using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace Turtle
{
    public class Parser : IDisposable
    {
        public string Path { get; private set; }

        public FileStream Stream { get; private set; }

        public Parser(string path)
        {
            Path = path;
            Stream = File.OpenRead(path);
        }

        public void Dispose()
        {
            Stream.Close();
            Stream.Dispose();
        }

        public Token FetchToken()
        {
            int c;

            while ((c = Stream.ReadByte()) != -1)
            {
                // string
                if (c >= (int)'a' && c <= (int)'z')
                {
                    StringBuilder s = new StringBuilder(Convert.ToString(Convert.ToChar(c)));

                    while ((c = Stream.ReadByte()) != -1)
                    {
                        if (c >= (int)'a' && c <= (int)'z')
                        {
                            s.Append(Convert.ToChar(c));
                        }
                        else
                        {
                            break;
                        }
                    }

                    Stream.Seek(-1, SeekOrigin.Current);

                    string str = s.ToString();

                    return new Token(TokenType.String, str);
                }

                // number
                else if ((c >= (int)'0' && c <= (int)'9') || c == (int)'-')
                {
                    StringBuilder s = new StringBuilder(Convert.ToString(Convert.ToChar(c)));

                    while ((c = Stream.ReadByte()) != -1)
                    {
                        if (c >= (int)'0' && c <= (int)'9')
                        {
                            s.Append(Convert.ToChar(c));
                        }
                        else
                        {
                            break;
                        }
                    }

                    Stream.Seek(-1, SeekOrigin.Current);

                    return new Token(TokenType.Number, Convert.ToInt32(s.ToString()));
                }

                // brackets
                else if (c == (int)'(')
                {
                    return new Token(TokenType.LeftBracket);
                }
                else if (c == (int)')')
                {
                    return new Token(TokenType.RightBracket);
                }
            }

            return null; // end of file
        }
    }
}