package host

import (
	"errors"
	"os"
	"path"
	"strings"

	"github.com/carlosframework/platform/internal/rootstate"
	"github.com/carlosframework/platform/internal/safefile"
	"golang.org/x/sys/unix"
)

func claimPredecessorGroup(group string) (rootstate.FileIdentity, bool, error) {
	var zero rootstate.FileIdentity
	if !claimPredecessorPlacement(path.Base(group), group) {
		return zero, false, os.ErrPermission
	}
	dir, err := safefile.OpenDir("/sys/fs/cgroup/" + group)
	if errors.Is(err, os.ErrNotExist) {
		return zero, false, nil
	}
	if err != nil {
		return zero, false, err
	}
	defer dir.Close()
	var st unix.Statfs_t
	if err = unix.Fstatfs(int(dir.Fd()), &st); err != nil {
		return zero, false, err
	}
	if st.Type != unix.CGROUP2_SUPER_MAGIC {
		return zero, false, os.ErrPermission
	}
	id, err := rootstate.Identity(dir)
	if err != nil {
		return zero, false, err
	}
	fd, err := unix.Openat(int(dir.Fd()), "cgroup.events", unix.O_RDONLY|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0)
	if err != nil {
		return zero, false, err
	}
	file := os.NewFile(uintptr(fd), "cgroup.events")
	defer file.Close()
	var buf [1024]byte
	n, err := file.Read(buf[:])
	if err != nil {
		return zero, false, err
	}
	if n == len(buf) {
		return zero, false, os.ErrPermission
	}
	for _, line := range strings.Split(string(buf[:n]), "\n") {
		if line == "populated 0" {
			return id, false, nil
		}
		if line == "populated 1" {
			return id, true, nil
		}
	}
	return zero, false, os.ErrPermission
}

func claimUnitBoot() (string, error) {
	raw, err := os.ReadFile("/proc/sys/kernel/random/boot_id")
	if err != nil {
		return "", err
	}
	boot := strings.TrimSpace(string(raw))
	if boot == "" {
		return "", os.ErrPermission
	}
	return boot, nil
}