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Pagination for the Elixir ecosystem

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scrivener lib scrivener.ex
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lib/scrivener.ex 

defmodule Scrivener do

  import Ecto.Query



  alias Scrivener.Config



  defmacro __using__(opts) do

    quote do

      @scrivener_defaults unquote(opts)

      def paginate(query, options \\ []) do

        Scrivener.paginate(__MODULE__, @scrivener_defaults, query, options)

      end

    end

  end



  def paginate(query, %Config{} = config) do

    %Scrivener.Page{

      page_size: config.page_size,

      page_number: config.page_number,

      entries: entries(query, config.repo, config.page_number, config.page_size),

      total_pages: total_pages(query, config.repo, config.page_size)

    }

  end



  def paginate(repo, defaults, query, opts) do

    paginate(query, Config.new(repo, defaults, opts))

  end



  defp ceiling(float) do

    t = trunc(float)



    case float - t do

      neg when neg < 0 ->

        t

      pos when pos > 0 ->

        t + 1

      _ -> t

    end

  end



  defp entries(query, repo, page_number, page_size) do

    offset = page_size * (page_number - 1)



    query

    |> limit([_], ^page_size)

    |> offset([_], ^offset)

    |> repo.all

  end



  def total_pages(query, repo, page_size) do

    count = query

    |> exclude(:order_by)

    |> exclude(:preload)

    |> exclude(:select)

    |> select([e], count(e.id))

    |> repo.one



    ceiling(count / page_size)

  end

end