module Prawn
  class Document
    
    # Defines the grid system for a particular document.  Takes the number of 
    # rows and columns and the width to use for the gutter as the 
    # keys :rows, :columns, :gutter, :row_gutter, :column_gutter
    #
    def define_grid(options = {})
      @grid = Grid.new(self, options)
    end
  
    # A method that can either be used to access a particular grid on the page 
    # or work with the grid system directly.
    #
    #   @pdf.grid                 # Get the Grid directly
    #   @pdf.grid([0,1])          # Get the box at [0,1]
    #   @pdf.grid([0,1], [1,2])   # Get a multi-box spanning from [0,1] to [1,2]
    #
    def grid(*args)
      @boxes ||= {}
      @boxes[args] ||= if args.empty?
        @grid
      else
        g1, g2 = args
        if(g1.class == Array && g2.class == Array && 
          g1.length == 2 && g2.length == 2)
          multi_box(single_box(*g1), single_box(*g2))
        else
          single_box(g1, g2)
        end
      end
    end
  
    # A Grid represents the entire grid system of a Page and calculates 
    # the column width and row height of the base box.
    class Grid
      attr_reader :pdf, :columns, :rows, :gutter, :row_gutter, :column_gutter
      def initialize(pdf, options = {}) # :nodoc:
        valid_options = [:columns, :rows, :gutter, :row_gutter, :column_gutter]
        Prawn.verify_options valid_options, options
      
        @pdf = pdf
        @columns = options[:columns]
        @rows = options[:rows]
        set_gutter(options)
      end

      # Calculates the base width of boxes.
      def column_width
        @column_width ||= subdivide(pdf.bounds.width, columns, column_gutter)
      end
    
      # Calculates the base height of boxes.
      def row_height
       @row_height ||= subdivide(pdf.bounds.height, rows, row_gutter)
      end

      # Diagnostic tool to show all of the grids.  Defaults to gray.
      def show_all(color = "CCCCCC")
        self.rows.times do |i|
          self.columns.times do |j|
            pdf.grid(i,j).show(color)
          end
        end
      end

      private
      
      def subdivide(total, num, gutter)
        (total.to_f - (gutter * (num - 1).to_f)) / num.to_f
      end
      
      def set_gutter(options)
        if options.has_key?(:gutter)
          @gutter = options[:gutter].to_f
          @row_gutter, @column_gutter = @gutter, @gutter
        else
          @row_gutter    = options[:row_gutter].to_f
          @column_gutter = options[:column_gutter].to_f
          @gutter = 0
        end
      end
    end
  
    # A Box is a class that represents a bounded area of a page.  
    # A Grid object has methods that allow easy access to the coordinates of 
    # its corners, which can be plugged into most existing prawnmethods.
    #
    class Box #:nodoc:
      attr_reader :pdf
    
      def initialize(pdf, i, j)
        @pdf = pdf
        @i = i
        @j = j
      end
    
      # Mostly diagnostic method that outputs the name of a box as 
      # col_num, row_num
      #
      def name
        "#{@i.to_s},#{@j.to_s}"
      end
      
      # :nodoc
      def total_height
        pdf.bounds.height.to_f
      end
      
      # Width of a box
      def width
        grid.column_width.to_f
      end
    
      # Height of a box
      def height
        grid.row_height.to_f
      end
      
      # Width of the gutter
      def gutter
        grid.gutter.to_f
      end
      
      # x-coordinate of left side
      def left
        @left ||= (width + grid.column_gutter) * @j.to_f
      end
    
      # x-coordinate of right side 
      def right
        @right ||= left + width
      end
    
      # y-coordinate of the top
      def top
        @top ||= total_height - ((height + grid.row_gutter) * @i.to_f)
      end
    
      # y-coordinate of the bottom
      def bottom
        @bottom ||= top - height
      end
    
      # x,y coordinates of top left corner
      def top_left
        [left, top]
      end
    
      # x,y coordinates of top right corner    
      def top_right
        [right, top]
      end
    
      # x,y coordinates of bottom left corner
      def bottom_left
        [left, bottom]
      end
    
      # x,y coordinates of bottom right corner
      def bottom_right
        [right, bottom]
      end
    
      # Creates a standard bounding box based on the grid box.
      def bounding_box(&blk)
        pdf.bounding_box(top_left, :width => width, :height => height, &blk)
      end
    
      # Diagnostic method
      def show(grid_color = "CCCCCC")
        self.bounding_box do
          original_stroke_color = pdf.stroke_color

          pdf.stroke_color = grid_color
          pdf.text self.name
          pdf.stroke_bounds
          
          pdf.stroke_color = original_stroke_color
        end
      end
    
      private
      def grid
        pdf.grid
      end
    end
  
    # A MultiBox is specified by 2 Boxes and spans the areas between.
    class MultiBox < Box #:nodoc:
      def initialize(pdf, b1, b2)
        @pdf = pdf
        @bs = [b1, b2]
      end
    
      def name
        @bs.map {|b| b.name}.join(":")
      end
    
      def total_height
        @bs[0].total_height
      end

      def width
        right_box.right - left_box.left
      end
    
      def height
        top_box.top - bottom_box.bottom
      end
    
      def gutter
        @bs[0].gutter
      end
    
      def left
        left_box.left
      end
    
      def right
        right_box.right
      end
    
      def top
        top_box.top
      end
    
      def bottom
        bottom_box.bottom
      end
    
      private
      def left_box
        @left_box ||= @bs.min {|a,b| a.left <=> b.left}
      end
    
      def right_box
        @right_box ||= @bs.max {|a,b| a.right <=> b.right}
      end
    
      def top_box
        @top_box ||= @bs.max {|a,b| a.top <=> b.top}
      end
    
      def bottom_box
        @bottom_box ||= @bs.min {|a,b| a.bottom <=> b.bottom}
      end
    end
  
    private
    def single_box(i, j)
      Box.new(self, i, j)
    end
  
    def multi_box(b1, b2)
      MultiBox.new(self, b1, b2)
    end
  end
end