require 'tk'

class TkMove
  def initialize( canvas )
    @x0, @y0 = 0, 0
    @canvas = canvas
    @tag = 'item'
  end

  def bind
    @canvas.itembind( @tag, '1', proc{|x, y| plotDown x, y},"%x %y")
    @canvas.itembind( @tag, 'B1-Motion', proc{|x, y| plotMove x, y},"%x %y")
  end
  def unbind
    @canvas.itembind( @tag, '1', proc{} )
    @canvas.itembind( @tag, 'B1-Motion', proc{} )
  end

  def plotDown(x, y)
    @canvas.dtag 'selected'
    @canvas.addtag_withtag 'selected', 'current'
    @canvas.raise 'current'
    @x0, @y0 = x, y
  end
  def plotMove(x, y)
    @canvas.move 'selected', x - @x0, y - @y0
    @x0, @y0 = x, y
  end
end

class TkDraw
  def initialize( canvas )
    @canvas = canvas
    @tag = 'item'
    @type = 'default'
    @x0, @y0 = 0, 0
  end

  def bind
    @canvas.bind('1', proc{|x, y| create_item(x, y)}, "%x %y")
    @canvas.bind('B1-Motion', proc{|x, y| adjust_item(x, y)}, "%x %y")
  end
  def unbind
    @canvas.bind('1', proc{})
    @canvas.bind('B1-Motion', proc{})
  end

  def create_item(x, y)
    @item = new_item(x, y)
    @item.addtag( @tag )
    @canvas.dtag 'selected'
    @canvas.addtag_withtag 'selected', @item.id
    @x0, @y0 = x, y
  end
  def new_item(x, y)
    'not defined'
  end
  def adjust_item(x, y)
    @item.coords( @x0, @y0, x, y )
  end
end

class TkdLine < TkDraw
  def initialize( canvas )
    super
    @type = 'line'
  end
  def new_item(x, y)
    TkcLine.new( @canvas, x, y, x, y, 'width'=>2 )
  end
end

class TkdRectangle < TkDraw
  def initialize( canvas )
    super
    @type = 'rectangle'
  end
  def new_item(x, y)
    TkcRectangle.new( @canvas, x, y, x, y, 'fill'=>'white' )
  end
end

class TkdOval < TkDraw
  def initialize( canvas )
    super
    @type = 'oval'
  end
  def new_item(x, y)
    TkcOval.new( @canvas, x, y, x, y, 'fill'=>'red' )
  end
end

class TkDelete
  def initialize( canvas )
    @canvas = canvas
    @tag = 'item'
  end

  def bind
    @canvas.itembind( @tag, '1', proc{ delete } )
    @canvas.itembind( @tag, 'B1-Motion', proc{} )
  end
  def unbind
    @canvas.itembind( @tag, '1', proc{} )
    @canvas.itembind( @tag, 'B1-Motion', proc{} )
  end

  def delete
    @canvas.delete('current')
  end
end

# main routine #

c = TkCanvas.new.pack
m = TkMove.new( c )
l = TkdLine.new( c )
r = TkdRectangle.new( c )
o = TkdOval.new( c )
d = TkDelete.new( c )

TkFrame.new{|f|
  TkButton.new(f, 'text'=>'Lin', 'command'=>proc{m.unbind; l.bind}).pack('side'=>'left')
  TkButton.new(f, 'text'=>'Rct', 'command'=>proc{m.unbind; r.bind}).pack('side'=>'left')
  TkButton.new(f, 'text'=>'Ovl', 'command'=>proc{m.unbind; o.bind}).pack('side'=>'left')
  TkButton.new(f, 'text'=>'Mv', 'command'=>proc{l.unbind; m.bind}).pack('side'=>'left')
  TkButton.new(f, 'text'=>'Del', 'command'=>proc{l.unbind; m.unbind; d.bind}).pack('side'=>'left')
  TkButton.new(f, 'text'=>'Bye', 'command'=>proc{exit}).pack('side'=>'left')
}.pack

Tk.mainloop