// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

// Directory delegations: the store of granted directory delegations, the
// GET_DIR_DELEGATION handler and the notification the server pushes to a
// deleg holder when the directory changes under it.

package nfs4server

import (
	"sync"

	"sourcedock.dev/petrbalvin/nfs/internal/nfs4"
	"sourcedock.dev/petrbalvin/nfs/internal/nfsfs"
	"sourcedock.dev/petrbalvin/nfs/internal/xdr"
)

// A dirDeleg is one granted directory delegation.
type dirDeleg struct {
	stateid  nfs4.Stateid
	sessID   nfs4.SessionID
	clientid uint64
	fh       nfsfs.Handle
	types    nfs4.Bitmap
}

// dirDelegStore tracks the live directory delegations. A directory
// carries at most one.
type dirDelegStore struct {
	mu    sync.Mutex
	next  uint64
	byDir map[string]*dirDeleg
}

func newDirDelegStore() *dirDelegStore {
	return &dirDelegStore{byDir: make(map[string]*dirDeleg)}
}

// grant issues the directory delegation; a second client asking for the
// same directory is denied, the same client receives its live stateid.
func (s *dirDelegStore) grant(sessID nfs4.SessionID, clientid uint64, fh nfsfs.Handle) (*dirDeleg, uint32) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if d, ok := s.byDir[fileKey(fh)]; ok {
		if d.clientid == clientid {
			return d, nfs4.ErrOK
		}
		return nil, nfs4.ErrDenied
	}
	s.next++
	var st nfs4.Stateid
	setStateidSeq(&st, 1)
	copy(st[4:], "DDEL")
	for i := range 8 {
		st[15-i] = byte(s.next >> (8 * i))
	}
	d := &dirDeleg{stateid: st, sessID: sessID, clientid: clientid, fh: fh}
	s.byDir[fileKey(fh)] = d
	return d, nfs4.ErrOK
}

// dropClient and dropSession remove the delegations that die with the
// client or the session.
func (s *dirDelegStore) dropClient(clientid uint64) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for key, d := range s.byDir {
		if d.clientid == clientid {
			delete(s.byDir, key)
		}
	}
}

func (s *dirDelegStore) dropSession(sessID nfs4.SessionID) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for key, d := range s.byDir {
		if d.sessID == sessID {
			delete(s.byDir, key)
		}
	}
}

// count reports how many directory delegations are live.
func (s *dirDelegStore) count() int {
	s.mu.Lock()
	defer s.mu.Unlock()
	return len(s.byDir)
}

// dirDelegs returns the directory delegation store, made once per
// handler.
func (h *Handler) dirDelegs() *dirDelegStore {
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.dirDelegSt == nil {
		h.dirDelegSt = newDirDelegStore()
	}
	return h.dirDelegSt
}

// getDirDelegationOp serves GET_DIR_DELEGATION over the current
// directory: the stateid hangs from an open of the directory and the
// notification types are echoed back, this server can produce them all.
func (h *Handler) getDirDelegationOp(d *xdr.Decoder, reg *fhreg, sessID nfs4.SessionID, clientid uint64) ([]byte, uint32, error) {
	signalAvail, err := d.Bool()
	if err != nil {
		return nil, 0, err
	}
	notifyTypes, err := nfs4.ReadBitmap(d)
	if err != nil {
		return nil, 0, err
	}
	for range 2 {
		if _, err = d.Int64(); err != nil { // attr delay seconds
			return nil, 0, err
		}
		if _, err = d.Uint32(); err != nil { // attr delay nseconds
			return nil, 0, err
		}
	}
	if _, err = nfs4.ReadBitmap(d); err != nil { // child attributes
		return nil, 0, err
	}
	if _, err = nfs4.ReadBitmap(d); err != nil { // dir attributes
		return nil, 0, err
	}
	_ = signalAvail
	if !reg.haveCur {
		return nil, nfs4.ErrNoFileHandle, nil
	}
	// Only directories carry directory delegations.
	if info, gerr := h.FS.Getattr(reg.cur); gerr == nil && !info.IsDir() {
		return nil, nfs4.ErrWrongType, nil
	}
	dg, status := h.dirDelegs().grant(sessID, clientid, reg.cur)
	if status != nfs4.ErrOK {
		return nil, status, nil
	}
	verf := h.writeVerifier()
	return nfs4.AppendGetDirDelegationResOK(nil, verf, dg.stateid, notifyTypes, nfs4.Bitmap{}, nfs4.Bitmap{}), nfs4.ErrOK, nil
}

// notifyDir pushes one CB_NOTIFY to the holder of the directory
// delegation, if the changed directory is delegated to somebody else.
// The notification is advisory and queued onto the holder's callback
// worker, so a mutation served on the holder's own connection never
// waits for the reply only that connection's read loop can route.
func (h *Handler) notifyDir(dir nfsfs.Handle, change nfs4.Notify4) {
	dd, ok := h.dirDelegByFH(dir)
	if !ok {
		return
	}
	args := nfs4.AppendCBNotifyArgs(nil, dd.stateid, dir, []nfs4.Notify4{change})
	_ = h.queueCB(dd.sessID, "dir-notify", [][]byte{args})
}

// dirDelegByFH finds the live delegation of a directory.
func (h *Handler) dirDelegByFH(dir nfsfs.Handle) (*dirDeleg, bool) {
	h.mu.Lock()
	store := h.dirDelegSt
	h.mu.Unlock()
	if store == nil {
		return nil, false
	}
	store.mu.Lock()
	defer store.mu.Unlock()
	d, ok := store.byDir[fileKey(dir)]
	return d, ok
}

// notifyDirOf is the helper the mutating operations call: it reads the
// parent through the backend and pushes the change. nameCookie carries
// the cookie semantics of the event; zero suffices for the wire shape
// this build answers with.
func (h *Handler) notifyDirOf(dir nfsfs.Handle, mask nfs4.Bitmap, name string) {
	vals := buildNotifyBody(mask, name)
	if vals == nil {
		return
	}
	h.notifyDir(dir, nfs4.Notify4{Mask: mask, Vals: vals})
}

// buildNotifyBody encodes the change body the mask names.
func buildNotifyBody(mask nfs4.Bitmap, name string) []byte {
	if mask.Has(nfs4.NotifyAddEntry) {
		return nfs4.AppendNotifyAdd(nil, name, 0, true)
	}
	if mask.Has(nfs4.NotifyRemoveEntry) {
		return nfs4.AppendNotifyRemove(nil, name, 0)
	}
	return nil
}

// notifyAppendCB walks the decoded notify body for the tests: it splits
// the name out of a notify_entry4 payload.
func notifyNameOf(body []byte) string {
	d := xdr.NewDecoder(body)
	if _, err := d.Uint32(); err != nil { // nad_old_entry count
		return ""
	}
	name, err := d.String()
	if err != nil {
		return ""
	}
	return name
}