text_line.rb

module TinyBasic

class TextLine
  attr_reader :no, :statements
  attr_reader :pointer

  Commands = [
    :list,
    :run,
    :new,
    :next,
    :let,
    :if,
    :goto,
    :gosub,
    :return,
    :rem,
    :for,
    :input,
    :print,
    :stop,
  ]

  Functions = [
    :rnd,
    :abs,
    :size
  ]

  Operators = [
    :">=",
    :"#",
    :">",
    :"=",
    :"<=",
    :"<",
  ]

  OtherKeys = [
    :to,
    :step,
  ]

  def initialize line
    case line
    when String
      if /^(\d*)\s*(.*)\s*/ =~ line
        @no = ($1 || 0)&.to_i
        @statements = $2.upcase
      else
        raise WhatError.new(self)
      end
      start
    when TextLine
      @no = line.no
      @statements = line.statements
      @pointer = line.pointer
    end
  end

  def error_message
    "#{no} #{statements[0...pointer]}?#{statements[pointer..-1]}"
  end

  def direct?
    no == 0
  end

  def has_statements?
    @statements&.length != 0
  end

  def skip_space
    loop do
      if statements[pointer] == ' '
        move_pointer(1)
      else
        break
      end
    end
  end

  def current
    statements[pointer]
  end

  def command?
    skip_space
    Commands.each do |cmd|
      cmd_str = cmd.to_s.upcase
      len = cmd_str.length
      0.upto len do |i|
        ch = statements[pointer + i]
        if ch == "."
          move_pointer(i + 1)
          return cmd
        end
        if cmd_str[i] == ch
          if i == len - 1
            move_pointer(i + 1)
            return cmd
          end
        else
          break
        end
      end
    end
    return nil
  end

  def number?
    skip_space
    str = ""
    i = 0
    while ch = statements[pointer + i]
      case ch
      when '0'..'9'
        str << ch
      else
        break
      end
      i += 1
    end
    move_pointer(i)
    if str.empty?
      nil
    else
      n = str.to_i
      raise HowError(self) unless n <= 32768
      n
    end
  end

  def string?
    skip_space
    i = 0
    quote = nil
    loop do
      ch = statements[pointer + i]
      case ch
      when '"', "'"
        quote = ch
        move_pointer(1)
        break
      else
        return nil
      end
    end

    str = ""
    loop do
      ch = statements[pointer + i]
      case ch
      when quote, nil
        move_pointer(1)
        return str
      else
        str += ch
        move_pointer(1)
      end
    end
  end

  def function?
    skip_space
    Functions.each do |func|
      func_str = func.to_s.upcase
      len = func_str.length
      0.upto len do |i|
        ch = statements[pointer + i]
        if ch == "."
          move_pointer(i + 1)
          return func
        end
        if func_str[i] == ch
          if i == len - 1
            move_pointer(i + 1)
            return func
          end
        else
          break
        end
      end
    end
    return nil
  end

  def operator?
    skip_space
    Operators.each do |oper|
      oper_str = oper.to_s.upcase
      len = oper_str.length
      0.upto len do |i|
        ch = statements[pointer + i]
        if oper_str[i] == ch
          if i == len - 1
            move_pointer(i + 1)
            return oper
          end
        else
          break
        end
      end
    end
    return nil
  end

  def other_key?
    skip_space
    OtherKeys.each do |key|
      key_str = key.to_s.upcase
      len = key_str.length
      0.upto len do |i|
        ch = statements[pointer + i]
        if key_str[i] == ch
          if i == len - 1
            move_pointer(i + 1)
            return key
          end
        else
          break
        end
      end
    end
    return nil
  end

  def end_line?
    skip_space
    i = 0
    loop do
      case statements[pointer + i]
      when nil
        break
      else
        move_pointer(i)
        return false
      end
    end
    move_pointer(i)
    true
  end

  def variable?
    skip_space
    var = statements[pointer]
    if ('A'..'Z').include?(var) || var == '@'
      move_pointer(1)
      return var
    end
    nil
  end

  def separator?
    charactor? ';'
  end

  def sharp?
    charactor? '#'
  end

  def comma?
    charactor? ','
  end

  def left_parenthesis?
    charactor? '('
  end
  
  def right_parenthesis?
    charactor? ')'
  end

  def adding?
    charactor? '+'
  end
  
  def subtracting?
    charactor? '-'
  end
  
  def multiplying?
    charactor? '*'
  end
  
  def dividing?
    charactor? '/'
  end
  
  def equal?
    charactor? '='
  end


  # pointer operations

  def start
    @pointer = 0
  end

  def stop
    @pointer = @statements.size
  end

  def move_pointer n
    @pointer = [@pointer + n, @statements.size].min
  end

  private

  def charactor? ch
    skip_space
    if statements[pointer] == ch
      move_pointer(1)
      true
    else
      false
    end
  end


end

end