Resolve day 2

02/script.rb

@@ -0,0 +1,57 @@
+#!/usr/bin/env ruby
+
+require_relative '../common'
+
+class Day02 < Day
+  def part1
+    input.each_with_object(Position.new) { |cmd, position| position.process cmd }.result
+  end
+
+  def part2
+    input.each_with_object(Position.new(use_aim: true)) { |cmd, position| position.process cmd }.result
+  end
+
+  class Position
+    def initialize(use_aim: false)
+      @use_aim = use_aim
+
+      @horizontal_position = 0
+      @depth = 0
+      @aim = 0
+    end
+
+    def process command
+      direction, value = command.match(/\A(forward|down|up) ([0-9]+)\z/).captures
+      send direction, value.to_i
+    end
+
+    def result
+      @horizontal_position * @depth
+    end
+
+    private
+
+    def forward value
+      @horizontal_position += value
+      @depth += @aim * value if @use_aim
+    end
+
+    def down value
+      if @use_aim
+        @aim += value
+      else
+        @depth += value
+      end
+    end
+
+    def up value
+      if @use_aim
+        @aim -= value
+      else
+        @depth -= value
+      end
+    end
+  end
+end
+
+Day02.run