# frozen_string_literal: true
 
class Slide
  attr_accessor :commands
 
  def initialize(field, commands)
    commands  = optimise(commands.gsub(/[LR]+(?<m>[LR])|[UD]+(?<m>[UD])/, '\k<m>'))
    @commands = {
      initial:   commands[0].to_s,
      direction: ('LDRUL'.include?(commands[0, 2]) ? :+ : :-),
      size:      commands.size
    }
    @angle    = ('ULDR'.index(@commands[:initial]) - (clockwise? ? 1 : 0) ) % 4
    @field    = normalize(field)
    @width    = field.index(/\n|\z/)
    @height   = @field.size
    @initial_state = Marshal.load(Marshal.dump(@field)).freeze
  end
 
  def to_s
    return @field.map(&:join).join($/) if @commands[:size] < 2
    ary = @field.map { |s| s.ljust(@width, ?.).split('') }
    upright(ary)
    ary.map(&:join).join($/)
  end
 
  def upright(ary)
    return if @angle == 0
    ary.reverse! if @angle <= 2
    ary.each(&:reverse!) if @angle >= 2
  end
 
  def clockwise?
    @commands[:direction] == :-
  end
 
  def optimise(dirs)
    nil while dirs.gsub!(/(?<m>.).\k<m>(?=.)|(?<m>(?<n>.).)\k<n>\z/, '\k<m>')
    dirs
  end
 
  def normalize(field)
    ary = field.split.map { |s| s.split('') }
    f = ->(a) { a.select { |c| c != ?. }.join }
    return ary  if @commands[:size] == 0
    incline_ary(ary, @commands[:initial])
    return ary if @commands[:size] == 1
    rotate_ary(ary, clockwise? ? :+ : :-)
    incline_ary(ary, @commands[:initial])
    rotate_ary(ary, @commands[:direction])
    upright(ary)
    ary.map(&f)
  end
 
  def incline_ary(ary, direction)
    rotate_ary(ary, :+) if %w[U D].include?(direction)
    f = case direction
        when ?R, ?D then ->c{c == ?.}
        when ?L, ?U then ->c{c != ?.}
        end
    ary.replace(ary.map { |a| a.partition(&f).flatten })
    %w[U D].include?(direction) ? rotate_ary(ary, :-) : ary
  end
 
  def rotate_ary(ary, dir = :+)
    a = ary.transpose
    case dir
    when :+ then ary.replace(a.reverse)
    when :- then ary.replace(a.map(&:reverse))
    end
  end
 
  def incline_all(count = @commands[:size] - 2)
    f = %w[L R].include?(@commands[:initial]) ? ->(a) { a.even? } : ->(a) { a.odd? }
    angle = clockwise? ? -1 : 1 
    count.times do |i|
      f.call(i) ? inversion_h : inversion_v
      @angle = (@angle + angle) % 4
      break(incline_all((count - i - 1) % (i + 1))) if @field == @initial_state
    end
  end
 
  def inversion_h
    @field.map(&:reverse!)
  end
 
  def inversion_v
    verticals = @width.times.map { |i| @field.map { |s| s[i] }.compact }
    @field = @height.times.map { |i| verticals.map { |s| s[~i]}.join }
  end
end
 
samples = [[<<~EOT, ''], [<<~EOT, 'U'], [<<~EOT, 'UR'], [<<~EOT, 'LRRLLUDRRLRLRRURRRRLLLRULDUDULDLLRDULURULUDLDLUDDL'], [<<~EOT, 'LURD'*10**6]]
  ...
  .a.
  ...
EOT
  ...
  ...
  .a.
EOT
  ...
  .a.
  ...
EOT
  .....
  .d.i.
  kmegk
  ..tu.
EOT
  .....
  .d.i.
  kmegk
  ..tu.
EOT
 
samples.each do |field, commands|
  pre = Time.now
  s = Slide.new(field, commands)
  s.incline_all
  singular = commands.size == 1 ? ['', 'is'] : ['s', 'are']
  puts "%s\n%d command%s (%s%s) %s reduced to %d\n%s=>\n%s\n# %f sec" % [
    ?-*70, commands.size, singular.first, commands[0, 20],
    commands.size > 20 ? '...' : '', singular.last,
    s.commands[:size], field, s, Time.now - pre
  ]
end
 

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