using System;
using System.Text.RegularExpressions;

namespace Lexer
{
    public class Lexer
    {
        private string text, buf;
        private int line = 1, col = 0, tmp = 0;

        public Lexer(string text)
        {
            this.text = text;
        }

        public Token Next()
        {
            Token t = Peek();
            buf = null;
            return t;

        }

		public Token Peek()
		{
            bool eow = false, isID = true;
            char tmpChar;
            string num = null;
            int tmpCol = col, tmpLine = line;

            while (buf == null) {
                tmpCol = col;
                tmpLine = line;
                eow = false;
                while (!eow)
                {
                    tmpChar = text[col];
                    if (text[col] == ' ')
                    {
                        col++;
                        eow = true;
                    }
                    else if (text[col] == '\n' || text[col] == '\r')
                    {
                        if (buf == null)
                        {
                            if (text[++col] == '\n') col++;
                            line++;
                            tmp = col;
                        }
                        eow = true;
                    }
                    else if (text[col] == '\t')
                    {
                        tmp -= 8;
                    }
                    else if (text[col] == '(' || text[col] == ')' || text[col] == ',' || text[col] == ';')
                    {
                        if (buf == null)
                        {
                            buf += text[col++];
                            Token tmpTok = new Token(Token.Type.SEP, buf, tmpLine, (tmpCol - tmp)+1);
                            return tmpTok;
                        }
                        eow = true;
                    }
                    else if (text[col] == '^' && text[col + 1] == 'D')
                    {
                        buf += text[col] + text[col + 1];
                        Token tmpTok = new Token(Token.Type.EOF, null, tmpLine, (tmpCol - tmp) + 1);
                        return tmpTok;
                    }
                    else if (Char.IsLetter(text[col]) || Char.IsDigit(text[col]))
                    {
                        buf += text[col++];
                    }
                    else if ( text[col] == '+' || text[col] == ':')
                    {
                        if (buf == null)
                        {
                            buf += text[col++];
                            if (text[col] == '=')
                            {
                                buf += text[col++];
                            }
                            Token tmpTok = new Token(Token.Type.OP, buf, tmpLine, (tmpCol - tmp) + 1);
                            return tmpTok;
                        }
                        eow = true;
                    }
                    else
                    {
                        col++;
                        eow = true;
                    }

                }
            }
            if (string.Equals(buf, "print"))
            {
                Token tmpTok = new Token(Token.Type.KEYW, buf, tmpLine, (tmpCol - tmp) + 1);
                return tmpTok;
            }
            else
            {
                if (Char.IsDigit(buf[0]))
                {
                    num += buf[0];
                    for (int i = 1; i < buf.Length; i++)
                    {
                        if (!Char.IsDigit(buf[i]))
                        {
                            col -= buf.Length - i;
                            i = buf.Length;
                        }
                        else
                        {
                            num += buf[i];
                        }
                    }
                    Token tmpTok = new Token(Token.Type.NUM, num, tmpLine, (tmpCol - tmp) + 1);
                    return tmpTok;
                }
                else if (Char.IsLetter(buf[0]))
                {
                    for (int i = 1; i < buf.Length; i++)
                    {
                        if (Char.IsLetter(buf[i]) || Char.IsDigit(buf[i]))
                            isID = true;
                        else
                            isID = false;
                    }
                    if (isID)
                    {
                        Token tmpTok = new Token(Token.Type.ID, buf, line, (tmpCol - tmp) + 1);
                        return tmpTok;
                    }
                }
            }

            Token t = new Token(0, null,0,0);
            return t;
        }

	}
}