DIRS = [ :up, :right, :down, :left ]

Pos = Struct.new(:x, :y) do
  def move(dir)
    case dir
    when :up
      Pos.new(x, y - 1)
    when :right
      Pos.new(x + 1, y)
    when :down
      Pos.new(x, y + 1)
    when :left
      Pos.new(x - 1, y)
    end
  end

  def dir_from(pos)
    diff_x = x - pos.x
    diff_y = y - pos.y

    case Pos.new(diff_x, diff_y)
    when Pos.new(0, -1)
      :up
    when Pos.new(1, 0)
      :right
    when Pos.new(0, 1)
      :down
    when Pos.new(-1, 0)
      :left
    end
  end

  def to_s()
    "(#{x}, #{y})"
  end
end

Tile = Struct.new(:pos, :up, :right, :down, :left)

class Maze
  attr_reader :width
  attr_reader :height

  def initialize(width, height)
    @width = width
    @height = height
    @h_walls = Array.new(@width) { Array.new(@height + 1, true) }
    @v_walls = Array.new(@width + 1) { Array.new(@height, true) }
  end

  def inBounds?(pos)
    x = pos.x
    y = pos.y

    x >= 0 && y >= 0 && x < @width && y < @height
  end

  def get(pos)
    raise IndexError unless inBounds?(pos)

    x = pos.x
    y = pos.y

    Tile.new(pos, @h_walls[x][y], @v_walls[x + 1][y], @h_walls[x][y + 1], @v_walls[x][y])
  end

  def neighbors(pos)
    neighbors = []

    DIRS.each do |dir|
      neighbors.push(pos.move(dir)) if inBounds?(pos.move(dir))
    end

    neighbors
  end

  def set(pos, dir, state)
    raise IndexError if pos.x >= @width
    raise IndexError if pos.y >= @height

    case dir
    when :up
      @h_walls[pos.x][pos.y] = state
    when :right
      @v_walls[pos.x + 1][pos.y] = state
    when :down
      @h_walls[pos.x][pos.y + 1] = state
    when :left
      @v_walls[pos.x][pos.y] = state
    end
  end

  def to_s
    drawingField = Array.new(@height * 2 + 1) { " " * (@width * 2 + 1) }

    @v_walls.each_index do |x|
      @v_walls[x].each_index do |y|
        next if @v_walls[x][y] == false

        drawingField[y * 2][x * 2] = "█"
        drawingField[y * 2 + 1][x * 2] = "█"
        drawingField[y * 2 + 2][x * 2] = "█"
      end
    end

    @h_walls.each_index do |x|
      @h_walls[x].each_index do |y|
        next if @h_walls[x][y] == false

        drawingField[y * 2][x * 2] = "█"
        drawingField[y * 2][x * 2 + 1] = "█"
        drawingField[y * 2][x * 2 + 2] = "█"
      end
    end

    drawingField.join("\n")
  end
end

class MazeGenerator
  attr_reader :maze

  def initialize(width, height)
    @maze = Maze.new(width, height)
  end

  def generate()
    @visitedCells = [@currentPos]
    @stack = [Pos.new(0, 0)]

    while !@stack.empty?
      step()
    end
  end

  def step()
    neighbors = @maze.neighbors(@stack.last)
    neighbors.select! do |neighbor|
      !@visitedCells.include? neighbor
    end

    if neighbors.empty?
      @stack.pop()
    else
      randomNeighbor = neighbors.sample
      print "Removing wall between ", @stack.last, " and ", randomNeighbor, "\n"
      @maze.set(@stack.last, randomNeighbor.dir_from(@stack.last), false)

      @stack.push(randomNeighbor)
      @visitedCells.push(randomNeighbor)
    end
  end
end

mazeGenerator = MazeGenerator.new(15, 15)
mazeGenerator.generate
puts mazeGenerator.maze