RubyAlgebra/lib/ruby_algebra/parser.rb

# frozen_string_literal: true

module RubyAlgebra
  module Parser
    class Token
      attr_reader :type
    end

    class NumberToken < Token
      attr_reader :value

      def initialize(value)
        @type = :num
        @value = value
      end
    end

    class IdentifierToken < Token
      attr_reader :name

      def initialize(name)
        @type = :id
        @name = name
      end
    end

    class BinaryOperatorToken < Token
      attr_reader :op

      def initialize(op)
        @type = :op
        @op = op
      end
    end

    class UnaryOperatorToken < Token
      attr_reader :op

      def initialize(op)
        @type = :unary_op
        @op = op
      end
    end

    class ParenthesisToken < Token
      attr_reader :closing

      def initialize(closing)
        @type = :paren
        @closing = closing
      end
    end

    class EndToken < Token
      def initialize()
        @type = :end
      end
    end

    def self.tokenize(e)
      i = 0
      add_implicit_mul = false
      while i < e.length
        c = e[i]
        if c.match?(/\p{Alpha}/)
          yield BinaryOperatorToken.new(:mult) if add_implicit_mul
          j = i + 1
          j += 1 while j < e.length && e[j].match?(/\p{Alnum}/)
          add_implicit_mul = true
          yield IdentifierToken.new(e[i...j])
          i = j
        elsif c.match?(/[+\-*\/^()]/)
          yield BinaryOperatorToken.new(:mult) if c == "(" && add_implicit_mul
          i += 1
          case c
          when "+"
            if add_implicit_mul
              yield BinaryOperatorToken.new(:add)
            else
              yield UnaryOperatorToken.new(:positive)
            end
          when "-"
            if add_implicit_mul
              yield BinaryOperatorToken.new(:sub)
            else
              yield UnaryOperatorToken.new(:negative)
            end
          when "*"
            yield BinaryOperatorToken.new(:mult)
          when "/"
            yield BinaryOperatorToken.new(:div)
          when "^"
            yield BinaryOperatorToken.new(:pow)
          when "("
            yield ParenthesisToken.new(false)
          when ")"
            yield ParenthesisToken.new(true)
          end
          add_implicit_mul = c == ")"
        elsif c.match?(/\p{Digit}|\./)
          yield BinaryOperatorToken.new(:mult) if add_implicit_mul
          j = i + 1
          j += 1 while j < e.length && e[j].match?(/\p{Digit}|\./)
          s = e[i...j]
          fl = s.count "."
          if fl > 1
            raise Exception.new
          end
          add_implicit_mul = true
          if fl == 0
            yield NumberToken.new(s.to_i)
          else
            yield NumberToken.new(s.to_f)
          end
          i = j
        elsif c == " "
          i += 1
        else
          i += 1
        end
      end
      yield EndToken.new
    end

    def self.parse(expr)
      operators = []
      out_stack = []
      tokenize(expr) do |token|
        if token.type == :num
          out_stack.push(Constant.new(token.value))
        elsif token.type == :end
          _parse_make_op(operators, out_stack) until operators.empty?
        elsif token.type == :op || token.type == :unary_op
          p = _parse_op_prio token
          while operators.length != 0 && (operators.last.type == :op || operators.last.type == :unary_op) && (_parse_op_prio(operators.last) > p || (_parse_op_prio(operators.last) == p && token.op != :pow && token.op != :positive && token.op != :negative))
            _parse_make_op(operators, out_stack)
          end
          operators.push(token)
        elsif token.type == :paren
          if token.closing
            until operators.empty? || (operators.last.type == :paren && !operators.last.closing)
              _parse_make_op(operators, out_stack)
            end
            if operators.empty? || operators.last.type != :paren || operators.last.closing
              raise Exception.new
            else
              operators.pop
            end
          else
            operators.push token
          end
        elsif token.type == :id
          out_stack.push(Variable.new(token.name))
        end
      end
      out_stack[0]
    end

    def self._parse_make_op(operators, out_stack)
      oper = operators.pop
      unless (oper.type == :op && out_stack.length >= 2) || (oper.type == :unary_op && out_stack.length >= 1)
        raise Exception.new
      end
      b = out_stack.pop if oper.type == :op
      a = out_stack.pop

      case oper.op
      when :add
        out_stack.push Addition.new(a, b)
      when :sub
        out_stack.push Subtraction.new(a, b)
      when :mult
        out_stack.push Multiplication.new(a, b)
      when :div
        out_stack.push Division.new(a, b)
      when :pow
        out_stack.push Power.new(a, b)
      when :positive
        out_stack.push a
      when :negative
        if a.type == :constant
          out_stack.push Constant.new(-a.value)
        else
          out_stack.push Multiplication.new(Constant.new(-1), a)
        end
      end
    end

    def self._parse_op_prio(op_token)
      case op_token.op
      when :add, :sub
        1
      when :mult, :div
        2
      when :pow, :positive, :negative
        3
      end
    end
  end
end