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

// Migration and referrals of RFC 5661 section 11: names the handler
// marks as referrals resolve to stub handles whose GETATTR answers the
// fs_locations and fs_locations_info attributes and whose other
// operations answer NFS4ERR_MOVED.

package nfs4server

import (
	"sync"

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

// A Referral names the file system the client is sent to: the replica
// server list and the path of the referred root on those servers.
type Referral struct {
	Servers  []string
	RootPath []string
}

// referralStore keeps the configured referrals by name and the stub
// handles issued for them.
type referralStore struct {
	mu    sync.Mutex
	byRef map[string]Referral     // by component name
	byKey map[string]nfsfs.Handle // by component name: the stub
	names map[string]string       // by stub handle: the component
	next  uint64
}

func newReferralStore() *referralStore {
	return &referralStore{
		byRef: make(map[string]Referral),
		byKey: make(map[string]nfsfs.Handle),
		names: make(map[string]string),
	}
}

// put registers a referral and answers its stable stub handle.
func (s *referralStore) put(name string, r Referral) nfsfs.Handle {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.byRef[name] = r
	if stub, ok := s.byKey[name]; ok {
		return stub
	}
	s.next++
	stub := nfsfs.Handle(append([]byte("REF/"), []byte(name)...))
	s.byKey[name] = stub
	s.names[string(stub)] = name
	return stub
}

// byName resolves the referral configured for a component name.
func (s *referralStore) byName(name string) (Referral, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	r, ok := s.byRef[name]
	return r, ok
}

// byHandle resolves the referral a stub handle names.
func (s *referralStore) byHandle(fh nfsfs.Handle) (Referral, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	name, ok := s.names[string(fh)]
	if !ok {
		return Referral{}, false
	}
	r, ok := s.byRef[name]
	return r, ok
}

// referrals returns the referral store, made once per handler.
func (h *Handler) referrals() *referralStore {
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.refSt == nil {
		h.refSt = newReferralStore()
	}
	return h.refSt
}

// SetReferral registers a referral: LOOKUP of the component name lands
// on a stub whose GETATTR answers the location attributes and whose
// other operations answer NFS4ERR_MOVED.
func (h *Handler) SetReferral(name string, r Referral) {
	h.referrals().put(name, r)
}

// isReferralStub reports whether the handle names a referral stub.
func (h *Handler) isReferralStub(fh nfsfs.Handle) bool {
	_, ok := h.referrals().byHandle(fh)
	return ok
}

// stubAttrs builds the attributes of a referral stub: an absent
// directory whose location attributes carry the referral.
func (h *Handler) stubAttrs(fh nfsfs.Handle) nfs4.Attrs {
	r, _ := h.referrals().byHandle(fh)
	fsRoot := []string{""}
	a := nfs4.Attrs{
		Type:          nfs4.NF4Dir,
		FHExpireType:  nfs4.FH4Persistent,
		NamedAttr:     false,
		UniqueHandles: true,
	}
	var servers []nfs4.FsServer
	for i, s := range r.Servers {
		currency := int32(0)
		info := []byte{rpcNoneInfo}
		if i == 0 {
			info[0] |= nfs4.Fsli4gfCurReq
		}
		info[0] |= nfs4.Fsli4gfWritable
		servers = append(servers, nfs4.FsServer{Currency: currency, Info: info, Server: s})
	}
	a.FsLocations = nfs4.AppendFsLocations(nil, fsRoot, []nfs4.FsLocation{{
		Servers:  r.Servers,
		RootPath: r.RootPath,
	}})
	a.FsLocationsInfo = nfs4.AppendFsLocationsInfo(nil, 0, 60, fsRoot,
		[]nfs4.FsItem{{Entries: servers, RootPath: r.RootPath}})
	return a
}

// The value of the fls_info class byte that marks this build's single
// homogeneous replica set.
const rpcNoneInfo = 0x00