/// <summary>
/// Filter expression can be a literal string, "Hello World" or it can contain logical
/// conjunctions "or" and "and", like this "Hello and Hi" or "Hello & Hi" or "Hello or Hi"
/// and it can have parentheses "Hello and (foo or bar)" and so on. It can also have
/// a "not" or "!" for negation.
/// </summary>
public Filter <T> Parse(string quickFilter)
{
if (string.IsNullOrWhiteSpace(quickFilter))
{
return(null);
}
foreach (Tuple <QuickFilterToken, string> token in GetFilterTokens(quickFilter))
{
string literal = token.Item2;
switch (token.Item1)
{
case QuickFilterToken.Literal: // shift
stack.Push(new FilterKeyword <T>(new FilterLiteral(literal)));
break;
case QuickFilterToken.And: // reduce
stack.Push(new FilterAnd <T>()
{
Left = Reduce(QuickFilterToken.And)
});
break;
case QuickFilterToken.Or: // reduce
stack.Push(new FilterOr <T>()
{
Left = Reduce(QuickFilterToken.Or)
});
break;
case QuickFilterToken.Not: // reduce
stack.Push(new FilterNot <T>()
{
});
break;
case QuickFilterToken.LeftParen: // shift
stack.Push(new FilterParens <T>());
break;
case QuickFilterToken.RightParen: // reduce
Filter <T> op = Reduce(QuickFilterToken.RightParen);
FilterParens <T> parens = op as FilterParens <T>;
if (parens != null)
{
// eliminate parens
stack.Push(parens.Expression);
}
else
{
// missing open parens, now what?
stack.Push(op);
}
break;
}
}
return(Reduce(QuickFilterToken.None));
}
private Filter <T> Reduce(QuickFilterToken token)
{
while (stack.Count > 0)
{
Filter <T> top = stack.Pop();
if (stack.Count == 0)
{
return(top);
}
Filter <T> op = stack.Peek();
if (token > op.Precidence)
{
return(top);
}
op = stack.Pop();
// now combine "top" and "op"
if (op is FilterKeyword <T> )
{
FilterKeyword <T> keyword = (FilterKeyword <T>)op;
op = Combine(keyword, top);
}
else if (op is FilterAnd <T> )
{
FilterAnd <T> and = (FilterAnd <T>)op;
and.Right = Combine(and.Right, top);
}
else if (op is FilterOr <T> )
{
FilterOr <T> or = (FilterOr <T>)op;
or.Right = Combine(or.Right, top);
}
else if (op is FilterNot <T> )
{
FilterNot <T> not = (FilterNot <T>)op;
not.Right = Combine(not.Right, top);
}
else if (op is FilterParens <T> )
{
FilterParens <T> parens = (FilterParens <T>)op;
parens.Expression = Combine(parens.Expression, top);
}
stack.Push(op);
}
return(null);
}
