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

// The file system location attributes of RFC 5661 section 11.10: the
// fs_locations and fs_locations_info attributes that migration and
// referrals hand to the client.

package nfs4

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

// The attribute numbers of the location family.
const (
	AttrFsLocations     = 24 // fs_locations4
	AttrFsLocationsInfo = 67 // fs_locations_info4
)

// The general flags of fli_flags, RFC 5661 section 11.10.1.
const (
	Fsli4ifVarSub = 0x1
)

// The general flags of the fls_info GFLAGS byte.
const (
	Fsli4gfWritable = 0x01
	Fsli4gfCurReq   = 0x02
	Fsli4gfAbsent   = 0x04
	Fsli4gfGoing    = 0x08
	Fsli4gfSplit    = 0x10
)

// An FsLocation is one fs_location4: the servers that share a root
// path.
type FsLocation struct {
	Servers  []string
	RootPath []string
}

// An FsServer is one fs_locations_server4 replica entry: the currency
// hint, the opaque info bytes and the server name.
type FsServer struct {
	Currency int32
	Info     []byte
	Server   string
}

// An FsItem is one fs_locations_item4: the replicas of one root path.
type FsItem struct {
	Entries  []FsServer
	RootPath []string
}

// AppendPathname encodes a pathname4: an array of components.
func AppendPathname(b []byte, components []string) []byte {
	b = xdr.AppendUint32(b, uint32(len(components)))
	for _, c := range components {
		b = xdr.AppendString(b, c)
	}
	return b
}

// AppendFsLocations encodes the fs_locations4 attribute.
func AppendFsLocations(b []byte, fsRoot []string, locations []FsLocation) []byte {
	b = AppendPathname(b, fsRoot)
	b = xdr.AppendUint32(b, uint32(len(locations)))
	for _, l := range locations {
		b = xdr.AppendUint32(b, uint32(len(l.Servers)))
		for _, s := range l.Servers {
			b = xdr.AppendString(b, s)
		}
		b = AppendPathname(b, l.RootPath)
	}
	return b
}

// AppendFsLocationsInfo encodes the fs_locations_info4 attribute: the
// flags, the validity window, the root and the replica items.
func AppendFsLocationsInfo(b []byte, flags uint32, validFor int32, fsRoot []string, items []FsItem) []byte {
	b = xdr.AppendUint32(b, flags)
	b = xdr.AppendInt32(b, validFor)
	b = AppendPathname(b, fsRoot)
	b = xdr.AppendUint32(b, uint32(len(items)))
	for _, item := range items {
		b = xdr.AppendUint32(b, uint32(len(item.Entries)))
		for _, e := range item.Entries {
			b = xdr.AppendInt32(b, e.Currency)
			b = xdr.AppendVarOpaque(b, e.Info)
			b = xdr.AppendString(b, e.Server)
		}
		b = AppendPathname(b, item.RootPath)
	}
	return b
}

// DecodeFsLocations reads the fs_locations4 attribute back.
func DecodeFsLocations(payload []byte) (fsRoot []string, locations []FsLocation, err error) {
	d := xdr.NewDecoder(payload)
	if fsRoot, err = decodePathname(d); err != nil {
		return
	}
	var n uint32
	if n, err = d.Uint32(); err != nil {
		return
	}
	for i := uint32(0); i < n; i++ {
		var l FsLocation
		var count uint32
		if count, err = d.Uint32(); err != nil {
			return
		}
		for j := uint32(0); j < count; j++ {
			var s string
			if s, err = d.String(); err != nil {
				return
			}
			l.Servers = append(l.Servers, s)
		}
		if l.RootPath, err = decodePathname(d); err != nil {
			return
		}
		locations = append(locations, l)
	}
	return
}

func decodePathname(d *xdr.Decoder) ([]string, error) {
	n, err := d.Uint32()
	if err != nil {
		return nil, err
	}
	var out []string
	for range n {
		s, err := d.String()
		if err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, nil
}

// AppendOpenattrArgs encodes the OPENATTR argop: the created flag.
func AppendOpenattrArgs(b []byte, created bool) []byte {
	b = xdr.AppendUint32(b, OpOpenattr)
	return xdr.AppendBool(b, created)
}

// AppendReadArgs encodes the READ argop.
func AppendReadArgs(b []byte, st Stateid, offset uint64, count uint32) []byte {
	b = xdr.AppendUint32(b, OpRead)
	b = st.Append(b)
	b = xdr.AppendUint64(b, offset)
	return xdr.AppendUint32(b, count)
}