CustomOrderEnumerator.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading.Tasks;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Abstraction.Sets;
using Waher.Script.Model;
using Waher.Script.Exceptions;
 
namespace Waher.Script.Persistence.SQL.Enumerators
{
    public class CustomOrderEnumerator : IResultSetEnumerator
    {
        private readonly Dictionary<Type, ObjectProperties> propertiesX = new Dictionary<Type, ObjectProperties>();
        private readonly Dictionary<Type, ObjectProperties> propertiesY = new Dictionary<Type, ObjectProperties>();
        private readonly KeyValuePair<ScriptNode, bool>[] order;
        private readonly IResultSetEnumerator items;
        private readonly Variables variables;
        private IEnumerator<object> e = null;
 
        public CustomOrderEnumerator(IResultSetEnumerator ItemEnumerator, Variables Variables, KeyValuePair<ScriptNode, bool>[] Order)
        {
            this.order = Order;
            this.items = ItemEnumerator;
            this.variables = Variables;
        }
 
        public object Current => this.e.Current;
 
        public void Dispose()
        {
            this.e?.Dispose();
            this.e = null;
        }
 
        public bool MoveNext()
        {
            return this.MoveNextAsync().Result;
        }
 
        public async Task<bool> MoveNextAsync()
        {
            if (this.e is null)
            {
                List<object> Items = new List<object>();
 
                while (await this.items.MoveNextAsync())
                    Items.Add(this.items.Current);
 
                Items.Sort((x, y) =>
                {
                    if (x is null)
                    {
                        if (y is null)
                            return 0;
                        else
                            return -1;
                    }
                    else if (y is null)
                        return 1;
 
                    Type Tx = x.GetType();
                    Type Ty = y.GetType();
 
                    if (this.propertiesX.TryGetValue(Tx, out ObjectProperties Vx))
                        Vx.Object = x;
                    else
                    {
                        Vx = new ObjectProperties(x, this.variables);
                        this.propertiesX[Tx] = Vx;
                    }
 
                    if (this.propertiesY.TryGetValue(Ty, out ObjectProperties Vy))
                        Vy.Object = y;
                    else
                    {
                        Vy = new ObjectProperties(y, this.variables);
                        this.propertiesY[Ty] = Vy;
                    }
 
                    int i, j, c = this.order.Length;
                    IElement Ex, Ey;
                    ScriptNode Node;
 
                    for (i = 0; i < c; i++)
                    {
                        Node = this.order[i].Key;
                        Ex = Node.Evaluate(Vx);     // TODO: Async
                        Ey = Node.Evaluate(Vy);     // TODO: Async
 
                        if (!(Ex.AssociatedSet is IOrderedSet S))
                            throw new ScriptRuntimeException("Result not member of an ordered set.", Node);
 
                        j = S.Compare(Ex, Ey);
                        if (j != 0)
                        {
                            if (this.order[i].Value)
                                return j;
                            else
                                return -j;
                        }
                    }
 
                    return 0;
                });
 
                this.e = Items.GetEnumerator();
            }
 
            return this.e.MoveNext();
        }
 
        public void Reset()
        {
            this.items.Reset();
            this.e = null;
        }
    }
}