feat: implement persistant configuration

game/config.go

@@ -0,0 +1,21 @@
+package game
+
+import (
+	"io"
+
+	"tetris/game/config"
+)
+
+// Global config variable with default values.
+var Config = &config.Config{
+	SoundVolume: 255,
+}
+
+func LoadConfig(configPath string) error {
+	cfg, err := config.LoadFromFile(configPath)
+	if err != nil && err != io.EOF {
+		return err
+	}
+	Config = cfg
+	return nil
+}

game/config/config.go

@@ -0,0 +1,45 @@
+package config
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+)
+
+type Config struct {
+	fd          *os.File
+	SoundVolume byte `json:"sound_volume"`
+}
+
+func DefaultConfig(fd *os.File) *Config {
+	cfg := Config{
+		SoundVolume: 255,
+	}
+	cfg.fd = fd
+	return &cfg
+}
+
+func LoadFromFile(filename string) (*Config, error) {
+	fd, err := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, 0o644)
+	if err != nil {
+		return nil, err
+	}
+
+	cfg := DefaultConfig(fd)
+	err = json.NewDecoder(fd).Decode(cfg)
+	return cfg, err
+}
+
+func (c Config) Save() error {
+	if err := c.fd.Truncate(0); err != nil {
+		return err
+	}
+	if _, err := c.fd.Seek(0, io.SeekStart); err != nil {
+		return err
+	}
+	return json.NewEncoder(c.fd).Encode(c)
+}
+
+func (c Config) Close() error {
+	return c.fd.Close()
+}

game/state/handlers/options.go

@@ -5,6 +5,7 @@ import (
 	"tetris/engine/audio"
 	"tetris/engine/core"
 	"tetris/engine/render"
+	"tetris/game"
 	"tetris/game/state"
 	"tetris/game/ui"
 	"tetris/game/ui/layouts"
@@ -24,6 +25,10 @@ func soundVolumeChanged(widget *widgets.Slider) {
 
 	audio.SetVolume(value)
 	audio.Play(assets.SFX_MENU_SOUND_VOLUME_SELECT)
+
+	// Store in config and save
+	game.Config.SoundVolume = byte(widget.Value)
+	game.Config.Save()
 }
 
 func NewOptionsMenu() *OptionsMenu {