the console
stream_handler = logging.StreamHandler()
stream_handler.setLevel(logging_level)
stream_handler.setFormatter(formatter)

file_handler = logging.FileHandler("logs.log")
file_handler.setLevel(logging_level)
file_handler.setFormatter(formatter)

# Add handlers to logger
main_logger.addHandler(stream_handler)
main_logger.addHandler(file_handler)

@asynccontextmanager
async def lifespan(app: FastAPI):
    """
    On startup of application we check that all the product variations
    have their unique IDs
    """

    products_list = read_dir(
        settings.git_repo,
        settings.document_match,
        settings.document_exclude,
        settings.block_types,
        exclude_doc="products",
        tree="products",
    )

    for single_product in products_list:
        write_variation_id(single_product, settings)


    yield

app = FastAPI(docs_url=None, redoc_url=None, lifespan=lifespan)

# -- read settings
settings = read_settings("settings.toml")


# -- mount static files
app.mount(
    "/static",
    StaticFiles(directory=Path(__file__).parent.parent / "static"),
    name="static",
)

# mount media folder from git content repo
app.mount("/media", StaticFiles(directory=settings.git_repo), name="media")

# -- setup templates
templates = Jinja2Templates(directory=Path(__file__).parent / "templates")
templates.env.filters["md"] = md
templates.env.filters["to_srcset"] = to_srcset
templates.env.filters["assets_hashing"] = assets_hashing
templates.env.filters["slugify"] = make_slugify

templates.env.globals.update(CACHE=os.getenv('CACHE'))

# -- add middlewares for CSRF and Session
app.add_middleware(
    asgi_csrf,
    signing_secret=os.getenv("CSRF_SECRET_KEY"),
    always_protect={"/", "/products", "/checkout"},
)

session_store = CookieStore(secret_key=os.getenv("SESSION_SECRET_KEY"))
app.add_middleware(SessionAutoloadMiddleware)
app.add_middleware(
    SessionMiddleware,
    store=session_store,
    lifetime=3600 * 24 * 14,
    cookie_https_only=os.getenv("ENV") == "dev",
)


# -- load Stripe and set API key
if os.getenv("ENV") == "production":
    stripe.api_key = os.getenv("STRIPE_SECRET_KEY")
else:
    stripe.api_key = os.getenv("STRIPE_TEST_SECRET_KEY")


@app.get("/", response_class=HTMLResponse)
async def root(request: Request):
    """The Main view of the website. It gives access to all the pages."""
    session_data = request.session
    initialize_cart(session_data, settings.currency.default)
    cart = CartSession(**request.session["cart"])

    doc = read_file(
        settings.git_repo,
        "index",
        settings.document_match,
        settings.block_types,
        "",
    )

    categories = get_products_by_category(settings)
    sets = prepare_sets_for_menu(settings)

    site = read_file(
        settings.git_repo,
        "site",
        settings.document_match,
        settings.block_types,
    )

    response = templates.TemplateResponse(
        "index.html",
        {
            "request": request,
            "nav": None,
            "doc": doc,
            "categories": categories,
            "sets": sets,
            "site": site,
            "cart": cart,
        },
    )

    return response


@app.get("/products", response_class=RedirectResponse, status_code=301)
async def products():
    """
    The products view does not exist, so we return the user to the main view.
    """

    return "/"
    

@app.get("/products/{product_id}", response_class=HTMLResponse)
async def product(
    request: Request,
    product_id: str,
    js: bool = False,
    size: str | None = None,
    style: str | None = None,
    quantity: int = 1,
):
    """The product view displaying the content of the selected product PRODUCT ID.
    By default we check if the product exists in quantity = 1, unless
    a different value is explicitly pass to the GET request.
    """
    session_data = request.session
    initialize_cart(session_data, settings.currency.default)
    cart = CartSession(**request.session["cart"])

    tree = "products"
    doc = read_file(
        settings.git_repo,
        product_id,
        settings.document_match,
        settings.block_types,
        tree,
    )

    # we set quantity=0 because we are in a GET view and are not
    # adding anything to the cart yet, just want to see if we could
    # add 1 more item to it.
    quantity_requested_by_user = calculate_quantity_requested_by_user(
        session_data["cart"]["items"], doc.meta.product_id, quantity=0,
    )

    triplet = check_product_availability(
        doc, product_id, quantity_requested_by_user, size, style, settings
    )

    is_product_available, is_product_selectable, inventory_amount = triplet

    if js:
        product_selected = make_product_selected(size, style, quantity)

        json_response = {
            "is_product_available": is_product_available,
            "is_product_selectable": is_product_selectable,
            "product_selected": product_selected,
        }

        return JSONResponse(content=json_response, status_code=200)

    else:
        doc.blocks = prepare_product(doc)

        size_guide = None
        if doc.meta.options:
            size_guide = read_file(
                settings.git_repo,
                "products",
                settings.document_match,
                settings.block_types,
                None,
            )

        products = read_dir(
            settings.git_repo,
            settings.document_match,
            settings.document_exclude,
            settings.block_types,
            exclude_doc=doc.meta.path,
            tree="products",
        )

        related_products = prepare_related_products(products, product_id)

        site = read_file(
            settings.git_repo,
            "site",
            settings.document_match,
            settings.block_types,
        )

        response = templates.TemplateResponse(
            "product.html",
            {
                "request": request,
                "nav": None,
                "doc": doc,
                "size_guide": size_guide,
                "related_products": related_products,
                "is_product_available": is_product_available,
                "is_product_selectable": is_product_selectable,
                "product_form": {
                    "size": size,
                    "style": style,
                    "quantity": quantity,
                },
                "site": site,
                "cart": cart,
            },
        )

        return response


@app.get("/pages", response_class=RedirectResponse, status_code=301)
async def products():
    """
    The pages view does not exist, so we return the user to the main view.
    """

    return "/"
    

@app.get("/pages/{page_id}", response_class=HTMLResponse)
async def page(request: Request, page_id: str):
    """The Page view displaying the content of the selected PAGE ID."""
    tree = "pages"
    doc = read_file(
        settings.git_repo,
        page_id,
        settings.document_match,
        settings.block_types,
        tree,
    )

    site = read_file(
        settings.git_repo,
        "site",
        settings.document_match,
        settings.block_types,
    )

    response = templates.TemplateResponse(
        "page.html",
        {
            "request": request,
            "nav": None,
            "doc": doc,
            "site": site,
        },
    )

    return response


@app.get("/checkout", response_class=HTMLResponse)
async def checkout(request: Request):
    """The Checkout view (GET, read-only)."""
    filename = request.url.path[1:]
    doc = read_file(
        settings.git_repo, filename, settings.document_match, settings.block_types
    )

    products = read_dir(
        settings.git_repo,
        settings.document_match,
        settings.document_exclude,
        settings.block_types,
        exclude_doc="products",
        tree="products",
    )

    session_data = request.session
    initialize_cart(session_data, settings.currency.default)

    update_cart_meta(
        session_data["cart"], session_data["cart"]["meta"]["shipping"], products
    )

    cart = CartSession(**request.session["cart"])
    
    checkout_data = prepare_checkout(cart, settings, doc, products)

    site = read_file(
        settings.git_repo,
        "site",
        settings.document_match,
        settings.block_types,
    )

    response = templates.TemplateResponse(
        "checkout.html",
        {
            "request": request,
            "nav": None,
            "data": checkout_data,
            "site": site,
            "cart": cart,
        },
    )

    return response


@app.post("/checkout")
async def checkout_update(
    request: Request,
    js: bool = False,
    page: Literal["product", "checkout"] = Form(...),
    redirect_with_items: bool | None = Form(None),
    operation: Literal["add", "remove", "delete", "manual"] = Form(...),
    product_id: str = Form(...),
    product_path: str = Form(...),
    price: int = Form(...),
    quantity: int = Form(...),
    size: Literal["s", "m", "l", "xl", "xxl"] | None = Form(None),
    style: str | None = Form(None),
):
    """The Checkout view, (POST, read-write). This view updates (add /
    remove) the user's session cart. If the item is already present in
    the cart, it increases or decreases the item quantity. Else, it
    will be created or removed accordingly. It will also check if any
    selected item in the cart is still available or it has sold out
    meanwhile. Morever, it displays the Checkout view.
    """
    session_data = request.session
    initialize_cart(session_data, settings.currency.default)

    shipping_amount = session_data["cart"]["meta"]["shipping"]

    if operation == "manual":
        selected_product_id = session_data["cart"]["items"][product_id]
        price = quantity * selected_product_id["price"]

    tree = "products"
    product_filename = Path(product_path).stem
    selected_product = read_file(
        settings.git_repo,
        product_filename,
        settings.document_match,
        settings.block_types,
        tree,
    )

    product_variation_id = get_variation_id(selected_product, size, style)

    form = CartUpdate(
        operation=operation,
        product_id=product_id,
        options={"size": size,
                 "style": style,
                 "product_variation_id": product_variation_id
                 },
        price=price,
    )    

    quantity_requested_by_user = calculate_quantity_requested_by_user(
        session_data["cart"]["items"], product_id, quantity
    )

    triplet = check_product_availability(
        selected_product,
        product_path,
        quantity_requested_by_user,
        size,
        style,
        settings,
    )

    is_product_available, is_product_selectable, inventory_amount = triplet

    product_exists = product_exist_in_cart(
        product_id, size, style, product_variation_id, session_data["cart"]["items"]
    )

    update_cart(
        session_data["cart"],
        form,
        product_exists,
        shipping_amount,
        quantity,
        inventory_amount,
    )

    cart = CartSession(**request.session["cart"])

    if js:
        # -- return JSON res for js-handled form update

        if page == "product":
            cart_breakdown = jsonable_encoder(cart.meta)

            product_selected = make_product_selected(size, style, quantity)

            json_response = {
                "cart_breakdown": cart_breakdown,
                "is_product_available": is_product_available,
                "is_product_selectable": is_product_selectable,
                "product_selected": product_selected,
            }

        elif page == "checkout":
            filename = request.url.path[1:]
            doc = read_file(
                settings.git_repo,
                filename,
                settings.document_match,
                settings.block_types,
            )

            products = read_dir(
                settings.git_repo,
                settings.document_match,
                settings.document_exclude,
                settings.block_types,
                exclude_doc="products",
                tree="products",
            )

            checkout_data = prepare_checkout(
                cart, settings, doc, products, js_update=False
            )

            cart_items = [
                jsonable_encoder(item) for item in checkout_data["checkout_items"]
            ]

            cart_breakdown = jsonable_encoder(cart.meta)

            json_response = {
                "cart_items": cart_items,
                "cart_breakdown": cart_breakdown,
            }

        return JSONResponse(content=json_response, status_code=200)

    else:
        redirect_URL = urljoin(
            request.headers["referer"], urlparse(request.headers["referer"]).path
        )
        redirect_URL = f"{redirect_URL}"

        if redirect_with_items:
            URI_options = []
            param_options = {"size": size, "style": style, "quantity": quantity}

            for idx, option in enumerate(param_options.keys()):
                if param_options[option]:
                    param = f"{option}={param_options[option]}"
                    URI_options.append(param)

            if len(URI_options) > 0:
                URI_params = "&".join(URI_options)
                redirect_URL = f"{redirect_URL}?{URI_params}"

            else:
                redirect_URL = f"{redirect_URL}"

        return RedirectResponse(redirect_URL, status_code=303)


@app.post("/checkout/shipping")
async def checkout_shipping(request: Request,
                            js: bool = False,
                            country: str = Form(...),
                            weight: int = Form(...)):
    """
    This view returns the region to which the given submitted country belongs to.
    This is used in /checkout to update shipping costs in real time.    
    """

    countries = [country.name for country in pycountry.countries]
    if (
            country not in countries
            or weight <= 0
    ):
        raise HTTPException(status_code=403, detail="Shipping info are incorrect.")


    shipping_rate = calculate_shipping_cost(country, weight, settings.currency.default)

    if shipping_rate:

        # update cart with new shipping costs
        session_data = request.session
        initialize_cart(session_data, settings.currency.default)

        update_cart_meta(session_data["cart"], shipping_rate.price)
        cart = CartSession(**request.session['cart'])

        if js:
            return cart.meta
        else:
            return RedirectResponse(f"{request.base_url}checkout", status_code=303)


    raise HTTPException(status_code=403, detail="Shipping info are missing.")


@app.post("/stripe-checkout-session", response_class=RedirectResponse, status_code=303)
async def create_checkout_session(
    request: Request,
    order_id: str = Form(...),
    weight: int = Form(...),
    email: EmailStr = Form(...),
    first_name: str | None = Form(None),
    last_name: str = Form(...),
    address: str = Form(...),
    address_no: str = Form(...),        
    address_extra: str | None = Form(None),
    postal_code: str = Form(...),
    city: str = Form(...),
    country: str = Form(...),
    phone_number: str = Form(None),
    note: str | None = Form(None),
):
    """Stripe-based checkout session. Prepare order data and create a new
    Stripe Checkout session. Handle gracefully in case of errors, or
    if order exists already in local-db and has not `status: Open`.
    """

    # -- initial form-data validation
    form_data = await request.form()

    try:
        form = form_validation_checkout_session(form_data)
        
    except ValidationError as e:
        for error in e.errors():
            main_logger.error(f"form-validation-stripe-checkout-session => {error}")


    # -- check if order-id is unique
    orders_settings = {
        "git_repo": settings.git_repo,
        "document_match": settings.document_match,
        "block_types": settings.block_types,
    }

    if not is_order_id_open(orders_settings, form.order_id):
        main_logger.error("stripe-checkout error: Order ID is wrong.")
        raise HTTPException(status_code=422, detail="Order ID is wrong.")

    shipping_info = {
        "email": form.email,
        "first_name": form.first_name,
        "last_name": form.last_name,
        "address": form.address,
        "address_no": form.address_no,        
        "address_extra": form.address_extra,
        "postal_code": form.postal_code,
        "city": form.city,
        "country": form.country,
        "phone_number": form.phone_number,
        "note": form.note,
    }

    shipping_info = ShippingInfo(**shipping_info)

    session_data = request.session
    initialize_cart(session_data, settings.currency.default)

    if "cart" not in session_data and len(session_data["cart"].keys()) == 0:
        main_logger.error("stripe-checkout error: Cart is empty.")
        raise HTTPException(status_code=403, detail="Cart is empty.")

    cart = CartSession(**request.session["cart"])

    try:
        line_items = prepare_stripe_data(cart)

        shipping_rate = prepare_shipping_rate(shipping_info.country, form.weight, settings.currency.default)
        if shipping_rate is None:
            main_logger.error("stripe-checkout error: Shipping info are missing.")
            raise HTTPException(status_code=403, detail="Shipping info are missing.")

        checkout_session = stripe.checkout.Session.create(
            mode="payment",
            line_items=line_items,
            shipping_options=[shipping_rate],
            customer_email=shipping_info.email,
            client_reference_id=form.order_id,
            success_url=f"{request.base_url}checkout/success",
            cancel_url=f"{request.base_url}checkout",
        )

        product_list = create_product_list(settings, cart.items)

        # -- save transaction to local-db
        customer_order = prepare_customer_order_data(
            settings.git_repo,
            settings.document_match,
            settings.document_exclude,
            settings.block_types,
            checkout_session["id"],
            product_list,
            "Stripe",
            form.order_id,
            cart,
            shipping_info,
        )

        save_shipping_info(
            customer_order, settings.git_repo, settings.local_db.filepath
        )

        # -- redirect to Stripe Checkout page
        return checkout_session.url

    except stripe.error.CardError as e:
        main_logger.error(
            f"stripe-checkout error: A payment error occurred: {e.user_message}"
        )
        raise HTTPException(status_code=400, detail="Stripe payment error.")

    except stripe.error.InvalidRequestError as e:
        main_logger.error(f"stripe-checkout error: An invalid request occurred. => {e}")
        raise HTTPException(
            status_code=400, detail="Stripe payment error (invalid request)."
        )

    except Exception as e:
        main_logger.error(
            f"stripe-checkout error: Another problem occurred, maybe unrelated to Stripe. {e}"
        )
        raise HTTPException(status_code=400, detail="Stripe payment error.")


@app.post("/stripe-webhook", response_class=JSONResponse)
async def stripe_webhook(request: Request, background_tasks: BackgroundTasks):
    """Stripe webhook endpoint to receive updates from Stripe's checkout
    operations.  Send email after successful order confirmation.
    """
    main_logger.info("stripe-webhook => ...")

    event = None
    payload = await request.body()
    sig_header = request.headers["stripe-signature"]

    try:
        if os.getenv("ENV") == "production":
            endpoint_secret = os.getenv("STRIPE_ENDPOINT_SECRET")
        else:
            endpoint_secret = os.getenv("STRIPE_TEST_ENDPOINT_SECRET")

        event = stripe.Webhook.construct_event(payload, sig_header, endpoint_secret)

    except ValueError as e:
        main_logger.error(
            f"stripe-webhook error: Webhook error while parsing basic request. {e}"
        )
        raise HTTPException(status_code=400, detail="Stripe payment error.")

    except stripe.error.SignatureVerificationError as e:
        main_logger.error(
            f"stripe-webhook error: Webhook signature verification failed. {e}"
        )
        raise HTTPException(status_code=400, detail="Stripe payment error.")

    if event:
        checkout = event["data"]["object"]

        if "client_reference_id" in checkout:
            status_res = update_status_order(
                event["type"],
                checkout["client_reference_id"],
                settings.git_repo,
                settings.local_db.filepath,
            )

            if status_res is False:
                main_logger.error("stripe-webhook error: order could not be updated.")
                raise HTTPException(
                    status_code=400, detail="Order could not be updated."
                )

            if event["type"] in [
                "checkout.session.completed",
                "checkout.session.async_payment_succeeded",
            ]:
                order_id = checkout["client_reference_id"]

                product_list = fetch_order_product_list(
                    order_id, settings.git_repo, settings.local_db.filepath
                )

                if product_list:
                    for product_info in product_list:
                        update_product_inventory(
                            product_info.filename,
                            product_info.quantity,
                            product_info.product_variation_id,
                            settings,
                        )

                # -- send email
                email_settings = {
                    "git_repo": settings.git_repo,
                    "document_match": settings.document_match,
                    "block_types": settings.block_types,
                }

                order = prepare_email_order(order_id, email_settings)
                await send_email(email_settings, order, background_tasks)

            elif event["type"] == "checkout.session.async_payment_failed":
                main_logger.error(
                    f"stripe-webhook error: Stripe payment error. {event['type']}"
                )
                raise HTTPException(status_code=400, detail="Stripe payment error.")

    else:
        main_logger.error(f"stripe-webhook error: Unhandled event type {event['type']}")
        raise HTTPException(status_code=400, detail="Stripe payment error.")

    # -- return 200
    return {"success": True}


@app.post("/create-now-payments", response_class=RedirectResponse, status_code=303)
async def create_now_payments(
    request: Request,
    order_id: str = Form(...),
    weight: int = Form(...),
    email: EmailStr = Form(...),
    first_name: str | None = Form(None),
    last_name: str = Form(...),
    address: str = Form(...),
    address_no: str = Form(...),        
    address_extra: str | None = Form(None),
    postal_code: str = Form(...),
    city: str = Form(...),
    country: str = Form(...),
    phone_number: str = Form(None),        
    note: str | None = Form(None),
):
    """NOWPayments checkout session. User selects with which currency to pay.
    Sort of a custom NOW Payments Invoice page.
    """

    # -- initial form-data validation
    form_data = await request.form()

    try:
        form = form_validation_checkout_session(form_data)
        
    except ValidationError as e:
        for error in e.errors():
            main_logger.error(f"form-validation-stripe-checkout-session => {error}")


    # -- check if order-id is unique
    orders_settings = {
        "git_repo": settings.git_repo,
        "document_match": settings.document_match,
        "block_types": settings.block_types,
    }

    if not is_order_id_open(orders_settings, form.order_id):
        main_logger.error("now-payments-checkout error: Order ID is wrong.")
        raise HTTPException(status_code=422, detail="Order ID is wrong.")

    shipping_info = {
        "email": form.email,
        "first_name": form.first_name,
        "last_name": form.last_name,
        "address": form.address,
        "address_no": form.address_no,
        "address_extra": form.address_extra,
        "postal_code": form.postal_code,
        "city": form.city,
        "country": form.country,
        "phone_number": form.phone_number,
        "note": form.note,
    }

    shipping_info = ShippingInfo(**shipping_info)

    session_data = request.session
    initialize_cart(session_data, settings.currency.default)

    if "cart" not in session_data and len(session_data["cart"].keys()) == 0:
        main_logger.error("now-payments-checkout error: Cart is empty.")
        raise HTTPException(status_code=403, detail="Cart is empty.")

    cart = CartSession(**request.session["cart"])

    data = {
        "price_amount": cart.meta.total,
        "price_currency": settings.currency.now_payments,
        "order_id": form.order_id,
        "ipn_callback_url": f"{request.base_url}now-webhook",
        "success_url": f"{request.base_url}checkout/success",
        "cancel_url": f"{request.base_url}checkout",
    }

    data = NowPaymentsInvoice(**data)
    payment_url, np_order_id = await generate_payment_link(data)

    product_list = create_product_list(settings, cart.items)    

    # -- save transaction to local-db
    customer_order = prepare_customer_order_data(
        settings.git_repo,
        settings.document_match,
        settings.document_exclude,
        settings.block_types,
        np_order_id,
        product_list,        
        "NOW Payments",
        data.order_id,
        cart,
        shipping_info,
    )

    save_shipping_info(customer_order, settings.git_repo, settings.local_db.filepath)

    # -- redirect to NOWPayments Checkout page
    return payment_url


@app.post("/now-webhook")
async def now_webhook(request: Request, background_tasks: BackgroundTasks):
    """NOW Payments IPN (Instant Payment Notification) webhook.
    Send email after successful payment confirmation.
    """
    main_logger.info("now-webhook...")

    payload = await request.json()
    sig_header = request.headers["x-nowpayments-sig"]

    if os.getenv("ENV") == "production":
        ipn_secret_key = os.getenv("NOWPAYMENTS_IPN")
    else:
        ipn_secret_key = os.getenv("NOWPAYMENTS_SANDBOX_IPN")

    is_verified = ipn_signature_check(ipn_secret_key, sig_header, payload)

    if is_verified:
        # check payment status, update order if
        # status has changed (finished, expired, failed)
        # send email if status: finished.

        event_type = payload["payment_status"]

        if event_type in ["finished", "expired", "failed"]:
            if "payment_id" in payload:
                order_id = payload["order_id"]

                status_res = update_status_order(
                    event_type,
                    order_id,
                    settings.git_repo,
                    settings.local_db.filepath,
                )

                if status_res is False:
                    raise HTTPException(
                        status_code=400, detail="Order could not be updated."
                    )

                if event_type == "finished":
                    product_list = fetch_order_product_list(
                        order_id, settings.git_repo, settings.local_db.filepath
                    )

                    if product_list:
                        for product_info in product_list:
                            update_product_inventory(
                                product_info.filename,
                                product_info.quantity,
                                product_info.product_variation_id,
                                settings,
                            )

                    # -- send email
                    email_settings = {
                        "git_repo": settings.git_repo,
                        "document_match": settings.document_match,
                        "block_types": settings.block_types,
                    }

                    order = prepare_email_order(order_id, email_settings)
                    await send_email(email_settings, order, background_tasks)

                elif event_type == "failed":
                    main_logger.error(
                        f"(NowPayments) Unhandled event type {event_type}"
                    )
                    raise HTTPException(
                        status_code=400, detail="NOWPayments payment error."
                    )
            else:
                main_logger.error("(NowPayments) payment_id not in payload")
                raise HTTPException(
                    status_code=400, detail="NOWPayments payment error."
                )


@app.get("/checkout/success", response_class=HTMLResponse)
async def checkout_success(request: Request):
    """View that confirms to the user that the checkout procedure was successful."""
    session_data = request.session

    # if there's no cart session, redirect the user to `/`
    if "cart" not in session_data:
        clear_cart(session_data, settings.currency.default)
        return RedirectResponse(f"{request.base_url}", status_code=303)

    cart = CartSession(**request.session["cart"])

    filename = "orders"
    orders = read_file(
        settings.git_repo, filename, settings.document_match, settings.block_types
    )

    customer_order = [
        order for order in orders.blocks if order.order_id == cart.meta.order_id
    ]

    # if cart.meta.order_id does not match any order, redirect the user to `/`
    if len(customer_order) == 0:
        clear_cart(session_data, settings.currency.default)
        return RedirectResponse(f"{request.base_url}", status_code=303)

    # -- save data and clear cart, return view
    data = {
        "title": "Checkout Success",
        "order_id": cart.meta.order_id,
        "customer_email": customer_order[0].shipping_info.email,
    }

    # -- prepare order to xlsx format
    product_list = fetch_order_product_list(
                        cart.meta.order_id, settings.git_repo, settings.local_db.filepath
                    )

    if not product_list:
        raise HTTPException(status_code=403, detail="Order checkout is missing information.")

    products_shipping_meta = []
    for product_info in product_list:
        product = read_file(settings.git_repo, f"products/{product_info.filename}", settings.document_match, settings.block_types)
        products_shipping_meta.append(
            ProductShippingMeta(
                weight=product.meta.weight,
                customs_tariff_code=product.meta.customs_tariff_code,
                origin_country_iso=product.meta.origin_country_iso,
            )
        )

    email_from = os.getenv("MAIL_FROM")
    export_order_to_xlsx(
        customer_order[0],
        products_shipping_meta,
        settings.order_upload.filepath,
        settings.currency.default,
        settings.git_repo,
        email_from,
    )

    clear_cart(session_data, settings.currency.default)
    cart = CartSession(**request.session["cart"])

    site = read_file(
        settings.git_repo,
        "site",
        settings.document_match,
        settings.block_types,
    )

    return templates.TemplateResponse(
        "checkout-success.html",
        {"request": request, "site": site, "data": data, "cart": cart},
    )


@app.get("/checkout/error", response_class=HTMLResponse)
async def checkout_error(request: Request):
    """View for when the checkout procedure fails."""
    cart = CartSession(**request.session["cart"])

    site = read_file(
        settings.git_repo,
        "site",
        settings.document_match,
        settings.block_types,
    )

    data = {
        "title": "Checkout",
    }

    return templates.TemplateResponse(
        "checkout-error.html",
        {"request": request, "site": site, "data": data, "cart": cart},
    )


@app.post("/cart/clear")
async def cart_clear(
    request: Request,
    js: bool = False,
):
    """Clear cart."""
    request.session.clear()

    return RedirectResponse(request.base_url, status_code=303)


# -- set custom HTTP errors
@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc):
    """Handle invalid data exception by returning an HTML response
    rather than a JSON one.
    """
    site = read_file(
        settings.git_repo,
        "site",
        settings.document_match,
        settings.block_types,
    )
    message = "We can't process your request."

    main_logger.error(exc)

    t = templates.TemplateResponse(
        "error.html",
        {
            "request": request,
            "site": site,
            "data": {
                "title": "Error",
                "error": message,
                "status_code": 422,
            },
            "cart": None,
        },
    )

    return HTMLResponse(content=t.body, status_code=422)


@app.exception_handler(StarletteHTTPException)
async def http_exception_handler(request, exc):
    """Custom handling of HTTP exception (400-500).
    Prepare an appropriate user-facing message and pass it
    to the error.html template.
    """
    message = ""

    main_logger.error(f"http-exception: error => {exc}")

    if exc.status_code == 404:
        message = "Nothing was found here."
    elif exc.status_code == 500:
        message = "Server error."
    elif 400 <= exc.status_code <= 499:
        message = "Something went wrong."
        if exc.detail:
            message = exc.detail

    site = read_file(
        settings.git_repo,
        "site",
        settings.document_match,
        settings.block_types,
    )

    data = {
        "title": "Error",
        "error": message,
        "status_code": exc.status_code,
    }

    t = templates.TemplateResponse(
        "error.html",
        {
            "request": request,
            "site": site,
            "data": data,
            "cart": None,
        },
    )

    return HTMLResponse(content=t.body, status_code=exc.status_code)