CanonSharp/CanonSharp.Common/LexicalAnalyzer/NondeterministicFiniteAutomation.cs

namespace CanonSharp.Common.LexicalAnalyzer;

public class NondeterministicState : IEquatable<NondeterministicState>
{
    public Guid Id { get; } = Guid.NewGuid();

    public Dictionary<EmptyChar, HashSet<NondeterministicState>> Transactions { get; } = [];

    public bool Equals(NondeterministicState? other) => other is not null && Id.Equals(other.Id);

    public void AddTransaction(EmptyChar c, NondeterministicState state)
    {
        if (Transactions.TryGetValue(c, out HashSet<NondeterministicState>? states))
        {
            states.Add(state);
        }
        else
        {
            Transactions.Add(c, [state]);
        }
    }

    public override bool Equals(object? obj) => obj is NondeterministicState other && Equals(other);

    public override int GetHashCode() => Id.GetHashCode();

    public HashSet<NondeterministicState> CalculateEmptyClosure()
    {
        HashSet<NondeterministicState> result = [];
        Queue<NondeterministicState> queue = [];
        queue.Enqueue(this);

        while (queue.TryDequeue(out NondeterministicState? state))
        {
            result.Add(state);

            if (!state.Transactions.TryGetValue(EmptyChar.Empty, out HashSet<NondeterministicState>? next))
            {
                continue;
            }

            foreach (NondeterministicState s in next.Where(s => !result.Contains(s)))
            {
                queue.Enqueue(s);
            }
        }

        return result;
    }
}

public class NondeterministicStateSet(HashSet<NondeterministicState> states) : IEquatable<NondeterministicStateSet>
{
    private readonly HashSet<NondeterministicState> _states = states;

    public bool Equals(NondeterministicStateSet? other)
    {
        if (other is null)
        {
            return false;
        }

        return _states.Count == other._states.Count && _states.All(s => other._states.Contains(s));
    }

    public override bool Equals(object? obj) => obj is NondeterministicStateSet other && Equals(other);

    public override int GetHashCode() => _states.Aggregate(0, (current, state) => current ^ state.GetHashCode());
}

public class NondeterministicFiniteAutomation(NondeterministicState start, HashSet<NondeterministicState> finalStates)
{
    public NondeterministicState Start { get; } = start;

    public HashSet<NondeterministicState> FinalStates { get; } = finalStates;
}