/Libraries/core/net40/Query/Algebra/PropertyPathOperators.cs

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using System;

using System.Collections.Generic;

using System.Linq;

using VDS.RDF.Query.Paths;

using VDS.RDF.Query.Patterns;



namespace VDS.RDF.Query.Algebra

{

    /// <summary>

    /// Interface for Property Path Operators

    /// </summary>

    public interface IPathOperator : ISparqlAlgebra

    {

        /// <summary>

        /// Gets the Path Start

        /// </summary>

        PatternItem PathStart

        {

            get;

        }



        /// <summary>

        /// Gets the Path End

        /// </summary>

        PatternItem PathEnd

        {

            get;

        }



        /// <summary>

        /// Gets the Property Path

        /// </summary>

        ISparqlPath Path

        {

            get;

        }

    }



    /// <summary>

    /// Abstract Base Class for Path Operators

    /// </summary>

    public abstract class BasePathOperator 

        : IPathOperator

    {

        private PatternItem _start, _end;

        private ISparqlPath _path;

        private HashSet<String> _vars = new HashSet<string>();



        /// <summary>

        /// Creates a new Path Operator

        /// </summary>

        /// <param name="start">Path Start</param>

        /// <param name="path">Property Path</param>

        /// <param name="end">Path End</param>

        public BasePathOperator(PatternItem start, ISparqlPath path, PatternItem end)

        {

            this._start = start;

            this._end = end;

            this._path = path;



            if (this._start.VariableName != null) this._vars.Add(this._start.VariableName);

            if (this._end.VariableName != null) this._vars.Add(this._end.VariableName);

        }



        /// <summary>

        /// Gets the Path Start

        /// </summary>

        public PatternItem PathStart

        {

            get 

            { 

                return this._start; 

            }

        }



        /// <summary>

        /// Gets the Path End

        /// </summary>

        public PatternItem PathEnd

        {

            get 

            { 

                return this._end; 

            }

        }



        /// <summary>

        /// Gets the Property Path

        /// </summary>

        public ISparqlPath Path

        {

            get 

            { 

                return this._path;

            }

        }



        /// <summary>

        /// Evaluates the Property Path

        /// </summary>

        /// <param name="context">SPARQL Evaluation Context</param>

        /// <returns></returns>

        public abstract BaseMultiset Evaluate(SparqlEvaluationContext context);



        /// <summary>

        /// Gets the Variables used in the Algebra

        /// </summary>

        public IEnumerable<string> Variables

        {

            get 

            {

                return this._vars;

            }

        }



        /// <summary>

        /// Transforms the Algebra back into a Query

        /// </summary>

        /// <returns></returns>

        public SparqlQuery ToQuery()

        {

            SparqlQuery q = new SparqlQuery();

            q.RootGraphPattern = this.ToGraphPattern();

            q.Optimise();

            return q;

        }



        /// <summary>

        /// Transforms the Algebra back into a Graph Pattern

        /// </summary>

        /// <returns></returns>

        public abstract GraphPattern ToGraphPattern();



        /// <summary>

        /// Gets the String representation of the Algebra

        /// </summary>

        /// <returns></returns>

        public abstract override string ToString();

    }



    /// <summary>

    /// Abstract Base Class for Arbitrary Length Path Operators

    /// </summary>

    public abstract class BaseArbitraryLengthPathOperator : BasePathOperator

    {

        /// <summary>

        /// Creates a new Arbitrary Lengh Path Operator

        /// </summary>

        /// <param name="start">Path Start</param>

        /// <param name="end">Path End</param>

        /// <param name="path">Property Path</param>

        public BaseArbitraryLengthPathOperator(PatternItem start, PatternItem end, ISparqlPath path)

            : base(start, path, end) { }



        /// <summary>

        /// Determines the starting points for Path evaluation

        /// </summary>

        /// <param name="context">Evaluation Context</param>

        /// <param name="paths">Paths</param>

        /// <param name="reverse">Whether to evaluate Paths in reverse</param>

        protected void GetPathStarts(SparqlEvaluationContext context, List<List<INode>> paths, bool reverse)

        {

            HashSet<KeyValuePair<INode, INode>> nodes = new HashSet<KeyValuePair<INode, INode>>();

            if (this.Path is Property)

            {

                INode predicate = ((Property)this.Path).Predicate;

                foreach (Triple t in context.Data.GetTriplesWithPredicate(predicate))

                {

                    if (reverse)

                    {

                        nodes.Add(new KeyValuePair<INode, INode>(t.Object, t.Subject));

                    }

                    else

                    {

                        nodes.Add(new KeyValuePair<INode, INode>(t.Subject, t.Object));

                    }

                }

            }

            else

            {

                BaseMultiset initialInput = context.InputMultiset;

                context.InputMultiset = new IdentityMultiset();

                VariablePattern x = new VariablePattern("?x");

                VariablePattern y = new VariablePattern("?y");

                Bgp bgp = new Bgp(new PropertyPathPattern(x, this.Path, y));



                BaseMultiset results = context.Evaluate(bgp);//bgp.Evaluate(context);

                context.InputMultiset = initialInput;



                if (!results.IsEmpty)

                {

                    foreach (ISet s in results.Sets)

                    {

                        if (s["x"] != null && s["y"] != null)

                        {

                            if (reverse)

                            {

                                nodes.Add(new KeyValuePair<INode, INode>(s["y"], s["x"]));

                            }

                            else

                            {

                                nodes.Add(new KeyValuePair<INode, INode>(s["x"], s["y"]));

                            }

                        }

                    }

                }

            }



            paths.AddRange(nodes.Select(kvp => new List<INode>(new INode[] { kvp.Key, kvp.Value })));

        }



        /// <summary>

        /// Evaluates a setp of the Path

        /// </summary>

        /// <param name="context">Context</param>

        /// <param name="path">Paths</param>

        /// <param name="reverse">Whether to evaluate Paths in reverse</param>

        /// <returns></returns>

        protected List<INode> EvaluateStep(SparqlEvaluationContext context, List<INode> path, bool reverse)

        {

            if (this.Path is Property)

            {

                HashSet<INode> nodes = new HashSet<INode>();

                INode predicate = ((Property)this.Path).Predicate;

                IEnumerable<Triple> ts = (reverse ? context.Data.GetTriplesWithPredicateObject(predicate, path[path.Count - 1]) : context.Data.GetTriplesWithSubjectPredicate(path[path.Count - 1], predicate));

                foreach (Triple t in ts)

                {

                    if (reverse)

                    {

                        if (!path.Contains(t.Subject))

                        {

                            nodes.Add(t.Subject);

                        }

                    }

                    else

                    {

                        if (!path.Contains(t.Object))

                        {

                            nodes.Add(t.Object);

                        }

                    }

                }

                return nodes.ToList();

            }

            else

            {

                HashSet<INode> nodes = new HashSet<INode>();



                BaseMultiset initialInput = context.InputMultiset;

                Multiset currInput = new Multiset();

                VariablePattern x = new VariablePattern("?x");

                VariablePattern y = new VariablePattern("?y");

                Set temp = new Set();

                if (reverse)

                {

                    temp.Add("y", path[path.Count - 1]);

                }

                else

                {

                    temp.Add("x", path[path.Count - 1]);

                }

                currInput.Add(temp);

                context.InputMultiset = currInput;



                Bgp bgp = new Bgp(new PropertyPathPattern(x, this.Path, y));

                BaseMultiset results = context.Evaluate(bgp);//bgp.Evaluate(context);

                context.InputMultiset = initialInput;



                if (!results.IsEmpty)

                {

                    foreach (ISet s in results.Sets)

                    {

                        if (reverse)

                        {

                            if (s["x"] != null)

                            {

                                if (!path.Contains(s["x"]))

                                {

                                    nodes.Add(s["x"]);

                                }

                            }

                        }

                        else

                        {

                            if (s["y"] != null)

                            {

                                if (!path.Contains(s["y"]))

                                {

                                    nodes.Add(s["y"]);

                                }

                            }

                        }

                    }

                }



                return nodes.ToList();

            }

        }

    }

}