feat: add BVK exchange library

store_file.go

@@ -0,0 +1,84 @@
+package mila
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"os"
+	"path/filepath"
+	"sync"
+)
+
+type FileStore struct {
+	path string
+	mu   sync.Mutex
+	mem  *MemoryStore
+}
+
+func NewFileStore(path string) *FileStore {
+	return &FileStore{
+		path: path,
+		mem:  NewMemoryStore(),
+	}
+}
+
+func (s *FileStore) Get(ctx context.Context) (ContentState, error) {
+	if state, err := s.mem.Get(ctx); err == nil {
+		return state, nil
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	data, err := os.ReadFile(s.path)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return ContentState{}, ErrNotReady
+		}
+		return ContentState{}, err
+	}
+
+	var state ContentState
+	if err := json.Unmarshal(data, &state); err != nil {
+		return ContentState{}, err
+	}
+	if state.IsZero() {
+		return ContentState{}, ErrNotReady
+	}
+
+	if err := s.mem.Set(ctx, state); err != nil {
+		return ContentState{}, err
+	}
+	return state, nil
+}
+
+func (s *FileStore) Set(ctx context.Context, state ContentState) error {
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if err := os.MkdirAll(filepath.Dir(s.path), 0o755); err != nil {
+		return err
+	}
+
+	data, err := json.MarshalIndent(state, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	tmp := s.path + ".tmp"
+	if err := os.WriteFile(tmp, data, 0o644); err != nil {
+		return err
+	}
+	if err := os.Rename(tmp, s.path); err != nil {
+		_ = os.Remove(tmp)
+		return err
+	}
+
+	return s.mem.Set(ctx, state)
+}