// Copyright © 2008, 2015, Oracle and/or its affiliates. All rights reserved.
//
// MySQL Connector/NET is licensed under the terms of the GPLv2
// <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most 
// MySQL Connectors. There are special exceptions to the terms and 
// conditions of the GPLv2 as it is applied to this software, see the 
// FLOSS License Exception
// <http://www.mysql.com/about/legal/licensing/foss-exception.html>.
//
// This program is free software; you can redistribute it and/or modify 
// it under the terms of the GNU General Public License as published 
// by the Free Software Foundation; version 2 of the License.
//
// This program is distributed in the hope that it will be useful, but 
// WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 
// for more details.
//
// You should have received a copy of the GNU General Public License along 
// with this program; if not, write to the Free Software Foundation, Inc., 
// 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA

using System;
using System.Diagnostics;
using System.Text;
using System.Data;
using System.Collections.Generic;
using MySql.Data.MySqlClient;
using System.Globalization;
#if EF6
using System.Data.Entity.Core.Common.CommandTrees;
using System.Data.Entity.Core.Metadata.Edm;
#else
using System.Data.Common.CommandTrees;
using System.Data.Metadata.Edm;
#endif


namespace MySql.Data.Entity
{
  abstract class SqlGenerator : DbExpressionVisitor<SqlFragment>
  {
    protected string tabs = String.Empty;
    private int parameterCount = 1;
    protected Scope scope = new Scope();
    protected int propertyLevel;
    protected Dictionary<EdmMember, SqlFragment> values;
    protected internal Stack<OpType> Ops = new Stack<OpType>();

    public SqlGenerator()
    {
      Parameters = new List<MySqlParameter>();
    }

    protected internal OpType GetTopOp() 
    {
      if (Ops.Count == 0)
        return OpType.Join;
      else
        return Ops.Peek();
    }

    #region Properties

    public List<MySqlParameter> Parameters { get; private set; }
    //        protected SymbolTable Symbols { get; private set; }

    #endregion

    public virtual string GenerateSQL(DbCommandTree commandTree)
    {
      throw new NotImplementedException();
    }

    protected string CreateUniqueParameterName()
    {
      return String.Format("@gp{0}", parameterCount++);
    }

    #region DbExpressionVisitor Base Implementations

    public override SqlFragment Visit(DbVariableReferenceExpression expression)
    {
      PropertyFragment fragment = new PropertyFragment();
      fragment.Properties.Add(expression.VariableName);
      return fragment;
    }

    public override SqlFragment Visit(DbPropertyExpression expression)
    {
      propertyLevel++;
      PropertyFragment fragment = expression.Instance.Accept(this) as PropertyFragment;
      fragment.Properties.Add(expression.Property.Name);
      propertyLevel--;

      // if we are not at the top level property then just return
      if (propertyLevel > 0) return fragment;

      ColumnFragment column = new ColumnFragment(null, fragment.LastProperty);
      column.PropertyFragment = fragment;
      InputFragment input = scope.FindInputFromProperties(fragment);
      if (input != null)
        column.TableName = input.Name;

      // now we need to check if our column name was possibly renamed
      if (input is TableFragment )
      {
        if (!string.IsNullOrEmpty(input.Name))
        {
          SelectStatement sf = scope.GetFragment(input.Name) as SelectStatement;
          if (sf != null)
          {
            // Special case: undo alias in case of query fusing
            for (int i = 0; i < sf.Columns.Count; i++)
            {
              ColumnFragment cf = sf.Columns[i];
              if (column.ColumnName == cf.ColumnAlias)
              {
                column.ColumnName = cf.ColumnName;
                column.ColumnAlias = cf.ColumnAlias;
                column.TableName = input.Name;
                return column;
              }
            }
          }
        }
        return column;
      }

      SelectStatement select = input as SelectStatement;
      UnionFragment union = input as UnionFragment;

      if (select != null)      
        select.HasDifferentNameForColumn(column);
      else if (union != null)
        union.HasDifferentNameForColumn(column);

      // input is a table, selectstatement, or unionstatement
      return column;
    }

    public override SqlFragment Visit(DbScanExpression expression)
    {
      EntitySetBase target = expression.Target;
      TableFragment fragment = new TableFragment();

      MetadataProperty property;
      bool propExists = target.MetadataProperties.TryGetValue("DefiningQuery", true, out property);
      if (propExists && property.Value != null)
      {
        
        MetadataProperty prop2;

        if( target.MetadataProperties.TryGetValue( "http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator:Type", true, out prop2 ) && ( prop2.Value as string == "Views" ))

        {
          
          // avoid storing view query as DefiningQuery because that hurts query fusing.
          fragment.Schema = target.MetadataProperties.GetValue("http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator:Schema", true).Value as string;
          fragment.Table = target.Name;
       
        } else {
          fragment.DefiningQuery = new LiteralFragment(property.Value as string);

        }

      }

      else
      {
        fragment.Schema = target.EntityContainer.Name;
        fragment.Table = target.Name;

        propExists = target.MetadataProperties.TryGetValue("Schema", true, out property);
        if (propExists && property.Value != null)
          fragment.Schema = property.Value as string;
        propExists = target.MetadataProperties.TryGetValue("Table", true, out property);
        if (propExists && property.Value != null)
          fragment.Table = property.Value as string;
      }
      return fragment;
    }

    public override SqlFragment Visit(DbParameterReferenceExpression expression)
    {
      return new LiteralFragment("@" + expression.ParameterName);
    }

    public override SqlFragment Visit(DbNotExpression expression)
    {
      SqlFragment f = expression.Argument.Accept(this);
      Debug.Assert(f is NegatableFragment);
      NegatableFragment nf = f as NegatableFragment;
      nf.Negate();
      return nf;
    }

    public override SqlFragment Visit(DbIsEmptyExpression expression)
    {
      ExistsFragment f = new ExistsFragment(expression.Argument.Accept(this));
      f.Negate();
      return f;
    }

    public override SqlFragment Visit(DbFunctionExpression expression)
    {
      FunctionProcessor gen = new FunctionProcessor();
      return gen.Generate(expression, this);
    }

    public override SqlFragment Visit(DbConstantExpression expression)
    {
      PrimitiveTypeKind pt = ((PrimitiveType)expression.ResultType.EdmType).PrimitiveTypeKind;
      string literal = Metadata.GetNumericLiteral(pt, expression.Value);
      if (literal != null)
        return new LiteralFragment(literal);
      else if (pt == PrimitiveTypeKind.Boolean)
        return new LiteralFragment((bool)expression.Value ? "1" : "0");
      else
      {
        // use a parameter for non-numeric types so we get proper
        // quoting
        MySqlParameter p = new MySqlParameter();
        p.ParameterName = CreateUniqueParameterName();
        p.DbType = Metadata.GetDbType(expression.ResultType);
        p.Value = Metadata.NormalizeValue(expression.ResultType, expression.Value);
        Parameters.Add(p);
        return new LiteralFragment(p.ParameterName);
      }
    }

    public override SqlFragment Visit(DbComparisonExpression expression)
    {
      return VisitBinaryExpression(expression.Left, expression.Right,
          Metadata.GetOperator(expression.ExpressionKind));
    }    

    public override SqlFragment Visit(DbAndExpression expression)
    {
      return VisitBinaryExpression(expression.Left, expression.Right, "AND");
    }

    public override SqlFragment Visit(DbOrExpression expression)
    {
      return VisitBinaryExpression(expression.Left, expression.Right, "OR");
    }

    public override SqlFragment Visit(DbCastExpression expression)
    {
      //TODO: handle casting
      return expression.Argument.Accept(this);
    }

#if EF6
    public override SqlFragment Visit(DbInExpression expression)
    {
      SqlFragment sf = expression.Item.Accept(this);
      InFragment inf = new InFragment();
      inf.Argument = sf;
      for( int i = 0; i < expression.List.Count; i++ )
      {
        LiteralFragment lf = Visit( expression.List[ i ] as DbConstantExpression ) as LiteralFragment;
        inf.InList.Add( lf );
      }
      return inf;
    }

    public override SqlFragment Visit(DbLambdaExpression expression)
    {
      throw new NotImplementedException();
    }
#endif

    public override SqlFragment Visit(DbLikeExpression expression)
    {
      LikeFragment f = new LikeFragment();

      f.Argument = expression.Argument.Accept(this);
      f.Pattern = expression.Pattern.Accept(this);      

      return f;
    }

    public override SqlFragment Visit(DbCaseExpression expression)
    {
      CaseFragment c = new CaseFragment();

      Debug.Assert(expression.When.Count == expression.Then.Count);

      for (int i = 0; i < expression.When.Count; ++i)
      {
        c.When.Add(expression.When[i].Accept(this));
        c.Then.Add(expression.Then[i].Accept(this));
      }
      if (expression.Else != null && !(expression.Else is DbNullExpression))
        c.Else = expression.Else.Accept(this);
      return c;
    }

    public override SqlFragment Visit(DbIsNullExpression expression)
    {
      IsNullFragment f = new IsNullFragment();
      f.Argument = expression.Argument.Accept(this);
      return f;
    }

    public override SqlFragment Visit(DbIntersectExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbNullExpression expression)
    {
      return new LiteralFragment("NULL");
    }

    public override SqlFragment Visit(DbArithmeticExpression expression)
    {
      if (expression.ExpressionKind == DbExpressionKind.UnaryMinus)
      {
        ListFragment f = new ListFragment();
        f.Append("-(");
        f.Append(expression.Arguments[0].Accept(this));
        f.Append(")");
        return f;
      }

      string op = String.Empty;
      switch (expression.ExpressionKind)
      {
        case DbExpressionKind.Divide:
          op = "/"; break;
        case DbExpressionKind.Minus:
          op = "-"; break;
        case DbExpressionKind.Modulo:
          op = "%"; break;
        case DbExpressionKind.Multiply:
          op = "*"; break;
        case DbExpressionKind.Plus:
          op = "+"; break;
        default:
          throw new NotSupportedException();
      }
      return VisitBinaryExpression(expression.Arguments[0], expression.Arguments[1], op);
    }

    protected void VisitNewInstanceExpression(SelectStatement select,
        DbNewInstanceExpression expression)
    {
      Debug.Assert(expression.ResultType.EdmType is RowType);

      RowType row = expression.ResultType.EdmType as RowType;

      for (int i = 0; i < expression.Arguments.Count; i++)
      {
        ColumnFragment col;

        SqlFragment fragment = expression.Arguments[i].Accept(this);
        if (fragment is ColumnFragment)
          col = fragment as ColumnFragment;
        else
        {
          col = new ColumnFragment(null, null);
          col.Literal = fragment;
        }

        col.ColumnAlias = row.Properties[i].Name;
        select.Columns.Add(col);
      }
    }

    public override SqlFragment Visit(DbTreatExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbRelationshipNavigationExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbRefExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbOfTypeExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbIsOfExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbRefKeyExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbEntityRefExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbExceptExpression expression)
    {
      throw new NotSupportedException();
    }

    public override SqlFragment Visit(DbExpression expression)
    {
      throw new InvalidOperationException();
    }

    public override SqlFragment Visit(DbDerefExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbApplyExpression expression)
    {
      throw new NotSupportedException();
    }

    #endregion

    #region DBExpressionVisitor methods normally overridden

    public override SqlFragment Visit(DbUnionAllExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbSortExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbSkipExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbQuantifierExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbProjectExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbNewInstanceExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbLimitExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbJoinExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbGroupByExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbFilterExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbElementExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbDistinctExpression expression)
    {
      throw new NotImplementedException();
    }

    public override SqlFragment Visit(DbCrossJoinExpression expression)
    {
      throw new NotImplementedException();
    }

    #endregion

    #region "Optimization"

    /// <summary>
    /// If current fragment is select and its from clause is another select, try fuse the inner select with the outer select.
    /// (Thus removing a nested query, which may have bad performance in Mysql).
    /// </summary>
    /// <param name="f">The fragment to probe and posibly optimize</param>
    /// <returns>The fragment fused, or the original one.</returns>
    protected internal InputFragment TryFusingSelect(InputFragment f)
    {
      SelectStatement result = f as SelectStatement;
      if (!CanFuseSelect(f as SelectStatement)) return f;
      result = FuseSelectWithInnerSelect(result, result.From as SelectStatement);
      return result;
    }

    protected internal SelectStatement FuseSelectWithInnerSelect(SelectStatement outer, SelectStatement inner)
    {
      string oldTableName = (inner.From as TableFragment).Name;
      string newTableName = inner.Name;
      Dictionary<string, ColumnFragment> dicColumns = new Dictionary<string, ColumnFragment>();

      foreach (ColumnFragment cf in inner.Columns)
      {
        if (cf.ColumnAlias != null)
          dicColumns.Add(cf.ColumnAlias, cf);
      }
      outer.From = inner.From;
      (outer.From as TableFragment).Name = newTableName;
      // Dispatch Where
      if (outer.Where == null)
      {
        outer.Where = inner.Where;
      }
      else if (inner.Where != null)
      {
        outer.Where = new BinaryFragment() { Left = outer.Where, Right = inner.Where, Operator = "AND" };
      }
      VisitAndReplaceTableName(outer.Where, oldTableName, newTableName, dicColumns);
      // For the next constructions, either is defined on outer or at inner, not both
      // Dispatch Limit
      if (outer.Limit == null)
      {
        outer.Limit = inner.Limit;
        VisitAndReplaceTableName(outer.Limit, oldTableName, newTableName, dicColumns);
      }
      // Dispatch GroupBy
      if (outer.GroupBy == null && inner.GroupBy != null)
      {
        foreach (SqlFragment sf in inner.GroupBy)
          outer.AddGroupBy(sf);
        foreach (SqlFragment sf in outer.GroupBy)
          VisitAndReplaceTableName(sf, oldTableName, newTableName, dicColumns);
      }
      // Dispatch OrderBy
      if (outer.OrderBy != null || inner.OrderBy != null)
      {
        if (inner.OrderBy != null)
        {
          foreach (SortFragment sf in inner.OrderBy)
            outer.AddOrderBy(sf);
        }
        foreach (SortFragment sf in outer.OrderBy)
          VisitAndReplaceTableName(sf, oldTableName, newTableName, dicColumns);
      }
      // Dispatch Skip
      if (outer.Skip == null)
        outer.Skip = inner.Skip;
      return outer;
    }

    protected internal bool CanFuseSelect(SelectStatement select)
    {
      SelectStatement innerSelect = null;
      if (select == null || select.Columns.Count != 0) return false;
      innerSelect = select.From as SelectStatement;
      if ((innerSelect == null) || !( innerSelect.From is TableFragment )) return false;
      // Cannot fuse, unless construction is semantically compatible
      // ie. Where's can be combined, Group by's no.
      if ((select.Limit == null || innerSelect.Limit == null) &&
          (select.GroupBy == null || innerSelect.GroupBy == null) &&
          (select.OrderBy == null || innerSelect.OrderBy == null) &&
          (select.Skip == null || innerSelect.Skip == null) && 
          ( select.IsDistinct == innerSelect.IsDistinct ) )
      {
        List<ColumnFragment> cols = innerSelect.Columns;
        for (int i = 0; i < cols.Count; i++)
          if (cols[i].Literal != null)
            return false;
        return true;
      }
      else
      {
        return false;
      }
    }

    protected internal void VisitAndReplaceTableName(SqlFragment sf, string oldTable, string newTable, 
      Dictionary<string, ColumnFragment> dicColumns)
    {
      if (sf == null) return;
      ReplaceTableNameVisitor visitor = new ReplaceTableNameVisitor(oldTable, newTable, dicColumns);
      sf.Accept(visitor);
    }

    #endregion

    protected InputFragment VisitInputExpression(DbExpression e, string name, TypeUsage type)
    {
      SqlFragment f = e.Accept(this);
      Debug.Assert(f is InputFragment);      

      InputFragment inputFragment = f as InputFragment;
      inputFragment.Name = name;
      TryFusingSelect(inputFragment);

      if (inputFragment is TableFragment && type != null)
        (inputFragment as TableFragment).Type = type;

      SelectStatement select = inputFragment as SelectStatement;
      if ((select != null) && (select.From is TableFragment))
      {
        (select.From as TableFragment).Type = type;
      }

      if (name != null)
        scope.Add(name, inputFragment);
      
      return inputFragment;
    }

    protected virtual SelectStatement GenerateReturningSql(DbModificationCommandTree tree, DbExpression returning)
    {
      SelectStatement select = new SelectStatement(this);

      Debug.Assert(returning is DbNewInstanceExpression);
      VisitNewInstanceExpression(select, returning as DbNewInstanceExpression);

      select.From = (InputFragment)tree.Target.Expression.Accept(this);

      ListFragment where = new ListFragment();      
      select.Where = where;
      return select;
    }

    #region Private Methods

    /// <summary>
    /// Examines a binary expression to see if it is an special case suitable to conversion 
    /// to a more efficient and equivalent LIKE sql expression.
    /// </summary>
    /// <param name="left"></param>
    /// <param name="right"></param>
    /// <param name="op"></param>
    /// <returns></returns>
    protected LikeFragment TryPromoteToLike(DbExpression left, DbExpression right, string op)
    {
      DbFunctionExpression fl = left as DbFunctionExpression;
      if ((fl != null) && (right is DbConstantExpression))
      {        
        LikeFragment like = new LikeFragment();
        if (fl.Function.FullName == "Edm.IndexOf")
        {
          DbParameterReferenceExpression par;
          DbPropertyExpression prop;
          int value = Convert.ToInt32(((DbConstantExpression)right).Value);
          like.Argument = fl.Arguments[1].Accept(this);
          if ((value == 1) && (op == "="))
          {
            DbFunctionExpression fr1;
            DbFunctionExpression fr2;
            if ((fl.Arguments[0] is DbConstantExpression))
            {
              // Case LIKE 'pattern%'
              DbConstantExpression c = (DbConstantExpression)fl.Arguments[0];
              like.Pattern = new LiteralFragment(string.Format("'{0}%'", c.Value.ToString().Replace( "'", "''" ) ));
              return like;
            }
            else if ((fl.Arguments.Count == 2) &&
              ((fr1 = fl.Arguments[0] as DbFunctionExpression) != null) &&
              ((fr2 = fl.Arguments[1] as DbFunctionExpression) != null) &&
              (fr1.Function.FullName == "Edm.Reverse") &&
              (fr2.Function.FullName == "Edm.Reverse"))
            {
              // Case LIKE '%pattern' in EF .NET 4.0
              if (fr1.Arguments[0] is DbConstantExpression)
              {
                DbConstantExpression c = (DbConstantExpression)fr1.Arguments[0];
                like.Pattern = new LiteralFragment(string.Format("'%{0}'", c.Value.ToString().Replace("'", "''") ));                
                like.Argument = fr2.Arguments[0].Accept(this);
                return like;
              } 
              else if( /* For EF6 */
                (( par = fr1.Arguments[0] as DbParameterReferenceExpression  ) != null ) &&
                (( prop = fr2.Arguments[0] as DbPropertyExpression) != null ))
              {
                // Pattern LIKE "%..." in EF6              
                like.Pattern = par.Accept(this);                                
                like.Argument = prop.Accept(this);
                return like;
              }
            }
            else if( ( fl.Arguments.Count == 2) &&
              (( par = fl.Arguments[0] as DbParameterReferenceExpression ) != null ) && 
              (( prop = fl.Arguments[1] as DbPropertyExpression ) != null ) )
            {
              // Case LIKE "pattern%" in EF6              
              like.Pattern = par.Accept(this);              
              like.Argument = prop.Accept(this);
              return like;
            }
          }
          else if (value == 0)
          {
            if ( op == ">") 
            {
              if (fl.Arguments[0] is DbConstantExpression)
              {
                // Case LIKE '%pattern%'
                DbConstantExpression c = (DbConstantExpression)fl.Arguments[0];
                like.Pattern = new LiteralFragment(string.Format("%{0}%", c.Value.ToString()));                
                return like;
              } 
              else if ((par = fl.Arguments[0] as DbParameterReferenceExpression) != null) 
              {
                // Case LIKE "%pattern%" in EF6                
                like.Pattern = fl.Arguments[0].Accept(this);
                return like;
              }
            }
          }
        }
        // Like '%pattern' in EF .NET 3.5 (yes, is different than in .NET 4.0)
        else if (fl.Function.FullName == "Edm.Right")
        {
          DbFunctionExpression fLength = fl.Arguments[1] as DbFunctionExpression;
          if ((fLength != null) && (fLength.Function.FullName == "Edm.Length") && (fLength.Arguments[0] is DbConstantExpression))
          {
            DbConstantExpression c2 = fLength.Arguments[0] as DbConstantExpression;
            DbConstantExpression c1 = (DbConstantExpression)right;
            if (c1.Value == c2.Value)
            {
              like.Argument = fl.Arguments[0].Accept(this);
              like.Pattern = new LiteralFragment(string.Format("'%{0}'", c1.Value.ToString().Replace("'", "''") ));
              return like;
            }
          }
        }
      }
      return null;
    }

    protected virtual SqlFragment VisitBinaryExpression(DbExpression left, DbExpression right, string op)
    {
      // Optimization: try to use 'like' instead of 'locate' (Edm.IndexOf) for these
      // cases: (like 'word%'), (like '%word') & (like '%word%').
      LikeFragment like = TryPromoteToLike(left, right, op);
      if (like != null)
        return like;
      // normal flow
      BinaryFragment f = new BinaryFragment();
      f.Operator = op;
      f.Left = left.Accept(this);
      f.WrapLeft = ShouldWrapExpression(left);
      f.Right = right.Accept(this);
      f.WrapRight = ShouldWrapExpression(right);
      // Optimization, try to promote to In expression
      // NOTE: In EF6, this optimization is already done, we just implement Visit(DbInExpression).
#if !EF6   
      return TryToPromoteToIn(f);
#else
      return f;
#endif
    }

    protected virtual SqlFragment TryToPromoteToIn(BinaryFragment bf)
    {
      // TODO: Remember Morgan's theorem
      // Only try to merge if they are OR'ed.
      if ((bf.Operator == "OR") )
      {
        InFragment inf = bf.Left as InFragment;
        InFragment inf2 = bf.Right as InFragment;
        if (inf == null)
        {
          BinaryFragment bfLeft = bf.Left as BinaryFragment;
          if( bfLeft == null ) 
            return bf;
          if (inf2 == null)
          {
            // try to create a new infragment
            BinaryFragment bfRight = bf.Right as BinaryFragment;
            if (bfRight == null)
              return bf;
            InFragment inff = TryMergeTwoBinaryFragments(bfLeft, bfRight);
            if (inff != null)
              return inff;
          }
          else
          {
            // try to merge an existing infragment & a binaryfragment.
            SqlFragment sf = TryMergeBinaryFragmentAndInFragment(bfLeft, inf2);
            if (sf != null)
              return sf;
          }
        }
        else if (inf2 == null)
        {
          BinaryFragment bfRight = bf.Right as BinaryFragment;
          if (bfRight == null)
            return bf;
          else
          {
            // try to merge an existing infragment & a binaryfragment.
            SqlFragment sf = TryMergeBinaryFragmentAndInFragment(bfRight, inf);
            if (sf != null)
              return sf;
          }
        }
        else
        {
          // try to merge both InFragments
          SqlFragment sf = TryMergeTwoInFragments( inf, inf2 );
          if (sf != null)
            return sf;
        }
      }
      return bf;
    }

    protected InFragment TryMergeTwoInFragments(InFragment infLeft, InFragment infRight)
    {
      if (infLeft.Argument.Equals(infRight.Argument) && 
        ( infLeft.IsNegated == infRight.IsNegated ) && ( !infLeft.IsNegated ) )
      {
        infLeft.InList.AddRange(infRight.InList);
        return infLeft;
      }
      return null;
    }

    protected InFragment TryMergeTwoBinaryFragments(BinaryFragment left, BinaryFragment right)
    {
      if( ( left.IsNegated == right.IsNegated ) && ( ! left.IsNegated ) &&
        ( left.Operator == "=" ) && ( right.Operator == "=" ) )
      {
        ColumnFragment cf;
        LiteralFragment lf;
        GetBinaryFragmentPartsForIn(left, out lf, out cf);
        if ((lf != null) && (cf != null))
        {
          ColumnFragment cf2;
          LiteralFragment lf2;
          GetBinaryFragmentPartsForIn(right, out lf2, out cf2);          
          if ( (lf2 != null) && (cf2 != null) && cf.Equals(cf2))
          {
            InFragment inf = new InFragment();
            inf.Argument = cf;
            inf.InList.Add(lf);
            inf.InList.Add(lf2);
            return inf;
          }
        }
      }
      return null;
    }    

    protected InFragment TryMergeBinaryFragmentAndInFragment(BinaryFragment bf, InFragment inf)
    {
      if( !bf.IsNegated && ( bf.Operator == "=" ))
      {
        ColumnFragment cf;
        LiteralFragment lf;
        GetBinaryFragmentPartsForIn(bf, out lf, out cf);
        if ((lf != null) && (cf != null))
        {
          if (inf.Argument.Equals(cf))
          {
            if (!inf.InList.Contains(lf))
              inf.InList.Add(lf);
            return inf;
          }
        }
      }
      return null;
    }

    protected void GetBinaryFragmentPartsForIn(BinaryFragment bf, out LiteralFragment lf, out ColumnFragment cf)
    {
      cf = bf.Right as ColumnFragment;
      lf = bf.Left as LiteralFragment;
      if (lf == null)
      {
        lf = bf.Right as LiteralFragment;
        cf = bf.Left as ColumnFragment;
      }
    }

    protected bool ShouldWrapExpression(DbExpression e)
    {
      switch (e.ExpressionKind)
      {
        case DbExpressionKind.Property:
        case DbExpressionKind.ParameterReference:
        case DbExpressionKind.Constant:
          return false;
      }
      return true;
    }

    #endregion

  }
}