// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause

package main

import (
	"fmt"
	"net/netip"

	"tailscale.com/tailcfg"
)

// buildPeerAPIURL returns the HTTP base URL for a peer's peerAPI server,
// selecting IPv4 when available and falling back to IPv6. Returns an empty
// string if the peer advertises no reachable peerAPI port.
func buildPeerAPIURL(p tailcfg.NodeView, selfHave4, selfHave6 bool) string {
	var pp4, pp6 uint16
	for _, s := range p.Hostinfo().Services().All() {
		switch s.Proto {
		case tailcfg.PeerAPI4:
			pp4 = s.Port
		case tailcfg.PeerAPI6:
			pp6 = s.Port
		}
	}
	if selfHave4 && pp4 != 0 {
		for _, a := range p.Addresses().All() {
			if a.IsSingleIP() && a.Addr().Is4() {
				return fmt.Sprintf("http://%v", netip.AddrPortFrom(a.Addr(), pp4))
			}
		}
	}
	if selfHave6 && pp6 != 0 {
		for _, a := range p.Addresses().All() {
			if a.IsSingleIP() && a.Addr().Is6() {
				return fmt.Sprintf("http://%v", netip.AddrPortFrom(a.Addr(), pp6))
			}
		}
	}
	return ""
}