module SimplePagination
  class PageCollection
    ##
    # Create a new PageCollection object.  The following options are available.
    # [:current_offset] The zero-based offset of the first record in the current page of results
    # [:current_page]   The one-based offset of the current page of results (alternative to :current_offset)
    # [:total_records]  The total number of results across all pages
    # [:total_pages]    The total number of pages (alternative to :total_records)
    # [:page_size]      The page size
    #
    # You can choose between :current_offset and :current_page based on your
    # needs.  Same goes for :total_records and :total_pages.  :page_size
    # is required.
    #
    # A typical use of this class would be to define a <tt>pages</tt> method on your
    # result set class which returns an instance of PageCollection. (So you can 
    # do, e.g., <tt>my_result_set.pages.current</tt> and so on.)
    def initialize(options={})
      check_options(options)
      @pages, @page_size = {}, options[:page_size]
      @length = options[:total_pages] || (options[:total_records] / @page_size.to_f).ceil
      @current_page = options[:current_page] || (options[:current_offset]/@page_size)+1
    end
    
    ##
    # A Page object representing the page at a given page number (one-based).
    def [](i)
      @pages[i] ||= Page.new(i, self) unless out_of_bounds?(i)
    end
    
    ##
    # A Page object representing the current page in the collection.
    def current
      self[@current_page]
    end
    
    ##
    # A Page object representing the first page in the collection.
    def first
      self[1]
    end

    ##
    # A Page object representing the last page in the collection.
    def last
      self[length]
    end

    ##
    # The number of pages in the collection.
    attr_reader :length

    ## 
    # The number of records shown on each page in the collection.
    attr_reader :page_size
    
  private
  
    def check_options(options)
      raise ArgumentError, "requires :current_offset or :current_page" unless options[:current_offset] || options[:current_page]
      raise ArgumentError, "requires :page_size" unless options[:page_size]
      raise ArgumentError, "requires :total_pages or :total_records" unless options[:total_pages] or options[:total_records]
    end
    
    def out_of_bounds?(i)
      i > length || i < 1
    end
  end
end