package app

import (
	"fmt"
	"log"
	"os/exec"
	"strings"
)

// hasDHCPAddress reports whether iface holds an IPv4 address that ip(8) marks
// as "dynamic" — the flag set on addresses with a finite valid_lft, which is
// how DHCP-assigned leases appear (static addresses are "permanent").
func hasDHCPAddress(iface string) (bool, error) {
	out, err := exec.Command("ip", "-4", "-o", "addr", "show", "dev", iface).Output()
	if err != nil {
		return false, fmt.Errorf("ip addr show %s: %w", iface, err)
	}
	for _, line := range strings.Split(string(out), "\n") {
		fields := strings.Fields(line)
		hasInet := false
		hasDynamic := false
		for _, f := range fields {
			switch f {
			case "inet":
				hasInet = true
			case "dynamic":
				hasDynamic = true
			}
		}
		if hasInet && hasDynamic {
			return true, nil
		}
	}
	return false, nil
}

// ensureUplink boots the WiFi uplink only if Ethernet is not already providing
// connectivity: when iface has no DHCP-assigned IPv4, start wpa_supplicant so
// the WiFi backend can take over.
func ensureUplink(iface string) {
	has, err := hasDHCPAddress(iface)
	if err != nil {
		log.Printf("Could not probe %s for DHCP address (%v); starting wpa_supplicant as fallback", iface, err)
	} else if has {
		log.Printf("DHCP address present on %s, leaving wpa_supplicant alone", iface)
		return
	} else {
		log.Printf("No DHCP address on %s, starting wpa_supplicant", iface)
	}

	if out, err := exec.Command("systemctl", "start", "wpa_supplicant").CombinedOutput(); err != nil {
		log.Printf("Failed to start wpa_supplicant: %v: %s", err, strings.TrimSpace(string(out)))
	}
}