package yookassa

import (
	"encoding/json"
	"fmt"
	"net/netip"
)

// Notification events this integration subscribes to. An event name is "<object>.<status>": the
// object whose status changed and the status it entered.
const (
	// EventPaymentSucceeded means the money was taken and the order may be credited.
	EventPaymentSucceeded = "payment.succeeded"
	// EventPaymentCanceled means the payment was actively declined or abandoned; nothing is credited
	// and the payer is told the attempt failed.
	EventPaymentCanceled = "payment.canceled"
	// EventRefundSucceeded reports a completed refund. Refunds here are always initiated by an
	// operator through the API, which records them synchronously, so this event is informational.
	EventRefundSucceeded = "refund.succeeded"
)

// notificationType is the fixed value of a notification envelope's type field.
const notificationType = "notification"

// Notification is an incoming webhook envelope. Object is left raw because its shape depends on the
// event — a payment for payment.*, a refund for refund.* — and because nothing in it may be acted on
// before GetPayment confirms it: YooKassa does not sign notifications.
type Notification struct {
	Type   string          `json:"type"`
	Event  string          `json:"event"`
	Object json.RawMessage `json:"object"`
}

// ParseNotification decodes a webhook body and checks the envelope is a notification with an event.
// It deliberately validates nothing else: the body is untrusted input whose only job is to name an
// object to re-read from the API.
func ParseNotification(body []byte) (Notification, error) {
	var n Notification
	if err := json.Unmarshal(body, &n); err != nil {
		return Notification{}, fmt.Errorf("yookassa: decode notification: %w", err)
	}
	if n.Type != notificationType || n.Event == "" {
		return Notification{}, fmt.Errorf("yookassa: not a notification envelope (type %q, event %q)", n.Type, n.Event)
	}
	return n, nil
}

// Payment decodes the notification's object as a payment. Use it only for payment.* events; it
// yields the payment id to re-read, never the payment state to act on.
func (n Notification) Payment() (Payment, error) {
	var p Payment
	if err := json.Unmarshal(n.Object, &p); err != nil {
		return Payment{}, fmt.Errorf("yookassa: decode notification payment: %w", err)
	}
	if p.ID == "" {
		return Payment{}, fmt.Errorf("yookassa: notification payment has no id")
	}
	return p, nil
}

// senderPrefixes are the address ranges YooKassa delivers notifications from
// (https://yookassa.ru/developers/using-api/webhooks). Single addresses are expressed as /32 and
// /128 prefixes. The list is defence in depth only — the confirming GetPayment is what actually
// establishes authenticity — so it is kept deliberately literal and easy to audit against the docs.
var senderPrefixes = []netip.Prefix{
	netip.MustParsePrefix("185.71.76.0/27"),
	netip.MustParsePrefix("185.71.77.0/27"),
	netip.MustParsePrefix("77.75.153.0/25"),
	netip.MustParsePrefix("77.75.156.11/32"),
	netip.MustParsePrefix("77.75.156.35/32"),
	netip.MustParsePrefix("77.75.154.128/25"),
	netip.MustParsePrefix("2a02:5180::/32"),
}

// AllowedIP reports whether addr is one of YooKassa's notification senders. An IPv4-mapped IPv6
// address is unmapped first, so a dual-stack listener's view of an IPv4 sender still matches.
func AllowedIP(addr netip.Addr) bool {
	addr = addr.Unmap()
	if !addr.IsValid() {
		return false
	}
	for _, p := range senderPrefixes {
		if p.Contains(addr) {
			return true
		}
	}
	return false
}

// AllowedSender reports whether the textual address ip is one of YooKassa's notification senders. An
// unparseable address is not allowed.
func AllowedSender(ip string) bool {
	addr, err := netip.ParseAddr(ip)
	if err != nil {
		return false
	}
	return AllowedIP(addr)
}