JoinedTripleEnumerator.cs

using System.Collections;
using System.Collections.Generic;
 
namespace Waher.Content.Semantic
{
    public class JoinedTripleEnumerator : IEnumerator<ISemanticTriple>
    {
        private readonly Dictionary<ISemanticTriple, bool> reported;
        private readonly IEnumerable<IEnumerator<ISemanticTriple>> enumerators;
        private IEnumerator<IEnumerator<ISemanticTriple>> e;
        private IEnumerator<ISemanticTriple> current;
        private readonly bool removeDuplicates;
 
        public JoinedTripleEnumerator(IEnumerable<IEnumerator<ISemanticTriple>> Enumerators,
            bool RemoveDuplicates)
        {
            this.enumerators = Enumerators;
            this.removeDuplicates = RemoveDuplicates;
 
            if (this.removeDuplicates)
                this.reported = new Dictionary<ISemanticTriple, bool>();
        }
 
        public ISemanticTriple Current => this.current?.Current;
 
        object IEnumerator.Current => this.current?.Current;
 
        public void Dispose()
        {
            this.e?.Dispose();
            this.e = null;
 
            foreach (IEnumerator<ISemanticTriple> Enumerator in this.enumerators)
                Enumerator.Dispose();
        }
 
        public bool MoveNext()
        {
            if (this.e is null)
            {
                this.e = this.enumerators.GetEnumerator();
 
                if (!this.e.MoveNext())
                    return false;
 
                this.current = this.e.Current;
            }
 
            while (true)
            {
                if (this.current.MoveNext())
                {
                    if (this.removeDuplicates)
                    {
                        if (this.reported.ContainsKey(this.current.Current))
                            continue;
 
                        this.reported[this.current.Current] = true;
                    }
 
                    return true;
                }
 
                if (!this.e.MoveNext())
                    return false;
 
                this.current = this.e.Current;
            }
        }
 
        public void Reset()
        {
            this.current = null;
        
            this.e?.Dispose();
            this.e = null;
        }
    }
}