time_in_states.rb

class CreateTimeInStates < ActiveRecord::Migration[5.0]
  def up
    execute <<-SQL
      CREATE TYPE state_trackable_models AS ENUM ('AutoProcess', 'Partner');
    SQL

    create_table :time_in_states do |t|
      t.integer :state, null: false

      t.column :state_trackable_id,   :integer,                 null: false
      t.column :state_trackable_type, :state_trackable_models,  null: false

      t.datetime :begin_at, null: false
      t.datetime :end_at
    end

    add_index :time_in_states, [:state_trackable_type, :state_trackable_id], name: 'time_in_state_trackable_index'
  end
end

class TimeInState < ApplicationRecord
  belongs_to :state_trackable, polymorphic: true

  # Для вызова в цепочки
  # пример: auto_process.time_in_state.track_state
  def self.track_state
    owner = all.proxy_association.owner
    return false unless owner.present?

    if owner.state != last&.state
      current = Time.now
      update(end_at:   current) if last.present?
      create(begin_at: current, state: owner.state)
    end
  end
end

class AutoProcess < ApplicationRecord
  has_many :time_in_states, as: :state_trackable
end