module PaperTrail
  module Cleaner
    # Destroys all but the most recent version(s) for items on a given date
    # (or on all dates). Useful for deleting drafts.
    #
    # Options:
    #
    # - :keeping - An `integer` indicating the number of versions to be kept for
    #   each item per date. Defaults to `1`. The most recent matching versions
    #   are kept.
    # - :date - Should either be a `Date` object specifying which date to
    #   destroy versions for or `:all`, which will specify that all dates
    #   should be cleaned. Defaults to `:all`.
    # - :item_id - The `id` for the item to be cleaned on, or `nil`, which
    #   causes all items to be cleaned. Defaults to `nil`.
    #
    def clean_versions!(options = {})
      options = { keeping: 1, date: :all }.merge(options)
      gather_versions(options[:item_id], options[:date]).each do |_item_id, item_versions|
        group_versions_by_date(item_versions).each do |_date, date_versions|
          # Remove the number of versions we wish to keep from the collection
          # of versions prior to destruction.
          date_versions.pop(options[:keeping])
          date_versions.map(&:destroy)
        end
      end
    end

    private

    # Returns a hash of versions grouped by the `item_id` attribute formatted
    # like this: {:item_id => PaperTrail::Version}. If `item_id` or `date` is
    # set, versions will be narrowed to those pointing at items with those ids
    # that were created on specified date. Versions are returned in
    # chronological order.
    def gather_versions(item_id = nil, date = :all)
      unless date == :all || date.respond_to?(:to_date)
        raise ArgumentError.new("`date` argument must receive a Timestamp or `:all`")
      end
      versions = item_id ? PaperTrail::Version.where(item_id: item_id) : PaperTrail::Version
      versions = versions.order(PaperTrail::Version.timestamp_sort_order)
      versions = versions.between(date.to_date, date.to_date + 1.day) unless date == :all

      # If `versions` has not been converted to an ActiveRecord::Relation yet,
      # do so now.
      versions = PaperTrail::Version.all if versions == PaperTrail::Version
      versions.group_by(&:item_id)
    end

    # Given an array of versions, returns a hash mapping dates to arrays of
    # versions.
    # @api private
    def group_versions_by_date(versions)
      versions.group_by { |v| v.send(PaperTrail.timestamp_field).to_date }
    end
  end
end