Refactor application structure and initialize core components

I decided to rewrite the program taking into account the experience gained.

internal/application/setting/setting.go

@@ -0,0 +1,65 @@
+package setting
+
+import (
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/lang"
+	"golang.org/x/text/language"
+)
+
+type SettingContract interface {
+	GetLanguages() []Lang
+	GetCurrentLangOrDefaultLang() (currentLang Lang, isDefault bool)
+	SetLang(language Lang) error
+	GetFFmpegPath() string
+	SetFFmpegPath(path string)
+	GetFFprobePath() string
+	SetFFprobePath(path string)
+	GetFFplayPath() string
+	SetFFplayPath(path string)
+}
+
+type setting struct {
+	fyneApp fyne.App
+}
+
+func NewSetting(fyneApp fyne.App) SettingContract {
+	return &setting{
+		fyneApp: fyneApp,
+	}
+}
+
+func (s *setting) GetLanguages() []Lang {
+	items := []Lang{}
+	for _, item := range supportedLanguages {
+		items = append(items, item)
+	}
+	return items
+}
+
+func (s *setting) GetCurrentLangOrDefaultLang() (currentLang Lang, isDefault bool) {
+	languageCode := s.fyneApp.Preferences().String("language")
+
+	if languageCode == "" {
+		languageTag, err := language.Parse(lang.SystemLocale().LanguageString())
+		if err != nil {
+			return currentLang, true
+		}
+		base, _ := languageTag.Base()
+		languageCode = base.String()
+	}
+
+	if currentLang, ok := supportedLanguages[languageCode]; ok {
+		return currentLang, false
+	}
+
+	return defaultLang(), true
+}
+
+func (s *setting) SetLang(language Lang) error {
+	err := ChangeLang(language)
+	if err != nil {
+		return err
+	}
+	s.fyneApp.Preferences().SetString("language", language.Code)
+	return nil
+}