Initial SWOOSH executor and reducer implementation

snapshot.go

@@ -0,0 +1,117 @@
+package swoosh
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// Snapshot captures a serialized view of the orchestrator state and replay cursor.
+type Snapshot struct {
+	State            OrchestratorState `json:"state"`
+	LastAppliedHLC   string            `json:"last_applied_hlc"`
+	LastAppliedIndex uint64            `json:"last_applied_index"`
+}
+
+// SnapshotStore persists and loads orchestrator snapshots.
+type SnapshotStore interface {
+	Save(s Snapshot) error
+	LoadLatest() (Snapshot, error)
+}
+
+// ErrSnapshotNotFound indicates there is no stored snapshot.
+var ErrSnapshotNotFound = errors.New("snapshot not found")
+
+// FileSnapshotStore stores snapshots using atomic file replacement.
+type FileSnapshotStore struct {
+	path string
+}
+
+// NewFileSnapshotStore creates a snapshot store at the supplied path.
+func NewFileSnapshotStore(path string) *FileSnapshotStore {
+	return &FileSnapshotStore{path: path}
+}
+
+// Save writes the snapshot with atomic replace semantics.
+func (s *FileSnapshotStore) Save(snapshot Snapshot) error {
+	dir := filepath.Dir(s.path)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("create snapshot directory: %w", err)
+	}
+
+	payload, err := canonicalJSON(snapshot)
+	if err != nil {
+		return fmt.Errorf("marshal snapshot: %w", err)
+	}
+
+	temp, err := os.CreateTemp(dir, "snapshot-*.tmp")
+	if err != nil {
+		return fmt.Errorf("create temp snapshot: %w", err)
+	}
+	tempName := temp.Name()
+
+	if _, err := temp.Write(payload); err != nil {
+		temp.Close()
+		os.Remove(tempName)
+		return fmt.Errorf("write snapshot: %w", err)
+	}
+
+	if err := temp.Sync(); err != nil {
+		temp.Close()
+		os.Remove(tempName)
+		return fmt.Errorf("sync snapshot: %w", err)
+	}
+
+	if err := temp.Close(); err != nil {
+		os.Remove(tempName)
+		return fmt.Errorf("close snapshot temp file: %w", err)
+	}
+
+	if err := os.Rename(tempName, s.path); err != nil {
+		os.Remove(tempName)
+		return fmt.Errorf("rename snapshot: %w", err)
+	}
+
+	return nil
+}
+
+// LoadLatest returns the persisted snapshot or ErrSnapshotNotFound if absent.
+func (s *FileSnapshotStore) LoadLatest() (Snapshot, error) {
+	payload, err := os.ReadFile(s.path)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return Snapshot{}, ErrSnapshotNotFound
+		}
+		return Snapshot{}, fmt.Errorf("read snapshot: %w", err)
+	}
+
+	var snapshot Snapshot
+	if err := json.Unmarshal(payload, &snapshot); err != nil {
+		return Snapshot{}, fmt.Errorf("decode snapshot: %w", err)
+	}
+
+	return snapshot, nil
+}
+
+// InMemorySnapshotStore fulfills SnapshotStore in memory for testing.
+type InMemorySnapshotStore struct {
+	snapshot Snapshot
+	has      bool
+}
+
+// Save stores the snapshot in memory.
+func (s *InMemorySnapshotStore) Save(snapshot Snapshot) error {
+	s.snapshot = snapshot
+	s.has = true
+	return nil
+}
+
+// LoadLatest retrieves the stored snapshot or ErrSnapshotNotFound.
+func (s *InMemorySnapshotStore) LoadLatest() (Snapshot, error) {
+	if !s.has {
+		return Snapshot{}, ErrSnapshotNotFound
+	}
+	return s.snapshot, nil
+}