//go:build linux

package host

import (
	"io"
	"os"

	"github.com/carlosframework/platform/internal/hostbox"
)

func servingParkBootID() (string, error) {
	f, err := os.Open("/proc/sys/kernel/random/boot_id")
	if err != nil {
		return "", err
	}
	defer f.Close()
	b, err := io.ReadAll(io.LimitReader(f, 38))
	if err != nil || len(b) != 37 || b[36] != '\n' {
		return "", hostbox.ErrChanged
	}
	return string(b[:36]), nil
}

func (f *servingParkFS) currentBoot() (string, error) {
	if f == nil || f.boot == nil {
		return "", hostbox.ErrUnsupported
	}
	id, err := f.boot()
	if err != nil {
		return "", err
	}
	if !validServingParkBootID(id) {
		return "", hostbox.ErrChanged
	}
	return id, nil
}

// A mount number is meaningful only in the boot that supplied it. Old records
// without a boot remain readable, but cannot authorize namespace mutations.
func (f *servingParkFS) checkBoot(expected string) error {
	current, err := f.currentBoot()
	if err != nil {
		return err
	}
	if expected == "" || current != expected {
		return hostbox.ErrChanged
	}
	return nil
}

func (f *servingParkFS) checkRecordBoot(r *servingParkRecord) error {
	if r.Source.BootID != "" {
		return f.checkBoot(r.Source.BootID)
	}
	b, err := servingParkReadBinding(f.state, "namespace")
	if err != nil {
		return err
	}
	if b != nil {
		return hostbox.ErrChanged
	}
	return nil
}