OrderResultSet.cs

using System;
using System.Collections.Generic;
using Waher.Content.Semantic;
using Waher.Content.Semantic.Model;
using Waher.Content.Semantic.Model.Literals;
using Waher.Script.Exceptions;
using Waher.Script.Model;
using Waher.Script.Persistence.SQL;
 
namespace Waher.Script.Persistence.SPARQL
{
    public class OrderResultSet : IComparer<ISparqlResultRecord>
    {
        private readonly string[] variables;
        private readonly ScriptNode[] expression;
        private readonly bool[] ascending;
        private readonly bool[] calculated;
        private readonly int count;
 
        public OrderResultSet(KeyValuePair<ScriptNode, bool>[] OrderBy)
        {
            ScriptNode Node;
            int i;
 
            this.count = OrderBy.Length;
            this.variables = new string[this.count];
            this.expression = new ScriptNode[this.count];
            this.ascending = new bool[this.count];
            this.calculated = new bool[this.count];
 
            for (i = 0; i < this.count; i++)
            {
                this.expression[i] = Node = OrderBy[i].Key;
                this.ascending[i] = OrderBy[i].Value;
 
                if (Node is VariableReference Ref)
                {
                    this.variables[i] = Ref.VariableName;
                    this.calculated[i] = false;
                }
                else
                    this.calculated[i] = true;
            }
        }
 
        public int Compare(ISparqlResultRecord x, ISparqlResultRecord y)
        {
            ISemanticElement e1, e2;
            int i, j;
 
            for (i = 0; i < this.count; i++)
            {
                if (this.calculated[i])
                {
                    Variables v = new Variables();
                    ObjectProperties v1 = new ObjectProperties(x, v);
                    ObjectProperties v2 = new ObjectProperties(y, v);
 
                    e1 = EvaluateElement(this.expression[i], v1);
                    e2 = EvaluateElement(this.expression[i], v2);
                }
                else
                {
                    e1 = x[this.variables[i]];
                    e2 = y[this.variables[i]];
                }
 
                if (e1 is null)
                {
                    if (!(e2 is null))
                        return -1;
                }
                else if (e2 is null)
                    return 1;
                else
                {
                    j = e1.CompareTo(e2);
                    if (j != 0)
                        return this.ascending[i] ? j : -j;
                }
            }
 
            return 0;
        }
 
        internal static ISemanticElement EvaluateElement(ScriptNode Expression, Variables Variables)
        {
            object Obj;
 
            try
            {
                Obj = Expression.Evaluate(Variables)?.AssociatedObjectValue;
            }
            catch (ScriptReturnValueException ex)
            {
                Obj = ex.ReturnValue.AssociatedObjectValue;
            }
            catch (Exception ex)
            {
                return new StringLiteral(ex.Message);
            }
 
            return SemanticElements.Encapsulate(Obj);
        }
    }
}