//go:build linux

package netdetect

import (
	"context"
	"fmt"
	"os"
	"os/exec"
	"time"
)

// routeQueryTimeout bounds the external route-table query.
const routeQueryTimeout = 2 * time.Second

// DefaultRoutes returns the host's IPv4 default routes. It prefers the `ip`
// command and falls back to reading /proc/net/route.
func DefaultRoutes() ([]Route, error) {
	ctx, cancel := context.WithTimeout(context.Background(), routeQueryTimeout)
	defer cancel()

	out, err := exec.CommandContext(ctx,
		"ip", "-4", "route", "show", "default").Output()
	if err == nil {
		if routes := parseIPRoute(string(out)); len(routes) > 0 {
			return routes, nil
		}
	}

	data, err := os.ReadFile("/proc/net/route")
	if err != nil {
		return nil, fmt.Errorf("reading /proc/net/route: %w", err)
	}

	return parseProcNetRoute(string(data)), nil
}