ConditionalEnumerator.cs

using System;
using System.Collections;
using System.Threading.Tasks;
using Waher.Persistence;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Model;
 
namespace Waher.Script.Persistence.SQL.Enumerators
{
    public class ConditionalEnumerator : IResultSetEnumerator
    {
        private readonly ScriptNode conditions;
        private readonly Variables variables;
        private readonly IResultSetEnumerator e;
        private ObjectProperties properties = null;
 
        public ConditionalEnumerator(IResultSetEnumerator ItemEnumerator, Variables Variables, ScriptNode Conditions)
        {
            this.e = ItemEnumerator;
            this.variables = Variables;
            this.conditions = Conditions;
        }
 
        public object Current => this.e.Current;
 
        public bool MoveNext()
        {
            while (this.e.MoveNext())
            {
                if (this.MatchesCondition())
                    return true;
            }
 
            return false;
        }
 
        public async Task<bool> MoveNextAsync()
        {
            while (await this.e.MoveNextAsync())
            {
                if (await this.MatchesConditionAsync())
                    return true;
            }
 
            return false;
        }
 
        private bool MatchesCondition()
        {
            try
            {
                if (this.properties is null)
                    this.properties = new ObjectProperties(this.e.Current, this.variables);
                else
                    this.properties.Object = this.e.Current;
 
                IElement E = this.conditions.Evaluate(this.properties);
                if (!(E.AssociatedObjectValue is bool B) || !B)
                    return false;
 
                return true;
            }
            catch (Exception)
            {
                return false;
            }
        }
 
        private async Task<bool> MatchesConditionAsync()
        {
            try
            {
                if (this.properties is null)
                    this.properties = new ObjectProperties(this.e.Current, this.variables);
                else
                    this.properties.Object = this.e.Current;
 
                IElement E = await this.conditions.EvaluateAsync(this.properties);
                if (!(E.AssociatedObjectValue is bool B) || !B)
                    return false;
 
                return true;
            }
            catch (Exception)
            {
                return false;
            }
        }
 
        public void Reset()
        {
            this.e.Reset();
        }
    }
}