package storage

import (
	"errors"
	"fmt"
	"galaxy/util"
	"path/filepath"
)

const (
	// Name of the file under the storage's root where [model.State] is stored.
	stateFileName = "state.dat"

	// Suffix of a Game's file inder the storage's root where [model.GameData] is stored.
	gameDataFileSuffix = ".dat"
)

type storage struct {
	root string
}

// NewStorage returns implementation of the "galaxy/client.Storage" interface
// or nil with a non-nil error when filesystem storage initialisation failed.
func NewStorage(rootPath string) (*storage, error) {
	ok, err := util.Writable(rootPath)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, errors.New("user does not have write permissions to the storage root")
	}
	s := &storage{
		root: rootPath,
	}
	return s, nil
}

// StateFilePath returns client's state file path relative to the root,
// file name and extension are pre-defined constant.
func StateFilePath(root string) string {
	return filepath.Join(root, stateFileName)
}

// GameDataPath returns game's data file path relative to the root,
// data file name is GameID string representation and extension is a pre-defined constant.
func GameDataFilePath(root string, id fmt.Stringer) string {
	return filepath.Join(root, id.String()) + gameDataFileSuffix
}