/// <summary>
/// Merge current expression with previous expression and the new operand just got before current expression
/// </summary>
/// <param name="prevExpression"></param>
/// <param name="curExpression"></param>
/// <param name="newOperand"></param>
/// <param name="errMsg"></param>
/// <returns></returns>
public static bool MergeExpressions(ArithmeticExpression <ICalculator> prevExpression, ref ArithmeticExpression <ICalculator> curExpression, ref ArithmeticOperand <ICalculator> newOperand, ref string errMsg)
{
if (prevExpression == null || curExpression == null)
{
errMsg += "prevExpression is null or curExpression is null in MergeExpressions.";
return(false);
}
if (prevExpression.Priority() < curExpression.Priority())
{
curExpression.AddOperand(newOperand);
prevExpression.AddOperand(curExpression);
}
else if (prevExpression.Priority() > curExpression.Priority())
{
prevExpression.AddOperand(newOperand);
if (prevExpression.ParentExpression != null && prevExpression.ParentExpression.Priority() == curExpression.Priority())
{
prevExpression.ParentExpression.Operators.AddRange(curExpression.Operators);
prevExpression.ParentExpression.AddOperands(curExpression.Operands);
curExpression = prevExpression.ParentExpression;
}
else
{
curExpression.AddOperand(prevExpression);
}
}
else
{
prevExpression.AddOperand(newOperand);
prevExpression.Operators.AddRange(curExpression.Operators);
prevExpression.AddOperands(curExpression.Operands);
curExpression = prevExpression;
}
newOperand = null;
return(true);
}
/// <summary>
/// Parse string expression to an arithmetic expression object
/// </summary>
/// <param name="s"></param>
/// <param name="endIndex"></param>
/// <param name="errMsg"></param>
/// <param name="startIndex"></param>
/// <param name="recurLevel"></param>
/// <returns></returns>
private static ArithmeticExpression <ICalculator> ParseExpression(string s, out int endIndex, out string errMsg, int startIndex = 0, int recurLevel = 0)
{
endIndex = startIndex;
errMsg = string.Empty;
ArithmeticExpression <ICalculator> root = null;
if (!string.IsNullOrWhiteSpace(s) && s.Length > startIndex)
{
int index = startIndex;
ArithmeticExpression <ICalculator> prevExpression = null;
ArithmeticExpression <ICalculator> curExpression = null;
ArithmeticOperand <ICalculator> newOperand = null;
bool prevOperand = false;
bool prevOperator = false;
while (index < s.Length)
{
char c = s[index];
// Check operator
if (c == '+' || c == '-' || c == '*' || c == '/')
{
if (curExpression != null)
{
prevExpression = curExpression;
}
curExpression = ArithmeticExpressionFactory.CreateArithmeticExpression(c, index, ref prevOperator, ref prevOperand, ref errMsg);
if (curExpression == null)
{
break;
}
else if (prevExpression != null)
{
if (!ArithmeticExpressionFactory.MergeExpressions(prevExpression, ref curExpression, ref newOperand, ref errMsg))
{
break;
}
}
else
{
prevExpression = curExpression;
if (newOperand != null)
{
curExpression.AddOperand(newOperand);
newOperand = null;
}
}
}
// Check number
else if (c == '(')
{
int childEndIndex;
string childErrMsg;
ArithmeticExpression <ICalculator> childExpression = ParseExpression(s, out childEndIndex, out childErrMsg, index + 1, recurLevel + 1);
if (!string.IsNullOrWhiteSpace(childErrMsg))
{
errMsg += childErrMsg;
break;
}
else if (childExpression == null)
{
errMsg += $"Expression missing in parentheses: [index: {index}].";
break;
}
else if (prevOperand)
{
errMsg += $"Operator is missing before character: ( [index: {index}].";
break;
}
else
{
index = childEndIndex; // ')'
newOperand = new ArithmeticOperand <ICalculator>
{
Expression = childExpression
};
prevOperand = true;
prevOperator = false;
}
}
else if (c == ')')
{
recurLevel--;
if (recurLevel < 0)
{
errMsg += $"Redundant right parenthesis: [index: {index}].";
}
break;
}
else if (c >= '0' && c <= '9')
{
IntCalculator intCalculator = ArithmeticExpressionFactory.CreateCalculator(s, ref index, ref prevOperator, ref prevOperand, ref errMsg) as IntCalculator;
if (intCalculator == null)
{
break;
}
else
{
newOperand = new ArithmeticOperand <ICalculator>
{
SimpleValue = intCalculator
};
}
}
// Support spaces
else if (c == ' ')
{
}
// Not support characters
else
{
errMsg += $"Illegal characters in the expression: {c} [index: {index}].";
break;
}
if (root == null && curExpression != null)
{
root = curExpression;
}
index++;
}
if (prevOperator)
{
errMsg += $"Operand is missing at the end of the expressioin.";
}
if (index == s.Length && recurLevel > 0)
{
errMsg += $"Missing {recurLevel} right parenthesis.";
}
else if (newOperand != null && curExpression != null)
{
curExpression.AddOperand(newOperand);
newOperand = null;
}
endIndex = index;
}
if (!string.IsNullOrEmpty(errMsg))
{
root = null;
}
if (root != null)
{
while (root.ParentExpression != null)
{
root = root.ParentExpression;
}
}
return(root);
}
