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

package nfs4

import (
	"slices"

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

// Attribute numbers of the fattr4 table, RFC 8881 section 5. The numbers
// were verified against the XDR description of the standard rather than
// recalled: an off by one here shows up as garbage on the client.
const (
	AttrSupportedAttrs    = 0  // bitmap4
	AttrType              = 1  // enum
	AttrFHExpireType      = 2  // uint32
	AttrChange            = 3  // uint64
	AttrSize              = 4  // uint64
	AttrLinkSupport       = 5  // bool
	AttrSymlinkSupport    = 6  // bool
	AttrNamedAttr         = 7  // bool
	AttrFSID              = 8  // uint64, uint64
	AttrUniqueHandles     = 9  // bool
	AttrLeaseTime         = 10 // uint32
	AttrRdattrError       = 11 // enum
	AttrFileHandle        = 19 // opaque
	AttrFileID            = 20 // uint64
	AttrMaxName           = 29 // uint32
	AttrMaxRead           = 30 // uint64
	AttrMaxWrite          = 31 // uint64
	AttrMode              = 33 // uint32
	AttrNumlinks          = 35 // uint32
	AttrOwner             = 36 // string
	AttrOwnerGroup        = 37 // string
	AttrRawDev            = 41 // specdata
	AttrSpaceUsed         = 45 // uint64
	AttrTimeAccessSet     = 48 // settime4
	AttrTimeModifySet     = 54 // settime4
	AttrTimeAccess        = 47 // nfstime4
	AttrTimeMetadata      = 52 // nfstime4
	AttrTimeModify        = 53 // nfstime4
	AttrMountedOnFileID   = 55 // uint64
	AttrSuppattrExclCreat = 75 // bitmap4
)

// SupportedAttrs is the attribute set this server advertises. A client asks
// only for attributes inside the set it read from here.
var SupportedAttrs = OfBits(
	AttrSupportedAttrs,
	AttrType,
	AttrFHExpireType,
	AttrChange,
	AttrSize,
	AttrLinkSupport,
	AttrSymlinkSupport,
	AttrNamedAttr,
	AttrFSID,
	AttrUniqueHandles,
	AttrFileHandle,
	AttrFileID,
	AttrMaxName,
	AttrMaxRead,
	AttrMaxWrite,
	AttrMode,
	AttrNumlinks,
	AttrOwner,
	AttrOwnerGroup,
	AttrSpaceUsed,
	AttrTimeAccess,
	AttrTimeMetadata,
	AttrTimeModify,
	AttrMountedOnFileID,
)

// ServerLimits carries the per export constants the advertised attributes
// report back.
type ServerLimits struct {
	MaxName  uint32
	MaxRead  uint64
	MaxWrite uint64
}

// DefaultLimits are the limits the server advertises.
var DefaultLimits = ServerLimits{MaxName: 255, MaxRead: 1 << 22, MaxWrite: 1 << 22}

// Attrs holds the values the fattr4 builder emits. A zero field for an
// attribute the server does not have is simply not requested by a client
// that honoured the advertised set.
type Attrs struct {
	Type            uint32
	FHExpireType    uint32
	Change          uint64
	Size            uint64
	LinkSupport     bool
	SymlinkSupport  bool
	NamedAttr       bool
	FSID            [2]uint64
	UniqueHandles   bool
	FileHandle      []byte
	FileID          uint64
	Mode            uint32
	Numlinks        uint32
	Owner           string // decimal uid, RFC 8881 section 5.8
	OwnerGroup      string // decimal gid
	SpaceUsed       uint64
	TimeAccess      NfsTime
	TimeMetadata    NfsTime
	TimeModify      NfsTime
	MountedOnFileID uint64
	Limits          ServerLimits

	// FsLocations and FsLocationsInfo carry the pre encoded attributes
	// for referral stubs; nil omits them.
	FsLocations     []byte
	FsLocationsInfo []byte
}

// A NfsTime is an nfstime4: seconds and nanoseconds since the epoch.
type NfsTime struct {
	Seconds  int64
	Nseconds uint32
}

// NfsTimeOf converts a Go time.
func NfsTimeOf(sec int64, nsec uint32) NfsTime { return NfsTime{sec, nsec} }

func appendNfsTime(b []byte, t NfsTime) []byte {
	b = xdr.AppendInt64(b, t.Seconds)
	return xdr.AppendUint32(b, t.Nseconds)
}

// AppendFattr emits an fattr4 for the requested attributes: the request
// bitmap filtered to what this server has, then the length prefixed list of
// values in numeric order, as the encoding requires.
func AppendFattr(b []byte, request Bitmap, a Attrs) []byte {
	var body []byte
	response := Bitmap{}
	for _, n := range sortedBits(request) {
		switch n {
		case AttrSupportedAttrs:
			body = SupportedAttrs.AppendTo(body)
			response = response.With(n)
		case AttrType:
			body = xdr.AppendUint32(body, a.Type)
			response = response.With(n)
		case AttrFHExpireType:
			body = xdr.AppendUint32(body, a.FHExpireType)
			response = response.With(n)
		case AttrChange:
			body = xdr.AppendUint64(body, a.Change)
			response = response.With(n)
		case AttrSize:
			body = xdr.AppendUint64(body, a.Size)
			response = response.With(n)
		case AttrLinkSupport:
			body = xdr.AppendBool(body, a.LinkSupport)
			response = response.With(n)
		case AttrSymlinkSupport:
			body = xdr.AppendBool(body, a.SymlinkSupport)
			response = response.With(n)
		case AttrNamedAttr:
			body = xdr.AppendBool(body, a.NamedAttr)
			response = response.With(n)
		case AttrFSID:
			body = xdr.AppendUint64(body, a.FSID[0])
			body = xdr.AppendUint64(body, a.FSID[1])
			response = response.With(n)
		case AttrUniqueHandles:
			body = xdr.AppendBool(body, a.UniqueHandles)
			response = response.With(n)
		case AttrFileHandle:
			body = xdr.AppendVarOpaque(body, a.FileHandle)
			response = response.With(n)
		case AttrFileID:
			body = xdr.AppendUint64(body, a.FileID)
			response = response.With(n)
		case AttrMaxName:
			body = xdr.AppendUint32(body, a.Limits.MaxName)
			response = response.With(n)
		case AttrMaxRead:
			body = xdr.AppendUint64(body, a.Limits.MaxRead)
			response = response.With(n)
		case AttrMaxWrite:
			body = xdr.AppendUint64(body, a.Limits.MaxWrite)
			response = response.With(n)
		case AttrMode:
			body = xdr.AppendUint32(body, a.Mode)
			response = response.With(n)
		case AttrNumlinks:
			body = xdr.AppendUint32(body, a.Numlinks)
			response = response.With(n)
		case AttrOwner:
			body = xdr.AppendString(body, a.Owner)
			response = response.With(n)
		case AttrOwnerGroup:
			body = xdr.AppendString(body, a.OwnerGroup)
			response = response.With(n)
		case AttrSpaceUsed:
			body = xdr.AppendUint64(body, a.SpaceUsed)
			response = response.With(n)
		case AttrTimeAccess:
			body = appendNfsTime(body, a.TimeAccess)
			response = response.With(n)
		case AttrTimeMetadata:
			body = appendNfsTime(body, a.TimeMetadata)
			response = response.With(n)
		case AttrTimeModify:
			body = appendNfsTime(body, a.TimeModify)
			response = response.With(n)
		case AttrMountedOnFileID:
			body = xdr.AppendUint64(body, a.MountedOnFileID)
			response = response.With(n)
		case AttrFsLocations:
			if a.FsLocations != nil {
				body = append(body, a.FsLocations...)
				response = response.With(n)
			}
		case AttrFsLocationsInfo:
			if a.FsLocationsInfo != nil {
				body = append(body, a.FsLocationsInfo...)
				response = response.With(n)
			}
		}
	}
	b = response.AppendTo(b)
	return xdr.AppendVarOpaque(b, body)
}

// sortedBits lists the attribute numbers set in the bitmap, ascending.
func sortedBits(m Bitmap) []uint32 {
	var out []uint32
	for w, word := range m.Words() {
		for bit := range 32 {
			if word&(1<<bit) != 0 {
				out = append(out, uint32(w*32+bit))
			}
		}
	}
	slices.Sort(out)
	return out
}