namespace Lunar.Evil_Calculator
{
    internal static class ReversePolishNotationSolver
    {
        private static List<Token> ToReversePolishNotation(List<Token> equation)
        {
            List<Token> reversedEquation = new List<Token>();
            Stack<Token> operators = new Stack<Token>();
            foreach (Token token in equation)
            {
                if (token.tokenType == Token.TokenType.Operand)
                {
                    reversedEquation.Add(token);
                }
                if (token.tokenType == Token.TokenType.Operator)
                {
                    if (token.value == "(")
                    {
                        operators.Push(token);
                    }
                    else if (token.value == ")")
                    {
                        while (operators.Peek().value != "(")
                        {
                            reversedEquation.Add(operators.Pop());
                        }
                        operators.Pop();
                    }
                    else
                    {
                        while (operators.Count != 0 && operators.Peek().priority >= token.priority)
                        {
                            reversedEquation.Add(operators.Pop());
                        }
                        operators.Push(token);
                    }
                }
            }
            while (operators.Count != 0)
            {
                reversedEquation.Add(operators.Pop());
            }

            return reversedEquation;
        }

        
        public static string Solve(List<Token> originalEquation)
        {
            List<Token> reversedEquation = ToReversePolishNotation(originalEquation);
            Stack<Token> stack = new Stack<Token>();
            foreach (Token token in reversedEquation)
            {
                double result, left, right;
                if (token.tokenType == Token.TokenType.Operand)
                {
                    stack.Push(token);
                }
                if (token.tokenType == Token.TokenType.Operator)
                {
                    switch (token.value)
                    {
                        case "+":
                            right = Convert.ToDouble(stack.Pop().value);
                            left = Convert.ToDouble(stack.Pop().value);
                            result = left + right;
                            stack.Push(new Token(Token.TokenType.Operand, result.ToString()));
                            break;
                        case "-":
                            right = Convert.ToDouble(stack.Pop().value);
                            left = Convert.ToDouble(stack.Pop().value);
                            result = left - right;
                            stack.Push(new Token(Token.TokenType.Operand, result.ToString()));
                            break;
                        case "*":
                            right = Convert.ToDouble(stack.Pop().value);
                            left = Convert.ToDouble(stack.Pop().value);
                            result = left * right;
                            stack.Push(new Token(Token.TokenType.Operand, result.ToString()));
                            break;
                        case "/":
                            right = Convert.ToDouble(stack.Pop().value);
                            left = Convert.ToDouble(stack.Pop().value);
                            result = left / right;
                            stack.Push(new Token(Token.TokenType.Operand, result.ToString()));
                            break;
                        case "^":
                            right = Convert.ToDouble(stack.Pop().value);
                            left = Convert.ToDouble(stack.Pop().value);
                            result = Math.Pow(left, right);
                            stack.Push(new Token(Token.TokenType.Operand, result.ToString()));
                            break;
                    }
                }
            }
            return stack.Pop().value;
        }
    }
}