using System.Text;

namespace tlang
{
    public class Lexer
    {
        TextReader reader;
        public Lexer(string fName) : this(new StreamReader(fName))
        {

        }
        public Lexer(TextReader reader)
        {
            this.reader = reader;
        }
        List<LexToken> tokens=new List<LexToken>();
        public List<LexToken> Tokens
        {
            get{
                if(!set)
                {
                    set=true;
                    tokens = _getTokens();
                }
                return tokens;
            }
        }
        bool set=false;
        List<LexToken> _tokens = new List<LexToken>();
        StringBuilder b = new StringBuilder();
        private void FlushBuilder()
        {
            if(b.Length > 0)
            {
                _tokens.Add(LexToken.FromGeneralToken(b.ToString()));
                b.Clear();
            }
        }
        bool escaped=false;
        private char getChar()
        {
            int read = reader.Read();
            if(read == '\\')
            {
                escaped = true;
                read = reader.Read();
                if(read == 'x')
                {
                    
                    return (char)short.Parse($"0x{(char)reader.Read()}{(char)reader.Read()}",System.Globalization.NumberStyles.AllowHexSpecifier);
                }
                else if(read == 'n')
                {
                    return '\n';
                }
                else if(read == 't')
                {
                    return '\t';
                }
                else if(read == 'r')
                {
                    return '\r';
                }
                return (char)read;
            }
            escaped=false;
            return (char)read;
        }
        private List<LexToken> _getTokens()
        {
            
            int read;
            while((read = reader.Read()) != -1)
            {
                int next=reader.Peek();
                switch(read)
                {
                    case '\"':
                        FlushBuilder();
                        //"Some \"Some String\" Is OK"
                        while(true)
                        {
                            char r = getChar();
                            if(r == -1 || (!escaped && r == '\"'))
                            {
                                break;
                            }
                            b.Append(r);
                        }
                        _tokens.Add(LexToken.FromString(b.ToString()));
                        b.Clear();
                        break;
                    case '\'':
                        FlushBuilder();
                        _tokens.Add(LexToken.FromChar(getChar().ToString()));
                        reader.Read();
                        break;
                    case '#':
                         while(true)
                            {
                                read = reader.Read();
                                if(read == -1) return _tokens;
                                
                                if(read == '\n')
                                {
                                    break;
                                }
                                
                            }
                        break;
                    case '/':
                        FlushBuilder();
                        if(next == '=')
                        {
                            reader.Read();
                            _tokens.Add(LexToken.FromGeneralToken($"{(char)read}{(char)next}"));
                        }
                        else if(next == '/')
                        {
                            reader.Read();
                            
                            while(true)
                            {
                                read = reader.Read();
                                if(read == -1) return _tokens;
                                
                                if(read == '\n')
                                {
                                    break;
                                }
                                
                            }
                        }
                        else if(next == '*')
                        {
                            reader.Read();
                            bool lastIsAstrick=false;
                            while(true)
                            {
                                read = reader.Read();
                                if(read == -1) return _tokens;
                                if(read == '*')
                                {
                                    lastIsAstrick=true;
                                    continue;
                                }
                                else if(read == '/')
                                {
                                    if(lastIsAstrick)
                                    {
                                        break;
                                    }
                                }
                                lastIsAstrick=false;
                            }
                        }
                        else
                        {
                            _tokens.Add(LexToken.FromGeneralToken(read));
                        }
                        
                        break;
                    case '^':
                    case '*':
                    case '%':
                         FlushBuilder();
                        if(next == '=')
                        {
                            reader.Read();
                            _tokens.Add(LexToken.FromGeneralToken($"{(char)read}{(char)next}"));
                        }
                        else
                        {
                            _tokens.Add(LexToken.FromGeneralToken(read));
                        }
                        break;
                    case '|':
                    case '&':
                    case '<':
                    case '>':
                    case '+':
                    case '-':
                    case '!':
                         FlushBuilder();
                        if(next == read || next == '=')
                        {
                            reader.Read();
                            _tokens.Add(LexToken.FromGeneralToken($"{(char)read}{(char)next}"));
                        }
                        else
                        {
                            _tokens.Add(LexToken.FromGeneralToken(read));
                        }
                        break;
                    case '{':
                    case '}':
                    case '[':
                    case ']':
                    case '(':
                    case ')':
                    case '.':
                    case '?':
                    case ':':
                    case ',':
                    case ';':
                    case '=':
                        FlushBuilder();
                        _tokens.Add(LexToken.FromGeneralToken(read));
                        break;
                    case ' ':
                    case '\n':
                    case '\t':
                    case '\r':
                        FlushBuilder();
                        break;
                    default:
                        b.Append((char)read);
                        break;
                         
                }

            }
            FlushBuilder();
            return _tokens;
        }
    }
}