feat: implement persistant configuration

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()
+}