Add new progression game

Author: thedoorbell

bin/brain-progression.js

@@ -0,0 +1,5 @@
+#!/usr/bin/env node
+
+import run from '../src/games/progression.js';
+
+run();

src/games/progression.js

@@ -0,0 +1,22 @@
+import playGame from '../index.js';
+
+const rules = 'What number is missing in the progression?';
+
+const findNumberInProgression = () => {
+  const increasedBy = Math.floor(Math.random() * 10) + 1;
+  let progressionNumber = Math.floor(Math.random() * 50);
+  const progression = [progressionNumber];
+
+  for (let i = 1; i < 10; i += 1) {
+    progressionNumber += increasedBy;
+    progression.push(progressionNumber);
+  }
+
+  const position = Math.floor(Math.random() * 10);
+  const correctAnswer = progression[position];
+  progression[position] = '..';
+
+  return [progression.join(' '), String(correctAnswer)];
+};
+
+export default () => playGame(rules, findNumberInProgression);