Generating spiral matrices

spiral.rb

def spiral(n)
	arr = Array.new(n){Array.new(n){0}}
	diff = [[0, 1], [1, 0], [0, -1], [-1, 0]]
	i, j = 0, 0
	dindex = 0
	turns = 0
	curr_square = n
	shift = 0
	
	(n*n).times do |index|
		arr[i][j] = index + 1
		
		if index == (shift + 4*curr_square - 5)
			curr_square -= 2
			turns, dindex = 0, 0
			shift = index + 1
			j += 1
			next
		end
		
		i += diff[dindex][0]
		j += diff[dindex][1]
		
		if index == (shift + (turns + 1)*(curr_square - 1) - 1)
			turns += 1
			dindex += 1
		end
	end
	
	arr
end

arr = spiral(10)
puts arr.map{|ia| ia.join(' ')}.join("\n")