using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Engine
{
    public partial class Form1 : Form
    {
        //Invert over all expression (i + 7) ^ 2 -> -(i + 7) ^ 2

        private Stack<Node> Tree = new Stack<Node>();
        private Dictionary<string, double> Symbols = new Dictionary<string, double>();

        public Form1()
        {
            InitializeComponent();
        }

        private void Button1_Click(object sender, EventArgs e)
        {
            var s = textBox1.Text;
            var f = FlattenInput(s);
            PrintFlatList(f);
            f.Reverse();
            var stack = new Stack<Token>(f);
            ActionsListView.Items.Clear();

            button1.Text = "Result: " + NewCalc(stack);
            //var f2 = GetSubExpressions(f);
            //PrintSteps(f2);
            //PrintSymbolsTable();
            //var result = Calc(f2);
            //button1.Text = $"Result: {result}";
            //var result = Calc(FlattenInput(s));            
        }

        void PrintSteps(List<List<Node>> expressions)
        {
            StepsListView.Items.Clear();

            for(var i = 0; i < expressions.Count; i++)
            {
                var expression = expressions[i];
                var item = new ListViewItem($"Step {i + 1}");
                var ex = string.Empty;

                foreach (var token in expression)
                {
                    if (!token.IsCoefficent)
                        ex += token.Value + " ";
                    else
                        ex += token.Value;
                }

                item.SubItems.Add(ex);
                StepsListView.Items.Add(item);
            }
        }

        void PrintSymbolsTable()
        {
            SymbolsListView.Items.Clear();

            foreach(var k in Symbols)
            {
                var item = new ListViewItem(k.Key);
                item.SubItems.Add(k.Value.ToString());

                SymbolsListView.Items.Add(item);
            }
        }

        void PrintFlatList(List<Token> tokens)
        {
            ExpressionBreakdownListView.Items.Clear();

            foreach(var token in tokens)
            {  
                var item = new ListViewItem(token.Value);
                if(!token.IsCoefficent) item.SubItems.Add(token.Type.ToString());
                else item.SubItems.Add(token.Type.ToString() + " (Coefficent)");

                ExpressionBreakdownListView.Items.Add(item);
            }
        }

        double NewCalc(Stack<Token> tokens, double co = 1)
        {
            var previousToken = new Token() { Type = TokenType.Unknown };
            var runningValue = 0d;

            while(tokens.Count > 0)
            {
                var token = tokens.Pop();

                if (token.Type == TokenType.ExpEnd)
                {
                    if(tokens.Count > 0 && tokens.Peek().Type == TokenType.Power)
                    {
                        var op = tokens.Pop();
                        var powerOf = tokens.Pop();

                        if(powerOf.Type == TokenType.Constant)
                        {
                            ActionsListView.Items.Add($"Taking {runningValue} to the power of {powerOf.Value}.");
                            runningValue = Operate(runningValue, Convert.ToDouble(powerOf.Value), op.Type);
                        }
                    }

                    break;
                }

                if(token.Type == TokenType.ExpStart)
                {
                    runningValue = NewCalc(tokens);
                    continue;
                }

                if(token.IsCoefficent)
                {
                    var lookAHead = tokens.Pop();

                    if (lookAHead.Type == TokenType.Variable)
                    {
                        ActionsListView.Items.Add($"{token.Value} is a coeffiecent, multiplying it against {Symbols[lookAHead.Value]} (Symbol '{lookAHead.Value}').");
                        runningValue += Convert.ToDouble(token.Value) * Symbols[lookAHead.Value];
                        if (previousToken.Type != TokenType.Unknown) throw new Exception("Token shouldn't have a valid value!");
                        //2a(
                        if(tokens.Count != 0 && tokens.Peek().Type == TokenType.ExpStart)
                        {
                            runningValue += NewCalc(tokens, runningValue);
                        }

                        previousToken = new Token() { Type = TokenType.Constant, Value = runningValue.ToString(), IsCoefficent = false };
                        continue;
                    }
                    else if (lookAHead.Type == TokenType.ExpStart)
                    {
                        runningValue += NewCalc(tokens, Convert.ToDouble(token.Value));
                        previousToken = new Token() { Type = TokenType.Constant, Value = runningValue.ToString(), IsCoefficent = false };
                        continue;
                    }
                    else throw new Exception("Invalid grammar!");
                }
                //If token is an operator
                if(GetOperator(token.Value[0]) != TokenType.Unknown)
                {
                    //Operator found
                    var lookAHead = tokens.Pop();

                    if(lookAHead.Type == TokenType.Constant && !lookAHead.IsCoefficent)
                    {
                        var tmpValue = 0d;

                        while (tokens.Count > 0 && (tokens.Peek().Type == TokenType.Multiply || tokens.Peek().Type == TokenType.Divide || tokens.Peek().Type == TokenType.Power))
                        {                            
                            var op = tokens.Pop();

                            if (op.Type != TokenType.Power)
                            {
                                var next = tokens.Pop();

                                if (next.Type == TokenType.ExpStart)
                                {
                                    var returnValue = NewCalc(tokens);

                                    if (tmpValue != 0)
                                    {
                                        ActionsListView.Items.Add($"{GetOperatorVerb(op.Type)} {tmpValue} (tmp) and {returnValue} (returnValue).");
                                        tmpValue = Operate(tmpValue, returnValue, op.Type);
                                        lookAHead.Value = tmpValue.ToString();
                                    }
                                    else
                                    {
                                        ActionsListView.Items.Add($"{GetOperatorVerb(op.Type)} {Convert.ToDouble(lookAHead.Value) * co} (lookAHead) and {returnValue} (returnValue).");
                                        tmpValue = Operate(Convert.ToDouble(lookAHead.Value) * co, returnValue, op.Type);
                                        lookAHead.Value = tmpValue.ToString();
                                    }

                                    continue;
                                }

                                if (tmpValue != 0)
                                {
                                    ActionsListView.Items.Add($"{GetOperatorVerb(op.Type)} {tmpValue} (tmp) and {Convert.ToDouble(next.Value) * co} (next).");
                                    tmpValue = Operate(tmpValue, Convert.ToDouble(next.Value) * co, op.Type);
                                    lookAHead.Value = tmpValue.ToString();
                                }
                                else
                                {
                                    ActionsListView.Items.Add($"{GetOperatorVerb(op.Type)} {Convert.ToDouble(lookAHead.Value) *co} (lookAHead) and {next.Value} (next).");
                                    tmpValue = Operate(Convert.ToDouble(lookAHead.Value) *co, Convert.ToDouble(next.Value) *co, op.Type);
                                    lookAHead.Value = tmpValue.ToString();
                                }
                            }
                            else if (op.Type == TokenType.Power)
                            {

                            }
                        }

                        //if(tokens.Count > 0 && (tokens.Peek().Type == TokenType.Divide || tokens.Peek().Type == TokenType.Multiply || tokens.Peek().Type == TokenType.Power))
                        //{
                        //    var op = tokens.Pop();
                        //    var con = tokens.Pop();
                        //    //TODO: check if "con" is a variable, right now we're assuming its a constant.
                        //    ActionsListView.Items.Add($"{GetOperatorVerb(op.Type)} {Convert.ToDouble(lookAHead.Value) * co} and {Convert.ToDouble(con.Value) * co} (Oder of Operations).");
                        //    var tmp = Operate(Convert.ToDouble(lookAHead.Value) * co, Convert.ToDouble(con.Value) * co, op.Type);

                        //    ActionsListView.Items.Add($"{GetOperatorVerb(token.Type)} {Convert.ToDouble(previousToken.Value) * co} and {tmp}.");
                        //    runningValue += Operate(Convert.ToDouble(previousToken.Value) * co, tmp, token.Type);
                        //    previousToken = new Token { Type = TokenType.Unknown };
                        //}
                        //else
                        //{
                        if (previousToken.Type != TokenType.Unknown)
                        {
                            ActionsListView.Items.Add($"{GetOperatorVerb(token.Type)} {Convert.ToDouble(previousToken.Value) * co} and {Convert.ToDouble(lookAHead.Value) * co}.");
                            runningValue += Operate(Convert.ToDouble(previousToken.Value) * co, Convert.ToDouble(lookAHead.Value) * co, token.Type);
                        }
                        else
                        {
                            ActionsListView.Items.Add($"{GetOperatorVerb(token.Type)} {runningValue} and {Convert.ToDouble(lookAHead.Value) * co}.");
                            runningValue = Operate(runningValue, Convert.ToDouble(lookAHead.Value) * co, token.Type);
                        }
                        //}
                    }
                }
                else if(token.Type == TokenType.Constant)
                {
                    previousToken = token;
                }
            }

            return runningValue;
        }

        List<List<Node>> GetSubExpressions(List<Node> tokens)
        {
            var expressions = new List<List<Node>>();
            var stack = new Stack<List<Node>>();
            var tmp = new List<Node>();
            var skipCount = 0;
            var nestingLevel = 0;

            for(var i = 0; i < tokens.Count; i++)
            {
                if(skipCount > 0)
                {
                    skipCount--;
                    continue;
                }

                var token = tokens[i];

                //if (stack.Count > 0 && nestingLevel == 0)
                //{
                //    if (!stack.Peek()[0].IsCoefficent)
                //    {
                //        var offset = 0;

                //        while(stack.Count > 0)
                //        {
                //            expressions.Insert(0, stack.Pop());

                //            offset++;
                //        }
                //    }
                //}

                if (token.IsCoefficent)
                {
                    //var lookAhead = tokens[i + 1];

                    //if(lookAhead.Type != Node.Token.ExpStart)
                    //{
                        if (tmp.Count > 0) expressions.Add(new List<Node>(tmp));
                        expressions.Add(new List<Node>() { token });
                    //}
                    //else
                    //{
                    //    stack.Push(new List<Node>(tmp));
                    //}

                    tmp.Clear();
                }
                else if (token.Type == Node.Token.ExpStart)
                {
                    nestingLevel++;

                    //if (i - 1 >= 0)
                    //{
                    //    var lookBehind = tokens[i - 1];

                    //    if (lookBehind.IsCoefficent)
                    //    {
                    //        tmp.Remove(tmp.Last());
                    //        expressions.Add(new List<Node>(tmp));
                    //        tmp.Clear();
                    //        stack.Push(new List<Node> { lookBehind });
                    //        //tmp.Add(token);
                    //        continue;
                    //    }
                    //}

                    if (tmp.Count > 0) expressions.Add(new List<Node>(tmp));
                    tmp.Clear();
                    tmp.Add(token);
                }
                else if(token.Type == Node.Token.ExpEnd)
                {
                    nestingLevel--;

                    if (i + 1 < tokens.Count)
                    {
                        var lookAHead = tokens[i + 1];

                        if (lookAHead.Type == Node.Token.Power)
                        {
                            var toPowerOf = tokens[i + 2];

                            tmp.Add(token);
                            tmp.Add(lookAHead);
                            tmp.Add(toPowerOf);
                            expressions.Add(new List<Node>(tmp));
                            tmp.Clear();
                            skipCount = 2;
                            continue;
                        }
                    }

                    tmp.Add(token);
                    if (tmp.Count > 0) expressions.Add(new List<Node>(tmp));
                    tmp.Clear();
                }
                else
                {
                    tmp.Add(token);
                }
            }

            if(tmp.Count > 0)
            {
                expressions.Add(new List<Node>(tmp));
            }

            return expressions;
        }

        List<Token> FlattenInput(string expression)
        {
            //if (expression.Count(x => x == '(') == 1 && expression.Count(x => x == ')') == 1) throw new Exception("Unbalanced params!");
            //if(expression.Count(x => x == '(') % 2 != 0 || expression.Count(x => x == ')') % 2 != 0) throw new Exception("Unbalanced params!");
            Symbols.Clear();

            var tokens = new List<Token>();
            var tmp = string.Empty;
            var parsingNumber = false;

            for(var i = 0; i < expression.Length; i++)
            {
                var c = expression[i];
                var op = GetOperator(c);

                if (c == '.' || int.TryParse(c.ToString(), out int _))
                {
                    if(tokens.Count > 1)
                    {
                        var lookBehind = tokens[tokens.Count - 1];

                        if(lookBehind.Type == TokenType.ExpEnd)
                        {
                            tokens.Add(new Token() { Value = "^", Type = TokenType.Power, IsCoefficent = false });
                        }
                    }

                    if((i + 1) == expression.Length)
                    {
                        tokens.Add(new Token() { Value = $"{tmp}{c}", Type = TokenType.Constant, IsCoefficent = false });//new Node($"{tmp}{c}", Node.Token.Constant));
                    }

                    parsingNumber = true;
                    tmp += c;

                    continue;
                }
                else if(c == '(')
                {
                    if (parsingNumber)
                    {
                        tokens.Add(new Token() { Value = tmp, Type = TokenType.Constant, IsCoefficent = true });//new Node(tmp, Node.Token.Constant) { IsCoefficent = true });
                    }

                    tokens.Add(new Token() { Value = "(", Type = TokenType.ExpStart, IsCoefficent = false });//new Node("(", Node.Token.ExpStart));
                    parsingNumber = false;
                    tmp = string.Empty;
                    continue;
                }
                else if(c == ')')
                {
                    if (parsingNumber)
                    {
                        tokens.Add(new Token() { Value = tmp, Type = TokenType.Constant, IsCoefficent = false }); //new Node(tmp, Node.Token.Constant));                        
                    }

                    tokens.Add(new Token() { Value = ")", Type = TokenType.ExpEnd, IsCoefficent = false }); //new Node(c.ToString(), Node.Token.ExpEnd));
                    parsingNumber = false;
                    tmp = string.Empty;
                    continue;
                }
                else if(op != TokenType.Unknown)
                {
                    if(parsingNumber)
                    {
                        tokens.Add(new Token() { Value = tmp, Type = TokenType.Constant, IsCoefficent = false }); //new Node(tmp, Node.Token.Constant));
                    }

                    tokens.Add(new Token() { Value = c.ToString(), Type = op, IsCoefficent = false });//new Node(c.ToString(), op));
                    parsingNumber = false;
                    tmp = string.Empty;
                    continue;
                }
                else if(c != ' ')
                {
                    if (!Symbols.ContainsKey(c.ToString()))
                    {
                        Symbols.Add(c.ToString(), 1);
                    }
                    else
                    {
                        Symbols[c.ToString()]++;
                    }

                    if (tokens.Count > 1)
                    {
                        var lookBehind = tokens[tokens.Count - 1];

                        if (lookBehind.Type == TokenType.ExpEnd)
                        {
                            tokens.Add(new Token() { Value = "^", Type = TokenType.Power, IsCoefficent = false });//new Node("^", Node.Token.Power));
                        }
                    }

                    if ((i + 1) < expression.Length)
                    {
                        var lookAHead = expression[i + 1];

                        if(lookAHead == '(')
                        {
                            tokens.Add(new Token() { Value = c.ToString(), Type = TokenType.Variable, IsCoefficent = true });
                            tmp = string.Empty;
                            parsingNumber = false;
                            continue;
                        }
                    }

                    if (parsingNumber)
                    {
                        tokens.Add(new Token() {Value = tmp, Type = TokenType.Constant, IsCoefficent = true });
                    }

                    tokens.Add(new Token() { Value = c.ToString(), Type = TokenType.Variable, IsCoefficent = false });
                    parsingNumber = false;
                    tmp = string.Empty;
                }
            }

            return tokens;
        }

        //double Calc(List<List<Node>> expressions, double co = 1)
        //{
        //    //Assumption: an operator is never last in the list.
        //    //double runningTotal = 0;
        //    double lastValue = 0;
        //    var next = true;
        //    Node previousToken = new Node("zzzz", Node.Token.Unknown);

        //    for(var i = 0; i < expressions.Count;)
        //    {
        //        if (!next) break;

        //        var tokens = expressions[i];
        //        expressions.RemoveAt(i);

        //        for (var j = 0; j < tokens.Count; j++)
        //        {
        //            var token = tokens[j];

        //            if(token.IsCoefficent)
        //            {
        //                if(tokens.Count == 1)
        //                {
        //                    return Calc(expressions, Convert.ToDouble(token.Value));
        //                }
        //            }
        //            else if(token.Type == Node.Token.Constant)
        //            {
        //                previousToken = token;
        //            }
        //            else if(token.Type == Node.Token.Variable)
        //            {
        //                //TODO: do symbol lookup to get value for this variale.
        //                previousToken = new Node("666", Node.Token.Variable);
        //            }
        //            else if(GetOperator(token.Value[0]) != Node.Token.Unknown)
        //            {
        //                if(tokens.Count > j + 1)
        //                {
        //                    j++;
        //                    var lookAHead = tokens[j];

        //                    if(lookAHead.Type == Node.Token.Constant)
        //                    {
        //                        if (previousToken.Type != Node.Token.Unknown)
        //                        {
        //                            lastValue = Operate(Convert.ToDouble(previousToken.Value) * co, Convert.ToDouble(lookAHead.Value) * co, token.Type);
        //                            previousToken = new Node("zzzz", Node.Token.Unknown);
        //                        }
        //                        else
        //                            lastValue = Operate(lastValue * co, Convert.ToDouble(lookAHead.Value) * co, token.Type);
        //                    }
        //                }
        //                else
        //                {
        //                    lastValue = Operate(Convert.ToDouble(previousToken.Value), Calc(expressions), token.Type);
        //                }
        //            }
        //            else if(token.Type == Node.Token.ExpStart)
        //            {

        //            }
        //            else if(token.Type == Node.Token.ExpEnd)
        //            {
        //                if(tokens.Count > j + 1)
        //                {
        //                    var lookAHead = tokens[j + 1];

        //                    if(lookAHead.Type == Node.Token.Power)
        //                    {
        //                        lookAHead = tokens[j + 2];
        //                        lastValue = Operate(lastValue, Convert.ToDouble(lookAHead.Value), Node.Token.Power);
        //                    }
        //                }

        //                next = false;
        //            }
        //        }
        //    }

        //    return lastValue;
        //}

        double Operate(double n1, double n2, TokenType operation)
        {
            switch(operation)
            {
                case TokenType.Add:
                    return n1 + n2;
                case TokenType.Divide:
                    return n1 / n2;
                case TokenType.Multiply:
                    return n1 * n2;
                case TokenType.Power:
                    return Math.Pow(n1, n2);
                case TokenType.Subtract:
                    return n1 - n2;
                default:
                    throw new Exception("Token must be an operator!");
            }
        }

        TokenType GetOperator(char c)
        {
            switch (c)
            {
                case '+':
                    return TokenType.Add;
                case '-':
                    return TokenType.Subtract;
                case '*':
                    return TokenType.Multiply;
                case '^':
                    return TokenType.Power;
                case '/':
                    return TokenType.Divide;
                default:
                    return TokenType.Unknown;
            }
        }

        string GetOperatorVerb(TokenType type)
        {
            switch (type)
            {
                case TokenType.Add:
                    return "Adding";
                case TokenType.Divide:
                    return "Dividing";
                case TokenType.Multiply:
                    return "Multiplying";
                case TokenType.Power:
                    return "Raising";
                case TokenType.Subtract:
                    return "Subtracting";
                default:
                    throw new Exception("Token must be an operator!");
            }
        }

        struct Token
        {
            public string Value;
            public bool IsCoefficent;
            public TokenType Type;
        }

        enum TokenType
        {
            Add,
            Subtract,
            Multiply,
            Divide,
            Power,
            Variable,
            Constant,
            ExpStart,
            ExpEnd,
            SubScript,
            SuperScript,
            Unknown
        }
    }
}