class Sprite < Widget
 
  attr_reader :left, :top, :width, :height, :canvas,
              :velocity_x, :velocity_y, 
              :max_velocity_x, :max_velocity_y, 
              :min_velocity_x, :min_velocity_y, 
              :gravity_x, :gravity_y,
              :friction_x, :friction_y
 
  alias_method :x,  :left
  alias_method :y,  :top
 
  def initialize( args={}, &block )
    super()
    @args = { :width => 32,
              :height => 32,
              :top => 0,
              :left => 0 }.merge!( args )
 
    @left, @top = @args[:left], @args[:top]
    @width, @height = @args[:width], @args[:height]
 
    @velocity_x, @velocity_y = 0, 0
    @max_velocity_x, @max_velocity_y = 200, 200
    @min_velocity_x, @min_velocity_y = 4, 4 
    @gravity_x, @gravity_y = 0, 80
    @friction_x, @friction_y = 0.70, 0.70
 
    @canvas = image args
    @canvas.instance_eval( &block )
 
    @canvas.animate( 24 ) do |n|
      now = Time.now.to_f
      @last_time ||= now
 
      update_movement( now - @last_time )
      @last_time = now
    end
  end
 
  def siblings
    parent.contents.select { |c| c != self }
  end
 
  def relations
    siblings.unshift parent
  end
 
  def gravity( gx, gy )
    @gravity_x, @gravity_y = gx, gy
    @stuck = false
  end
 
  def push( px, py )
    @velocity_x += px
    @velocity_y += py
 
    @velocity_x = @max_velocity_x  if @velocity_x > @max_velocity_x
    @velocity_y = @max_velocity_y  if @velocity_y > @max_velocity_y
    @velocity_x = -@max_velocity_x if @velocity_x < -@max_velocity_x
    @velocity_y = -@max_velocity_y if @velocity_y < -@max_velocity_y
 
    @stuck = false
  end
 
  def update_bounce( dx, dy )
    if parent.style[:bouncy]
      pw, ph = parent.width, parent.height
 
      if @left < 0
        @left = 1
        if @gravity_x < 0 &&
           (@gravity_x * @friction_x - @velocity_x) < @min_velocity_x
          @velocity_x = 0
        else
          @velocity_x = -@velocity_x
        end
      elsif @left + @width > pw
        @left = pw - @width - 1
        if @gravity_x > 0 &&
           (@velocity_x - @gravity_x * @friction_x) < @min_velocity_x
          @velocity_x = 0
        else
          @velocity_x = -@velocity_x
        end
      end
 
      if @top < 0
        @top = 1
        if @gravity_y < 0 &&
           (@gravity_y * @friction_y - @velocity_y) < @min_velocity_y
          @velocity_y = 0
        else
          @velocity_y = -@velocity_y
        end
      elsif @top + @height > ph
        @top = ph - @height - 1
        if @gravity_y > 0 &&
           (@velocity_y - @gravity_y * @friction_y) < @min_velocity_y
          @velocity_y = 0
        else
          @velocity_y = -@velocity_y
        end
      end
    end
 
    siblings.each do |sib|
      next unless sib.style[:bouncy]
 
      sx, sy, sw, sh = sib.left, sib.top, sib.width, sib.height
      rebound = sib.style[:push]
 
      unless @left + @width <= sx || @left >= sx + sw ||
             @top + @height <= sy || @top >= sy + sh
 
        # collision!
 
        if @velocity_y < 0 && @top - dy > sy + sh
          @top = sy + sh - 1
          @velocity_y = -@velocity_y + rebound
        end
 
        if @velocity_y > 0 && @top - dy + @height < sy
          @top = sy - @height + 1
          @velocity_y = -@velocity_y - rebound
        end
 
        if @velocity_x < 0 && @left - dx > sx + sw
          @left = sx + sw - 1
          @velocity_x = -@velocity_x + rebound
        end
 
        if @velocity_x > 0 && @left - dx + @width < sx
          @left = sx - @width + 1
          @velocity_x = -@velocity_x - rebound
        end
      end
    end
  end
 
  def update_stick( dx, dy )
    if parent.style[:sticky]
      pw, ph = parent.width, parent.height
 
      if @velocity_y < 0 && @top < 0
        @top = 1
        @velocity_x = 0
        @velocity_y = 0
        @stuck = true
      end
 
      if @velocity_y > 0 && @top + @height > ph
        @top = ph - @height - 1
        @velocity_x = 0
        @velocity_y = 0
        @stuck = true
      end
 
      if @velocity_x < 0 && @left < 0
        @left = 1
        @velocity_x = 0
        @velocity_y = 0
        @stuck = true
      end
 
      if @velocity_x > 0 && @left + @width > pw
        @left = pw - @width - 1
        @velocity_x = 0
        @velocity_y = 0
        @stuck = true
      end
    end
 
    siblings.each do |sib|
      next unless sib.style[:sticky]
 
      sx, sy, sw, sh = sib.left, sib.top, sib.width, sib.height
      rebound = sib.style[:push]
 
      unless @left + @width < sx || @left > sx + sw ||
             @top + @height < sy || @top > sy + sh
 
        # collision!
        @stuck = true
 
        if @velocity_y < 0 && @top - dy > sy + sh
          @top = sy + sh + 1
          @velocity_x = 0
          @velocity_y = 0
        end
 
        if @velocity_y > 0 && @top - dy + @height < sy
          @top = sy - @height - 1
          @velocity_x = 0
          @velocity_y = 0
        end
 
        if @velocity_x < 0 && @left - dx > sx + sw
          @left = sx + sw + 1
          @velocity_x = 0
          @velocity_y = 0
        end
 
        if @velocity_x > 0 && @left - dx + @width < sx
          @left = sx - @width - 1
          @velocity_x = 0
          @velocity_y = 0
        end
      end
    end
  end
 
  def touching?( sibling, edge )
    sx, sy, sw, sh = sibling.left, sibling.top, sibling.width, sibling.height
 
    case edge
      when :top    
        @top == sy - @height - 1 && 
        ! (@left > sx + sw || @left + @width < sx)
      when :bottom 
        @top == sy + sh + 1 &&
        ! (@left > sx + sw || @left + @width < sx)
      when :left   
        @left == sx - @width - 1 &&
        ! (@top > sy + sh || @top + @height < sy)
      when :right
        @left == sx + sw + 1 &&
        ! (@top > sy + sh || @top + @height < sy)
    end
  end
 
  def update_movement( delta )
    return if @stuck
 
    if (@gravity_x > 0 && @left + @width < parent.width) ||
       (@gravity_x < 0 && @left > 0)
 
      if (@gravity_x > 0 && ! siblings.any? { |s| touching?( s, :left ) }) ||
         (@gravity_x < 0 && ! siblings.any? { |s| touching?( s, :right ) }) 
 
        @velocity_x += @gravity_x * delta
      end
    end
 
    if (@gravity_y > 0 && @top + @height < parent.height) ||
       (@gravity_y < 0 && @top > 0) 
 
      if (@gravity_y > 0 && ! siblings.any? { |s| touching?( s, :top ) }) ||
         (@gravity_y < 0 && ! siblings.any? { |s| touching?( s, :bottom ) })
 
        @velocity_y += @gravity_y * delta
      end
    end
 
    return if @velocity_x == 0.0 && @velocity_y == 0.0
 
    @left += (dx = @velocity_x * delta)
    @top  += (dy = @velocity_y * delta)
 
    update_bounce( dx, dy )
    update_stick( dx, dy )
 
    @velocity_x *= 1.0 - (1.0 - @friction_x) * delta
    @velocity_y *= 1.0 - (1.0 - @friction_y) * delta
 
    if @gravity_x == 0 && @velocity_x.abs < @min_velocity_x
      @velocity_x = 0
    end
 
    if @gravity_y == 0 && @velocity_y.abs < @min_velocity_y
      @velocity_y = 0
    end
 
    self.canvas.move( @left.to_i, @top.to_i )
  end
 
end
 
Shoes.app :width => 400, :height => 400, :title => "Sprite Demo" do
  background white
 
  stack :top => 0, :left => 0, :width => 400, :height => 400, :bouncy => true do
  
    stack :top => 186, :left => 100, :width => 200, :height => 28,
                   :bouncy => true, :push => 100 do
      background "ddd"
      @p = para "down", :align => 'center'
    end
 
    @s = sprite( :left => 100, :top => 50, :width => 64, :height => 64 ) do 
      fill blue 
      oval 1, 1, 62, 62
    end
  end
 
  keypress do |k|
    case k
      when :left  then @s.push( -90,   0 )
      when :right then @s.push(  90,   0 )
      when :up    then @s.push(   0, -90 )
      when :down  then @s.push(   0,  90 )
 
      when :shift_left  then @s.gravity( -80,   0 ); @p.text = "left"
      when :shift_right then @s.gravity(  80,   0 ); @p.text = "right"
      when :shift_up    then @s.gravity(   0, -80 ); @p.text = "up"
      when :shift_down  then @s.gravity(   0,  80 ); @p.text = "down"
 
      when :alt_s 
        @s.relations.each do |r| 
          r.style[:bouncy] = false
          r.style[:sticky] = true
        end
        @p.text = "sticky"
 
      when :alt_b 
        @s.relations.each do |r| 
          r.style[:bouncy] = true
          r.style[:sticky] = false
        end
        @p.text = "bouncy"
    end
  end
 
end