[ETCM-186] Fix strict pick

src/main/scala/io/iohk/ethereum/blockchain/sync/regular/BlockFetcherState.scala

@@ -8,7 +8,6 @@ import io.iohk.ethereum.network.{Peer, PeerId}
 import io.iohk.ethereum.network.p2p.messages.PV62.BlockHash
 import BlockFetcherState._
 import cats.syntax.either._
-import cats.syntax.option._
 
 import scala.collection.immutable.Queue
 
@@ -110,11 +109,14 @@ case class BlockFetcherState(
   def strictPickBlocks(from: BigInt, atLeastWith: BigInt): Option[(NonEmptyList[Block], BlockFetcherState)] = {
     val lower = from.min(atLeastWith)
     val upper = from.max(atLeastWith)
-    readyBlocks.some
-      .filter(_.headOption.exists(block => block.number <= lower))
-      .filter(_.lastOption.exists(block => block.number >= upper))
-      .filter(_.nonEmpty)
-      .map(blocks => (NonEmptyList(blocks.head, blocks.tail.toList), copy(readyBlocks = Queue())))
+
+    val readyBlocksAfterLower = readyBlocks.dropWhile( _.number < lower)
+
+    val amount: Int = (upper - lower + 1).toInt
+    val (strickedPickedBlock, readyBlocksAfterUpper) = readyBlocksAfterLower.splitAt(amount)
+    NonEmptyList.fromList(strickedPickedBlock.toList).map { nelStrickedPickedBlock =>
+      (nelStrickedPickedBlock, copy(readyBlocks = readyBlocksAfterUpper))
+    }
   }
 
   def invalidateBlocksFrom(nr: BigInt): (Option[PeerId], BlockFetcherState) = invalidateBlocksFrom(nr, Some(nr))