From 3bcb0426c3e021c86856f3e71cdd76992a824973 Mon Sep 17 00:00:00 2001
From: Patrick Nagurny <patrick@bitpay.com>
Date: Fri, 4 Sep 2015 13:52:54 -0400
Subject: [PATCH] get block reward

---
 lib/blocks.js  | 17 ++++++++++++++++-
 test/blocks.js | 16 ++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/lib/blocks.js b/lib/blocks.js
index 7b862ae..30892e7 100644
--- a/lib/blocks.js
+++ b/lib/blocks.js
@@ -4,6 +4,7 @@ var common = require('./common');
 var async = require('async');
 var bitcore = require('bitcore');
 var BufferUtil = bitcore.util.buffer;
+var BN = bitcore.crypto.BN;
 
 function BlockController(node) {
   this.node = node;
@@ -52,7 +53,7 @@ BlockController.prototype.transformBlock = function(block, info) {
     chainwork: info.chainWork,
     previousblockhash: blockObj.header.prevHash,
     nextblockhash: null, // placeholder
-    reward: 0, // First output of first transaction gives us the reward + fees. How to isolate just reward?
+    reward: this.getBlockReward(info.height) / 1e8,
     isMainChain: true // placeholder
   }
 };
@@ -125,4 +126,18 @@ BlockController.prototype.list = function(req, res) {
   });
 };
 
+BlockController.prototype.getBlockReward = function(height) {
+  var halvings = Math.floor(height / 210000);
+  // Force block reward to zero when right shift is undefined.
+  if (halvings >= 64) {
+    return 0;
+  }
+
+  // Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
+  var subsidy = new BN(50 * 1e8);
+  subsidy = subsidy.shrn(halvings);
+  
+  return parseInt(subsidy.toString(10));
+};
+
 module.exports = BlockController;
\ No newline at end of file
diff --git a/test/blocks.js b/test/blocks.js
index 07ef4e3..77520f8 100644
--- a/test/blocks.js
+++ b/test/blocks.js
@@ -200,4 +200,20 @@ describe('Blocks', function() {
       blocks.blockIndex(req, res, next, height);
     });
   });
+
+  describe('#getBlockReward', function() {
+    var blocks = new BlockController({});
+
+    it('should give a block reward of 50 * 1e8 for block before first halvening', function() {
+      blocks.getBlockReward(100000).should.equal(50 * 1e8);
+    });
+
+    it('should give a block reward of 25 * 1e8 for block between first and second halvenings', function() {
+      blocks.getBlockReward(373011).should.equal(25 * 1e8);
+    });
+
+    it('should give a block reward of 12.5 * 1e8 for block between second and third halvenings', function() {
+      blocks.getBlockReward(500000).should.equal(12.5 * 1e8);
+    });
+  });
 });
\ No newline at end of file