package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"strings"

	"git.k6n.net/mats/go-cart-actor/pkg/cart"
	"git.k6n.net/mats/go-cart-actor/pkg/checkout"
	"git.k6n.net/mats/platform/tax"
	adyenCheckout "github.com/adyen/adyen-go-api-library/v21/src/checkout"
	"github.com/adyen/adyen-go-api-library/v21/src/common"
)

// defaultCallbackBaseURL is where Klarna's server-to-server callbacks
// (push/notification/validate) are sent when CHECKOUT_CALLBACK_BASE_URL is unset.
// These must be a publicly reachable https origin for the checkout service.
const defaultCallbackBaseURL = "https://cart.k6n.net"

var (
	// checkoutPublicURL overrides the request-derived site base for the
	// shopper-facing Klarna URLs (terms/checkout/confirmation). Set this to a
	// public https origin (e.g. a tunnel or shop-test.tornberg.me) for local
	// KCO testing, since Klarna rejects non-https merchant_urls. Empty = derive
	// from the request (X-Forwarded-Host + https).
	checkoutPublicURL = strings.TrimRight(os.Getenv("CHECKOUT_PUBLIC_URL"), "/")
	// checkoutCallbackBaseURL is the base for Klarna's server-to-server
	// callbacks. Defaults to defaultCallbackBaseURL.
	checkoutCallbackBaseURL = func() string {
		if v := strings.TrimRight(os.Getenv("CHECKOUT_CALLBACK_BASE_URL"), "/"); v != "" {
			return v
		}
		return defaultCallbackBaseURL
	}()
)

// CheckoutMeta carries the external / URL metadata required to build a
// Klarna CheckoutOrder from a CartGrain snapshot. It deliberately excludes
// any Klarna-specific response fields (HTML snippet, client token, etc.).
type CheckoutMeta struct {
	SiteUrl string
	// CallbackBaseUrl is the base for Klarna server-to-server callbacks
	// (push/notification/validate); may differ from SiteUrl in prod where the
	// checkout service and storefront are on different hosts.
	CallbackBaseUrl string
	ClientIp        string
	Country         string
	Currency        string // optional override (defaults to "SEK" if empty)
	Locale          string // optional override (defaults to "sv-se" if empty)
}

// BuildCheckoutOrderPayload converts the current cart grain + meta information
// into a CheckoutOrder domain struct and returns its JSON-serialized payload
// (to send to Klarna) alongside the structured CheckoutOrder object.
//
// This function is PURE: it does not perform any network I/O or mutate the
// grain. The caller is responsible for:
//
//  1. Choosing whether to create or update the Klarna order.
//  2. Invoking KlarnaClient.CreateOrder / UpdateOrder with the returned payload.
//  3. Applying an InitializeCheckout mutation (or equivalent) with the
//     resulting Klarna order id + status.
//
// If you later need to support different tax rates per line, you can extend
// CartItem / Delivery to expose that data and propagate it here.
// tp is an optional TaxProvider; when non-nil, its DefaultTaxRate is used for
// delivery lines instead of the hardcoded 2500 (25 % as CartItem format).
func BuildCheckoutOrderPayload(grain *checkout.CheckoutGrain, meta *CheckoutMeta, tp tax.Provider) ([]byte, *CheckoutOrder, error) {
	if grain == nil {
		return nil, nil, fmt.Errorf("nil grain")
	}
	if meta == nil {
		return nil, nil, fmt.Errorf("nil checkout meta")
	}

	currency := meta.Currency
	if currency == "" {
		currency = "SEK"
	}
	locale := meta.Locale
	if locale == "" {
		locale = "sv-se"
	}
	country := meta.Country
	if country == "" {
		country = "SE" // sensible default; adjust if multi-country support changes
	}

	lines := make([]*Line, 0, len(grain.CartState.Items)+len(grain.Deliveries))

	// Item lines
	for _, it := range grain.CartState.Items {
		if it == nil {
			continue
		}
		lines = append(lines, &Line{
			Type:           "physical",
			Reference:      it.Sku,
			Name:           it.Meta.Name,
			Quantity:       int(it.Quantity),
			UnitPrice:      int(it.Price.IncVat),
			TaxRate:        it.Tax, // TODO: derive if variable tax rates are introduced
			QuantityUnit:   "st",
			TotalAmount:    int(it.TotalPrice.IncVat),
			TotalTaxAmount: int(it.TotalPrice.TotalVat()),
			ImageURL:       fmt.Sprintf("https://www.elgiganten.se%s", it.Meta.Image),
		})
	}

	hasFreeShipping := false
	if grain.CartState != nil {
		for _, ap := range grain.CartState.AppliedPromotions {
			if ap.Type == "free_shipping" && !ap.Pending {
				hasFreeShipping = true
				break
			}
		}
	}

	total := cart.NewPrice()
	total.Add(*grain.CartState.TotalPrice)

	// Delivery lines — use the configured default tax rate for the purchase country.
	defaultKlarnaRate := defaultKlarnaTaxRate(tp, country)
	for _, d := range grain.Deliveries {
		if d == nil {
			continue
		}
		unitPrice := d.Price.IncVat
		taxAmount := d.Price.TotalVat()
		if hasFreeShipping {
			unitPrice = 0
			taxAmount = 0
		}
		if unitPrice <= 0 && !hasFreeShipping {
			continue
		}
		//total.Add(d.Price)
		lines = append(lines, &Line{
			Type:           "shipping_fee",
			Reference:      d.Provider,
			Name:           "Delivery",
			Quantity:       1,
			UnitPrice:      int(unitPrice),
			TaxRate:        defaultKlarnaRate,
			QuantityUnit:   "st",
			TotalAmount:    int(unitPrice),
			TotalTaxAmount: int(taxAmount),
		})
	}

	order := &CheckoutOrder{
		PurchaseCountry:    country,
		PurchaseCurrency:   currency,
		Locale:             locale,
		OrderAmount:        int(total.IncVat),
		OrderTaxAmount:     int(total.TotalVat()),
		OrderLines:         lines,
		MerchantReference1: grain.Id.String(),
		MerchantURLS: &CheckoutMerchantURLS{
			Terms:        fmt.Sprintf("%s/terms", meta.SiteUrl),
			Checkout:     fmt.Sprintf("%s/kassa?order_id={checkout.order.id}&provider=klarna", meta.SiteUrl),
			Confirmation: fmt.Sprintf("%s/kassa?order_id={checkout.order.id}&provider=klarna", meta.SiteUrl),
			Notification: fmt.Sprintf("%s/payment/klarna/notification", meta.CallbackBaseUrl),
			Validation:   fmt.Sprintf("%s/payment/klarna/validate", meta.CallbackBaseUrl),
			Push:         fmt.Sprintf("%s/payment/klarna/push?order_id={checkout.order.id}", meta.CallbackBaseUrl),
		},
	}

	payload, err := json.Marshal(order)
	if err != nil {
		return nil, nil, fmt.Errorf("marshal checkout order: %w", err)
	}

	return payload, order, nil
}

// defaultKlarnaTaxRate returns the default tax rate for the purchase country, in Klarna
// format (percent x 100, e.g. 2500 = 25.00 %). This matches the platform basis-point
// scale exactly, so DefaultTaxRate is passed through. When tp is nil, falls back to 2500.
func defaultKlarnaTaxRate(tp tax.Provider, country string) int {
	if tp == nil {
		return 2500
	}
	return tp.DefaultTaxRate(country)
}

// defaultAdyenTaxRate returns the default tax rate for the purchase country, in Adyen
// format (taxPercentage in basis points, e.g. 2500 = 25 %). This matches the platform
// basis-point scale exactly, so DefaultTaxRate is passed through. When tp is nil, falls
// back to 2500.
func defaultAdyenTaxRate(tp tax.Provider, country string) int64 {
	if tp == nil {
		return 2500
	}
	return int64(tp.DefaultTaxRate(country))
}

func GetCheckoutMetaFromRequest(r *http.Request) *CheckoutMeta {
	host := getOriginalHost(r)
	country := getCountryFromHost(host)
	siteUrl := fmt.Sprintf("%s://%s", getScheme(r), host)
	if checkoutPublicURL != "" {
		siteUrl = checkoutPublicURL
	}
	return &CheckoutMeta{
		ClientIp:        getClientIp(r),
		SiteUrl:         siteUrl,
		CallbackBaseUrl: checkoutCallbackBaseURL,
		Country:         country,
		Currency:        getCurrency(country),
		Locale:          getLocale(country),
	}
}

func BuildAdyenCheckoutSession(grain *checkout.CheckoutGrain, meta *CheckoutMeta, tp tax.Provider) (*adyenCheckout.CreateCheckoutSessionRequest, error) {
	if grain == nil {
		return nil, fmt.Errorf("nil grain")
	}
	if meta == nil {
		return nil, fmt.Errorf("nil checkout meta")
	}

	currency := meta.Currency
	if currency == "" {
		currency = "SEK"
	}
	country := meta.Country
	if country == "" {
		country = "SE"
	}

	lineItems := make([]adyenCheckout.LineItem, 0, len(grain.CartState.Items)+len(grain.Deliveries))

	// Item lines
	for _, it := range grain.CartState.Items {
		if it == nil {
			continue
		}
		lineItems = append(lineItems, adyenCheckout.LineItem{
			Quantity:           common.PtrInt64(int64(it.Quantity)),
			AmountIncludingTax: common.PtrInt64(it.TotalPrice.IncVat.Int64()),
			Description:        common.PtrString(it.Meta.Name),
			AmountExcludingTax: common.PtrInt64(it.TotalPrice.ValueExVat().Int64()),
			TaxAmount:          common.PtrInt64(it.TotalPrice.TotalVat().Int64()),
			TaxPercentage:      common.PtrInt64(int64(it.Tax)),
		})
	}
	hasFreeShipping := false
	if grain.CartState != nil {
		for _, ap := range grain.CartState.AppliedPromotions {
			if ap.Type == "free_shipping" && !ap.Pending {
				hasFreeShipping = true
				break
			}
		}
	}

	total := cart.NewPrice()
	total.Add(*grain.CartState.TotalPrice)

	// Delivery lines — use the configured default tax rate for the purchase country.
	defaultAdyenRate := defaultAdyenTaxRate(tp, country)
	for _, d := range grain.Deliveries {
		if d == nil {
			continue
		}
		amountIncTax := d.Price.IncVat.Int64()
		amountExTax := d.Price.ValueExVat().Int64()
		if hasFreeShipping {
			amountIncTax = 0
			amountExTax = 0
		}
		if amountIncTax <= 0 && !hasFreeShipping {
			continue
		}
		lineItems = append(lineItems, adyenCheckout.LineItem{
			Quantity:           common.PtrInt64(1),
			AmountIncludingTax: common.PtrInt64(amountIncTax),
			Description:        common.PtrString("Delivery"),
			AmountExcludingTax: common.PtrInt64(amountExTax),
			TaxPercentage:      common.PtrInt64(defaultAdyenRate),
		})
	}

	return &adyenCheckout.CreateCheckoutSessionRequest{
		Reference: grain.Id.String(),
		Amount: adyenCheckout.Amount{
			Value:    total.IncVat.Int64(),
			Currency: currency,
		},
		CountryCode:     common.PtrString(country),
		MerchantAccount: "ElgigantenECOM",
		Channel:         common.PtrString("Web"),
		ShopperIP:       common.PtrString(meta.ClientIp),
		ReturnUrl:       fmt.Sprintf("%s/payment/adyen/return", meta.SiteUrl),
		LineItems:       lineItems,
	}, nil

}