public IEnumerable <VariablesExpression> SearchGroups(string validatedFormula)
{
if (string.IsNullOrWhiteSpace(validatedFormula))
{
throw new InvalidFormulaException(validatedFormula, "formula is null or whitespace");
}
if (validatedFormula.IndexOf('=') < 0)
{
throw new InvalidFormulaException(validatedFormula, "must contain '=' sign");
}
var state = new SearchState(_pool.Get(), _expressionFactory, validatedFormula);
var formulaBuilder = _pool.Get().Append(validatedFormula);
try
{
for (int i = 0; i < formulaBuilder.Length; i++)
{
if (formulaBuilder[i] == ' ')
{
formulaBuilder.Remove(i--, 1);
continue;
}
var currentChar = formulaBuilder[i];
if (currentChar == '=')
{
// (x=
var hasOpenedGroup = state.OperatorsStack.Contains('(');
// x=x=
var hasAnotherEqualSign = state.OperatorsStack.Contains('=');
// =x
var noLeftSideVariables = state.VariableBuilder.Length == 0 && state.ExpressionsStack.Count == 0;
// x+=; length is important : x= (builder == x, operators stack is empty)
var hasOpenedOperator = state.VariableBuilder.Length == 0 && state.ExpressionsStack.Count > 0;
if (hasOpenedGroup || hasAnotherEqualSign || noLeftSideVariables)
{
throw new InvalidFormulaException(validatedFormula, "'=' operator should be single and follow ')' or variable");
}
}
switch (currentChar)
{
case '=':
case '-' when i == 0 || formulaBuilder[i - 1] != '^':
case '+':
{
state.CheckAndAddNilElement(currentChar);
if (state.OperatorsStack.Count > 0)
{
var prevOperator = state.OperatorsStack.Peek();
if (prevOperator == '-' || prevOperator == '+')
{
state.ApplyTopOperator();
}
}
state.PushOperator(currentChar, i);
}
break;
case '(':
state.PushOperator(currentChar, i);
break;
case ')':
state.ApplyParenthesis();
break;
default:
state.VariableBuilder.Append(currentChar);
break;
}
}
while (state.OperatorsStack.Count > 0)
{
state.ApplyTopOperator();
}
if (state.ExpressionsStack.Count > 1)
{
throw new InvalidFormulaException(validatedFormula, "cannot transform formula to single expression");
}
return(state.ExpressionsStack.Pop().Expressions);
}
finally
{
_pool.Return(state.VariableBuilder);
_pool.Return(formulaBuilder);
}
}