add latest sealed and executed

module/block_iterator/latest/sealed_and_executed.go

@@ -0,0 +1,80 @@
+package latest
+
+import (
+	"github.com/dgraph-io/badger/v2"
+
+	"github.com/onflow/flow-go/model/flow"
+	"github.com/onflow/flow-go/state/protocol"
+	"github.com/onflow/flow-go/storage/badger/procedure"
+)
+
+type LatestSealedAndExecuted struct {
+	root            *flow.Header
+	state           protocol.State
+	executedBlockDB *badger.DB
+}
+
+func NewLatestSealedAndExecuted(
+	root *flow.Header,
+	state protocol.State,
+	executedBlockDB *badger.DB,
+) *LatestSealedAndExecuted {
+	return &LatestSealedAndExecuted{
+		root:            root,
+		state:           state,
+		executedBlockDB: executedBlockDB,
+	}
+}
+
+// BelowLatest returns the header at the given threshold below the latest sealed and executed block.
+func (l *LatestSealedAndExecuted) BelowLatest(threshold uint64) (*flow.Header, error) {
+
+	minHeight := l.root.Height + threshold
+	latest, err := l.Latest()
+	if err != nil {
+		return nil, err
+	}
+
+	if minHeight > latest.Height {
+		return l.root, nil
+	}
+
+	height := latest.Height - threshold
+	return l.state.AtHeight(height).Head()
+}
+
+// Latest returns the latest sealed and executed block.
+func (l *LatestSealedAndExecuted) Latest() (*flow.Header, error) {
+	height, err := LatestSealedAndExecutedHeight(l.state, l.executedBlockDB)
+	if err != nil {
+		return nil, err
+	}
+
+	header, err := l.state.AtHeight(height).Head()
+	if err != nil {
+		return nil, err
+	}
+
+	return header, nil
+}
+
+// LatestSealedAndExecutedHeight returns the height of the latest sealed and executed block.
+func LatestSealedAndExecutedHeight(state protocol.State, db *badger.DB) (uint64, error) {
+	lastSealed, err := state.Sealed().Head()
+	if err != nil {
+		return 0, err
+	}
+
+	var blockID flow.Identifier
+	var lastExecuted uint64
+	err = db.View(procedure.GetLastExecutedBlock(&lastExecuted, &blockID))
+	if err != nil {
+		return 0, err
+	}
+
+	// the last sealed executed is min(last_sealed, last_executed)
+	if lastExecuted < lastSealed.Height {
+		return lastExecuted, nil
+	}
+	return lastSealed.Height, nil
+}