[NOD-1418] Implement DAG Traversal (#953)

* Implement DAG Traversal

* Update the DAGTraversalManager interface

domain/consensus/model/interface_processes_dagtraversalmanager.go

@@ -6,6 +6,6 @@ import "github.com/kaspanet/kaspad/domain/consensus/model/externalapi"
 // in the DAG
 type DAGTraversalManager interface {
 	HighestChainBlockBelowBlueScore(highHash *externalapi.DomainHash, blueScore uint64) (*externalapi.DomainHash, error)
-	SelectedParentIterator(highHash *externalapi.DomainHash) (SelectedParentIterator, error)
+	SelectedParentIterator(highHash *externalapi.DomainHash) SelectedParentIterator
 	BlueWindow(highHash *externalapi.DomainHash, windowSize uint64) ([]*externalapi.DomainHash, error)
 }

domain/consensus/processes/dagtraversalmanager/dagtraversalmanager.go

@@ -1,6 +1,7 @@
 package dagtraversalmanager
 
 import (
+	"fmt"
 	"github.com/kaspanet/kaspad/domain/consensus/model"
 	"github.com/kaspanet/kaspad/domain/consensus/model/externalapi"
 )
@@ -14,6 +15,29 @@ type dagTraversalManager struct {
 	ghostdagDataStore  model.GHOSTDAGDataStore
 }
 
+// selectedParentIterator implements the `model.SelectedParentIterator` API
+type selectedParentIterator struct {
+	databaseContext   model.DBReader
+	ghostdagDataStore model.GHOSTDAGDataStore
+	current           *externalapi.DomainHash
+}
+
+func (spi *selectedParentIterator) Next() bool {
+	if spi.current == nil {
+		return false
+	}
+	ghostdagData, err := spi.ghostdagDataStore.Get(spi.databaseContext, spi.current)
+	if err != nil {
+		panic(fmt.Sprintf("ghostdagDataStore is missing ghostdagData for: %v. '%s' ", spi.current, err))
+	}
+	spi.current = ghostdagData.SelectedParent
+	return spi.current != nil
+}
+
+func (spi *selectedParentIterator) Get() *externalapi.DomainHash {
+	return spi.current
+}
+
 // New instantiates a new DAGTraversalManager
 func New(
 	databaseContext model.DBReader,
@@ -28,8 +52,12 @@ func New(
 
 // SelectedParentIterator creates an iterator over the selected
 // parent chain of the given highHash
-func (dtm *dagTraversalManager) SelectedParentIterator(highHash *externalapi.DomainHash) (model.SelectedParentIterator, error) {
+func (dtm *dagTraversalManager) SelectedParentIterator(highHash *externalapi.DomainHash) model.SelectedParentIterator {
-	return nil, nil
+	return &selectedParentIterator{
+		databaseContext:   dtm.databaseContext,
+		ghostdagDataStore: dtm.ghostdagDataStore,
+		current:           highHash,
+	}
 }
 
 // HighestChainBlockBelowBlueScore returns the hash of the
@@ -37,5 +65,28 @@ func (dtm *dagTraversalManager) SelectedParentIterator(highHash *externalapi.Dom
 // blueScore in the block with the given highHash's selected
 // parent chain
 func (dtm *dagTraversalManager) HighestChainBlockBelowBlueScore(highHash *externalapi.DomainHash, blueScore uint64) (*externalapi.DomainHash, error) {
-	return nil, nil
+
+	blockHash := highHash
+	chainBlock, err := dtm.ghostdagDataStore.Get(dtm.databaseContext, highHash)
+	if err != nil {
+		return nil, err
+	}
+	if chainBlock.BlueScore < blueScore { // will practically return genesis.
+		blueScore = chainBlock.BlueScore
+	}
+
+	requiredBlueScore := chainBlock.BlueScore - blueScore
+
+	// If we used `SelectedParentIterator` we'd need to do more calls to `ghostdagDataStore` so we can get the blueScore
+	for chainBlock.BlueScore >= requiredBlueScore {
+		if chainBlock.SelectedParent == nil { // genesis
+			return blockHash, nil
+		}
+		blockHash = chainBlock.SelectedParent
+		chainBlock, err = dtm.ghostdagDataStore.Get(dtm.databaseContext, highHash)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return blockHash, nil
 }