CanonSharp/CanonSharp.Common/LexicalAnalyzer/LexicalScannerBuilder.cs

using CanonSharp.Common.Abstractions;

namespace CanonSharp.Common.LexicalAnalyzer;

public class LexicalScannerBuilder
{
    private readonly Dictionary<NondeterministicState, LexicalToken> _finalStateMap = [];
    private readonly List<NondeterministicFiniteAutomation> _nondeterministicFiniteAutomations = [];
    private readonly HashSet<LexicalToken> _skippedTokens = [];

    internal LexicalScannerBuilder()
    {

    }

    public void DefineToken(LexicalToken token)
    {
        NondeterministicFiniteAutomation automation = token.Expression.Convert2Nfa();
        _nondeterministicFiniteAutomations.Add(automation);

        foreach (NondeterministicState state in automation.FinalStates)
        {
            _finalStateMap.Add(state, token);
        }
    }

    public void AddSkippedToken(LexicalToken token) => _skippedTokens.Add(token);

    public LexicalScanner Build(ISourceReader reader)
    {
        NondeterministicFiniteAutomation finaAutomation = Combine();
        DeterministicFiniteAutomation deterministicFiniteAutomation =
            DeterministicFiniteAutomation.Create(finaAutomation);

        Dictionary<DeterministicState, LexicalToken> finalTokenMap = [];

        foreach (DeterministicState state in deterministicFiniteAutomation.FinalStates)
        {
            finalTokenMap.Add(state, state.Closure
                .Where(s => _finalStateMap.ContainsKey(s))
                .Select(s => _finalStateMap[s])
                .OrderByDescending(t => t.Priority)
                .First());
        }

        return new LexicalScanner(deterministicFiniteAutomation.Start, finalTokenMap, _skippedTokens, reader);
    }

    private NondeterministicFiniteAutomation Combine()
    {
        NondeterministicState head = new();
        NondeterministicFiniteAutomation result = new(head, []);

        foreach (NondeterministicFiniteAutomation automation in _nondeterministicFiniteAutomations)
        {
            head.AddTransaction(EmptyChar.Empty, automation.Start);
            result.FinalStates.UnionWith(automation.FinalStates);
        }

        return result;
    }
}