package gateway

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"sort"
	"strings"

	cmv1 "github.com/cert-manager/cert-manager/pkg/apis/certmanager/v1"
	gwapiv1 "sigs.k8s.io/gateway-api/apis/v1"
)

const defaultPort gwapiv1.PortNumber = 443

// BuildListenersFromCertificates creates the desired set of managed listeners
// from all annotated Certificate resources targeting a single Gateway.
func BuildListenersFromCertificates(certs []cmv1.Certificate, prefix string) []gwapiv1.Listener {
	var listeners []gwapiv1.Listener

	for _, cert := range certs {
		if cert.DeletionTimestamp != nil {
			continue
		}
		secretName := cert.Spec.SecretName
		if secretName == "" {
			continue
		}

		for _, dns := range cert.Spec.DNSNames {
			hostname := gwapiv1.Hostname(dns)
			listenerName := listenerNameFor(prefix, cert.Name, dns)

			// Determine the namespace of the secret (same as cert namespace).
			ns := gwapiv1.Namespace(cert.Namespace)

			listeners = append(listeners, gwapiv1.Listener{
				Name:     gwapiv1.SectionName(listenerName),
				Hostname: &hostname,
				Port:     defaultPort,
				Protocol: gwapiv1.HTTPSProtocolType,
				AllowedRoutes: &gwapiv1.AllowedRoutes{
					Namespaces: &gwapiv1.RouteNamespaces{
						From: ptrTo(gwapiv1.NamespacesFromAll),
					},
				},
				TLS: &gwapiv1.ListenerTLSConfig{
					Mode: ptrTo(gwapiv1.TLSModeTerminate),
					CertificateRefs: []gwapiv1.SecretObjectReference{
						{
							Group:     ptrTo(gwapiv1.Group("")),
							Kind:      ptrTo(gwapiv1.Kind("Secret")),
							Name:      gwapiv1.ObjectName(secretName),
							Namespace: &ns,
						},
					},
				},
			})
		}
	}

	// Sort for deterministic output.
	sort.Slice(listeners, func(i, j int) bool {
		return string(listeners[i].Name) < string(listeners[j].Name)
	})

	return listeners
}

// MergeListeners takes existing Gateway listeners and replaces all managed
// (prefixed) listeners with the desired set, preserving user-defined listeners.
func MergeListeners(existing, desired []gwapiv1.Listener, prefix string) []gwapiv1.Listener {
	var merged []gwapiv1.Listener

	// Keep all non-managed listeners.
	for _, l := range existing {
		if !strings.HasPrefix(string(l.Name), prefix) {
			merged = append(merged, l)
		}
	}

	// Append desired managed listeners.
	merged = append(merged, desired...)
	return merged
}

// ListenersEqual does a quick comparison of two listener slices by name+hostname+secretRef.
// Not a deep equal — we only check the fields we manage.
func ListenersEqual(a, b []gwapiv1.Listener) bool {
	if len(a) != len(b) {
		return false
	}
	aMap := listenerMap(a)
	bMap := listenerMap(b)
	if len(aMap) != len(bMap) {
		return false
	}
	for k, av := range aMap {
		bv, ok := bMap[k]
		if !ok || av != bv {
			return false
		}
	}
	return true
}

type listenerKey struct {
	name     string
	hostname string
	secret   string
	port     gwapiv1.PortNumber
}

func listenerMap(listeners []gwapiv1.Listener) map[string]listenerKey {
	m := make(map[string]listenerKey, len(listeners))
	for _, l := range listeners {
		key := listenerKey{
			name: string(l.Name),
			port: l.Port,
		}
		if l.Hostname != nil {
			key.hostname = string(*l.Hostname)
		}
		if l.TLS != nil && len(l.TLS.CertificateRefs) > 0 {
			ref := l.TLS.CertificateRefs[0]
			ns := ""
			if ref.Namespace != nil {
				ns = string(*ref.Namespace)
			}
			key.secret = fmt.Sprintf("%s/%s", ns, ref.Name)
		}
		m[key.name] = key
	}
	return m
}

// maxSectionNameLen is the Gateway API limit for listener names.
const maxSectionNameLen = 253

// listenerNameFor generates a deterministic listener name from cert name and DNS name.
// The result is a valid Gateway API SectionName: names that would exceed the limit
// are cut and get a hash of the full name appended, so distinct long names stay distinct.
func listenerNameFor(prefix, certName, dnsName string) string {
	name := strings.TrimRight(fmt.Sprintf("%s%s-%s", prefix, certName, sanitizeDNSName(dnsName)), "-.")
	if len(name) <= maxSectionNameLen {
		return name
	}
	sum := sha256.Sum256([]byte(name))
	suffix := "-" + hex.EncodeToString(sum[:4])
	return strings.TrimRight(name[:maxSectionNameLen-len(suffix)], "-.") + suffix
}

// sanitizeDNSName maps a certificate DNS name onto the characters allowed in a
// listener name. A wildcard label is spelled out so "*.example.com" and
// "example.com" stay distinct.
func sanitizeDNSName(dnsName string) string {
	var b strings.Builder
	for _, r := range strings.ToLower(dnsName) {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			b.WriteRune(r)
		case r == '*':
			b.WriteString("wildcard")
		default:
			b.WriteByte('-')
		}
	}
	return strings.Trim(b.String(), "-")
}

func ptrTo[T any](v T) *T {
	return &v
}