# Interpeterパターン
#
# Java言語で学ぶデザインパターンと同様の例題をRubyで記述した。
#
# coded by Takehiro Kaga
#


# <program> ::= program <command list>
class ProgramNode
  def perse(context)
    context.skipToken("program")
    @commandListNode = CommandListNode.new
    @commandListNode.perse(context)
  end
  def toString
    "[program " + @commandListNode.toString + "]"
  end
end

# <command list> ::= <command>* end
class CommandListNode
  def initialize
    @list = UserList.new
  end
  def perse(context)
    while true
      if context.currentToken == nil
        err
      elsif context.currentToken == "end"
        context.skipToken("end")
        break
      else
        @commandNode = CommandNode.new
        @commandNode.perse(context)
        @list.push(@commandNode)
      end
    end
  end
  def toString
    "" + @list.toString
  end
end

class UserList < Array
  def toString
    char = "["
    self.each{|item| 
      temp = "" + item.toString + ", "
      char += temp
      }
    if char != "["
    char = char.chop
    char = char.chop  
    end
    char += "]"
  end
end


# <command> ::= <repeat command> | <primitive command>
class CommandNode
  def perse(context)
    if context.currentToken == "repeat"
      @node = RepeatCommandNode.new
      @node.perse(context)
    else
      @node = PrimitiveCommandNode.new
      @node.perse(context)
    end
  end
  def toString
    @node.toString
  end
end

# <repeat command> ::= repeat <number> <command list>
class RepeatCommandNode
  def initialize
    @commandListNode = Array.new
  end
  def perse(context)
    context.skipToken("repeat")
    @number = context.currentNumber
    context.nextToken
    @commandListNode = CommandListNode.new
    @commandListNode.perse(context)
  end
  def toString
    "[repeat " + @number + " " + @commandListNode.toString + "]"
  end
end

# <primitive command> ::= go | right | left
class PrimitiveCommandNode
  def perse(context)
    @name = context.currentToken
    context.skipToken(@name)
    if @name != "go" and @name != "right" and @name != "left"
       puts "name error"
    end
  end
  def toString
    @name.to_s
  end
end

# newした時にカレントトークンをセットしておく。
# text をワード単位に取り出してアレイにセットしておく。#
# skipTokenではカレントトークンが引数と一致しなければ例外を発生する。
# currentNumberはカレントトークンのストリングを数値に変換する。
class Context
  def initialize(text)
    @tokenizer = text.scan(/\w+/) 
    nextToken
  end
  def nextToken
    @currentToken = @tokenizer.shift
  end
  def currentToken
    @currentToken
  end
  def skipToken(token)
    if token != @currentToken
      puts "skipToken Error"
    end
    nextToken
  end
  def currentNumber
    @number = @currentToken.to_s
    @number
  end
end


# ---- Main ---- #

textArray = ["program end",
             "program go end",
             "program go right go right go right go right end",
             "program repeat 4 go right end end", 
             "program repeat 4 repeat 3 go right go left end right end end"
             ]

textArray.each{|text| 
               puts "text = \"" + text + "\""
               node = ProgramNode.new
               node.perse(Context.new(text))
               puts "node = " + node.toString
              }