Beginning the Rule of Ready Project

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

namespace RuleOfReady.Core.DomainModels
{
    /// <summary>
    /// Object for storing a Partial Sequence (e.g. 2 3, as part of 2 3 4)
    /// </summary>
    public class MahjongPartialSequence : IEnumerable<MahjongTile>
    {

        /// <summary>
        /// The partial sequence this object represents
        /// </summary>
        public IEnumerable<MahjongTile> PartialSequence { get; private set; }

        /// <summary>
        /// The completed sequence this partial sequence is part of
        /// </summary>
        public IEnumerable<MahjongSequence> PossibleCompletions { get; private set; }

        /// <summary>
        /// This tile needed to complete this partial sequence
        /// </summary>
        public IEnumerable<MahjongTile> WaitingTiles { get; private set; }

        /// <summary>
        /// Create a new partial sequence given a sequence, at a partial sequence in it
        /// </summary>
        /// <param name="sequence">sequence that this partial sequence is part of</param>
        /// <param name="partialSequence">the partial sequence of tiles</param>
        public MahjongPartialSequence(MahjongSequence sequence, IEnumerable<MahjongTile> partialSequence)
        {
            if (!(sequence.Count() - 1 == partialSequence.Count()))
                throw new ArgumentException("Partial Sequence has the wrong number of tiles", "partialSequence");

            ;
            if (partialSequence.Except(sequence).Any())
                throw new ArgumentException("Partial sequence not (completely) part of sequence", "partialSequence");

            this.PartialSequence = partialSequence;
            this.PossibleCompletions = this.DeterminePossibleCompletions(sequence, partialSequence);
            this.WaitingTiles = this.PossibleCompletions.SelectMany(seq => seq.Except(partialSequence));
            
        }

        #region IEnumerable<MahjongTile> Implementation

        /// <summary>
        /// Gets the enumerator for the partial sequence list
        /// </summary>
        /// <returns>enumerator for the partial sequence list</returns>
        public IEnumerator<MahjongTile> GetEnumerator()
        {
            return this.PartialSequence.GetEnumerator();
        }
        /// <summary>
        /// Gets the enumerator for the partial sequence list
        /// </summary>
        /// <returns>enumerator for the partial sequence list</returns>
        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.PartialSequence.GetEnumerator();
        }

        private IEnumerable<MahjongSequence> DeterminePossibleCompletions(MahjongSequence sequence,
                                                                          IEnumerable<MahjongTile> partialSequence)
        {
            yield return sequence;
            // if the partial doesn't contain a terminal...

            IEnumerable<MahjongSuitTile> partialSeq = partialSequence.Cast<MahjongSuitTile>();

            Func<MahjongSuitTile, bool> NotATerminal =
                tile => (tile.SuitNumber != MahjongSuitNumber.One && tile.SuitNumber != MahjongSuitNumber.Nine);
                    
            if (partialSeq.All(tile => NotATerminal(tile)))
            {
                MahjongSuitTile firstCompletedTile = sequence.Except(partialSequence).Cast<MahjongSuitTile>().Single();
                IEnumerable<MahjongSuitTile> otherCompletedSequence = new List<MahjongSuitTile>();
                if (partialSequence.All(tile => tile < firstCompletedTile))
                    otherCompletedSequence = Enumerable.Repeat(new MahjongSuitTile(firstCompletedTile.SuitType, firstCompletedTile.SuitNumberInt - 3), 1)
                                                       .Concat(partialSeq);
                else if (partialSequence.All(tile => tile > firstCompletedTile))
                    otherCompletedSequence = partialSeq.Concat(
                        Enumerable.Repeat(new MahjongSuitTile(firstCompletedTile.SuitType, firstCompletedTile.SuitNumberInt + 3), 1));
                if (otherCompletedSequence.Any())
                    yield return new MahjongSequence(otherCompletedSequence);
            }
        }
        
        #endregion


    }
}