1 files changed, 56 insertions, 0 deletions
diff --git a/cache/with_snapshot.go b/cache/with_snapshot.go
new file mode 100644
index 00000000..674b6923
--- /dev/null
+++ b/cache/with_snapshot.go
@@ -0,0 +1,56 @@
+package cache
+
+import (
+	"sync"
+
+	"github.com/MichaelMure/git-bug/entity/dag"
+	"github.com/MichaelMure/git-bug/repository"
+)
+
+var _ dag.Interface[dag.Snapshot, dag.OperationWithApply[dag.Snapshot]] = &withSnapshot[dag.Snapshot, dag.OperationWithApply[dag.Snapshot]]{}
+
+// withSnapshot encapsulate an entity and maintain a snapshot efficiently.
+type withSnapshot[SnapT dag.Snapshot, OpT dag.OperationWithApply[SnapT]] struct {
+	dag.Interface[SnapT, OpT]
+	mu   sync.Mutex
+	snap *SnapT
+}
+
+func (ws *withSnapshot[SnapT, OpT]) Compile() SnapT {
+	ws.mu.Lock()
+	defer ws.mu.Unlock()
+	if ws.snap == nil {
+		snap := ws.Interface.Compile()
+		ws.snap = &snap
+	}
+	return *ws.snap
+}
+
+// Append intercept Bug.Append() to update the snapshot efficiently
+func (ws *withSnapshot[SnapT, OpT]) Append(op OpT) {
+	ws.mu.Lock()
+	defer ws.mu.Unlock()
+
+	ws.Interface.Append(op)
+
+	if ws.snap == nil {
+		return
+	}
+
+	op.Apply(*ws.snap)
+	(*ws.snap).AppendOperation(op)
+}
+
+// Commit intercept Bug.Commit() to update the snapshot efficiently
+func (ws *withSnapshot[SnapT, OpT]) Commit(repo repository.ClockedRepo) error {
+	ws.mu.Lock()
+	defer ws.mu.Unlock()
+
+	err := ws.Interface.Commit(repo)
+	if err != nil {
+		ws.snap = nil
+		return err
+	}
+
+	return nil
+}