educoder/app/services/attendance_statistics_service.rb

class AttendanceStatisticsService < ApplicationService

  attr_reader :attendances, :member_attendances

  def initialize(attendances, member_attendances)
    @attendances   = attendances
    @member_attendances = member_attendances
  end

  def call
    all_normal_rate = []
    all_absence_rate = []
    all_leave_rate = []

    history_attendances = []

    attendances.each do |attendance|
      normal_count = history_member_count(member_attendances, "NORMAL", attendance.id)
      absence_count = history_member_count(member_attendances, "ABSENCE", attendance.id)
      leave_count = history_member_count(member_attendances, "LEAVE", attendance.id)
      all_count = member_attendances.select{|member_attendance| member_attendance.course_attendance_id == attendance.id}.size

      normal_rate = all_count == 0 ? 1 : cal_rate(normal_count, all_count)
      all_normal_rate << normal_rate
      absence_rate = cal_rate(absence_count, all_count)
      all_absence_rate << absence_rate
      leave_rate =  cal_rate(leave_count, all_count)
      all_leave_rate << leave_rate

      history_attendances << {name: attendance.name, attendance_date: attendance.attendance_date.strftime("%Y-%m-%d"),
                              start_time: attendance.start_time.strftime("%H:%M"), end_time: attendance.end_time.strftime("%H:%M"),
                              normal_rate: normal_rate, absence_rate: absence_rate, leave_rate: leave_rate}
    end

    all_history_count = history_attendances.size
    history_attendances = history_attendances[0..9].reverse
    avg_normal_rate = all_history_count == 0 ? 1 : cal_rate(all_normal_rate.sum, all_history_count)
    avg_absence_rate = cal_rate(all_absence_rate.sum, all_history_count)
    avg_leave_rate = cal_rate(all_leave_rate.sum, all_history_count)

    {all_history_count: all_history_count, history_attendances: history_attendances, avg_normal_rate: avg_normal_rate,
     avg_absence_rate: avg_absence_rate, avg_leave_rate: avg_leave_rate}
  end

  private

  def history_member_count member_attendances, status, attendance_id
    member_attendances.select{|member_attendance| member_attendance.attendance_status == status && member_attendance.course_attendance_id == attendance_id}.size
  end

  def cal_rate base, sum
    sum == 0 ? 0 : (base.to_f / sum)
  end
end