Initial DDC release

internal/preferences/store.go

@@ -0,0 +1,87 @@
+package preferences
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"slices"
+	"sync"
+)
+
+type Store struct {
+	mutex   sync.RWMutex
+	path    string
+	current Preferences
+}
+
+func Open(path string, defaults Preferences) (*Store, error) {
+	store := &Store{path: path, current: defaults}
+
+	data, err := os.ReadFile(path)
+	if errors.Is(err, fs.ErrNotExist) {
+		return store, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	loaded := defaults
+	if err := json.Unmarshal(data, &loaded); err != nil {
+		return nil, fmt.Errorf("settings file %s: %w", path, err)
+	}
+	if err := loaded.Validate(); err != nil {
+		return nil, fmt.Errorf("settings file %s: %w", path, err)
+	}
+	store.current = loaded
+	return store, nil
+}
+
+func (store *Store) Get() Preferences {
+	store.mutex.RLock()
+	defer store.mutex.RUnlock()
+	current := store.current
+	current.AllowedPorts = slices.Clone(current.AllowedPorts)
+	if current.AllowedPorts == nil {
+		current.AllowedPorts = []uint16{}
+	}
+	return current
+}
+
+func (store *Store) Update(next Preferences) error {
+	if err := next.Validate(); err != nil {
+		return err
+	}
+	data, err := json.MarshalIndent(next, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	store.mutex.Lock()
+	defer store.mutex.Unlock()
+	if err := writeAtomically(store.path, data); err != nil {
+		return err
+	}
+	store.current = next
+	return nil
+}
+
+func writeAtomically(path string, data []byte) error {
+	temporary, err := os.CreateTemp(filepath.Dir(path), ".settings-*.tmp")
+	if err != nil {
+		return err
+	}
+	_, writeErr := temporary.Write(data)
+	closeErr := temporary.Close()
+	if writeErr != nil || closeErr != nil {
+		os.Remove(temporary.Name())
+		return errors.Join(writeErr, closeErr)
+	}
+	if err := os.Rename(temporary.Name(), path); err != nil {
+		os.Remove(temporary.Name())
+		return err
+	}
+	return nil
+}