require 'java'

%w(JPanel JTextField JLabel JFrame JButton Timer).each { |c| java_import "javax.swing.#{c}"}
%w(Rectangle Insets Color BasicStroke Dimension Canvas image.BufferStrategy BorderLayout GridBagLayout GridBagConstraints Font).each { |c| java_import "java.awt.#{c}" }

WORLD_WIDTH = 800
WORLD_HEIGHT = 600

DELAY = 50
G = 9.81
$current_time = 0
$images = []

Y_0 = 500
X_0 = 10
VX_0 = 40
VY_0 = 0

class Pair
  attr_accessor :first, :second
  def initialize(first, second)
    @first = first
    @second = second
  end
end

def find_impact(y_0, vy_0, radius)
  discriminant = vy_0.to_f*vy_0.to_f - 2*G*(y_0.to_f-WORLD_HEIGHT+radius*2) # Simplified 4*G*(y_0-h)/2
  puts "Discriminant: #{discriminant} #{y_0}, #{vy_0}" if $DEBUG
  first_solution = (-vy_0 - Math.sqrt(discriminant)) / -G # Simplified 2*G/2
  second_solution = (-vy_0 + Math.sqrt(discriminant)) / -G # Simplified 2*G/2

  puts "first solution: #{first_solution} - second solution: #{second_solution}" if $DEBUG
  if vy_0 < 0
    [first_solution, second_solution].min.abs
  else
    [first_solution, second_solution].max
  end
end


class Organism < Rectangle
  attr_accessor :x, :y, :radius, :vx_0, :vy_0, :x_final
  def initialize
    @x_final = false
  end

  def draw(g)
    recalculate(g)
    g.color = Color::ORANGE
    g.draw_oval(@x, @y, @radius*2, @radius*2)
    g.fill_oval(@x+@radius, @y+@radius, 1, 1)
  end

  def recalculate(g)
    if !@x_final
      @x_final_value = @vx_0*find_impact(@y, @vy_0, @radius) + @x
      @x_final = true
    end

    $current_time += DELAY/100.0
    t = $current_time
    if @y < (WORLD_HEIGHT - @radius*2)
      @y = 0.5*G*t*t + @vy_0*t + Y_0
    else
      @y = WORLD_HEIGHT - @radius*2
    end

    if @x < (WORLD_WIDTH - @radius*2) && @y < (WORLD_HEIGHT - @radius*2)
      @x = @vx_0*t + X_0
      $images << Pair.new(@x, @y)
    else
      @x = @x_final_value
      $images << Pair.new(@x, @y)
    end

    if @y == (WORLD_HEIGHT - @radius*2)
      vx = vy = 0
    else
      vx = @vx_0
      vy = G*t + @vy_0
    end

    g.color = Color::BLUE
    g.draw_line(@x+@radius, @y+@radius, @x+@radius+vx, @y+@radius+vy)

    g.color = Color::GREEN
    g.font = Font.new("Courier new", Font::BOLD, 12)
    g.draw_string("x = #{@x.round(1)}, y = #{@y.round(1)}, v_x = #{vx.round(1)}, v_y = #{vy.round(1)}", WORLD_WIDTH - 310, 20)
    puts "x = #{@x.round(1)}, y = #{@y.round(1)}, v_x = #{vx.round(1)}, v_y = #{vy.round(1)}" if $DEBUG

  end
end

class Universe < Canvas
  def initialize
    super()
    self.preferred_size = Dimension.new(WORLD_WIDTH, WORLD_HEIGHT)
    self.minimum_size = self.preferred_size
    self.background = Color::BLACK

    @running = true
    @organisms = []
  end

  def game_loop

    if @running
      last_run = Time.now

      create_buffer_strategy(2)
      @strategy = self.buffer_strategy
      now = Time.now
      delta = now - last_run
      last_run = now

      g = @strategy.draw_graphics
      draw_frame(g)

      $images.each do |p|
        g.color = Color::GRAY
        g.fill_oval(p.first, p.second, 10, 10)
      end

      @organisms.each do |o|
        o.draw(g)
      end

      # flip buffer
      g.dispose()
      @strategy.show()
    end
  end

  def add_organism(organism)
    @organisms << organism
  end

  private
  def draw_frame(g)
    g.color = Color::WHITE
    old_stroke = g.stroke
    thindashed = BasicStroke.new(1.0, BasicStroke::CAP_BUTT, BasicStroke::JOIN_BEVEL, 1.0, [8.0, 3.0, 2.0, 3.0].to_java(:float), 0.0)
    g.set_stroke(thindashed)
    (0..WORLD_WIDTH).step(40) do |x|
      (0..WORLD_HEIGHT).step(40) do |y|
        g.drawLine(0, y, WORLD_WIDTH, y)
        g.drawLine(x, 0, x, WORLD_HEIGHT)
      end
    end
    g.stroke = old_stroke
  end
end

class ControlPanel < JPanel


  def initialize(organism)
    super()
    self.layout = GridBagLayout.new
    self.preferred_size = Dimension.new(200, WORLD_HEIGHT)

    constraints = GridBagConstraints.new
    constraints.weightx = 1.0
    constraints.fill = GridBagConstraints::HORIZONTAL
    constraints.insets = Insets.new(3, 5, 3, 5)
    self.add(JLabel.new("v_x0:"), constraints)

    constraints.gridwidth = GridBagConstraints::REMAINDER
    constraints.weightx = 10.0
    @velocity_x_field = JTextField.new(VX_0.to_s)
    self.add(@velocity_x_field, constraints)

    constraints.weightx = 1.0
    constraints.gridwidth = GridBagConstraints::RELATIVE
    self.add(JLabel.new("v_y0:"), constraints)

    constraints.gridwidth = GridBagConstraints::REMAINDER
    @velocity_y_field = JTextField.new(VY_0.to_s)
    self.add(@velocity_y_field, constraints)

    constraints.weighty = 1
    constraints.anchor = GridBagConstraints::NORTH;
    constraints.gridheight = GridBagConstraints::REMAINDER
    constraints.fill = GridBagConstraints::NONE
    button = JButton.new("Restart")
    button.add_action_listener do |e|
      organism.x = X_0
      organism.y = Y_0
      organism.x_final = false

      organism.vx_0 = initial_velocity_x
      organism.vy_0 = initial_velocity_y
      $current_time = 0
    end
    self.add(button, constraints)

  end

  def initial_velocity_x
    @velocity_x_field.text.to_f
  end

  def initial_velocity_y
    @velocity_y_field.text.to_f
  end
end

class ShowFrame < JFrame
  attr_accessor :universe
  def initialize
    super()
    self.title = "First Try"
    self.ignore_repaint = true

    organism = Organism.new
    organism.x = X_0
    organism.y = Y_0
    organism.vx_0 = VX_0
    organism.vy_0 = VY_0
    organism.radius = 5

    @universe = Universe.new
    @universe.add_organism(organism)
    self.content_pane.add(@universe, BorderLayout::CENTER)
    self.content_pane.add(ControlPanel.new(organism), BorderLayout::WEST)

    self.default_close_operation = JFrame::EXIT_ON_CLOSE
    self.pack()
    self.visible = true
    self.resizable = false

    Timer.new(DELAY, ->(e) { @universe.game_loop }).start
  end

end

java.awt.EventQueue::invokeLater do
  ShowFrame.new
end