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

// The callback channel of RFC 8881: the CB_COMPOUND procedure the server
// calls on the connection the client opened, CB_SEQUENCE driving the back
// channel slot table, and CB_RECALL recalling a delegation.

package nfs4

import (
	"fmt"

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

// Callback operation numbers, RFC 8881 section 15.5.
const (
	OpCBGetattr    = 3
	OpCBRecall     = 4
	OpCBSequence   = 11
	OpCBPushDeleg  = 7
	OpCBNotify     = 6
	OpCBNotifyLock = 13
)

// The callback program rides on the same minor version and the COMPOUND
// shape as the fore channel.
const (
	CBDefaultProgram = 0x40000000
)

// AppendCBCompoundArgs encodes the CB_COMPOUND4args: the tag, the minor
// version, the callback identifier and the operations. The callback
// identifier is the slot the server reserved for this client when the
// back channel was negotiated; with sessions it stays zero.
func AppendCBCompoundArgs(b []byte, tag string, minorversion, callbackIdent uint32, ops [][]byte) []byte {
	b = xdr.AppendString(b, tag)
	b = xdr.AppendUint32(b, minorversion)
	b = xdr.AppendUint32(b, callbackIdent)
	b = xdr.AppendUint32(b, uint32(len(ops)))
	for _, op := range ops {
		b = append(b, op...)
	}
	return b
}

// CBCompoundHeader is the head of a decoded CB_COMPOUND4args.
type CBCompoundHeader struct {
	Tag           string
	Minor         uint32
	CallbackIdent uint32
	OpCount       uint32
}

// DecodeCBCompoundArgs splits CB_COMPOUND4args into its header and a
// decoder positioned at the first argop.
func DecodeCBCompoundArgs(payload []byte) (CBCompoundHeader, *xdr.Decoder, error) {
	d := xdr.NewDecoder(payload)
	var h CBCompoundHeader
	var err error
	if h.Tag, err = d.String(); err != nil {
		return h, nil, err
	}
	if h.Minor, err = d.Uint32(); err != nil {
		return h, nil, err
	}
	if h.CallbackIdent, err = d.Uint32(); err != nil {
		return h, nil, err
	}
	if h.OpCount, err = d.Uint32(); err != nil {
		return h, nil, err
	}
	if h.OpCount > maxOps {
		return h, nil, fmt.Errorf("nfs4: %d operations exceeds %d", h.OpCount, maxOps)
	}
	return h, d, nil
}

// AppendCBCompoundRes encodes a CB_COMPOUND4res: the top level status, the
// echoed tag and the result array.
func AppendCBCompoundRes(b []byte, status uint32, tag string, results [][]byte) []byte {
	return AppendCompoundRes(b, status, tag, results)
}

// AppendCBSequenceArgs encodes the CB_SEQUENCE argop.
func AppendCBSequenceArgs(b []byte, id SessionID, sequence, slot, highestSlot uint32, cacheThis bool) []byte {
	b = xdr.AppendUint32(b, OpCBSequence)
	return AppendSequenceArgsTail(b, id, sequence, slot, highestSlot, cacheThis)
}

// AppendSequenceArgsTail appends the shared SEQUENCE argument fields: the
// session id, the sequence, the slot ids and the caching flag.
func AppendSequenceArgsTail(b []byte, id SessionID, sequence, slot, highestSlot uint32, cacheThis bool) []byte {
	b = append(b, id[:]...)
	b = xdr.AppendUint32(b, sequence)
	b = xdr.AppendUint32(b, slot)
	b = xdr.AppendUint32(b, highestSlot)
	return xdr.AppendBool(b, cacheThis)
}

// A CBSequenceArgs is the decoded CB_SEQUENCE4args.
type CBSequenceArgs struct {
	SessionID   SessionID
	Sequence    uint32
	Slot        uint32
	HighestSlot uint32
	CacheThis   bool
}

// DecodeCBSequenceArgs decodes the CB_SEQUENCE4args from the decoder,
// which is positioned after the operation number.
func DecodeCBSequenceArgs(d *xdr.Decoder) (CBSequenceArgs, error) {
	var a CBSequenceArgs
	raw, err := d.Raw(16)
	if err != nil {
		return a, err
	}
	copy(a.SessionID[:], raw)
	var err2 error
	if a.Sequence, err2 = d.Uint32(); err2 != nil {
		return a, err2
	}
	if a.Slot, err2 = d.Uint32(); err2 != nil {
		return a, err2
	}
	if a.HighestSlot, err2 = d.Uint32(); err2 != nil {
		return a, err2
	}
	if a.CacheThis, err2 = d.Bool(); err2 != nil {
		return a, err2
	}
	return a, nil
}

// AppendCBSequenceRes encodes the successful CB_SEQUENCE4resok of
// RFC 7863: the session id, the echoed identifiers and the target
// highest slot. No further word follows.
func AppendCBSequenceRes(b []byte, id SessionID, sequence, slot, highestSlot uint32) []byte {
	b = append(b, id[:]...)
	b = xdr.AppendUint32(b, sequence)
	b = xdr.AppendUint32(b, slot)
	b = xdr.AppendUint32(b, highestSlot)
	return xdr.AppendUint32(b, highestSlot) // cbsr_target_highest_slotid
}

// DecodeCBSequenceRes decodes the successful CB_SEQUENCE4resok.
func DecodeCBSequenceRes(d *xdr.Decoder) (id SessionID, sequence, slot, highestSlot, targetHighestSlot uint32, err error) {
	raw, rerr := d.Raw(16)
	if rerr != nil {
		return id, 0, 0, 0, 0, rerr
	}
	copy(id[:], raw)
	if sequence, err = d.Uint32(); err != nil {
		return
	}
	if slot, err = d.Uint32(); err != nil {
		return
	}
	if highestSlot, err = d.Uint32(); err != nil {
		return
	}
	targetHighestSlot, err = d.Uint32()
	return
}

// AppendCBRecallArgs encodes the CB_RECALL argop: the delegation stateid,
// whether to truncate, and the file handle the delegation names.
func AppendCBRecallArgs(b []byte, stateid Stateid, truncate bool, fh []byte) []byte {
	b = xdr.AppendUint32(b, OpCBRecall)
	b = stateid.Append(b)
	b = xdr.AppendBool(b, truncate)
	return xdr.AppendVarOpaque(b, fh)
}

// A CBRecallArgs is the decoded CB_RECALL argop.
type CBRecallArgs struct {
	Stateid  Stateid
	Truncate bool
	FH       []byte
}

// DecodeCBRecallArgs decodes the CB_RECALL args from the decoder, which is
// positioned after the operation number.
func DecodeCBRecallArgs(d *xdr.Decoder) (CBRecallArgs, error) {
	var a CBRecallArgs
	raw, err := d.Raw(16)
	if err != nil {
		return a, err
	}
	copy(a.Stateid[:], raw)
	var err2 error
	if a.Truncate, err2 = d.Bool(); err2 != nil {
		return a, err2
	}
	a.FH, err2 = d.VarOpaque()
	return a, err2
}

// AppendCBGetattrArgs encodes the CB_GETATTR argop: the handle and the
// requested attribute bitmap.
func AppendCBGetattrArgs(b []byte, fh []byte, request Bitmap) []byte {
	b = xdr.AppendUint32(b, OpCBGetattr)
	b = xdr.AppendVarOpaque(b, fh)
	return request.AppendTo(b)
}