// fs implements galaxy/storage.Storage with filesystem
package fs

/*

Общие правила:

1. Все хранимые объекты сериализуются / десериализуются как JSON.

2. Структура хранения файлов:

- storageRoot \
			  |
			  +-- state.dat
			  |
			  +-- {GameID} \
			  |	           |
			  |			   +-- {Turn}.dat (client.GameData)
			  |			   +-- {Turn}.dat (client.GameData)
			  |			   +-- ...
			  |
			  +-- {GameID} \
			  			   |
						   +-- ...

*/

import (
	"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"
)

// 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
}

type fsStorage struct {
	storageRoot string
}

// NewFS returns on-filesystem implementation of the "galaxy/storage.Storage" with root located at storageRoot.
// storageRoot must me a directory and has write access to the current user. If initial checks failed, return nil and non-nil error.
func NewStorage(storageRoot string) (*fsStorage, error) {
	if ok, err := util.PathExists(storageRoot, true); err != nil {
		return nil, fmt.Errorf("new storage: check path %q exists: %w", storageRoot, err)
	} else if !ok {
		return nil, fmt.Errorf("new storage: path %q does not exists", storageRoot)
	}
	if ok, err := util.Writable(storageRoot); err != nil {
		return nil, fmt.Errorf("new storage: check path %q writable: %w", storageRoot, err)
	} else if !ok {
		return nil, fmt.Errorf("new storage: path %q is not writable", storageRoot)
	}
	s := &fsStorage{
		storageRoot: storageRoot,
	}
	return s, nil
}