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

namespace Implab.Parsing {
    /// <summary>
    /// Алфавит символами которого являются элементы перечислений.
    /// </summary>
    /// <typeparam name="T">Тип перечислений</typeparam>
    public class EnumAlphabet<T> : AlphabetBase<T> where T : struct, IConvertible {
        static readonly T[] _symbols;
        static readonly EnumAlphabet<T> _fullAlphabet;

        static EnumAlphabet() {
            if (!typeof(T).IsEnum)
                throw new InvalidOperationException("Invalid generic parameter, enumeration is required");

            if (Enum.GetUnderlyingType(typeof(T)) != typeof(Int32))
                throw new InvalidOperationException("Only enums based on Int32 are supported");

            _symbols = ((T[])Enum.GetValues(typeof(T)))
                .OrderBy(x => x.ToInt32(CultureInfo.InvariantCulture))
                .ToArray();

            if (
                _symbols[_symbols.Length - 1].ToInt32(CultureInfo.InvariantCulture) >= _symbols.Length
                || _symbols[0].ToInt32(CultureInfo.InvariantCulture) != 0
            )
                throw new InvalidOperationException("The specified enumeration must be zero-based and continuously numbered");

            _fullAlphabet = new EnumAlphabet<T>(_symbols.Select(x => x.ToInt32(CultureInfo.InvariantCulture)).ToArray());
        }

        

        public static EnumAlphabet<T> FullAlphabet {
            get {
                return _fullAlphabet;
            }
        }


        public EnumAlphabet()
            : base(_symbols.Length) {
        }

        public EnumAlphabet(int[] map)
            : base(map) {
            Debug.Assert(map.Length == _symbols.Length);
        }


        public override int GetSymbolIndex(T symbol) {
            return symbol.ToInt32(CultureInfo.InvariantCulture);
        }

        public override IEnumerable<T> InputSymbols {
            get { return _symbols; }
        }

    }
}