server: Allow to retrieve the latest block

server/app/com/xsn/explorer/data/BlockDataHandler.scala

@@ -13,6 +13,8 @@ trait BlockDataHandler[F[_]] {
   def getBy(blockhash: Blockhash): F[Block]
 
   def delete(blockhash: Blockhash): F[Block]
+
+  def getLatestBlock(): F[Block]
 }
 
 trait BlockBlockingDataHandler extends BlockDataHandler[ApplicationResult]

server/app/com/xsn/explorer/data/anorm/BlockPostgresDataHandler.scala

@@ -31,4 +31,9 @@ class BlockPostgresDataHandler @Inject() (
     val maybe = blockPostgresDAO.delete(blockhash)
     Or.from(maybe, One(BlockNotFoundError))
   }
+
+  override def getLatestBlock(): ApplicationResult[Block] = database.withConnection { implicit conn =>
+    val maybe = blockPostgresDAO.getLatestBlock
+    Or.from(maybe, One(BlockNotFoundError))
+  }
 }

server/app/com/xsn/explorer/data/anorm/dao/BlockPostgresDAO.scala

@@ -83,4 +83,16 @@ class BlockPostgresDAO {
       "hash" -> blockhash.string
     ).as(parseBlock.singleOpt).flatten
   }
+
+  def getLatestBlock(implicit conn: Connection): Option[Block] = {
+    SQL(
+      """
+        |SELECT hash, previous_blockhash, next_blockhash, tpos_contract, merkle_root, size,
+        |       height, version, time, median_time, nonce, bits, chainwork, difficulty
+        |FROM blocks
+        |ORDER BY height DESC
+        |LIMIT 1
+      """.stripMargin
+    ).as(parseBlock.singleOpt).flatten
+  }
 }

server/test/com/xsn/explorer/data/BlockPostgresDataHandlerSpec.scala

@@ -72,6 +72,35 @@ class BlockPostgresDataHandlerSpec extends PostgresDataHandlerSpec {
     }
   }
 
+  "getLatestBlock" should {
+    "return the block" in {
+      clearDatabase()
+
+      val block0 = BlockLoader.get("00000c822abdbb23e28f79a49d29b41429737c6c7e15df40d1b1f1b35907ae34")
+      val block1 = BlockLoader.get("000003fb382f6892ae96594b81aa916a8923c70701de4e7054aac556c7271ef7")
+      val block2 = BlockLoader.get("000004645e2717b556682e3c642a4c6e473bf25c653ff8e8c114a3006040ffb8")
+
+      List(block1, block2, block0).foreach(dataHandler.create)
+
+      val result = dataHandler.getLatestBlock()
+      result.isGood mustEqual true
+      matches(block2, result.get)
+    }
+
+    "fail on no blocks" in {
+      clearDatabase()
+
+      val result = dataHandler.getLatestBlock()
+      result mustEqual Bad(BlockNotFoundError).accumulating
+    }
+  }
+
+  private def clearDatabase() = {
+    database.withConnection { implicit conn =>
+      _root_.anorm.SQL("""DELETE FROM blocks""").execute()
+    }
+  }
+
   private def matches(expected: Block, result: Block) = {
     // NOTE: transactions and confirmations are not matched intentionally
     result.hash mustEqual expected.hash

server/test/resources/blocks/000003fb382f6892ae96594b81aa916a8923c70701de4e7054aac556c7271ef7

@@ -0,0 +1,19 @@
+{
+  "hash": "000003fb382f6892ae96594b81aa916a8923c70701de4e7054aac556c7271ef7",
+  "confirmations": 44905,
+  "size": 179,
+  "height": 1,
+  "version": 536870912,
+  "merkleroot": "024aba1d535cfe5dd3ea465d46a828a57b00e1df012d7a2d158e0f7484173f7c",
+  "tx": [
+    "024aba1d535cfe5dd3ea465d46a828a57b00e1df012d7a2d158e0f7484173f7c"
+  ],
+  "time": 1520276270,
+  "mediantime": 1520276270,
+  "nonce": 167906,
+  "bits": "1e0ffff0",
+  "difficulty": 0.000244140625,
+  "chainwork": "0000000000000000000000000000000000000000000000000000000000200020",
+  "previousblockhash": "00000c822abdbb23e28f79a49d29b41429737c6c7e15df40d1b1f1b35907ae34",
+  "nextblockhash": "000004645e2717b556682e3c642a4c6e473bf25c653ff8e8c114a3006040ffb8"
+}

server/test/resources/blocks/00000c822abdbb23e28f79a49d29b41429737c6c7e15df40d1b1f1b35907ae34

@@ -0,0 +1,18 @@
+{
+  "hash": "00000c822abdbb23e28f79a49d29b41429737c6c7e15df40d1b1f1b35907ae34",
+  "confirmations": 44906,
+  "size": 274,
+  "height": 0,
+  "version": 1,
+  "merkleroot": "922ab2360f766457416dfc59c6594248c5b79e33c8785bce491c0e01930738f6",
+  "tx": [
+    "922ab2360f766457416dfc59c6594248c5b79e33c8785bce491c0e01930738f6"
+  ],
+  "time": 1520274471,
+  "mediantime": 1520274471,
+  "nonce": 627829,
+  "bits": "1e0ffff0",
+  "difficulty": 0.000244140625,
+  "chainwork": "0000000000000000000000000000000000000000000000000000000000100010",
+  "nextblockhash": "000003fb382f6892ae96594b81aa916a8923c70701de4e7054aac556c7271ef7"
+}