Initial DDC release

internal/preferences/preferences.go

@@ -0,0 +1,41 @@
+package preferences
+
+import (
+	"errors"
+	"fmt"
+)
+
+const (
+	gigabyte             = int64(1) << 30
+	maxConcurrentLimit   = 10
+	maxReservedGigabytes = 100000
+)
+
+var ErrInvalid = errors.New("invalid settings")
+
+type Preferences struct {
+	MaxConcurrentDownloads int      `json:"maxConcurrentDownloads"`
+	MinFreeGB              int      `json:"minFreeGB"`
+	AllowedPorts           []uint16 `json:"allowedPorts"`
+	AutoExtract            bool     `json:"autoExtract"`
+	CleanupAfterMove       bool     `json:"cleanupAfterMove"`
+}
+
+func (preferences Preferences) MinFreeBytes() int64 {
+	return int64(preferences.MinFreeGB) * gigabyte
+}
+
+func (preferences Preferences) Validate() error {
+	if preferences.MaxConcurrentDownloads < 1 || preferences.MaxConcurrentDownloads > maxConcurrentLimit {
+		return fmt.Errorf("%w: parallel downloads must be between 1 and %d", ErrInvalid, maxConcurrentLimit)
+	}
+	if preferences.MinFreeGB < 0 || preferences.MinFreeGB > maxReservedGigabytes {
+		return fmt.Errorf("%w: free space to keep must be between 0 and %d GB", ErrInvalid, maxReservedGigabytes)
+	}
+	for _, port := range preferences.AllowedPorts {
+		if port == 0 {
+			return fmt.Errorf("%w: port 0 is not allowed", ErrInvalid)
+		}
+	}
+	return nil
+}

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
+}