//go:build linux

package cgroup

import (
	"errors"

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

type ContainmentIdentity struct{ Device, Inode uint64 }

func (p *Prepared) Identity() (ContainmentIdentity, error) {
	if p == nil || p.strictPreparedState == nil {
		return ContainmentIdentity{}, ErrStrictState
	}
	p.mu.Lock()
	defer p.mu.Unlock()
	if err := p.identityOK(); err != nil {
		return ContainmentIdentity{}, err
	}
	return ContainmentIdentity{Device: p.identity.device, Inode: p.identity.inode}, nil
}

// PrepareRoleChild pins a newly empty role group below the host parent. It
// never reuses the parent's populated group and inherits its aggregate limits.
func (p *Prepared) PrepareRoleChild(role string) (*Prepared, error) {
	return p.prepareRoleChild(role, nil)
}

// PrepareRoleChildWithIntent requires a new name and persists the caller's
// intention under the pinned parent before mkdir. A failed preparation retains
// that intention for stop recovery; it never authorizes execution by itself.
func (p *Prepared) PrepareRoleChildWithIntent(role string, intent func(ContainmentIdentity) error) (*Prepared, error) {
	if intent == nil {
		return nil, ErrStrictRefused
	}
	return p.prepareRoleChild(role, intent)
}

func (p *Prepared) prepareRoleChild(role string, intent func(ContainmentIdentity) error) (out *Prepared, err error) {
	if p == nil || p.strictPreparedState == nil || !controlname.ValidLabel(role) {
		return nil, ErrStrictRefused
	}
	p.mu.Lock()
	defer p.mu.Unlock()
	if p.parent != nil || p.empty || p.draining.Load() {
		return nil, ErrStrictState
	}
	if err = p.identityOK(); err != nil {
		return nil, err
	}
	name := "role-" + role
	beforeMkdir := func() error {
		if intent != nil {
			var st unix.Stat_t
			if e := unix.Fstatat(int(p.dir.Fd()), name, &st, unix.AT_SYMLINK_NOFOLLOW); !errors.Is(e, unix.ENOENT) {
				return ErrStrictRefused
			}
			if e := intent(ContainmentIdentity{Device: p.identity.device, Inode: p.identity.inode}); e != nil {
				return e
			}
		}
		return nil
	}
	allowExisting := intent == nil
	child, err := pinChild(p, name, beforeMkdir, allowExisting)
	if err != nil {
		return nil, err
	}
	return child, nil
}