translation.go

// SPDX-License-Identifier: Apache-2.0
// Copyright 2020,2022 Marcus Soll
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//	  http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"embed"
	"encoding/json"
	"log"
	"path/filepath"
	"reflect"
	"strings"
	"sync"
)

// Translation represents an object holding all translations
type Translation struct {
	Language                                  string
	CreatedBy                                 string
	Impressum                                 string
	PrivacyPolicy                             string
	ConnectionLost                            string
	ConnectionLostNotPermanentlySavedBrackets string
	ConnectedUser                             string
	NoSave                                    string
	Save                                      string
	OneUser                                   string
	ButtonActive                              string
	ButtonDownloadHTML                        string
	ButtonDownloadDelta                       string
	ButtonUploadDelta                         string
}

const defaultLanguage = "en"

//go:embed translation
var translationFiles embed.FS

var initialiseCurrent sync.Once
var current Translation
var rwlock sync.RWMutex
var translationPath = "./translation"

// GetTranslation returns a Translation struct of the given language.
// This function always loads translations from disk. Try to use GetDefaultTranslation where possible.
func GetTranslation(language string) (Translation, error) {
	t, err := getSingleTranslation(language)
	if err != nil {
		return Translation{}, err
	}
	d, err := getSingleTranslation(defaultLanguage)
	if err != nil {
		return Translation{}, err
	}

	// Set unknown strings to default value
	vp := reflect.ValueOf(&t)
	dv := reflect.ValueOf(d)
	v := vp.Elem()

	for i := 0; i < v.NumField(); i++ {
		if !v.Field(i).CanSet() {
			continue
		}
		if v.Field(i).Kind() != reflect.String {
			continue
		}
		if v.Field(i).String() == "" {
			v.Field(i).SetString(dv.Field(i).String())
		}
	}
	return t, nil
}

func getSingleTranslation(language string) (Translation, error) {
	if language == "" {
		return GetDefaultTranslation(), nil
	}

	file := strings.Join([]string{language, "json"}, ".")
	file = filepath.Join(translationPath, file)

	b, err := translationFiles.ReadFile(file)
	if err != nil {
		return Translation{}, err
	}
	t := Translation{}
	err = json.Unmarshal(b, &t)
	if err != nil {
		return Translation{}, err
	}
	return t, nil
}

// SetDefaultTranslation sets the default language to the provided one.
// Does nothing if it returns error != nil.
func SetDefaultTranslation(language string) error {
	if language == "" {
		return nil
	}

	t, err := GetTranslation(language)
	rwlock.Lock()
	defer rwlock.Unlock()
	if err != nil {
		return err
	}
	current = t
	return nil
}

// GetDefaultTranslation returns a Translation struct of the current default language.
func GetDefaultTranslation() Translation {
	initialiseCurrent.Do(func() {
		rwlock.RLock()
		c := current.Language
		rwlock.RUnlock()
		if c == "" {
			err := SetDefaultTranslation(defaultLanguage)
			if err != nil {
				log.Printf("Can not load default language (%s): %s", defaultLanguage, err.Error())
			}
		}
	})
	rwlock.RLock()
	defer rwlock.RUnlock()
	return current
}