osem-fcy/db/migrate/20140701123203_add_events_per_week_to_conference.rb

class AddEventsPerWeekToConference < ActiveRecord::Migration
  class TempVersion < ActiveRecord::Base
    self.table_name = 'versions'
    serialize :object_changes, HashWithIndifferentAccess
  end

  class TempEvent < ActiveRecord::Base
    self.table_name = 'events'
  end

  class TempConference < ActiveRecord::Base
    self.table_name = 'conferences'
    serialize :events_per_week, Hash
  end

  def up
    add_column :conferences, :events_per_week, :text
    TempConference.reset_column_information

    TempVersion.where(item_type: 'Event').each do |event_version|
      event = TempEvent.find_by_id(event_version.item_id)
      if event
        conference = TempConference.find_by_id(event.conference_id)
        if conference
        week = event_version.created_at.end_of_week

        no_events = {
            new: 0,
            withdrawn: 0,
            unconfirmed: 0,
            confirmed: 0,
            canceled: 0,
            rejected: 0,
        }

        if !conference.events_per_week
          conference.events_per_week = {
              week => no_events
          }
        elsif !conference.events_per_week[week]
          conference.events_per_week[week] = no_events
        end

        if event_version.object_changes &&
            event_version.event == 'create'

          # Increment the new state
          conference.events_per_week[week][:new] += 1
        elsif event_version.object_changes &&
            event_version.object_changes[:state]

          prev_state = event_version.object_changes[:state][0].to_sym
          next_state = event_version.object_changes[:state][1].to_sym

          # Backward compatibility: deprecated state :review now :new
          if prev_state == :review
            prev_state = :new
          elsif  next_state == :review
            next_state = :new
          end

          # Increment the next state
          conference.events_per_week[week][next_state] += 1

          # Decrement the previous state
          conference.events_per_week[week][prev_state] -= 1
        end
        conference.save
        end
      end
    end

    # Cumulate the previous weeks to get a snapshot
    TempConference.all.each do |conference|
      hash = conference.events_per_week.sort.to_h
      previous = nil

      hash.each do |week, values|
        if previous
          values.each do |state, _value|
            hash[week][state] += previous[state]
          end
        end
        previous = values
      end
      conference.events_per_week = hash
      conference.save
    end
  end

  def down
    remove_column :conferences, :events_per_week
  end
end