/// <summary>
/// Final part of the shunting yard algorithm
/// Pop and push elements to evaluate the search expression
/// Shlomo 2020
/// </summary>
/// <param name="result">Array of vehicle registrations that match search</param>
/// <param name="searchAlgorithm">Search algorithm instance to use</param>
public void searchFleet(out string[] result, SearchAlgorithm searchAlgorithm)
{
// Create and instantiate a new empty Stack for result sets.
Stack setStack = new Stack();
HashSet <string> hs1;
HashSet <string> hs2;
HashSet <string> hs;
int idx;
String[] temp = new string[] { };
for (int i = 0; i < searchAlgorithm.Postfix.Count; i++)
{
if (searchAlgorithm.Postfix[i].Equals("AND"))
{
// pop two sets off the stack and apply Intersect, push back result
hs1 = (HashSet <string>)setStack.Pop();
hs2 = (HashSet <string>)setStack.Pop();
temp = hs1.ToArray <string>(); // copy the elements of the set hs1
hs = new HashSet <string>(temp); // make a deep copy of hs1
hs.IntersectWith(hs2); // apply the Intersect to the new set
setStack.Push(hs); // push a reference to a new set
}
else if (searchAlgorithm.Postfix[i].Equals("OR"))
{
// pop two sets off the stack and apply Union
hs1 = (HashSet <string>)setStack.Pop();
hs2 = (HashSet <string>)setStack.Pop();
temp = hs1.ToArray <string>(); // copy the elements of the set hs1
hs = new HashSet <string>(temp); // make a deep copy of hs1
hs.UnionWith(hs2); // apply the Union to the new set
setStack.Push(hs); // push a reference to a new set
}
else
{
// here if an operand
idx = attributeSets.IndexOfKey(searchAlgorithm.Postfix[i]); // identify attribute set
if (idx >= 0)
{
hs1 = (HashSet <string>)attributeSets.GetByIndex(idx);
setStack.Push(hs1); // note: pushing a reference, not the actual set
}
else
{
throw new FormatException(string.Format("Invalid attribute {0}. Use attributes that exist on a vehicle.",
searchAlgorithm.Postfix[i]));
}
}
}
if (setStack.Count == 1)
{
//hs1 = (HashSet<string>)attributeSets.GetByIndex(1);
hs1 = (HashSet <string>)setStack.Pop();
result = hs1.ToList().ToArray();
}
else
{
throw new Exception("Invalid search query provided. Did you add an extra parenthesis?");
}
}
/// <summary>
/// Search using specified algorithm
/// </summary>
/// <param name="searchAlgorithm">Search algorithm instance to use</param>
/// <returns></returns>
private string[] search(SearchAlgorithm searchAlgorithm)
{
searchFleet(out string[] result, searchAlgorithm);
if (result.Length == 0)
{
throw new Exception("No matches found for this search query. Perhaps make your query less specific.");
}
return(result);
}