reader.rb

require_relative "util/userinput"
require_relative "lang/errors"
require_relative "lang/objects"
require_relative "lang/symboltable"

module Reader

  def self.read_input(input)
    if input.class != UserInput
      raise WrongInputError, input
    end

    while input.current == nil
      input.require_input
      input.skip_whitespace
    end

    # Needed for multiple input. You can do (cons 1 2)(cons 2 3) and (cons 1 2) (cons 2 3)  (See the space)
    #if input.current == ' '
      #input.next
    #end
    input.skip_whitespace

    if is_digit input.current or ((input.current == '+' or input.current=='-') and is_digit(input.get_next))
      #read a number
      number = read_number input
      if input.current == "."
        # read a float. Next must be a number again.
        input.next
        float_part = read_number input
        if input.current != " " && input.current != nil && input.current != ")" && input.current != "\n"
          # There must be a space, end of cons, or EOF now
          raise SchemeSyntaxError.new("Expected Space, ), \\n or EOF. Got #{input.current}", input)
        end
        return SchemeFloat.new("#{number.value}.#{float_part.value}")

      elsif input.current == "/"
        # read a rational. Next must be a number again.
        input.next
        denominator = read_number input
        if input.current != " " && input.current != nil && input.current != ")" && input.current != "\n"
          # There must be a space, end of cons, or EOF now
          raise SchemeSyntaxError.new("Expected Space, ), \\n or EOF. Got #{input.current}", input)
        end
        return SchemeRational.new(number.value ,denominator.value)

      else
        # Just a normal number
        return number
      end
    elsif input.current == "\""
      return read_string(input)
    elsif input.current == "("
      input.next
      return read_list(input)
    else
      return read_symbol(input)
    end
  end

  # Reads a list and returns Cons
  def self.read_list(input)
    while input.current == nil
      input.require_input
      input.skip_whitespace
    end

    input.skip_whitespace
    if input.current == ")"
      input.next # Recursion will always return SchemeNil, if we do not do this.
      return SchemeNil.instance
    end

    car = read_input(input)
    cdr = read_list(input)
    SchemeCons.new(car,cdr)
  end

  # Reads a symbol and returns the corresponding value from environment.
  def self.read_symbol(input)
    symbol = ""
    while input.current != "(" &&
      input.current != ")" &&
      input.current != " " &&
      input.current != nil &&
      input.current != "\n"
      symbol += input.current
      input.next
    end

    # Well known symbols
    case symbol
    when "nil"
      return SchemeNil.instance
    when "\#t"
      return SchemeTrue.instance
    when "\#f"
      return SchemeFalse.instance
    end
    return Symboltable.get_or_add(symbol)
  end

  # Reads a Number and returns SchemeInteger
  def self.read_number(input)
    is_negative = false
    if input.current == '-'
      is_negative = true
      input.next
    end
    if input.current == '+'
      input.next
    end

    number = ""
    while is_digit input.current
      number += input.current
      input.next
    end
    if input.current != ' ' && input.current != nil && input.current != ')' && input.current != '.' && input.current != '/' && input.current != "\n"
      # There must be a space, end of cons, dot (for floats), slash(for reationals), or EOF now
      raise SchemeSyntaxError.new("Expected Space, ), dot, slash, \\n or EOF. Got #{input.current}", input)
    end
    if is_negative
      return SchemeInteger.new(number.to_i * -1)
    else
      return SchemeInteger.new(number.to_i)
    end
  end

  # Reads a string and returns SchemeString
  def self.read_string(input)
    input.next # Skip "
    string = ""
    while input.current != "\""
      if input.current == nil
        input.require_input(true)
      end
      string += input.current
      input.next
    end

    if input.current != "\""
      raise UnterminatedStringError.new(input.input)
    end
    input.next
    SchemeString.new(string)
  end

  # Small helper to check if the given parameter is a number
  def self.is_digit(x)
    begin
      Integer(x)
      return true
    rescue ArgumentError, TypeError
      return false
    end
  end
end