diff --git a/2020/ruby/day_12.rb b/2020/ruby/day_12.rb
new file mode 100644
index 0000000..62c1c1c
--- /dev/null
+++ b/2020/ruby/day_12.rb
@@ -0,0 +1,54 @@
+actions = ARGF.read.scan(/(\w)(\d+)/).map {|a,v| [a, v.to_i] }
+
+dir = 0
+pos = [0, 0]
+way = [10, 1]
+actions.each do |a,v|
+  # delta = case a
+  #         when ?N
+  #           [ 0,  v]
+  #         when ?S
+  #           [ 0, -v]
+  #         when ?E
+  #           [ v,  0]
+  #         when ?W
+  #           [-v,  0]
+  #         when ?L
+  #           dir += v
+  #           [0, 0]
+  #         when ?R
+  #           dir -= v
+  #           [0, 0]
+  #         when ?F
+  #           rad = dir * Math::PI / 180.0
+  #           [v * Math.cos(rad), v * Math.sin(rad)].map(&:round)
+  #         else
+  #           fail
+  #         end
+  case a
+  when ?N
+    way[1] += v
+  when ?S
+    way[1] -= v
+  when ?E
+    way[0] += v
+  when ?W
+    way[0] -= v
+  when ?L
+    rad = Math.atan2(*way.reverse)
+    dis = Math.sqrt(way.map {|x| x**2 }.sum)
+    rad += v * Math::PI / 180
+    way = [dis * Math.cos(rad), dis * Math.sin(rad)].map(&:round)
+  when ?R
+    rad = Math.atan2(*way.reverse)
+    dis = Math.sqrt(way.map {|x| x**2 }.sum)
+    rad -= v * Math::PI / 180
+    way = [dis * Math.cos(rad), dis * Math.sin(rad)].map(&:round)
+  when ?F
+    delta = way.map {|i| v * i }
+    pos = pos.zip(delta).map {|a,b| a + b }
+  else
+    fail
+  end
+end
+p pos.map(&:abs).sum