class Card::Eventable::SystemCommenter
  attr_reader :card, :event

  def initialize(card, event)
    @card, @event = card, event
  end

  def comment
    return unless comment_body.present?

    if comment = find_replaceable_system_comment
      comment.update! body: comment_body
    else
      card.comments.create! creator: User.system, body: comment_body
    end
  end

  private
    REPLACEABLE_EVENTS = [
      %w(card_assigned card_unassigned),
      %w(card_staged card_unstaged),
      %w(card_due_date_added card_due_date_changed card_due_date_removed)
    ]

    def comment_body
      case event.action
        when "card_assigned"
          "Assigned to #{card.assignees.pluck(:name).to_sentence}."
        when "card_unassigned"
          if card.assignees.empty?
            "Unassigned from #{event.assignees.pluck(:name).to_sentence}."
          else
            "Assigned to #{card.assignees.pluck(:name).to_sentence}."
          end
        when "card_staged"
          "#{event.creator.name} moved this to '#{event.stage_name}'."
        when "card_closed"
          "Closed by #{ event.creator.name }"
        when "card_unstaged"
          "#{event.creator.name} removed this from '#{event.stage_name}'."
        when "card_due_date_added"
          "#{event.creator.name} set due date to #{event.particulars.dig('particulars', 'due_date').to_date.strftime('%B %-d')}."
        when "card_due_date_changed"
          "#{event.creator.name} changed due date to #{event.particulars.dig('particulars', 'due_date').to_date.strftime('%B %-d')}."
        when "card_due_date_removed"
          "#{event.creator.name} removed the date."
        when "card_title_changed"
          "#{event.creator.name} changed title from '#{event.particulars.dig('particulars', 'old_title')}' to '#{event.particulars.dig('particulars', 'new_title')}'."
      end
    end

    def find_replaceable_system_comment
      previous_comment, previous_event = card.comments.last, card.events[-2]
      if previous_comment&.creator&.system? && replaceable_event?(previous_event, event)
        previous_comment
      end
    end

    def replaceable_event?(candidate_event, replacement_event)
      candidate_event && replacement_event &&
        (candidate_event.action == replacement_event.action || REPLACEABLE_EVENTS.find { |related_actions| related_actions.include?(candidate_event.action) && related_actions.include?(replacement_event.action) })
    end
end