# see http://gist.github.com/341290 (sort_index_controller_usage.rb)
# see http://gist.github.com/341295 (sort_index_view_usage.html.erb)

# The classes in this module help to enable sorting on index pages
# building sql order clauses and rendering html table header links
module SortIndex
  SORT_KEY_ASC = 'asc'
  SORT_KEY_DESC = 'desc'

  SORT_DIRECTION_MAP = { 
    SORT_KEY_DESC => 'DESC', 
    SORT_KEY_ASC => 'ASC' 
  }

  # The +SortIndex::Config+ class specifies all possible sort columns
  # for a given controller action including the default column and the default order
  class Config
    attr_accessor :columns
    attr_accessor :default_direction
    
    def default
      return @default
    end
    
    # The +initialize+ method; 
    # both the default and columns parameters contain key value pairs 
    # where the key is passed in the query string to the action and the 
    # value contains the sql order by value
    # === Parameters
    # * _default_ = Hash; must contain only one pair; automatically gets added to the columns member
    # * _columns_ = Hash; one pair per sortable column
    # * _default_direction_ = String; optional, if not specified order will be DESC
    def initialize(default, columns, default_direction = nil)
      @columns = columns
      @default_direction = default_direction || SORT_KEY_DESC
      
      raise "default only supports 1 pair" if default.length != 1
      default.each_pair { |key, value|
        @default = value
        @columns[key] = value
      }
    end
  end

  # The +SortIndex::Sortable+ class enable sorting on index pages
  # avoids sql injection by only using values from the SortIndex::Config#columns
  # Hash and not the values passed in the query string
  class Sortable 
    
    # The +initialize+ method; 
    # === Parameters
    # * _params_ = the controllers params Hash
    # * _config_ = SortIndex::Config
    # * _index_url_ = String; optional, if not specified will be the name of the controller
    # ** Examples
    # *** not specified /employees (the index action)
    # *** specified /employees/special_action
    def initialize(params, config, index_url = nil)
      @config = config
      @params = params
      @index_url = index_url || params[:controller]
      
      # sets up for building the sql order by
      @sort_direction = SORT_DIRECTION_MAP[@params[:sort_direction]] || @config.default_direction
      @sort_by = @config.columns[@params[:sort_by]] || @config.default
    end
    
    # The +order+ method returns the sql order criteria
    # use with your find calls or via paginate from will_paginate plugin
    def order
      specified_sort_by || "#{@sort_by} #{@sort_direction}"
    end
    
    # The +header_link+ method returns a string of html containing the table header and a tags
    # Example: <th><a href="/employess?sort_by=first_name&amp;sort_direction=desc">First Name</a></th>
    # If the column is the currently sorted column then a css class of current-sort-asc or current-sort-describe
    # is applied; this allows you to use css to add visual indicators such as up and down arrows 
    # this method is called from the view; once per column
    # === Parameters
    # * _sort_key_ = String; must be one of the key values from SortIndex::Config
    # * _display_ = The display text
    # * _sortable_ = Boolean; default is true; 
    # ** passing false will not render an anchor tag; instead the display will be wrapped in a span
    def header_link(sort_key, display, sortable = true)
      if @config.columns[sort_key].nil? and sortable then
        raise "Sort key of '#{sort_key}' not found. Check your controllers SortIndex::Config variable" 
      end
      
      class_attr = ""
      if @config.columns[sort_key] == @sort_by then
        class_attr = " class='current-sort-#{@sort_direction.downcase}'"
      end
      
      a_href = "<a href=\"/#{@index_url}/?sort_by=#{sort_key}&sort_direction=#{next_direction}\" title=\"Sort by #{display}\">#{display}</a>"
      if sortable == false then
        a_href = "<span>#{display}</span>"
      end
      
      return "<th#{class_attr}>#{a_href}</th>"
    end
    
    # The +next_direction+ method is called by header_link and specifies which way the rendered
    # links should sort. Returns the opposite of the current sort
    def next_direction
      sort_direction = SORT_KEY_ASC
      if (@params[:sort_direction].nil?) then
        sort_direction = (@sort_direction == SORT_KEY_ASC) ? SORT_KEY_DESC : SORT_KEY_ASC
      elsif (@params[:sort_direction] == SORT_KEY_ASC) then
        sort_direction = SORT_KEY_DESC
      end
      return sort_direction
    end
    
    # The +specified_sort_by+ method is called by order returns the sql order by criteria
    # This can be more than one sql column; when it is multiple columns we apply the same direction to all
    # For Example if you had one header column for Employee#full_name which mapped to two 
    # database columns first_name and last_name of the employees table the result would look like
    # first_name DESC, last_name DESC or last_name DESC, first_name DESC depending on your configuration
    def specified_sort_by
      sort = @config.columns[@params[:sort_by]]
      return nil if sort.nil?
      return sort.split(',').map {|order_criteria| "#{order_criteria} #{@sort_direction}"}.join(',')
    end
  end
  
end