using Implab;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Implab.Automaton.RegularExpressions {
    /// <summary>
    /// Базовый абстрактный класс. Грамматика, позволяет формулировать выражения над алфавитом типа <c>char</c>.
    /// </summary>
        public abstract class Grammar<TSymbol, TTag> {
        
        public abstract IAlphabetBuilder<TSymbol> Alphabet {
            get;
        }

        public SymbolToken<TTag> UnclassifiedToken() {
            return new SymbolToken<TTag>(DFAConst.UNCLASSIFIED_INPUT);
        }

        public void DefineAlphabet(IEnumerable<TSymbol> alphabet) {
            Safe.ArgumentNotNull(alphabet, "alphabet");

            foreach (var ch in alphabet)
                Alphabet.DefineSymbol(ch);
        }

        public Token<TTag> SymbolToken(TSymbol symbol) {
            return Token<TTag>.New(TranslateOrAdd(symbol));
        }

        public Token<TTag> SymbolToken(IEnumerable<TSymbol> symbols) {
            Safe.ArgumentNotNull(symbols, "symbols");

            return Token<TTag>.New(TranslateOrAdd(symbols).ToArray());
        }

        public Token<TTag> SymbolSetToken(params TSymbol[] set) {
            return SymbolToken(set);
        }

        int TranslateOrAdd(TSymbol ch) {
            var t = Alphabet.Translate(ch);
            if (t == DFAConst.UNCLASSIFIED_INPUT)
                t = Alphabet.DefineSymbol(ch);
            return t;
        }

        IEnumerable<int> TranslateOrAdd(IEnumerable<TSymbol> symbols) {
            return symbols.Distinct().Select(TranslateOrAdd);
        }

        int TranslateOrDie(TSymbol ch) {
            var t = Alphabet.Translate(ch);
            if (t == DFAConst.UNCLASSIFIED_INPUT)
                    throw new ApplicationException(String.Format("Symbol '{0}' is UNCLASSIFIED", ch));
            return t;
        }

        IEnumerable<int> TranslateOrDie(IEnumerable<TSymbol> symbols) {
            return symbols.Distinct().Select(TranslateOrDie);
        }

        public Token<TTag> SymbolTokenExcept(IEnumerable<TSymbol> symbols) {
            Safe.ArgumentNotNull(symbols, "symbols");

            return Token<TTag>.New( Enumerable.Range(0, Alphabet.Count).Except(TranslateOrDie(symbols)).ToArray() );
        }

        protected CDFADefinition BuildDFA(Token<TTag> lang) {
            Safe.ArgumentNotNull(lang, "lang");

            var dfa = new CDFADefinition(Alphabet);
            
            var builder = new RegularDFABuilder<TTag>();

            lang.Accept( builder );

            builder.BuildDFA(dfa);
            if (dfa.InitialStateIsFinal)
                throw new ApplicationException("The specified language contains empty token");

            return dfa.Optimize();
        }

        

        //protected abstract TGrammar CreateInstance();
    }


}