Extract common functions from EthHasBlockMiner (#8)

The EthHashBlockMiner contains both the generic mining capabilities
and the EthHash JSON specific API.

The generic capabilities have been extracted into a base class which
can be reused for Clique (or other) consensus mechanisms.
Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/blockcreation/BlockMiner.java

@@ -24,19 +24,20 @@ import org.apache.logging.log4j.Logger;
  * <p>This class is responsible for mining a single block only - the AbstractBlockCreator maintains
  * state so must be destroyed between block mining activities.
  */
-public class BlockMiner<C> implements Runnable {
+public class BlockMiner<C, M extends AbstractBlockCreator<C>> implements Runnable {
 
   private static final Logger LOG = LogManager.getLogger();
 
-  private final AbstractBlockCreator<C> blockCreator;
-  private final ProtocolContext<C> protocolContext;
+  protected final M blockCreator;
+  protected final ProtocolContext<C> protocolContext;
+  protected final BlockHeader parentHeader;
+
   private final ProtocolSchedule<C> protocolSchedule;
   private final Subscribers<MinedBlockObserver> observers;
   private final AbstractBlockScheduler scheduler;
-  private final BlockHeader parentHeader;
 
   public BlockMiner(
-      final AbstractBlockCreator<C> blockCreator,
+      final M blockCreator,
       final ProtocolSchedule<C> protocolSchedule,
       final ProtocolContext<C> protocolContext,
       final Subscribers<MinedBlockObserver> observers,
@@ -67,13 +68,13 @@ public class BlockMiner<C> implements Runnable {
     }
   }
 
-  private boolean mineBlock() throws InterruptedException {
+  protected boolean mineBlock() throws InterruptedException {
     // Ensure the block is allowed to be mined - i.e. the timestamp on the new block is sufficiently
     // ahead of the parent, and still within allowable clock tolerance.
-    LOG.trace("Waiting for next block timestamp to be valid.");
+    LOG.trace("Started a mining operation.");
     long newBlockTimestamp = scheduler.waitUntilNextBlockCanBeMined(parentHeader);
 
-    LOG.trace("Started a mining operation.");
+    LOG.trace("Mining a new block with timestamp {}", newBlockTimestamp);
     Block block = blockCreator.createBlock(newBlockTimestamp);
     LOG.info(
         "Block created, importing to local chain, block includes {} transactions",

ethereum/core/src/main/java/net/consensys/pantheon/ethereum/blockcreation/EthHashBlockMiner.java

@@ -18,9 +18,7 @@ import java.util.Optional;
  * <p>All other aspects of mining (i.e. pre-block delays, block creation and importing to the chain)
  * are all conducted by the parent class.
  */
-public class EthHashBlockMiner extends BlockMiner<Void> {
-
-  private final EthHashBlockCreator blockCreator;
+public class EthHashBlockMiner extends BlockMiner<Void, EthHashBlockCreator> {
 
   public EthHashBlockMiner(
       final EthHashBlockCreator blockCreator,
@@ -30,7 +28,6 @@ public class EthHashBlockMiner extends BlockMiner<Void> {
       final AbstractBlockScheduler scheduler,
       final BlockHeader parentHeader) {
     super(blockCreator, protocolSchedule, protocolContext, observers, scheduler, parentHeader);
-    this.blockCreator = blockCreator;
   }
 
   public Optional<EthHashSolverInputs> getWorkDefinition() {