require 'tk'
require 'enumerator'

class Calculator  
  def initialize()  
    @number_buttons = []         #references of the buttons 0-9
    @operand_buttons = []        #references of the operand buttons
    @current_operand = ""        #the operand currently typed in
    @second_operand = "x"        #the second operand in the case of a binary operation
    @binary_operators = {'*' => 'asterisk', '/' => 'slash', '+' => 'plus', '-' => 'minus', '%' => 'percent'}
    @unary_operators = { 'x*x' => "operand ** 2",  'sqrt' => "Math.sqrt(operand)" ,
                         'sin' => "Math.sin(operand)", 'fact' => "factorial(operand)"}
    @root = TkRoot.new("geometry"=>"345x220") { title "Scientific calculator!" } 
    @result_ready = false                            
    setup_number_buttons
    setup_operand_buttons
    setup_display    
    bind_events
    Tk.mainloop
  end
      
  def setup_number_buttons
    @buttons_frame = TkFrame.new(@root).pack("side"=>"bottom")
    (1..9).to_a.each_slice(3) do |s|
      s.each {|n| @number_buttons << TkButton.new(@buttons_frame, "text"=> n.to_s) }
      TkGrid.grid(*@number_buttons.slice(s[0]-1..s[2]-1))
    end
    @number_buttons.unshift TkButton.new(@buttons_frame, "text"=> "0")
    @number_buttons[0].grid("columnspan"=>3, "sticky"=>"ew")
    TkGrid.configure(*@number_buttons) 
  end
  
  def setup_display
    @display_frame = TkFrame.new(@root).pack("side"=>"top")
    @display = TkText.new(@display_frame, 'background'=>"#FFF4C1").pack()
    @display.font(TkFont.new('arial').configure('size'=>18))
  end
  
  def setup_operand_buttons
    all_operators = @binary_operators.keys + @unary_operators.keys
    @c_button = TkButton.new(@buttons_frame, "text"=> "C")
    @c_button.grid("row"=>0, "column"=>3, "rowspan"=>2, "sticky"=>"ns")
    (0..8).to_a.each_slice(3) do |s|
      s.each { |n| @operand_buttons << TkButton.new(@buttons_frame, "text"=> all_operators[n]).grid("row"=>n % 3, "column"=>3+(s[2]+1)/3, "sticky"=>"ew") }
    end    
    @equal_button = TkButton.new(@buttons_frame, "text"=> "=")
    @equal_button.grid("row"=>3, "column"=>4, "columnspan"=>3, "sticky"=>"ew")
  end
  
  def bind_events
    @number_buttons.each do |button|
      @root.bind("Any-Key-#{button.text}") { update_display(button) }      
    end
    @operand_buttons.each do |button|
      keysym = @binary_operators[button.text]
      @root.bind("Shift-Key-#{keysym}") { update_display(button) } unless keysym == nil
    end
    @root.bind("Any-Key-equal") { calculate }
    @root.bind("Any-Button-1") {|event| update_display(event.widget)}
  end
  
  def update_display(target)
    return if !target.kind_of? TkButton #so that clicks on a non-button widget is not intercepted
    text = target.text
    if (text == '=')
      calculate
    elsif (text == 'C')
      clear_display
    elsif (@unary_operators.include? text)     
      @display.clear      
      @display.insert("end", result = "#{eval(@unary_operators[text].sub(/operand/, @current_operand.to_s ))}")
      @current_operand = result.to_s
    elsif (@binary_operators.include? text)
      @result_ready = false
      @current_operator = target.text
      @second_operand = ""
    else
      @display.clear if (@current_operand == "") || @result_ready
      if @result_ready
        @result_ready = false
        @current_operand = ""
      end
      if (@second_operand == 'x')
        @current_operand += target.text
      elsif (@second_operand == '')
        @display.clear        
        @second_operand += target.text
      else
        @second_operand += target.text
      end
      @display.insert('end', target.text)
    end
  end  
  
  #Thanks to James Edward Gray II - http://blog.grayproductions.net/articles/2006/01/17/recursion-and-callbacks
  def factorial( number ) (1..number).inject { |prod, n| prod * n } end    
  
  def calculate
    @display.clear
    @display.insert('end', result=eval("#{@current_operand} #{@current_operator} #{@second_operand}"))
    @current_operand = result.to_s
    @second_operand = "x"
    @result_ready = true
  end  
  
  def clear_display
    @result_ready = false
    @current_operand = ""
    @second_operand = "x"    
    @display.clear
  end
end

Calculator.new