using System;
using sharp.extensions;
using System.Collections.Generic;
using System.Linq;
namespace sharp.parser
{
	public class CharBuffer
	{
		char[] chars;
		int position;

		int lineno, linepos, linestart;

		int[] lineStarts;

		public char[] Characters { get { return this.chars; } }

		public CharBuffer(char[] source)
		{
			this.chars = source;
			this.initialize();
		}
		public CharBuffer(string source){
			this.chars = source.ToCharArray();
			this.initialize();
		}

		private void initialize(){
			this.lineno = 1;
			this.linepos = 1;
			this.linestart = 0;

			List<int> lineStartList = new List<int>();
			lineStartList.Add(0);

			for (int n = 0; n < this.chars.Length;n++)
			{
				if (this.chars[n] == 0x0a){
					lineStartList.Add(n);
				}
			}
			lineStartList.Add(this.chars.Length);

			this.lineStarts = lineStartList.ToArray();
		}

		private int lineEnd(){
			int p = position;
			while (this.chars[p]!='\n'){
				p++;
				if (p >= this.chars.Length){
					break;
				}
			}
			return p;
		}

		public string getLineAt(int pos){
			int n;

			if (pos >= this.chars.Length){
				return null;
			}

			for (n = 0; n < this.lineStarts.Count();n++){
				if (pos >= this.lineStarts[n]){
					break;
				}
			}

			return new string( this.chars.Segment(this.lineStarts[n],this.lineStarts[n+1]-this.lineStarts[n]) );
		}

		public int Position {
			get { return position; }
			set { this.position = value >= chars.Length ? chars.Length : value; }
		}

		public bool MoveNext(){
			if (position < this.chars.Length){
				position++;

				this.linepos++;

				if (Last == '\n'){
					this.linepos = 1;
					this.linestart = position;
					this.lineno++;
				}

				return true;
			}
			return false;
		}

		public bool MoveBack(){
			if (position > 0){
				position--;
				return true;
			}
			return false;
		}

		public bool EndOfBuffer(){
			return (this.position >= this.chars.Length);
		}

		public void BypassWhiteSpace(){
			while (Current <= 0x20){
				MoveNext();
			}
		}

		public int CurrentLineNumber { get { return this.lineno; } }
		public int CurrentLinePosition { get { return this.linepos; } }

		public string CurrentLine { get { return new String(this.chars.Segment(this.linestart,lineEnd()-this.linestart)); } }

		public char Last { 
			get { 
				if (position > 0) {
					return this.chars[position - 1]; 
				};
				throw new IndexOutOfRangeException("No character before the first one");
			}
		}
		public char Current
		{
			get {
				if (position < this.chars.Length){
					return this.chars[position];
				}
				throw new IndexOutOfRangeException("No character after the last one");
			}
		}
		public char Next
		{
			get {
				if (position < this.chars.Length-1) {
					return this.chars[position + 1]; 
				};
				throw new IndexOutOfRangeException("No character after the last one");

			}
		}

		public string Following(int len)
		{
			return new string(this.chars.Segment(position, len));
		}
		public string Preceding(int len)
		{
			return new string(this.chars.Segment(position-len, len));
		}

		public void Pass(char ch){
			if (Current != ch){
				throw new ParserFormatException(String.Format("Expected {0}, but got {1}",ch,Current),lineno,linepos,CurrentLine);
			}
			MoveNext();
		}

	}
}