private static AssignmentElement MoveVariableToLhs(AssignmentElement equals, string variable, out Element varEl)
{
if (ReferenceEquals(equals, null)) throw new MissingAssignmentException();
varEl = equals.Elements.Lhs.FindVariable(variable);
if (!ReferenceEquals(varEl, null)) return equals;
varEl = equals.Elements.Rhs.FindVariable(variable);
if (ReferenceEquals(varEl, null)) throw new UnrecognisedVariableException(variable);
// Swap lhs/rhs
return new AssignmentElement(equals.Elements.Swap());
}
private Element Rearrange(AssignmentElement root, Element targetVar)
{
while (true)
{
// Check for no rearrange necessary
if (root.Elements.Lhs == targetVar) return root.Elements.Rhs;
// Rearrange first part of tree
var targetPath = root.Elements.Lhs.FindPath(targetVar).ToArray();
var lastOperation = targetPath.First();
var varBranch = targetPath.Skip(1).FirstOrDefault() ?? targetVar;
var newRoot = root.Replace(lastOperation, varBranch) as AssignmentElement;
var inversion = lastOperation.Invert(varBranch, newRoot.Elements.Rhs);
root = newRoot.Replace(newRoot.Elements.Rhs, inversion) as AssignmentElement;
}
}