server: Remove the FirstBlockSynchronizerTask

The same job can be done by the BackwardsSynchronizerTask, there is no
need to keep both.

server/app/com/xsn/explorer/tasks/FirstBlockSynchronizerTask.scala

@@ -1,124 +0,0 @@
-package com.xsn.explorer.tasks
-
-import javax.inject.{Inject, Singleton}
-
-import com.alexitc.playsonify.core.FutureApplicationResult
-import com.alexitc.playsonify.core.FutureOr.Implicits.{FutureListOps, FutureOps, OrOps}
-import com.xsn.explorer.data.DatabaseSeeder
-import com.xsn.explorer.data.async.{BlockFutureDataHandler, DatabaseFutureSeeder}
-import com.xsn.explorer.errors.BlockNotFoundError
-import com.xsn.explorer.models.{Blockhash, Height}
-import com.xsn.explorer.services.{TransactionService, XSNService}
-import org.scalactic.{Bad, Good, One, Or}
-import org.slf4j.LoggerFactory
-
-import scala.concurrent.ExecutionContext.Implicits.global
-import scala.concurrent.Future
-import scala.util.control.NonFatal
-
-/**
- * The database might start to be filled from a block different to the genesis one.
- *
- * This task helps to sync it from the first saved block backwards to the genesis one.
- */
-@Singleton
-class FirstBlockSynchronizerTask @Inject() (
-    xsnService: XSNService,
-    transactionService: TransactionService,
-    blockDataHandler: BlockFutureDataHandler,
-    databaseSeeder: DatabaseFutureSeeder) {
-
-  private val logger = LoggerFactory.getLogger(this.getClass)
-  private val lock = new Object
-
-  /**
-   * TODO: Until https://github.com/X9Developers/XSN/issues/32 is fixed, ignore the genesis block.
-   */
-  private val FirstBlockHeight = Height(1)
-
-  private var running = false
-
-  def sync(): Unit = {
-    if (running) {
-      ()
-    } else {
-      lock.synchronized {
-        if (running) {
-          ()
-        } else {
-          running = true
-
-          tryToSync().onComplete { _ =>
-            running = false
-          }
-        }
-      }
-    }
-  }
-
-  private def tryToSync() = {
-    val futureOr = for {
-      firstBlock <- blockDataHandler.getFirstBlock().toFutureOr
-      previous <- Or.from(firstBlock.previousBlockhash, One(BlockNotFoundError)).toFutureOr
-      _ <- {
-        if (firstBlock.height == FirstBlockHeight) {
-          // no sync required
-          Future.successful(Good(()))
-        } else {
-          // sync
-          logger.info(s"Sync required until block ${firstBlock.height.int}")
-          val r = doSync(previous)
-
-          r.foreach {
-            case Good(_) =>
-              logger.info("Sync completed")
-            case _ => ()
-          }
-
-          r
-        }
-      }.toFutureOr
-    } yield ()
-
-    val result = futureOr.toFuture
-
-    result.foreach {
-      case Bad(errors) =>
-        logger.error(s"Failed to sync blocks, errors = $errors")
-
-      case _ => ()
-    }
-
-    result.recover {
-      case NonFatal(ex) =>
-        logger.error(s"Failed to sync blocks", ex)
-    }
-
-    result
-  }
-
-  private def doSync(blockhash: Blockhash): FutureApplicationResult[Unit] = {
-    val result = for {
-      block <- xsnService.getBlock(blockhash).toFutureOr
-      transactions <- block.transactions.map(transactionService.getTransaction).toFutureOr
-
-      command = DatabaseSeeder.CreateBlockCommand(block, transactions)
-      _ <- databaseSeeder.newBlock(command).toFutureOr
-      _ = logger.debug(s"Block ${block.height.int} saved")
-
-      _ <- block
-            .previousBlockhash
-            .filter(_ => block.height.int > FirstBlockHeight.int)
-            .map { previous =>
-              doSync(previous)
-            }
-            .getOrElse {
-              logger.debug(s"No more blocks to sync")
-              Future.successful(Good(()))
-            }
-            .toFutureOr
-    } yield ()
-
-    result.toFuture
-  }
-}

server/app/com/xsn/explorer/tasks/SQSSeederTask.scala

@@ -22,7 +22,6 @@ import scala.util.{Failure, Success}
 class SQSSeederTask @Inject() (
     config: SeederConfig,
     blockEventsProcessor: BlockEventsProcessor,
-    firstBlockSynchronizerTask: FirstBlockSynchronizerTask,
     backwardsSynchronizerTask: BackwardsSynchronizerTask)(
     implicit sqs: AmazonSQSAsync,
     materializer: Materializer) {
@@ -92,14 +91,12 @@ class SQSSeederTask @Inject() (
   }
 
   private def onBlockResult(eventResult: BlockEventsProcessor.Result) = eventResult match {
-    case BlockEventsProcessor.FirstBlockCreated(_) =>
-      firstBlockSynchronizerTask.sync()
+    case BlockEventsProcessor.FirstBlockCreated(block) =>
+      backwardsSynchronizerTask.sync(block)
 
-    case BlockEventsProcessor.NewBlockAppended(_) =>
-      firstBlockSynchronizerTask.sync()
+    case BlockEventsProcessor.NewBlockAppended(_) => ()
 
     case BlockEventsProcessor.RechainDone(_, newBlock) =>
-      firstBlockSynchronizerTask.sync()
       backwardsSynchronizerTask.sync(newBlock)
 
     case BlockEventsProcessor.MissingBlockProcessed(block) =>