ExpressionVisitor.cs

// Copyright (C) 2019-2023 Xtensive LLC.
// This code is distributed under MIT license terms.
// See the License.txt file in the project root for more information.

using System.Collections.ObjectModel;
using System.Linq.Expressions;
using Xtensive.Core;
using Xtensive.Linq;

namespace Xtensive.Orm.BulkOperations
{
  /// <summary>
  ///   This class visits every Parameter expression in an expression tree and calls a delegate
  ///   to optionally replace the parameter.  This is useful where two expression trees need to
  ///   be merged (and they don't share the same ParameterExpressions).
  /// </summary>
  internal class ExpressionVisitor<T> : ExpressionVisitor
    where T : Expression
  {
    private readonly Func<T, Expression> visitor;

    public static Expression Visit(Expression exp, Func<T, Expression> visitor)
    {
      return new ExpressionVisitor<T>(visitor).Visit(exp);
    }

    #region Non-public methods

    protected override Expression Visit(Expression exp)
    {
      if (exp is T && visitor != null)
        exp = visitor((T) exp);

      return base.Visit(exp);
    }

    #endregion

    private ExpressionVisitor(Func<T, Expression> visitor)
    {
      this.visitor = visitor;
    }
  }

  /// <summary>
  ///   Expression visitor
  ///   (from http://blogs.msdn.com/mattwar/archive/2007/07/31/linq-building-an-iqueryable-provider-part-ii.aspx)
  /// </summary>
  internal abstract class ExpressionVisitor
  {
    #region Non-public methods

    protected virtual Expression Visit(Expression exp)
    {
      if (exp == null)
        return null;
      switch (exp.NodeType) {
        case ExpressionType.Negate:
        case ExpressionType.NegateChecked:
        case ExpressionType.Not:
        case ExpressionType.Convert:
        case ExpressionType.ConvertChecked:
        case ExpressionType.ArrayLength:
        case ExpressionType.Quote:
        case ExpressionType.TypeAs:
          return VisitUnary((UnaryExpression) exp);
        case ExpressionType.Add:
        case ExpressionType.AddChecked:
        case ExpressionType.Subtract:
        case ExpressionType.SubtractChecked:
        case ExpressionType.Multiply:
        case ExpressionType.MultiplyChecked:
        case ExpressionType.Divide:
        case ExpressionType.Modulo:
        case ExpressionType.And:
        case ExpressionType.AndAlso:
        case ExpressionType.Or:
        case ExpressionType.OrElse:
        case ExpressionType.LessThan:
        case ExpressionType.LessThanOrEqual:
        case ExpressionType.GreaterThan:
        case ExpressionType.GreaterThanOrEqual:
        case ExpressionType.Equal:
        case ExpressionType.NotEqual:
        case ExpressionType.Coalesce:
        case ExpressionType.ArrayIndex:
        case ExpressionType.RightShift:
        case ExpressionType.LeftShift:
        case ExpressionType.ExclusiveOr:
          return VisitBinary((BinaryExpression) exp);
        case ExpressionType.TypeIs:
          return VisitTypeIs((TypeBinaryExpression) exp);
        case ExpressionType.Conditional:
          return VisitConditional((ConditionalExpression) exp);
        case ExpressionType.Constant:
          return VisitConstant((ConstantExpression) exp);
        case ExpressionType.Default:
          return VisitDefault((DefaultExpression) exp);
        case ExpressionType.Parameter:
          return VisitParameter((ParameterExpression) exp);
        case ExpressionType.MemberAccess:
          return VisitMemberAccess((MemberExpression) exp);
        case ExpressionType.Call:
          return VisitMethodCall((MethodCallExpression) exp);
        case ExpressionType.Lambda:
          return VisitLambda((LambdaExpression) exp);
        case ExpressionType.New:
          return VisitNew((NewExpression) exp);
        case ExpressionType.NewArrayInit:
        case ExpressionType.NewArrayBounds:
          return VisitNewArray((NewArrayExpression) exp);
        case ExpressionType.Invoke:
          return VisitInvocation((InvocationExpression) exp);
        case ExpressionType.MemberInit:
          return VisitMemberInit((MemberInitExpression) exp);
        case ExpressionType.ListInit:
          return VisitListInit((ListInitExpression) exp);
        default:
          throw new Exception($"Unhandled expression type: '{exp.NodeType}'");
      }
    }

    private Expression VisitBinary(BinaryExpression b)
    {
      Expression left = Visit(b.Left);
      Expression right = Visit(b.Right);
      Expression conversion = Visit(b.Conversion);
      if (left != b.Left || right != b.Right || conversion != b.Conversion) {
        if (b.NodeType == ExpressionType.Coalesce)
          return Expression.Coalesce(left, right, conversion as LambdaExpression);
        return Expression.MakeBinary(b.NodeType, left, right, b.IsLiftedToNull, b.Method);
      }
      return b;
    }

    private MemberBinding VisitBinding(MemberBinding binding)
    {
      switch (binding.BindingType) {
        case MemberBindingType.Assignment:
          return VisitMemberAssignment((MemberAssignment) binding);
        case MemberBindingType.MemberBinding:
          return VisitMemberMemberBinding((MemberMemberBinding) binding);
        case MemberBindingType.ListBinding:
          return VisitMemberListBinding((MemberListBinding) binding);
        default:
          throw new Exception($"Unhandled binding type '{binding.BindingType}'");
      }
    }

    private IEnumerable<MemberBinding> VisitBindingList(ReadOnlyCollection<MemberBinding> original)
    {
      List<MemberBinding> list = null;
      for (int i = 0, n = original.Count; i < n; i++) {
        MemberBinding b = VisitBinding(original[i]);
        if (list != null)
          list.Add(b);
        else if (b != original[i]) {
          list = new List<MemberBinding>(n);
          for (int j = 0; j < i; j++)
            list.Add(original[j]);
          list.Add(b);
        }
      }
      if (list != null)
        return list;
      return original;
    }

    private Expression VisitConditional(ConditionalExpression c)
    {
      Expression test = Visit(c.Test);
      Expression ifTrue = Visit(c.IfTrue);
      Expression ifFalse = Visit(c.IfFalse);
      if (test != c.Test || ifTrue != c.IfTrue || ifFalse != c.IfFalse)
        return Expression.Condition(test, ifTrue, ifFalse);
      return c;
    }

    private Expression VisitConstant(ConstantExpression c)
    {
      return c;
    }

    private Expression VisitDefault(DefaultExpression d)
    {
      return d.ToConstantExpression();
    }

    private ElementInit VisitElementInitializer(ElementInit initializer)
    {
      IEnumerable<Expression> arguments = VisitExpressionList(initializer.Arguments);
      if (arguments != initializer.Arguments)
        return Expression.ElementInit(initializer.AddMethod, arguments);
      return initializer;
    }

    private IEnumerable<ElementInit> VisitElementInitializerList(ReadOnlyCollection<ElementInit> original)
    {
      List<ElementInit> list = null;
      for (int i = 0, n = original.Count; i < n; i++) {
        ElementInit init = VisitElementInitializer(original[i]);
        if (list != null)
          list.Add(init);
        else if (init != original[i]) {
          list = new List<ElementInit>(n);
          for (int j = 0; j < i; j++)
            list.Add(original[j]);
          list.Add(init);
        }
      }
      if (list != null)
        return list;
      return original;
    }

    private IEnumerable<Expression> VisitExpressionList(ReadOnlyCollection<Expression> original)
    {
      List<Expression> list = null;
      for (int i = 0, n = original.Count; i < n; i++) {
        var p = Visit(original[i]);
        if (list != null)
          list.Add(p);
        else if (p != original[i]) {
          list = new List<Expression>(n);
          for (int j = 0; j < i; j++)
            list.Add(original[j]);
          list.Add(p);
        }
      }
      if (list != null)
        return list.AsReadOnly();
      return original;
    }

    private Expression VisitInvocation(InvocationExpression iv)
    {
      IEnumerable<Expression> args = VisitExpressionList(iv.Arguments);
      Expression expr = Visit(iv.Expression);
      if (args != iv.Arguments || expr != iv.Expression)
        return Expression.Invoke(expr, args);
      return iv;
    }

    private Expression VisitLambda(LambdaExpression lambda)
    {
      Expression body = Visit(lambda.Body);
      if (body != lambda.Body)
        return FastExpression.Lambda(lambda.Type, body, lambda.Parameters);
      return lambda;
    }

    private Expression VisitListInit(ListInitExpression init)
    {
      NewExpression n = VisitNew(init.NewExpression);
      IEnumerable<ElementInit> initializers = VisitElementInitializerList(init.Initializers);
      if (n != init.NewExpression || initializers != init.Initializers)
        return Expression.ListInit(n, initializers);
      return init;
    }

    private Expression VisitMemberAccess(MemberExpression m)
    {
      var originalExpression = m.Expression;
      Expression exp = Visit(originalExpression);
      if (exp != originalExpression)
        return Expression.MakeMemberAccess(exp, m.Member);
      return m;
    }

    private MemberAssignment VisitMemberAssignment(MemberAssignment assignment)
    {
      Expression e = Visit(assignment.Expression);
      if (e != assignment.Expression)
        return Expression.Bind(assignment.Member, e);
      return assignment;
    }

    private Expression VisitMemberInit(MemberInitExpression init)
    {
      NewExpression n = VisitNew(init.NewExpression);
      IEnumerable<MemberBinding> bindings = VisitBindingList(init.Bindings);
      if (n != init.NewExpression || bindings != init.Bindings)
        return Expression.MemberInit(n, bindings);
      return init;
    }

    private MemberListBinding VisitMemberListBinding(MemberListBinding binding)
    {
      IEnumerable<ElementInit> initializers = VisitElementInitializerList(binding.Initializers);
      if (initializers != binding.Initializers)
        return Expression.ListBind(binding.Member, initializers);
      return binding;
    }

    private MemberMemberBinding VisitMemberMemberBinding(MemberMemberBinding binding)
    {
      IEnumerable<MemberBinding> bindings = VisitBindingList(binding.Bindings);
      if (bindings != binding.Bindings)
        return Expression.MemberBind(binding.Member, bindings);
      return binding;
    }

    private Expression VisitMethodCall(MethodCallExpression m)
    {
      Expression obj = Visit(m.Object);
      IEnumerable<Expression> args = VisitExpressionList(m.Arguments);
      if (obj != m.Object || args != m.Arguments)
        return Expression.Call(obj, m.Method, args);
      return m;
    }

    private NewExpression VisitNew(NewExpression nex)
    {
      IEnumerable<Expression> args = VisitExpressionList(nex.Arguments);
      if (args != nex.Arguments)
        return Expression.New(nex.Constructor, args, nex.Members);
      return nex;
    }

    private Expression VisitNewArray(NewArrayExpression na)
    {
      IEnumerable<Expression> exprs = VisitExpressionList(na.Expressions);
      if (exprs != na.Expressions) {
        if (na.NodeType == ExpressionType.NewArrayInit)
          return Expression.NewArrayInit(na.Type.GetElementType(), exprs);
        return Expression.NewArrayBounds(na.Type.GetElementType(), exprs);
      }
      return na;
    }

    private Expression VisitParameter(ParameterExpression p)
    {
      return p;
    }

    private Expression VisitTypeIs(TypeBinaryExpression b)
    {
      Expression expr = Visit(b.Expression);
      if (expr != b.Expression)
        return Expression.TypeIs(expr, b.TypeOperand);
      return b;
    }

    private Expression VisitUnary(UnaryExpression u)
    {
      Expression operand = Visit(u.Operand);
      if (operand != u.Operand)
        return Expression.MakeUnary(u.NodeType, operand, u.Type, u.Method);
      return u;
    }

    #endregion
  }
}