Adjust the Difficulty in MineBlock

block.js

@@ -16,14 +16,15 @@ class Block {
   }
 
   static mineBlock({ lastBlock, data }) {
-    let hash, timestamp;
     const lastHash = lastBlock.hash;
-    const { difficulty } = lastBlock;
+    let hash, timestamp;
+    let { difficulty } = lastBlock;
     let nonce = 0;
 
     do {
       nonce++;
       timestamp = Date.now();
+      difficulty = Block.adjustDifficulty({ originalBlock: lastBlock, timestamp });
       hash = cryptoHash(timestamp, lastHash, data, nonce, difficulty);
     } while (hash.substring(0, difficulty) !== '0'.repeat(difficulty));
 
@@ -33,6 +34,8 @@ class Block {
   static adjustDifficulty({ originalBlock, timestamp }) {
     const { difficulty } = originalBlock;
 
+    if (difficulty < 1) return 1;
+
     if ((timestamp - originalBlock.timestamp) > MINE_RATE) return difficulty - 1;
 
     return difficulty + 1;

block.test.js

@@ -70,6 +70,12 @@ describe('Block', () => {
       expect(minedBlock.hash.substring(0, minedBlock.difficulty))
         .toEqual('0'.repeat(minedBlock.difficulty));
     });
+
+    it('adjusts the difficulty', () => {
+      const possibleResults = [lastBlock.difficulty+1, lastBlock.difficulty-1];
+
+      expect(possibleResults.includes(minedBlock.difficulty)).toBe(true);
+    });
   });
 
   describe('adjustDifficulty()', () => {
@@ -86,5 +92,11 @@ describe('Block', () => {
         timestamp: block.timestamp + MINE_RATE + 100
       })).toEqual(block.difficulty-1);
     });
+
+    it('has a lower limit of 1', () => {
+      block.difficulty = -1;
+
+      expect(Block.adjustDifficulty({ originalBlock: block })).toEqual(1);
+    });
   });
 });