module DataMapper
  class Pager

    ##
    # Total number of un-limited records.

    attr_reader :total

    ##
    # Records per page.

    attr_reader :per_page

    ##
    # Current page number.

    attr_reader :current_page

    ##
    # Previous page or nil when no previous page is available.

    attr_reader :previous_page

    ##
    # Next page or nil when no more pages are available.

    attr_reader :next_page

    ##
    # Total number of pages.

    attr_reader :total_pages

    ##
    # Initialize with _options_.

    def initialize options = {}
      @page_param = options.delete(:page_param) || :page
      @total = options.delete :total
      @per_page = options.delete :limit
      @current_page = options.delete @page_param
      @total_pages = total.quo(per_page).ceil
      @next_page = current_page + 1 unless current_page >= total_pages
      @previous_page = current_page - 1 unless current_page <= 1
    end

    ##
    # Render the pager with the given _uri_ and _options_.
    #
    # === Examples
    #
    #   User.page(2).pager.to_html('/users')
    #   User.page(2).pager.to_html('/users', :size => 3)
    #
    # === Options
    #
    #   :size   Number of intermediate page number links to be shown; Defaults to 7
    #

    def to_html uri, options = {}
      return unless total_pages > 1
      @uri, @options = uri, options
      @size = option :size
      raise ArgumentError, 'invalid :size; must be an odd number' if @size % 2 == 0
      @size /= 2
      [%(<ul class="#{Pagination.defaults[:pager_class]}">),
        first_link,
        previous_link,
        more(:before),
        intermediate_links.join("\n"),
        more(:after),
        next_link,
        last_link,
      '</ul>'].join
    end

    private

    ##
    # Fetch _key_ from the options passed to #to_html, or
    # its default value.

    def option key
      @options.fetch key, Pagination.defaults[key]
    end

    ##
    # Link to _page_ with optional anchor tag _contents_.

    def link_to page, contents = nil
      %(<a href="#{uri_for(page)}">#{contents || page}</a>)
    end

    ##
    # More pages indicator for _position_.

    def more position
      return '' if position == :before && (current_page <= 1 || first <= 1)
      return '' if position == :after && (current_page >= total_pages || last >= total_pages)
      li 'more', option(:more_text)
    end

    ##
    # Intermediate page links array.

    def intermediate_links
      (first..last).map do |page|
        classes = ["page-#{page}"]
        classes << 'active' if current_page == page
        li classes.join(' '), link_to(page)
      end
    end

    ##
    # Previous link.

    def previous_link
      li 'previous jump', link_to(previous_page, option(:previous_text)) if previous_page
    end

    ##
    # Next link.

    def next_link
      li 'next jump', link_to(next_page, option(:next_text)) if next_page
    end

    ##
    # Last link.

    def last_link
      li 'last jump', link_to(total_pages, option(:last_text)) if next_page && !option(:last_text).empty?
    end

    ##
    # First link.

    def first_link
      li 'first jump', link_to(1, option(:first_text)) if previous_page && !option(:first_text).empty?
    end

    ##
    # Determine first intermediate page.

    def first
      @first ||= begin
        first = [current_page - @size, 1].max
        if (current_page - total_pages).abs < @size
          first = [first - (@size - (current_page - total_pages).abs), 1].max
        end
        first
      end
    end

    ##
    # Determine last intermediate page.

    def last
      @last ||= begin
        last = [current_page + @size, total_pages].min
        if @size >= current_page
          last = [last + (@size - current_page) + 1, total_pages].min
        end
        last
      end
    end

    ##
    # Renders a <li> with the given _css_class_ and _contents_.

    def li css_class = nil, contents = nil
      "<li#{%( class="#{css_class}") if css_class}>#{contents}</li>\n"
    end

    ##
    # Uri for _page_. The following conversions are made
    # to the _uri_ previously passed to #to_html:
    #
    #   /items          # Appends query string => /items?page=2
    #   /items?page=1   # Adjusts current page => /items?page=2
    #   /items?foo=bar  # Appends page pair    => /items?foo=bar&page=1
    #

    def uri_for page
      case @uri
      when /\b#{@page_param}=/ ; @uri.gsub /\b#{@page_param}=\d+/, "#{@page_param}=#{page}"
      when /\?/      ; @uri += "&#{@page_param}=#{page}"
      else           ; @uri += "?#{@page_param}=#{page}"
      end
    end

  end
end