app.js

const express = require('express')
const cors = require('cors')
const google = require('googleapis')
const openGraph = require('open-graph-scraper')

const config = require('./config.json')
const {
  client_email,
  private_key
} = require('./dropcap-service-credentials.json')
const { encodeHTML, getPagePath, combineAndStripURLs } = require('./util')

const TIMEOUT = 10000
const VIEWS = config.views
const app = express()
app.use(cors())

const queryTopArticles = (viewName, maxResults) => {
  return new Promise((resolve, reject) => {
    const scopes = ['https://www.googleapis.com/auth/analytics.readonly']
    const jwt = new google.auth.JWT(
      client_email,
      null,
      private_key,
      scopes,
      null
    )

    jwt.authorize(err => {
      if (err) reject(err)

      const {
        data: { ga }
      } = google.analytics('v3')
      ga.get(
        {
          auth: jwt,
          ids: VIEWS[viewName].id,
          metrics: 'ga:pageViews',
          // Custom dimension1 is used for authors
          dimensions: 'ga:pageTitle,ga:pagePath,ga:dimension1',
          'start-date': '7daysAgo',
          'end-date': 'today',
          sort: '-ga:pageViews',
          // Query twice the maximum number of results to remove duplicates
          'max-results': maxResults * 2,
          filters: getPagePath(VIEWS[viewName].blogSlug)
        },
        (err, response) => {
          if (err) return reject(err)
          if (!response.rows)
            return reject(`Empty GA API response for ${VIEWS[viewName].name}`)

          const topURLs = combineAndStripURLs(response.rows, maxResults)
          return resolve(urlDataAsJSON(topURLs, viewName))
        }
      )
    })
  })
}

const urlDataAsJSON = (urlList, viewName) => {
  return new Promise((resolve, reject) => {
    const result = []

    for (const item of urlList) {
      const canonicalURL = VIEWS[viewName].baseURL + item[1]
      mergeOGData(canonicalURL, item).then(
        data => {
          result.push(data)

          // Check for done conditions
          if (result.length === urlList.length) {
            result.sort((o1, o2) => o2.views - o1.views)
            return resolve({ result: result })
          }
        },
        err => reject(err)
      )
    }
  })
}

const mergeOGData = (canonicalURL, urlData) => {
  return new Promise((resolve, reject) => {
    const options = {
      url: canonicalURL,
      timeout: TIMEOUT,
      headers: { 'User-Agent': 'DP-Dropcap' }
    }
    openGraph(options, (err, results) => {
      if (err) return reject(results)

      // Combine the Analytics data with the article's OG data
      resolve({
        gaTitle: encodeHTML(urlData[0]),
        ogTitle: encodeHTML(results.data.ogTitle),
        path: urlData[1],
        authors: urlData[2].split(', '),
        views: urlData[3],
        // On older images, convert from the preview size to thumbnail
        image: results.data.ogImage.url.replace('p.', 't.')
      })
    })
  })
}

// There isn't a favicon; just to keep it from throwing errors
app.get('/favicon.ico', (req, res) => res.status(204))

app.get('/:view', (req, res) => {
  const view = req.params.view.toUpperCase()

  // If this view isn't in the config, don't try to query for it
  if (!VIEWS[view])
    return res.status(404).send({ error: `Unknown view ${view}` })

  // 10-minute browser cache, 30-minute public cache
  res.set('Cache-Control', 'public, max-age=600, s-maxage=1800')
  res.set('Access-Control-Allow-Origin', '*')
  res.set('Access-Control-Allow-Methods', 'GET')
  // identifier for SNWorks
  res.set('User-Agent', 'DP-Dropcap')

  queryTopArticles(view, 10)
    .then(data => res.send(data))
    .catch(err => {
      res.status(500).send({ error: err })
      throw err
    })
})

exports.dropcap = app