/// <summary>
/// Initializes a new instance of the <see cref="FilterNode"/> class that is a terminal node.
/// </summary>
/// <remarks>
/// A terminal node is a relational expression, and contains no child nodes.
/// </remarks>
/// <param name="term">The expression term.</param>
public FilterNode(RelationalExpression term)
{
if (term == null)
{
throw new ArgumentNullException("term");
}
this.term = term;
}
/// <summary>
/// Parses the specified text into a binary expression tree.
/// </summary>
/// <param name="expression">The expression text to parse.</param>
/// <returns></returns>
public static FilterNode Parse(string expression)
{
var tokens = new List <Token>(new Tokenizer(expression));
// Combine terms and relational operators into expressions.
while (true)
{
var evaluationIndex = -1;
for (var i = 0; i < tokens.Count; i++)
{
if (tokens[i].Type == TokenType.Relation)
{
evaluationIndex = i;
break;
}
}
if (evaluationIndex > -1)
{
var expr = new RelationalExpression(tokens[evaluationIndex - 1].Term,
tokens[evaluationIndex + 1].Term,
tokens[evaluationIndex].Relation);
tokens.RemoveAt(evaluationIndex - 1);
tokens.RemoveAt(evaluationIndex - 1);
tokens.RemoveAt(evaluationIndex - 1);
tokens.Insert(evaluationIndex - 1, new Token(expr));
// Remove parentheses surrounding a resolved expression.
if (evaluationIndex - 2 > -1 && tokens[evaluationIndex - 2].Type == TokenType.OpenParen &&
evaluationIndex < tokens.Count && tokens[evaluationIndex].Type == TokenType.CloseParen)
{
// New resolved expression is now at evaluationIndex - 1.
tokens.RemoveAt(evaluationIndex - 2);
// New resolved expression is now at evaluationIndex - 2.
tokens.RemoveAt(evaluationIndex - 1);
}
}
else
{
break;
}
}
// If the token list contains only a single relational expression, we can return a simple filter node based on that.
if (tokens.Count == 1 && tokens[0].Type == TokenType.ResolvedExpression)
{
return(new FilterNode(tokens[0].ResolvedExpression));
}
// The token list now contains only RelationalExpressions, conditional operators (AND and OR) and parentheses.
// Combine the expressions and operators into nodes, prioritizing binding according to the natural order of precedence
// for boolean operators and parentheses.
var operatorPriorities = new Dictionary <LogicalOperator, int>();
operatorPriorities.Add(LogicalOperator.Or, 1);
operatorPriorities.Add(LogicalOperator.And, 2);
var parenAddedPriority = operatorPriorities.Count;
while (true)
{
var contextPriority = 0;
var evaluationPriorityMax = -1;
var evaluationIndex = -1;
for (var i = 0; i < tokens.Count; i++)
{
var type = tokens[i].Type;
if (type == TokenType.Condition)
{
var evaluationPriority = operatorPriorities[tokens[i].Condition] + contextPriority;
if (evaluationPriority > evaluationPriorityMax)
{
evaluationIndex = i;
evaluationPriorityMax = evaluationPriority;
}
}
else if (type == TokenType.OpenParen)
{
contextPriority += parenAddedPriority;
}
else if (type == TokenType.CloseParen)
{
contextPriority -= parenAddedPriority;
}
}
if (evaluationIndex > -1)
{
var prevToken = tokens[evaluationIndex - 1];
var nextToken = tokens[evaluationIndex + 1];
FilterNode nodeLeft = null;
FilterNode nodeRight = null;
// Tokens surrounding the AND or OR must now be either a relational expression or a resolved FilterNode.
if (prevToken.Type == TokenType.ResolvedExpression)
{
nodeLeft = new FilterNode(prevToken.ResolvedExpression);
}
else
{
nodeLeft = prevToken.ResolvedNode;
}
if (nextToken.Type == TokenType.ResolvedExpression)
{
nodeRight = new FilterNode(nextToken.ResolvedExpression);
}
else
{
nodeRight = nextToken.ResolvedNode;
}
var node = new FilterNode(nodeLeft, nodeRight, tokens[evaluationIndex].Condition);
tokens.RemoveAt(evaluationIndex - 1);
tokens.RemoveAt(evaluationIndex - 1);
tokens.RemoveAt(evaluationIndex - 1);
tokens.Insert(evaluationIndex - 1, new Token(node));
// Remove parentheses surrounding a resolved node.
if (evaluationIndex - 2 > -1 && tokens[evaluationIndex - 2].Type == TokenType.OpenParen &&
evaluationIndex < tokens.Count && tokens[evaluationIndex].Type == TokenType.CloseParen)
{
// New resolved node is now at evaluationIndex - 1.
tokens.RemoveAt(evaluationIndex - 2);
// New resolved node is now at evaluationIndex - 2.
tokens.RemoveAt(evaluationIndex - 1);
}
}
else
{
break;
}
}
// The token list should now contain a single FilterNode.
return(tokens[0].ResolvedNode);
}
public Token(RelationalExpression expression)
{
type = TokenType.ResolvedExpression;
expr = expression;
}
