refactoring and fixes #710

refactoring code from cells.rb to column_width_calculator, from now on
all complex width related code is in this file.
fixed #710 be eliminating an edge case as reported under issue #710

lib/prawn/table/cells.rb

@@ -228,56 +228,7 @@ def index_cells
       # each cell, grouped by +row_or_column+.
       #
       def aggregate_cell_values(row_or_column, meth, aggregate)
-        values = {}
-
-        #calculate values for all cells that do not span accross multiple cells
-        #this ensures that we don't have a problem if the first line includes
-        #a cell that spans across multiple cells
-        each do |cell|
-          #don't take spanned cells
-          if cell.colspan == 1 and cell.class != Prawn::Table::Cell::SpanDummy
-            index = cell.send(row_or_column)
-            values[index] = [values[index], cell.send(meth)].compact.send(aggregate)
-          end
-        end
-
-        #if there are only colspanned or rowspanned cells in a table
-        spanned_width_needs_fixing = true
-
-        each do |cell|
-          index = cell.send(row_or_column)
-          if cell.colspan > 1
-            #calculate current (old) return value before we do anything
-            old_sum = 0
-            cell.colspan.times { |i|
-              old_sum += values[index+i] unless values[index+i].nil?
-            }
-
-            #calculate future return value
-            new_sum = cell.send(meth) * cell.colspan
-
-            #due to float rounding errors we need to ignore a small difference in the new
-            #and the old sum the same had to be done in
-            #the column_width_calculator#natural_width
-            spanned_width_needs_fixing = ((new_sum - old_sum) > Prawn::FLOAT_PRECISION)
-
-            if spanned_width_needs_fixing
-              #not entirely sure why we need this line, but with it the tests pass
-              values[index] = [values[index], cell.send(meth)].compact.send(aggregate)
-              #overwrite the old values with the new ones, but only if all entries existed
-              entries_exist = true
-              cell.colspan.times { |i| entries_exist = false if values[index+i].nil? }
-              cell.colspan.times { |i|
-                values[index+i] = cell.send(meth) if entries_exist
-              }
-            end
-          else
-            if spanned_width_needs_fixing && cell.class == Prawn::Table::Cell::SpanDummy
-              values[index] = [values[index], cell.send(meth)].compact.send(aggregate)
-            end
-          end
-        end
-        values.values.inject(0, &:+)
+        ColumnWidthCalculator.new(self).aggregate_cell_values(row_or_column, meth, aggregate)
       end
 
       # Transforms +spec+, a column / row specification, into an object that

lib/prawn/table/column_width_calculator.rb

@@ -9,24 +9,75 @@ def initialize(cells)
 
         @widths_by_column        = Hash.new(0)
         @rows_with_a_span_dummy  = Hash.new(false)
-      end
 
-      def natural_widths
+        #calculate for each row if it includes a Cell:SpanDummy
         @cells.each do |cell|
           @rows_with_a_span_dummy[cell.row] = true if cell.is_a?(Cell::SpanDummy)
         end
+      end
+
+      # does this row include a Cell:SpanDummy?
+      #
+      # @param row - the row that should be checked for Cell:SpanDummy elements
+      #
+      def has_a_span_dummy?(row)
+        @rows_with_a_span_dummy[row]
+      end
+
+      # helper method
+      # column widths are stored in the values array
+      # a cell may span cells whose value is only partly given
+      # this function handles this special case
+      #
+      # @param values - The columns widths calculated up until now
+      # @param cell - The current cell
+      # @param index - The current column
+      # @param meth - Meth (min/max); used to calculate values to be filled
+      #
+      def fill_values_if_needed(values, cell, index, meth)
+        #have all spanned indices been filled with a value?
+        #e.g. values[0], values[1] and values[2] don't return nil given a index of 0 and a colspan of 3
+        number_of_nil_values = 0
+        cell.colspan.times do |i|
+          number_of_nil_values += 1 if values[index+i].nil?
+        end
+
+        #nothing to do? because
+        #a) all values are filled
+        return values if number_of_nil_values == 0
+        #b) no values are filled
+        return values if number_of_nil_values == cell.colspan
+        return values unless has_a_span_dummy?(cell.row)
+        #fill up the values array
+
+        #calculate the new sum
+        new_sum = cell.send(meth) * cell.colspan
+        #substract any calculated values
+        cell.colspan.times do |i|
+          new_sum -= values[index+i] unless values[index+i].nil?
+        end
+
+        #calculate value for the remaining - not yet filled - cells.
+        new_value = new_sum.to_f / number_of_nil_values
+        #fill the not yet filled cells
+        cell.colspan.times do |i|
+          values[index+i] = new_value if values[index+i].nil?
+        end
+        return values
+      end
 
+      def natural_widths
         #calculate natural column width for all rows that do not include a span dummy
         @cells.each do |cell|
-          unless @rows_with_a_span_dummy[cell.row]
+          unless has_a_span_dummy?(cell.row)
             @widths_by_column[cell.column] =
               [@widths_by_column[cell.column], cell.width.to_f].max
           end
         end
 
         #integrate natural column widths for all rows that do include a span dummy
         @cells.each do |cell|
-          next unless @rows_with_a_span_dummy[cell.row]
+          next unless has_a_span_dummy?(cell.row)
           #the width of a SpanDummy cell will be calculated by the "mother" cell
           next if cell.is_a?(Cell::SpanDummy)
 
@@ -58,6 +109,72 @@ def natural_widths
 
         @widths_by_column.sort_by { |col, _| col }.map { |_, w| w }
       end
+
+      # get column widths (either min or max depending on meth)
+      # used in cells.rb
+      #
+      # @param row_or_column - you may call this on either rows or columns
+      # @param meth - min/max
+      # @param aggregate - functions from cell.rb to be used to aggregate e.g. avg_spanned_min_width
+      #
+      def aggregate_cell_values(row_or_column, meth, aggregate)
+        values = {}
+
+        #calculate values for all cells that do not span accross multiple cells
+        #this ensures that we don't have a problem if the first line includes
+        #a cell that spans across multiple cells
+        @cells.each do |cell|
+          #don't take spanned cells
+          if cell.colspan == 1 and cell.class != Prawn::Table::Cell::SpanDummy
+            index = cell.send(row_or_column)
+            values[index] = [values[index], cell.send(meth)].compact.send(aggregate)
+          end
+        end
+
+        # if there are only colspanned or rowspanned cells in a table
+        spanned_width_needs_fixing = true
+
+        @cells.each do |cell|
+          index = cell.send(row_or_column)
+          #puts "index=#{index}"
+          if cell.colspan > 1
+            #special treatment if some but not all spanned indices in the values array have been calculated
+            #only applies to rows
+            values = fill_values_if_needed(values, cell, index, meth) if row_or_column == :column
+            #calculate current (old) return value before we do anything
+            old_sum = 0
+            cell.colspan.times { |i|
+              old_sum += values[index+i] unless values[index+i].nil?
+            }
+
+            #calculate future return value
+            new_sum = cell.send(meth) * cell.colspan
+
+            #due to float rounding errors we need to ignore a small difference in the new
+            #and the old sum the same had to be done in
+            #the column_width_calculator#natural_width
+            spanned_width_needs_fixing = ((new_sum - old_sum) > Prawn::FLOAT_PRECISION)
+
+            if spanned_width_needs_fixing
+              #not entirely sure why we need this line, but with it the tests pass
+              values[index] = [values[index], cell.send(meth)].compact.send(aggregate)
+              #overwrite the old values with the new ones, but only if all entries existed
+              entries_exist = true
+              cell.colspan.times { |i| entries_exist = false if values[index+i].nil? }
+              cell.colspan.times { |i|
+                values[index+i] = cell.send(meth) if entries_exist
+              }
+            end
+          else
+            if spanned_width_needs_fixing && cell.class == Prawn::Table::Cell::SpanDummy
+              values[index] = [values[index], cell.send(meth)].compact.send(aggregate)
+            end
+          end
+        end
+        puts values.values.inject(0, &:+)
+        return values.values.inject(0, &:+)
+      end
     end
+
   end
 end

spec/table_spec.rb

@@ -151,6 +151,34 @@
       table.column_widths.should == [50.0, 70.0]
     end
 
+    it "illustrates issue #710", :issue => 710 do
+      partial_width = 40
+      pdf = Prawn::Document.new({page_size: "LETTER", page_layout: :portrait})
+      col_widths = [
+        50,
+        partial_width, partial_width, partial_width, partial_width
+      ]
+
+      day_header = [{
+          content: "Monday, August 5th, A.S. XLIX",
+          colspan: 5,
+      }]
+
+      times = [{
+        content: "Loc",
+        colspan: 1,
+      }, {
+        content: "8:00",
+        colspan: 4,
+      }]
+
+      data = [ day_header ] + [ times ]
+
+      #raised a Prawn::Errors::CannotFit:
+      #Table's width was set larger than its contents' maximum width (max width 210, requested 218.0)
+      table = Prawn::Table.new data, pdf, :column_widths => col_widths
+    end
+
     it "illustrate issue #533" do
       data = [['', '', '', '', '',''],
               ['',{:content => '', :colspan => 5}]]