namespace Lunar.Evil_Calculator
{
    class EquationManager
    {
        private static readonly HashSet<string> _operators = new() { "+", "-", "*", "/", "^", "√" };

        List<Token> equation = new();
        string currentOperand = "";
        Label? outerEquationLabel;
        Label? outerOperandLabel;
        int openParentheses;


        //NO OPENING PARENTHESES AFTER NUMERICS OR CLOSING PARENTHESES => NULL, OPENING PARENTHESES OR OPERATOR EXPECTED
        //NO CLOSING PARENTHESES AFTER OPERATORS, EXCEPT IF $currentOperand IS NOT ""
        //NO CLOSING PARENTHESES WHEN $openParentheses <1
        //OPERATOR OR null BEFORE OPENING PARENTHESES EXPECTED
        //$openParentheses SHOULD BE 0 BEFORE SOLVING, DISPLAY ERROR OTHERWISE => HANDLED BY SOLVER
        //MINUS AFTER OPENING PARENTHESES OR null GOES TO OPERAND IF $currentOperand IS ""
        //NO OPERATORS AFTER OPERATORS, OPENING PARENTHESES OR null (EXCEPT FOR MINUS THAT GOES TO OPERAND AND SQRT THAT IS UNAR)
        //NO NUMERICS IF currentOperand.StartsWith("0") AND currentOperand.Length == 1, . ALLOWED-EXPECTED
        //NO . IF currentOperand.Contains(",")


        public void ProcessButtonInput(object? sender, EventArgs e)
        {
            if (sender is Button buttonPressed)
            {
                switch (buttonPressed.Text)
                {
                    //CLEAR
                    case "C":
                        currentOperand = "";
                        break;
                    case "CE":
                        equation.Clear();
                        currentOperand = "";
                        break;
                    //OPERATORS
                    // + -
                    case "+":
                        if ((!IsOperator() && !IsOpen() && !IsNull()) || currentOperand != "" && currentOperand != "-")
                        {
                            equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                            equation.Add(new Token(Token.TokenType.Operator, buttonPressed.Text, 1));
                            currentOperand = "";
                        }
                        break;
                    case "-":
                        if ((!IsOperator() || currentOperand != "") && currentOperand != "-")
                        {
                            if ((IsOpen() || IsNull()) && currentOperand == "")
                            {
                                currentOperand += "-";
                            }
                            else
                            {
                                equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                                equation.Add(new Token(Token.TokenType.Operator, buttonPressed.Text, 1));
                                currentOperand = "";
                            }
                        }
                        break;
                    // * /
                    case "*" or "/":
                        if ((!IsOperator() && !IsOpen() && !IsNull()) || currentOperand != "" && currentOperand != "-")
                        {
                            equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                            equation.Add(new Token(Token.TokenType.Operator, buttonPressed.Text, 2));
                            currentOperand = "";
                        }
                        break;
                    //SQUARE ROOT
                    case "√":
                        if (!IsClose())
                        {
                            equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                            equation.Add(new Token(Token.TokenType.Operator, buttonPressed.Text, 3));
                            currentOperand = "";
                        }
                        break;
                    //SQUARE AND POWER
                    case "x²":
                        if ((!IsOperator() && !IsOpen() && !IsNull()) || currentOperand != "" && currentOperand != "-")
                        {
                            equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                            equation.Add(new Token(Token.TokenType.Operator, "^", 3));
                            equation.Add(new Token(Token.TokenType.Operand, "2"));
                            currentOperand = "";
                        }
                        break;
                    case "xˣ":
                        if ((!IsOperator() && !IsOpen() && !IsNull()) || currentOperand != "" && currentOperand != "-")
                        {
                            equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                            equation.Add(new Token(Token.TokenType.Operator, "^", 3));
                            currentOperand = "";
                        }
                        break;
                    //PARENTHESES
                    case "(":
                        if (IsOperator() || IsOpen() || IsNull())
                        {
                            equation.Add(new Token(Token.TokenType.Operator, buttonPressed.Text));
                            openParentheses++;
                            currentOperand = "";
                        }
                        break;
                    case ")":
                        if ((!IsOperator() || currentOperand != "") && openParentheses > 0 && currentOperand != "-")
                        {
                            if (currentOperand.Length > 0)
                            {
                                equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                                currentOperand = "";
                            }
                            equation.Add(new Token(Token.TokenType.Operator, buttonPressed.Text));
                            openParentheses--;
                        }
                        break;
                    //POINT
                    case ",":
                        if (currentOperand.Length > 0 && !currentOperand.Contains(","))
                        {
                            currentOperand += buttonPressed.Text;
                        }
                        break;
                    //NUMERIC
                    default:
                        if (!(currentOperand.Length == 1 && currentOperand.StartsWith("0")))
                        {
                            currentOperand += buttonPressed.Text;
                        }
                        break;
                }
                
                UpdateLabels();
            }
        }

        public void EqualsButtonPressed(object? sender, EventArgs e)
        {
            if (sender is Button buttonEquals)
            {
                if (currentOperand != "") equation.Add(new Token(Token.TokenType.Operand, currentOperand));
                buttonEquals.Text = "#";
                currentOperand = ReversePolishNotationSolver.Solve(equation);
                UpdateLabels();
            }
        }

        public void AcquireOutputLabels(Label equationTextBox, Label currentOperandTextBox)
        {
            outerEquationLabel = equationTextBox;
            outerOperandLabel = currentOperandTextBox;
        }

        public string equationToString()
        {
            string equationString = "";
            foreach (Token token in equation)
            {
                equationString += token.value + " ";
            }
            return equationString;
        }

        private void UpdateLabels()
        {
            if (outerEquationLabel != null && outerOperandLabel != null)
            {
                outerEquationLabel.Text = equationToString();
                outerOperandLabel.Text = currentOperand == "" ? "0" : currentOperand;
            }
        }
        
        private bool IsOperator()
        {
            if (equation.Count == 0) return false;
            return _operators.Contains(equation.Last().value);
        }

        private bool IsOpen()
        {
            if (equation.Count == 0) return false;
            return equation.Last().value == "(";
        }

        private bool IsClose()
        {
            if (equation.Count == 0) return false;
            return equation.Last().value == ")";
        }

        private bool IsNull()
        {
            return equation.Count == 0;
        }
    }
}