entries_controller.rb

class Entry < ActiveRecord::Base

  ITEMS_PER_PAGE = 50
  belongs_to :subreddit

  def self.page_for(subreddit, page)

    if subreddit
      entries = subreddit.entries
    else
      entries = Entry.all
    end
    
    pages, extra = entries.count.divmod(ITEMS_PER_PAGE)

    pages += 1 if extra > 0
    page = 1 if page < 1
    skip = (page - 1) * ITEMS_PER_PAGE

    data = entries.limit(ITEMS_PER_PAGE).offset(skip).order("id DESC")

    next_page = page < pages ? page + 1 : page
    prev_page = page > 1 ? page - 1 : page
    next_page = "/entries/?page=#{next_page}"
    prev_page = "/entries/?page=#{prev_page}"
    {page: page, next: next_page, prev: prev_page, data: data} 
  end

end

class EntriesController < ApplicationController

  def index
    subreddit = Subreddit.find(params[:subreddit)
    if subreddit
      render json: Entry.page_for(subreddit, params[:page])
    else
      #something bad
    end
end