#
# This Module was developed by Thomas Hafner.
# No other references about the author.
#

# TITLE:
#
#   Cartesian
#
# SUMMARY:
#
#   Cartesian product and similar methods.
#
# AUTHORS:
#
#   - Thomas Hafner

#
module Enumerable

	class << self
		# Provides the cross-product of two or more Enumerables.
		# This is the class-level method. The instance method
		# calls on this.
		#
		#   Enumerable.cart([1,2], [4], ["apple", "banana"])
		#   #=> [[1, 4, "apple"], [1, 4, "banana"], [2, 4, "apple"], [2, 4, "banana"]]
		#
		#   Enumerable.cart([1,2], [3,4])
		#   #=> [[1, 3], [1, 4], [2, 3], [2, 4]]

		def cartesian_product(*enums, &block)
			result = [[]]
			while [] != enums
				t, result = result, []
				b, *enums = enums
				t.each do |a|
					b.each do |n|
						result << a + [n]
					end
				end
			end
			if block_given?
				result.each{ |e| block.call(e) }
			else
				result
			end
		end

		alias_method :cart, :cartesian_product
	end

	# The instance level version of <tt>Enumerable::cartesian_product</tt>.	
	#
	#   a = []
	#   [1,2].cart([4,5]){|elem| a << elem }
	#   a  #=> [[1, 4],[1, 5],[2, 4],[2, 5]]

	def cartesian_product(*enums, &block)
		Enumerable.cartesian_product(self, *enums, &block)
	end

	alias :cart :cartesian_product

	# Operator alias for cross-product.
	#
	#   a = [1,2] ** [4,5]
	#   a  #=> [[1, 4],[1, 5],[2, 4],[2, 5]]
	#
	def **(enum)
		Enumerable.cartesian_product(self, enum)
	end

	# Expected to be an enumeration of arrays. This method
	# iterates through combinations of each in position.
	#
	#   a = [ [0,1], [2,3] ]
	#   a.each_combo { |c| p c }
	#
	# produces
	#
	#   [0, 2]
	#   [0, 3]
	#   [1, 2]
	#   [1, 3]
	#
	def each_combo
		a = collect{ |x|
			x.respond_to?(:to_a) ? x.to_a : 0..x
		}

		if a.size == 1
			r = a.shift
			r.each{ |n|
				yield n
			}
		else
			r = a.shift
			r.each{ |n|
				a.each_combo{ |s|
					yield [n, *s]
				}
			}
		end
	end

	# As with each_combo but returns combos collected in an array.
	#
	def combos
		a = []
		each_combo{ |c| a << c }
		a
	end

end