feat(article): implement article read time

Extended the article model to include timeToRead column. Calculate time
to read article then save article.

- Add calculateTimeToRead helper method
- Add pre save hook
- include relevant tests

server/migrations/20180911074956-article-add-time-to-read-column.js

@@ -0,0 +1,18 @@
+module.exports = {
+  up: (queryInterface, Sequelize) => {
+    return queryInterface.addColumn(
+      'Articles',
+      'timeToRead',
+      {
+        type: Sequelize.INTEGER,
+      },
+    );
+  },
+
+  down: (queryInterface) => {
+    return queryInterface.removeColumn(
+      'Articles',
+      'timeToRead',
+    );
+  }
+};

server/models/article.js

@@ -1,3 +1,5 @@
+import calculateTimeToRead from '../utils/calculateTimeToRead';
+
 module.exports = (sequelize, DataTypes) => {
   const Article = sequelize.define('Article', {
     title: {
@@ -18,8 +20,15 @@ module.exports = (sequelize, DataTypes) => {
       type: DataTypes.INTEGER,
       allowNull: false,
     },
-    likeDislikeId: DataTypes.INTEGER
-  }, {});
+    likeDislikeId: DataTypes.INTEGER,
+    timeToRead: DataTypes.INTEGER,
+  }, {
+    hooks: {
+      beforeCreate: (articleData) => {
+        articleData.timeToRead = calculateTimeToRead(articleData);
+      }
+    }
+  });
 
   Article.associate = (models) => {
     const { Comment } = models;

server/tests/index.js

@@ -3,3 +3,4 @@ import './middleware/auth.test';
 import './routes/index';
 import './utils/token.test';
 import './models/index';
+import './utils/calculateTimeToRead.test';

server/tests/utils/calculateTimeToRead.test.js

@@ -0,0 +1,13 @@
+import { expect } from 'chai';
+import calculateTimeToRead from '../../utils/calculateTimeToRead';
+
+describe('calculateTimeToRead', () => {
+  it('should calculate time to read an article', () => {
+    const article = {
+      body: 'Some short article',
+    };
+
+    const timeToRead = calculateTimeToRead(article);
+    expect(timeToRead).to.be.a('number');
+  });
+});

server/utils/calculateTimeToRead.js

@@ -0,0 +1,17 @@
+/**
+ * calculates time to read an article
+ *
+ * @param {string} article
+ * @returns {number} timeToRead - time it takes to read an article
+ */
+const calculateTimeToRead = (article) => {
+  const averageReadSpeed = 265; // words per minute
+
+  // get article word count
+  const articleWordCount = article.body.split(' ').length;
+  const timeToRead = articleWordCount / averageReadSpeed;
+
+  return Math.ceil(timeToRead);
+};
+
+export default calculateTimeToRead;