/YieldProlog/Modules/BagofAnswers.cs

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using System;

using System.Collections;

using System.Collections.Generic;



namespace OpenSim.Region.ScriptEngine.Shared.YieldProlog

{

    /// <summary>

    /// A BagofAnswers holds answers for bagof and setof.

    /// </summary>

    public class BagofAnswers

    {

        private object _template;

        private Variable[] _freeVariables;

        private Dictionary<object[], List<object>> _bagForFreeVariables;

        private List<object> _findallBagArray;

        private static TermArrayEqualityComparer _termArrayEqualityComparer =

            new TermArrayEqualityComparer();



        /// <summary>

        /// To get the free variables, split off any existential qualifiers from Goal such as the X in

        /// "X ^ f(Y)", get the set of unbound variables in Goal that are not qualifiers, then remove

        /// the unbound variables that are qualifiers as well as the unbound variables in Template.

        /// </summary>

        /// <param name="Template"></param>

        /// <param name="Goal"></param>

        public BagofAnswers(object Template, object Goal)

        {

            _template = Template;



            // First get the set of variables that are not free variables.

            List<Variable> variableSet = new List<Variable>();

            YP.addUniqueVariables(Template, variableSet);

            object UnqualifiedGoal = YP.getValue(Goal);

            while (UnqualifiedGoal is Functor2 && ((Functor2)UnqualifiedGoal)._name == Atom.HAT)

            {

                YP.addUniqueVariables(((Functor2)UnqualifiedGoal)._arg1, variableSet);

                UnqualifiedGoal = YP.getValue(((Functor2)UnqualifiedGoal)._arg2);

            }



            // Remember how many non-free variables there are so we can find the unique free variables

            //   that are added.

            int nNonFreeVariables = variableSet.Count;

            YP.addUniqueVariables(UnqualifiedGoal, variableSet);

            int nFreeVariables = variableSet.Count - nNonFreeVariables;

            if (nFreeVariables == 0)

            {

                // There were no free variables added, so we won't waste time with _bagForFreeVariables.

                _freeVariables = null;

                _findallBagArray = new List<object>();

            }

            else

            {

                // Copy the free variables.

                _freeVariables = new Variable[nFreeVariables];

                for (int i = 0; i < nFreeVariables; ++i)

                    _freeVariables[i] = variableSet[i + nNonFreeVariables];



                _bagForFreeVariables = new Dictionary<object[], List<object>>(_termArrayEqualityComparer);

            }

        }



        public void add()

        {

            if (_freeVariables == null)

                // The goal has bound the values in _template but we don't bother with _freeVariables.

                _findallBagArray.Add(YP.makeCopy(_template, new Variable.CopyStore()));

            else

            {

                // The goal has bound the values in _template and _freeVariables.

                // Find the entry for this set of _freeVariables values.

                object[] freeVariableValues = new object[_freeVariables.Length];

                for (int i = 0; i < _freeVariables.Length; ++i)

                    freeVariableValues[i] = YP.getValue(_freeVariables[i]);

                List<object> bagArray;

                if (!_bagForFreeVariables.TryGetValue(freeVariableValues, out bagArray))

                {

                    bagArray = new List<object>();

                    _bagForFreeVariables[freeVariableValues] = bagArray;

                }



                // Now copy the template and add to the bag for the freeVariables values.

                bagArray.Add(YP.makeCopy(_template, new Variable.CopyStore()));

            }

        }



        // disable warning on l1, don't see how we can

        // code this differently

        #pragma warning disable 0168, 0219



        /// <summary>

        /// For each result, unify the _freeVariables and unify bagArrayVariable with the associated bag.

        /// </summary>

        /// <param name="bagArrayVariable">this is unified with the List<object> of matches for template that

        /// corresponds to the bindings for freeVariables.  Be very careful: this does not unify with a Prolog

        /// list.</param>

        /// <returns></returns>

        public IEnumerable<bool> resultArray(Variable bagArrayVariable)

        {

            if (_freeVariables == null)

            {

                // No unbound free variables, so we only filled one bag.  If empty, bagof fails.

                if (_findallBagArray.Count > 0)

                {

                    foreach (bool l1 in bagArrayVariable.unify(_findallBagArray))

                        yield return false;

                }

            }

            else

            {

                foreach (KeyValuePair<object[], List<object>> valuesAndBag in _bagForFreeVariables)

                {

                    foreach (bool l1 in YP.unifyArrays(_freeVariables, valuesAndBag.Key))

                    {

                        foreach (bool l2 in bagArrayVariable.unify(valuesAndBag.Value))

                            yield return false;

                    }

                    // Debug: Should we free memory of the answers already returned?

                }

            }

        }



        /// <summary>

        /// For each result, unify the _freeVariables and unify Bag with the associated bag.

        /// </summary>

        /// <param name="Bag"></param>

        /// <returns></returns>

        public IEnumerable<bool> result(object Bag)

        {

            Variable bagArrayVariable = new Variable();

            foreach (bool l1 in resultArray(bagArrayVariable))

            {

                foreach (bool l2 in YP.unify(Bag, ListPair.make((List<object>)bagArrayVariable.getValue())))

                    yield return false;

            }

        }



        /// <summary>

        /// For each result, unify the _freeVariables and unify Bag with the associated bag which is sorted

        /// with duplicates removed, as in setof.

        /// </summary>

        /// <param name="Bag"></param>

        /// <returns></returns>

        public IEnumerable<bool> resultSet(object Bag)

        {

            Variable bagArrayVariable = new Variable();

            foreach (bool l1 in resultArray(bagArrayVariable))

            {

                List<object> bagArray = (List<object>)bagArrayVariable.getValue();

                YP.sortArray(bagArray);

                foreach (bool l2 in YP.unify(Bag, ListPair.makeWithoutRepeatedTerms(bagArray)))

                    yield return false;

            }

        }



        public static IEnumerable<bool> bagofArray

            (object Template, object Goal, IEnumerable<bool> goalIterator, Variable bagArrayVariable)

        {

            BagofAnswers bagOfAnswers = new BagofAnswers(Template, Goal);

            foreach (bool l1 in goalIterator)

                bagOfAnswers.add();

            return bagOfAnswers.resultArray(bagArrayVariable);

        }



        public static IEnumerable<bool> bagof

            (object Template, object Goal, IEnumerable<bool> goalIterator, object Bag)

        {

            BagofAnswers bagOfAnswers = new BagofAnswers(Template, Goal);

            foreach (bool l1 in goalIterator)

                bagOfAnswers.add();

            return bagOfAnswers.result(Bag);

        }



        public static IEnumerable<bool> setof

            (object Template, object Goal, IEnumerable<bool> goalIterator, object Bag)

        {

            BagofAnswers bagOfAnswers = new BagofAnswers(Template, Goal);

            foreach (bool l1 in goalIterator)

                bagOfAnswers.add();

            return bagOfAnswers.resultSet(Bag);

        }

        #pragma warning restore 0168, 0219



        /// <summary>

        /// A TermArrayEqualityComparer implements IEqualityComparer to compare two object arrays using YP.termEqual.

        /// </summary>

        private class TermArrayEqualityComparer : IEqualityComparer<object[]>

        {

            public bool Equals(object[] array1, object[] array2)

            {

                if (array1.Length != array2.Length)

                    return false;

                for (int i = 0; i < array1.Length; ++i)

                {

                    if (!YP.termEqual(array1[i], array2[i]))

                        return false;

                }

                return true;

            }



            public int GetHashCode(object[] array)

            {

                int hashCode = 0;

                for (int i = 0; i < array.Length; ++i)

                    hashCode ^= array[i].GetHashCode();

                return hashCode;

            }

        }

    }

}