/// <summary>
/// Creates an expression node and adds it to the
/// give tree.
/// </summary>
/// <param name="root">Root node of expression tree</param>
/// <param name="term">Term for this node</param>
/// <param name="termForm">Indicates form of this term</param>
/// <param name="termExclude">Indicates if this is an excluded term</param>
/// <param name="conjunction">Conjunction used to join with other nodes</param>
/// <returns>The new root node</returns>
protected INode AddNode(INode root, string term, TermForms termForm, bool termExclude, ConjunctionTypes conjunction)
{
if (term.Length > 0)
{
INode node = new TerminalNode
{
Term = term,
TermForm = termForm,
Exclude = termExclude
};
root = AddNode(root, node, conjunction);
}
return(root);
}
INode AddNode(
INode root,
string term,
TermForms termForm,
bool termExclude,
ConjunctionTypes conjunction)
{
if (term.Length > 0 && !IsStopWord(term))
{
var node = new TerminalNode
{
Term = term,
TermForm = termForm,
Exclude = termExclude
};
root = AddNode(root, node, conjunction);
}
return(root);
}
/// <summary>
/// Parses a query segment and converts it to an expression
/// tree.
/// </summary>
/// <param name="query">Query segment to convert</param>
/// <param name="defaultConjunction">Implicit conjunction type</param>
/// <returns>Root node of expression tree</returns>
private INode ParseNode(string query, ConjunctionTypes defaultConjunction)
{
TermForms termForm = TermForms.Inflectional;
bool termExclude = false;
ConjunctionTypes conjunction = defaultConjunction;
bool resetState = true;
INode root = null;
INode node;
string term;
TextParser parser = new TextParser(query);
while (!parser.EndOfText)
{
if (resetState)
{
// Reset modifiers
termForm = TermForms.Inflectional;
termExclude = false;
conjunction = defaultConjunction;
resetState = false;
}
parser.MovePastWhitespace();
if (!parser.EndOfText &&
!Punctuation.Contains(parser.Peek()))
{
// Extract query term
int start = parser.Position;
parser.MoveAhead();
while (!parser.EndOfText &&
!Punctuation.Contains(parser.Peek()) &&
!Char.IsWhiteSpace(parser.Peek()))
{
parser.MoveAhead();
}
// Allow trailing wildcard
if (parser.Peek() == '*')
{
parser.MoveAhead();
termForm = TermForms.Literal;
}
// Interpret token
term = parser.Extract(start, parser.Position);
if (String.Compare(term, "AND", true) == 0)
{
conjunction = ConjunctionTypes.And;
}
else if (String.Compare(term, "OR", true) == 0)
{
conjunction = ConjunctionTypes.Or;
}
else if (String.Compare(term, "NEAR", true) == 0)
{
conjunction = ConjunctionTypes.Near;
}
else if (String.Compare(term, "NOT", true) == 0)
{
termExclude = true;
}
else
{
root = AddNode(root, term, termForm, termExclude, conjunction);
resetState = true;
}
continue;
}
else if (parser.Peek() == '"')
{
// Match next term exactly
termForm = TermForms.Literal;
// Extract quoted term
term = ExtractQuote(parser);
root = AddNode(root, term.Trim(), termForm, termExclude, conjunction);
resetState = true;
}
else if (parser.Peek() == '(')
{
// Parse parentheses block
term = ExtractBlock(parser, '(', ')');
node = ParseNode(term, defaultConjunction);
root = AddNode(root, node, conjunction, true);
resetState = true;
}
else if (parser.Peek() == '<')
{
// Parse angle brackets block
term = ExtractBlock(parser, '<', '>');
node = ParseNode(term, ConjunctionTypes.Near);
root = AddNode(root, node, conjunction);
resetState = true;
}
else if (parser.Peek() == '-')
{
// Match when next term is not present
termExclude = true;
}
else if (parser.Peek() == '+')
{
// Match next term exactly
termForm = TermForms.Literal;
}
else if (parser.Peek() == '~')
{
// Match synonyms of next term
termForm = TermForms.Thesaurus;
}
// Advance to next character
parser.MoveAhead();
}
return(root);
}
/// <summary>
/// Creates an expression node and adds it to the
/// give tree.
/// </summary>
/// <param name="root">Root node of expression tree</param>
/// <param name="term">Term for this node</param>
/// <param name="termForm">Indicates form of this term</param>
/// <param name="termExclude">Indicates if this is an excluded term</param>
/// <param name="conjunction">Conjunction used to join with other nodes</param>
/// <returns>The new root node</returns>
protected INode AddNode(INode root, string term, TermForms termForm, bool termExclude, ConjunctionTypes conjunction)
{
if (term.Length > 0)
{
INode node = new TerminalNode
{
Term = term,
TermForm = termForm,
Exclude = termExclude
};
root = AddNode(root, node, conjunction);
}
return root;
}
