ComplementPattern.cs

using System.Collections.Generic;
using System.Threading.Tasks;
using Waher.Content.Semantic;
using Waher.Runtime.Collections;
 
namespace Waher.Script.Persistence.SPARQL.Patterns
{
    public class ComplementPattern : BinaryOperatorPattern
    {
        public ComplementPattern(ISparqlPattern Left, ISparqlPattern Right)
            : base(Left, Right)
        {
        }
 
        public override async Task<IEnumerable<Possibility>> Search(ISemanticCube Cube, Variables Variables,
            IEnumerable<Possibility> ExistingMatches, SparqlQuery Query)
        {
            ExistingMatches = await this.Left.Search(Cube, Variables, ExistingMatches, Query);
            if (ExistingMatches is null)
                return null;
 
            ChunkedList<Possibility> Result = null;
 
            foreach (Possibility P in ExistingMatches)
            {
                IEnumerable<Possibility> NewMatches = await this.Right.Search(Cube, Variables,
                    new Possibility[] { P }, Query);
                bool Empty = NewMatches is null;
 
                if (!Empty)
                {
                    using (IEnumerator<Possibility> e = NewMatches.GetEnumerator())
                    {
                        if (!e.MoveNext())
                            Empty = true;
                    }
                }
 
                if (Empty)
                {
                    if (Result is null)
                        Result = new ChunkedList<Possibility>();
 
                    Result.Add(P);
                }
            }
 
            return Result;
        }
 
    }
}