require './ellipsoid.rb'

# One particle is basically a sprite, that moves itself by speed every tick along an angle.
# It also has a concept of decay, in how quickly the particle dies. In this case, the draw
# command takes into account decay to shrink the particles and make them more translucent.
class Particle 
  def initialize(window, x, y, ang, speed, decay)
    @x = x
    @y = y
    @angle =  90-ang
    @speed = speed
    @d_x = offset_x(@angle, @speed)
    @d_y = offset_y(@angle, @speed)
    @life = 1
    @decay = decay
    
    radius = (rand * 10).floor
    @img = Gosu::Image.new(window, Ellipsoid.new(radius), false)
  end
  
  def update
    @x = @x + @d_x
    @y = @y + @d_y
    @life = @life - @decay
    @angle += (@speed / 2)
  end
  
  def dead?
    @life <= 0
  end
  
  def draw_layer(layer, color, x = nil, y = nil)
     @img.draw_rot(x || @x, y || @y, layer, @angle, 0.5, 0.5, @life, @life, color, :default)    
  end
  
  def draw
    return if dead?
    draw_layer(ZOrder::Shadow, Gosu::Color.new((@life * 128).floor,0,0,0), @x+2, @y+2)
    draw_layer(ZOrder::Shape, Gosu::Color.new((@life * 255).floor, 128,128,128))
    draw_layer(ZOrder::Highlight, Gosu::Color.new((@life * 20).floor,200,200,200))
  end
end


# This class keeps track of our moving particles. It loads in a few white png files, and removes
# dead particles during every tick. They could probably be garbage collected less frequently.
class Particles
  
  def initialize(window)
    @particles = []
    @window = window
  end
  
  def update
    @particles.each {|p| p.update}
    @particles.delete_if {|p| p.dead?}
  end
  
  def draw
    @particles.each {|p| p.draw}
  end
  
  def create(x, y, angle, speed)
    @particles << Particle.new(@window, x, y, angle, speed, 0.01)
  end
  
end