/mcs/class/System.Core/System.Linq/QueryableTransformer.cs

//
// QueryableTransformer.cs
//
// Authors:
//	Roei Erez (roeie@mainsoft.com)
//	Jb Evain (jbevain@novell.com)
//
// Copyright (C) 2008 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Runtime.CompilerServices;

namespace System.Linq {

	class QueryableTransformer : ExpressionTransformer {

		protected override Expression VisitMethodCall (MethodCallExpression methodCall)
		{
			if (IsQueryableExtension (methodCall.Method))
				return ReplaceQueryableMethod (methodCall);

			return base.VisitMethodCall (methodCall);
		}

		protected override Expression VisitLambda (LambdaExpression lambda)
		{
			return lambda;
		}

		protected override Expression VisitConstant (ConstantExpression constant)
		{
			var qe = constant.Value as IQueryableEnumerable;
			if (qe == null)
				return constant;

			return Expression.Constant (qe.GetEnumerable ());
		}

		static bool IsQueryableExtension (MethodInfo method)
		{
			return HasExtensionAttribute (method) &&
				method.GetParameters () [0].ParameterType.IsAssignableTo (typeof (IQueryable));
		}

		static bool HasExtensionAttribute (MethodInfo method)
		{
			return method.GetCustomAttributes (typeof (ExtensionAttribute), false).Length > 0;
		}

		MethodCallExpression ReplaceQueryableMethod (MethodCallExpression old)
		{
			Expression target = null;
			if (old.Object != null)
				target = Visit (old.Object);

			var method = ReplaceQueryableMethod (old.Method);
			var parameters = method.GetParameters ();
			var arguments = new Expression [old.Arguments.Count];

			for (int i = 0; i < arguments.Length; i++) {
				arguments [i] = UnquoteIfNeeded (
					Visit (old.Arguments [i]),
					parameters [i].ParameterType);
			}

			return new MethodCallExpression (target, method, arguments.ToReadOnlyCollection ());
		}

		static Expression UnquoteIfNeeded (Expression expression, Type delegateType)
		{
			if (expression.NodeType != ExpressionType.Quote)
				return expression;

			var lambda = (LambdaExpression) ((UnaryExpression) expression).Operand;
			if (lambda.Type == delegateType)
				return lambda;

			return expression;
		}

		static Type GetTargetDeclaringType (MethodInfo method)
		{
			return method.DeclaringType == typeof (Queryable) ? typeof (Enumerable) : method.DeclaringType;
		}

		static MethodInfo ReplaceQueryableMethod (MethodInfo method)
		{
			var result = GetMatchingMethod (method, GetTargetDeclaringType (method));

			if (result != null)
				return result;

			throw new InvalidOperationException (
				string.Format (
					"There is no method {0} on type {1} that matches the specified arguments",
					method.Name,
					method.DeclaringType.FullName));
		}

		static MethodInfo GetMatchingMethod (MethodInfo method, Type declaring)
		{
			foreach (var candidate in declaring.GetMethods ()) {
				if (!MethodMatch (candidate, method))
					continue;

				if (method.IsGenericMethod)
					return candidate.MakeGenericMethodFrom (method);

				return candidate;
			}

			return null;
		}

		static bool MethodMatch (MethodInfo candidate, MethodInfo method)
		{
			if (candidate.Name != method.Name)
				return false;

			if (!HasExtensionAttribute (candidate))
				return false;

			var parameters = method.GetParameterTypes ();

			if (parameters.Length != candidate.GetParameters ().Length)
				return false;

			if (method.IsGenericMethod) {
				if (!candidate.IsGenericMethod)
					return false;

				if (candidate.GetGenericArguments ().Length != method.GetGenericArguments ().Length)
					return false;

				candidate = candidate.MakeGenericMethodFrom (method);
			}

			if (!TypeMatch (candidate.ReturnType, method.ReturnType))
				return false;

			var candidate_parameters = candidate.GetParameterTypes ();

			if (candidate_parameters [0] != GetComparableType (parameters [0]))
				return false;

			for (int i = 1; i < candidate_parameters.Length; ++i)
				if (!TypeMatch (candidate_parameters [i], parameters [i]))
					return false;

			return true;
		}

		static bool TypeMatch (Type candidate, Type type)
		{
			if (candidate == type)
				return true;

			return candidate == GetComparableType (type);
		}

		static Type GetComparableType (Type type)
		{
			if (type.IsGenericInstanceOf (typeof (IQueryable<>)))
				type = typeof (IEnumerable<>).MakeGenericTypeFrom (type);
			else if (type.IsGenericInstanceOf (typeof (IOrderedQueryable<>)))
				type = typeof (IOrderedEnumerable<>).MakeGenericTypeFrom (type);
			else if (type.IsGenericInstanceOf (typeof (Expression<>)))
				type = type.GetFirstGenericArgument ();
			else if (type == typeof (IQueryable))
				type = typeof (IEnumerable);

			return type;
		}
	}
}