Difficulty adjustment refactor

fixes #1157

backend/src/api/difficulty-adjustment.ts

@@ -0,0 +1,71 @@
+import config from '../config';
+import { IDifficultyAdjustment } from '../mempool.interfaces';
+import blocks from './blocks';
+
+class DifficultyAdjustmentApi {
+  constructor() { }
+
+  public getDifficultyAdjustment(): IDifficultyAdjustment {
+    const DATime = blocks.getLastDifficultyAdjustmentTime();
+    const previousRetarget = blocks.getPreviousDifficultyRetarget();
+    const blockHeight = blocks.getCurrentBlockHeight();
+    const blocksCache = blocks.getBlocks();
+    const latestBlock = blocksCache[blocksCache.length - 1];
+
+    const now = new Date().getTime() / 1000;
+    const diff = now - DATime;
+    const blocksInEpoch = blockHeight % 2016;
+    const progressPercent = (blocksInEpoch >= 0) ? blocksInEpoch / 2016 * 100 : 100;
+    const remainingBlocks = 2016 - blocksInEpoch;
+    const nextRetargetHeight = blockHeight + remainingBlocks;
+
+    let difficultyChange = 0;
+    if (remainingBlocks < 1870) {
+      if (blocksInEpoch > 0) {
+        difficultyChange = (600 / (diff / blocksInEpoch ) - 1) * 100;
+      }
+      if (difficultyChange > 300) {
+        difficultyChange = 300;
+      }
+      if (difficultyChange < -75) {
+        difficultyChange = -75;
+      }
+    }
+
+    const timeAvgDiff = difficultyChange * 0.1;
+
+    let timeAvgMins = 10;
+
+    if (timeAvgDiff > 0) {
+      timeAvgMins -= Math.abs(timeAvgDiff);
+    } else {
+      timeAvgMins += Math.abs(timeAvgDiff);
+    }
+
+    // Testnet difficulty is set to 1 after 20 minutes of no blockSize,
+    // therefore the time between blocks will always be below 20 minutes (1200s).
+    let timeOffset = 0;
+    if (config.MEMPOOL.NETWORK === 'testnet' && now - latestBlock.timestamp + timeAvgMins * 60 > 1200) {
+      timeOffset = -Math.min(now - latestBlock.timestamp, 1200) * 1000;
+      timeAvgMins = 20;
+    }
+
+    const timeAvg = timeAvgMins * 60 * 1000 ;
+    const remainingTime = (remainingBlocks * timeAvg) + (now * 1000);
+    const estimatedRetargetDate = remainingTime + now;
+
+    return {
+      progressPercent,
+      difficultyChange,
+      estimatedRetargetDate,
+      remainingBlocks,
+      remainingTime,
+      previousRetarget,
+      nextRetargetHeight,
+      timeAvg,
+      timeOffset,
+    };
+  }
+}
+
+export default new DifficultyAdjustmentApi();