#if NET20 || NET30 || !NET_4_6

// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

using System.Diagnostics;
using System.Dynamic.Utils;
using LinqInternal.Core;

namespace System.Linq.Expressions.Reimplement
{
    /// <summary>
    /// Represents an expression that has a constant value.
    /// </summary>
    [DebuggerTypeProxy(typeof(ConstantExpressionProxy))]
    public class ConstantExpression : Expression
    {
        // Possible optimization: we could have a Constant<T> subclass that
        // stores the unboxed value.
        private readonly object _value;

        internal ConstantExpression(object value)
        {
            _value = value;
        }

        internal static ConstantExpression Make(object value, Type type)
        {
            if ((value == null && type == typeof(object)) || (value != null && value.GetType() == type))
            {
                return new ConstantExpression(value);
            }
            else
            {
                return new TypedConstantExpression(value, type);
            }
        }

        /// <summary>
        /// Gets the static type of the expression that this <see cref="Expression" /> represents.
        /// </summary>
        /// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
        public override Type Type
        {
            get
            {
                if (_value == null)
                {
                    return typeof(object);
                }
                return _value.GetType();
            }
        }

        /// <summary>
        /// Returns the node type of this Expression. Extension nodes should return
        /// ExpressionType.Extension when overriding this method.
        /// </summary>
        /// <returns>The <see cref="ExpressionType"/> of the expression.</returns>
        public sealed override ExpressionType NodeType
        {
            get { return ExpressionType.Constant; }
        }

        /// <summary>
        /// Gets the value of the constant expression.
        /// </summary>
        public object Value
        {
            get { return _value; }
        }

        protected internal override Expression Accept(ExpressionVisitor visitor)
        {
            return visitor.VisitConstant(this);
        }
    }

    internal class TypedConstantExpression : ConstantExpression
    {
        private readonly Type _type;

        internal TypedConstantExpression(object value, Type type)
            : base(value)
        {
            _type = type;
        }

        public sealed override Type Type
        {
            get { return _type; }
        }
    }

    public partial class Expression
    {
        /// <summary>
        /// Creates a <see cref="ConstantExpression"/> that has the <see cref="P:ConstantExpression.Value"/> property set to the specified value. .
        /// </summary>
        /// <param name="value">An <see cref="System.Object"/> to set the <see cref="P:ConstantExpression.Value"/> property equal to.</param>
        /// <returns>
        /// A <see cref="ConstantExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
        /// <see cref="F:ExpressionType.Constant"/> and the <see cref="P:Expression.Value"/> property set to the specified value.
        /// </returns>
        public static ConstantExpression Constant(object value)
        {
            return ConstantExpression.Make(value, value == null ? typeof(object) : value.GetType());
        }

        /// <summary>
        /// Creates a <see cref="ConstantExpression"/> that has the <see cref="P:ConstantExpression.Value"/>
        /// and <see cref="P:ConstantExpression.Type"/> properties set to the specified values. .
        /// </summary>
        /// <param name="value">An <see cref="System.Object"/> to set the <see cref="P:ConstantExpression.Value"/> property equal to.</param>
        /// <param name="type">A <see cref="System.Type"/> to set the <see cref="P:Expression.Type"/> property equal to.</param>
        /// <returns>
        /// A <see cref="ConstantExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
        /// <see cref="F:ExpressionType.Constant"/> and the <see cref="P:ConstantExpression.Value"/> and
        /// <see cref="P:Expression.Type"/> properties set to the specified values.
        /// </returns>
        public static ConstantExpression Constant(object value, Type type)
        {
            ContractUtils.RequiresNotNull(type, "type");
            if (value == null && type.IsValueType && !type.IsNullableType())
            {
                throw Error.ArgumentTypesMustMatch();
            }
            if (value != null && !type.IsAssignableFrom(value.GetType()))
            {
                throw Error.ArgumentTypesMustMatch();
            }
            return ConstantExpression.Make(value, type);
        }
    }
}

#endif