// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

namespace System.Data.Entity.Core.Query.PlanCompiler
{
    using System.Collections.Generic;
    using System.Data.Entity.Core.Query.InternalTrees;

    // <summary>
    // This is a halper module for <see cref="JoinElimination" />
    // The VarRefManager keeps track of the child-parent relationships in order to be able
    // to decide whether a given var is referenced by children on right-side relatives of a given node.
    // It is used in JoinElimination when deciding whether it is possible to eliminate the child table participating
    // in a left-outer join when there is a 1 - 0..1 FK relationship.
    // </summary>
    internal class VarRefManager
    {
        #region Internal State

        private readonly Dictionary<Node, Node> m_nodeToParentMap; //child-parent mapping

        private readonly Dictionary<Node, int> m_nodeToSiblingNumber;
        //the index of the given node among its siblings, i.e. 0 for a first child

        private readonly Command m_command;

        #endregion

        #region Constructor

        // <summary>
        // Constructs a new VarRefManager given a command.
        // </summary>
        internal VarRefManager(Command command)
        {
            m_nodeToParentMap = new Dictionary<Node, Node>();
            m_nodeToSiblingNumber = new Dictionary<Node, int>();
            m_command = command;
        }

        #endregion

        #region Public Methods

        // <summary>
        // Tracks the information that the given node is a parent of its children (one level only)
        // </summary>
        internal void AddChildren(Node parent)
        {
            for (var i = 0; i < parent.Children.Count; i++)
            {
                //We do not use add on purpose, we may be updating a child's parent after join elimination in a subtree
                m_nodeToParentMap[parent.Children[i]] = parent;
                m_nodeToSiblingNumber[parent.Children[i]] = i;
            }
        }

        // <summary>
        // Determines whether any var from a given list of keys is referenced by any of defining node's right relatives,
        // with the exception of the relatives brunching at the given targetJoinNode.
        // </summary>
        // <param name="keys"> A list of vars to check for </param>
        // <param name="definingNode"> The node considered to be the defining node </param>
        // <param name="targetJoinNode"> The relatives branching at this node are skipped </param>
        // <returns> False, only it can determine that not a single var from a given list of keys is referenced by any of defining node's right relatives, with the exception of the relatives brunching at the given targetJoinNode. </returns>
        internal bool HasKeyReferences(VarVec keys, Node definingNode, Node targetJoinNode)
        {
            var currentChild = definingNode;
            Node parent;
            var continueUp = true;

            while (continueUp & m_nodeToParentMap.TryGetValue(currentChild, out parent))
            {
                if (parent != targetJoinNode)
                {
                    // Check the parent
                    if (HasVarReferencesShallow(parent, keys, m_nodeToSiblingNumber[currentChild], out continueUp))
                    {
                        return true;
                    }

                    //Check all the siblings to the right
                    for (var i = m_nodeToSiblingNumber[currentChild] + 1; i < parent.Children.Count; i++)
                    {
                        if (parent.Children[i].GetNodeInfo(m_command).ExternalReferences.Overlaps(keys))
                        {
                            return true;
                        }
                    }
                }
                currentChild = parent;
            }
            return false;
        }

        #endregion

        #region Private Methods

        // <summary>
        // Checks whether the given node has references to any of the vars in the given VarVec.
        // It only checks the given node, not its children.
        // </summary>
        // <param name="node"> The node to check </param>
        // <param name="vars"> The list of vars to check for </param>
        // <param name="childIndex"> The index of the node's subree from which this var is coming. This is used for SetOp-s, to be able to locate the appropriate var map that will give the vars corresponding to the given once </param>
        // <param name="continueUp"> If the OpType of the node's Op is such that it 'hides' the input, i.e. the decision of whether the given vars are referenced can be made on this level, it returns true, false otherwise </param>
        // <returns> True if the given node has references to any of the vars in the given VarVec, false otherwise </returns>
        private static bool HasVarReferencesShallow(Node node, VarVec vars, int childIndex, out bool continueUp)
        {
            switch (node.Op.OpType)
            {
                case OpType.ConstrainedSort:
                case OpType.Sort:
                    continueUp = true;
                    return HasVarReferences(((SortBaseOp)node.Op).Keys, vars);

                case OpType.Distinct:
                    continueUp = false;
                    return HasVarReferences(((DistinctOp)node.Op).Keys, vars);

                case OpType.Except:
                case OpType.Intersect:
                case OpType.UnionAll:
                    continueUp = false;
                    return HasVarReferences((SetOp)node.Op, vars, childIndex);

                case OpType.GroupBy:
                    continueUp = false;
                    return HasVarReferences(((GroupByOp)node.Op).Keys, vars);

                case OpType.PhysicalProject:
                    continueUp = false;
                    return HasVarReferences(((PhysicalProjectOp)node.Op).Outputs, vars);

                case OpType.Project:
                    continueUp = false;
                    return HasVarReferences(((ProjectOp)node.Op).Outputs, vars);

                default:
                    continueUp = true;
                    return false;
            }
        }

        // <summary>
        // Does the gvien VarList overlap with the given VarVec
        // </summary>
        private static bool HasVarReferences(VarList listToCheck, VarVec vars)
        {
            foreach (var var in vars)
            {
                if (listToCheck.Contains(var))
                {
                    return true;
                }
            }
            return false;
        }

        // <summary>
        // Do the two given varVecs overlap
        // </summary>
        private static bool HasVarReferences(VarVec listToCheck, VarVec vars)
        {
            return listToCheck.Overlaps(vars);
        }

        // <summary>
        // Does the given list of sort keys contain a key with a var that is the given VarVec
        // </summary>
        private static bool HasVarReferences(List<SortKey> listToCheck, VarVec vars)
        {
            foreach (var key in listToCheck)
            {
                if (vars.IsSet(key.Var))
                {
                    return true;
                }
            }
            return false;
        }

        // <summary>
        // Does the list of outputs of the given SetOp contain a var
        // from the given VarVec defined by the SetOp's child with the given index
        // </summary>
        private static bool HasVarReferences(SetOp op, VarVec vars, int index)
        {
            foreach (var var in op.VarMap[index].Values)
            {
                if (vars.IsSet(var))
                {
                    return true;
                }
            }
            return false;
        }

        #endregion
    }
}
