public static IAutomaton Repeat(IAutomaton automaton, int min = 0, int max = -1)
{
if (min < 0 || (max >= 0 && min > max))
{
throw new ArgumentException(nameof(min));
}
var builder = new AutomatonBuilder();
var start = builder.AddState();
var accept = builder.AddState();
var previousStart = -1;
builder.SetStartState(start);
builder.AcceptState(accept);
int?count = null;
if (max != -1)
{
count = max - min;
}
while (min > 0)
{
var end = builder.AddState();
automaton.CopyTo(builder, out var oldNewStart, out var oldNewAcceptings);
builder.AddEpsilonTransition(start, oldNewStart);
foreach (var st in oldNewAcceptings)
{
builder.AddEpsilonTransition(st, end);
}
min--;
previousStart = start;
start = end;
}
builder.AddEpsilonTransition(start, accept);
if (count == null) //no upper limit, loop!
{
if (previousStart == -1)
{
var end = builder.AddState();
automaton.CopyTo(builder, out var oldNewStart, out var oldNewAcceptings);
builder.AddEpsilonTransition(start, oldNewStart);
builder.AddEpsilonTransition(end, accept);
foreach (var st in oldNewAcceptings)
{
builder.AddEpsilonTransition(st, end);
}
previousStart = start;
start = end;
}
builder.AddEpsilonTransition(start, previousStart);
}
else
{
while (count > 0)//existing upper limit, no loop!
{
var end = builder.AddState();
automaton.CopyTo(builder, out var oldNewStart, out var oldNewAcceptings);
builder.AddEpsilonTransition(start, oldNewStart);
foreach (var st in oldNewAcceptings)
{
builder.AddEpsilonTransition(st, end);
}
builder.AddEpsilonTransition(end, accept);
count--;
start = end;
}
}
return(builder.Build());
}
