Write the Genesis block in the BlockStorage

Move the loading code into a separate load() method,
and get rid of the empty() method.

Loading should ideally never be done in the constructor.
Additionally, this ensures the block storage is in charge
of adding the hardcoded genesis block to the storage.

The load() method can be used by the Ledger to make sure
UTXOs are tracked when the block storage was empty on boot.

Fixes #286

source/agora/node/BlockStorage.d

@@ -46,12 +46,18 @@ public interface IBlockStorage
 
     /***************************************************************************
 
+        Load the block storage. If there was nothing to load,
+        a Genesis block will be added to the ledger. In this case the calling
+        code should treat the block as new and update the set of UTXOs, etc.
+
+        If the blockchain data is corrupt the application will be halted.
+
         Returns:
-            true if the storage is empty (height index was not loaded)
+            true if the blockchain was loaded from storage
 
     ***************************************************************************/
 
-    public bool isEmpty ();
+    public bool load ();
 
     /***************************************************************************
 
@@ -188,21 +194,32 @@ public class BlockStorage : IBlockStorage
 
         if (!this.path.exists)
             mkdirRecurse(this.path);
-
-        if (!this.loadAllIndexes())
-            assert(0);
     }
 
     /***************************************************************************
 
+        Load the blockchain from the storage
+
         Returns:
-            true if the storage is empty (height index was not loaded)
+            true if the blockchain was loaded from storage
 
     ***************************************************************************/
 
-    public bool isEmpty ()
+    public bool load ()
     {
-        return this.height_idx.length == 0;
+        if (!this.loadAllIndexes())
+            assert(0);
+
+        // Add Genesis if the storage is empty
+        if (this.height_idx.length == 0)
+        {
+            if (!this.saveBlock(GenesisBlock))
+                assert(0);
+
+            return false;
+        }
+
+        return true;
     }
 
     /***************************************************************************
@@ -962,14 +979,17 @@ public class MemBlockStorage : IBlockStorage
 
     /***************************************************************************
 
+        Adds the genesis block to the in-memory blockchain storage.
+
         Returns:
-            true if the storage is empty (height index was not loaded)
+            false as the storage was empty before the genesis block was added
 
     ***************************************************************************/
 
-    public bool isEmpty ()
+    public bool load ()
     {
-        return this.height_idx.length == 0;
+        this.saveBlock(GenesisBlock);
+        return false;
     }
 
     /***************************************************************************

source/agora/node/Ledger.d

@@ -47,13 +47,7 @@ public class Ledger
     {
         this.pool = pool;
         this.storage = storage;
-
-        // add the genesis block
-        if (this.storage.isEmpty())
-        {
-            this.storage.saveBlock(GenesisBlock);
-            assert(!this.storage.isEmpty());  // sanity check
-        }
+        this.storage.load();
 
         // ensure latest checksum can be read
         if (!this.storage.readLastBlock(this.last_block))