module.exports = function() {
  this.processSubredditSidebar = (subreddit, redis, fetch, RedditAPI) => {
    return new Promise(resolve => {
      (async () => {
        if(subreddit && !subreddit.includes('+')) {
          let key = `${subreddit}:sidebar`
          redis.get(key, (error, json) => {
            if(error) {
              console.error(`Error getting the ${subreddit}:sidebar key from redis.`, error)
              resolve(null)
            }
            if(json) {
              json = JSON.parse(json)
              let obj = {
                title: json.data.title,
                public_description_html: json.data.public_description_html,
                active_user_count: json.data.active_user_count,
                subscribers: json.data.subscribers,
                created_utc: json.data.created_utc,
                over18: json.data.over18,
                description_html: json.data.description_html
              }
              resolve(obj)
            } else {
              fetch(`https://oauth.reddit.com/r/${subreddit}/about`, redditApiGETHeaders())
              .then(result => {
                if(result.status === 200) {
                  result.json()
                  .then(json => {
                    redis.setex(key, config.setexs.sidebar, JSON.stringify(json), (error) => {
                      if(error) {
                        console.error('Error setting the sidebar key to redis.', error)
                        return res.render('index', { json: null, user_preferences: req.cookies })
                      } else {
                        console.log('Fetched the sidebar from reddit API.');
                        (async () => {
                          let obj = {
                            title: json.data.title,
                            public_description_html: json.data.public_description_html,
                            active_user_count: json.data.active_user_count,
                            subscribers: json.data.subscribers,
                            created_utc: json.data.created_utc,
                            over18: json.data.over18,
                            description_html: json.data.description_html
                          }
                          resolve(obj)
                        })()
                      }
                    })
                  })
                } else {
                console.error(`Something went wrong while fetching data from reddit API. ${result.status} – ${result.statusText}`)
                console.error(config.reddit_api_error_text)
                resolve(null)
                }
              }).catch(error => {
                console.error('Error fetching the sidebar.', error)
                resolve(null)
              })
            }
          })
        } else {
          resolve(null)
        }
      })()
    })
  }
}