var Errors = require("errors.js");

function isDigit(c) {return c >= '0' && c <= '9';}

exports.digit = function(stream, context){
	var c = stream.char();
	if (!isDigit(c))
		return false;
	context.handleChar(c);
	return true;
}

exports.hexDigit = function(stream, context){
	var c = stream.char();
	if (!isDigit(c) && (c < 'A' || c > 'F'))
		return false;
	context.handleChar(c);
	return true;
}

exports.point = function(stream, context){
	if (stream.char() != '.' 
		|| stream.peekChar() == '.') // not a diapason ".."
		return false;
	context.handleLiteral(".");
	return true;
}

exports.character = function(stream, context){
	var c = stream.char();
	if (c == '"')
		return false;
	context.handleChar(c);
	return true;
}

function isLetter(c) { return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');}

exports.ident = function(stream, context){
	if (!isLetter(stream.peekChar()))
		return false;
	
	var savePos = stream.pos();
	var result = "";
	stream.read(function(c){
		if (!isLetter(c) && !isDigit(c) /*&& c != '_'*/)
			return false;
		result += c;
		return true;
	});

	var keywords = ["ARRAY", "END", "VAR", "TYPE", "IF", "CASE", "WHILE", "REPEAT", "FOR", "NIL", "TRUE", "FALSE", "IS"];
	if (keywords.indexOf(result) != -1){
		stream.setPos(savePos);
		return false;
	}
	context.setIdent(result);
	return true;
}

function skipComment(stream){
	if (stream.peekStr(2) != "(*")
		return false;

	stream.next(2);
	while (stream.peekStr(2) != "*)"){
		if (stream.eof())
			throw new Errors.Error("comment was not closed");
		if (!skipComment(stream))
			stream.next(1);
		}
	stream.next(2);
	return true;
}

exports.skipSpaces = function(stream, context){
	if (context.isLexem && context.isLexem())
		return;

	stream.read(function(c){return ' \t\n\r'.indexOf(c) != -1;});
	skipComment(stream);
}

exports.separator = function(stream, context){
	return !isLetter(stream.peekChar());
}

exports.literal = function(s){
	return function(stream, context){
		if (stream.str(s.length) != s)
			return false;
		stream.next(s.length);
		
		if ((!context.isLexem || !context.isLexem()) && isLetter(s[s.length - 1])){
			var next = stream.peekChar();
			if (isLetter(next) || isDigit(next))
				return false;
		}
		
		context.handleLiteral(s);
		return true;
	}
}