private static bool TryTakeOperator(TokenKeeper tokenKeeper, out Token op)
{
if (tokenKeeper.Next.IsOperator())
{
op = tokenKeeper.Take();
return(true);
}
op = new Token(TokenType.Error, null);
return(false);
}
private static bool TryTakeData(TokenKeeper tokenKeeper, out Token data)
{
if (tokenKeeper.Next.IsData())
{
data = tokenKeeper.Take();
return(true);
}
data = new Token(TokenType.Error, null);
return(false);
}
public void Swap(TokenKeeper tokenKeeper)
{
var oldTokens = _tokens;
_tokens = tokenKeeper._tokens;
var oldIndex = _index;
_index = tokenKeeper._index;
tokenKeeper._tokens = oldTokens;
tokenKeeper._index = oldIndex;
}
private static FilterClause TakeClause(TokenKeeper tokenKeeper)
{
FilterClause clause;
if (TryTakeExpression(tokenKeeper, out clause))
{
if (tokenKeeper.Finished || TryTakeRelOp(tokenKeeper, ref clause))
{
return(clause);
}
}
return(new ErrorClause("Unable to parse filter string."));
}
private static bool TryTakeExpression(TokenKeeper tokenKeeper, out FilterClause clause)
{
if (TryTakeParenExpression(tokenKeeper, out clause) ||
TryTakeComparison(tokenKeeper, out clause))
{
var work = new TokenKeeper(tokenKeeper);
if (TryTakeRelOp(work, ref clause))
{
tokenKeeper.Swap(work);
}
return(true);
}
clause = null;
return(false);
}
private static FilterClause PerformParse(IEnumerable <Token> tokens, out string error)
{
var tokenKeeper = new TokenKeeper(tokens.ToList());
var clause = TakeClause(tokenKeeper);
if (clause is ErrorClause errorClause)
{
error = errorClause.Error;
}
else
{
error = null;
}
return(clause);
}
private static bool TryTakeComparison(TokenKeeper tokenKeeper, out FilterClause clause)
{
Token left, right, op;
var work = new TokenKeeper(tokenKeeper);
if (TryTakeData(work, out left) && TryTakeOperator(work, out op) &&
TryTakeData(work, out right))
{
tokenKeeper.Swap(work);
clause = new ComparisonClause(left, op, right);
return(true);
}
clause = null;
return(false);
}
private static bool TryTakeRelOp(TokenKeeper tokenKeeper, ref FilterClause clause)
{
if (tokenKeeper.Next.IsRelop())
{
var work = new TokenKeeper(tokenKeeper);
var op = work.Take();
FilterClause rhs;
if (TryTakeExpression(work, out rhs))
{
var relOpClause = new RelOpClause(clause, op, rhs);
tokenKeeper.Swap(work);
clause = relOpClause;
return(true);
}
}
return(false);
}
private static bool TryTakeParenExpression(TokenKeeper tokenKeeper, out FilterClause clause)
{
if (tokenKeeper.Next.TokenType == TokenType.OpenParen)
{
var work = new TokenKeeper(tokenKeeper);
work.Take();
FilterClause expression;
if (TryTakeExpression(work, out expression) && work.Next.TokenType == TokenType.CloseParen)
{
work.Take();
clause = new ParenClause(expression);
tokenKeeper.Swap(work);
return(true);
}
}
clause = null;
return(false);
}
public TokenKeeper(TokenKeeper tokenKeeper)
{
_tokens = tokenKeeper._tokens;
_index = tokenKeeper._index;
}