application_helper.rb

  def week_stat model
    period = 7
    table = model.name.tableize
    from = Time.now.utc.midnight - period.days

    query = <<-SQL
      select created_at as time, count(*) as count
      from #{table}
      where created_at > '#{from}'
      group by DAYOFWEEK(created_at)
    SQL

    w_stats = ActiveRecord::Base.connection.select(query)

    sparkline = []

    today = Time.now.utc

    0.upto(period) do |i|
      cur_day = today - i.day

      res = w_stats.select do |day|
        cur_day.beginning_of_day <= day['time'] && day['time'] <= cur_day.end_of_day
      end

      sparkline.push res.empty? ? 0 : res.first['count']
    end

    sparkline.reverse
  end