/// <inheritdoc />
public IEnumerable <QueryToken> ParseQueryTokens(string queryText)
{
if (queryText is null)
{
throw new ArgumentNullException(nameof(queryText));
}
var state = State.None;
var tokenStart = (int?)null;
var tolerance = 0;
QueryToken?createTokenForYielding(int endIndex)
{
if (tokenStart != null)
{
var token = QueryToken.ForText(queryText.Substring(tokenStart.Value, endIndex - tokenStart.Value));
tokenStart = null;
return(token);
}
return(null);
}
for (var i = 0; i < queryText.Length; i++)
{
var current = queryText[i];
if (char.IsWhiteSpace(current))
{
var token = createTokenForYielding(i);
if (token != null)
{
yield return(token.Value);
}
}
else
{
switch (state)
{
case State.None:
switch (current)
{
case '&':
yield return(QueryToken.ForOperator(QueryTokenType.AndOperator));
break;
case '|':
yield return(QueryToken.ForOperator(QueryTokenType.OrOperator));
break;
case '>':
yield return(QueryToken.ForOperator(QueryTokenType.PrecedingOperator));
break;
case '=':
if (tokenStart == null)
{
throw new QueryParserException(ExceptionMessages.UnexpectedOperator, "=");
}
yield return(QueryToken.ForFieldFilter(queryText.Substring(tokenStart.Value, i - tokenStart.Value)));
tokenStart = null;
break;
case ')':
var token = createTokenForYielding(i);
if (token != null)
{
yield return(token.Value);
}
yield return(QueryToken.ForOperator(QueryTokenType.CloseBracket));
break;
case '(':
yield return(QueryToken.ForOperator(QueryTokenType.OpenBracket));
break;
case '~':
tolerance = 0;
state = State.ProcessingNearOperator;
break;
case '"':
state = State.ProcessingString;
yield return(QueryToken.ForOperator(QueryTokenType.BeginAdjacentTextOperator));
break;
default:
tokenStart = tokenStart ?? i;
break;
}
break;
case State.ProcessingString:
switch (current)
{
case '"':
state = State.None;
var token = createTokenForYielding(i);
if (token != null)
{
yield return(token.Value);
}
yield return(QueryToken.ForOperator(QueryTokenType.EndAdjacentTextOperator));
break;
default:
tokenStart = tokenStart ?? i;
break;
}
break;
case State.ProcessingNearOperator:
switch (current)
{
case '>':
yield return(QueryToken.ForOperatorWithTolerance(QueryTokenType.PrecedingNearOperator, tolerance));
state = State.None;
break;
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
tolerance = (tolerance * 10) + (current - '0');
break;
default:
yield return(QueryToken.ForOperatorWithTolerance(QueryTokenType.NearOperator, tolerance));
state = State.None;
// Skip back a character to re-process it now state is None
i -= 1;
break;
}
break;
}
}
}
if (tokenStart != null)
{
yield return(QueryToken.ForText(queryText.Substring(tokenStart.Value, queryText.Length - tokenStart.Value)));
}
}
