package nfs

import (
	"context"
	"io/fs"
	"net"

	"git.kmsign.ru/royalcat/tstor/pkg/ctxbilly"
)

// Handler represents the interface of the file system / vfs being exposed over NFS
type Handler interface {
	// Required methods

	Mount(context.Context, net.Conn, MountRequest) (MountStatus, Filesystem, []AuthFlavor)

	// Change can return 'nil' if filesystem is read-only
	// If the returned value can be cast to `UnixChange`, mknod and link RPCs will be available.
	Change(Filesystem) Change

	// Optional methods - generic helpers or trivial implementations can be sufficient depending on use case.

	// Fill in information about a file system's free space.
	FSStat(context.Context, Filesystem, *FSStat) error

	// represent file objects as opaque references
	// Can be safely implemented via helpers/cachinghandler.
	ToHandle(fs Filesystem, path []string) []byte
	FromHandle(fh []byte) (Filesystem, []string, error)
	InvalidateHandle(Filesystem, []byte) error

	// How many handles can be safely maintained by the handler.
	HandleLimit() int
}

// UnixChange extends the billy `Change` interface with support for special files.
type UnixChange interface {
	ctxbilly.Change
	Mknod(ctx context.Context, path string, mode uint32, major uint32, minor uint32) error
	Mkfifo(ctx context.Context, path string, mode uint32) error
	Socket(ctx context.Context, path string) error
	Link(ctx context.Context, path string, link string) error
}

// CachingHandler represents the optional caching work that a user may wish to over-ride with
// their own implementations, but which can be otherwise provided through defaults.
type CachingHandler interface {
	VerifierFor(path string, contents []fs.FileInfo) uint64

	// fs.FileInfo needs to be sorted by Name(), nil in case of a cache-miss
	DataForVerifier(path string, verifier uint64) []fs.FileInfo
}