// ****************************************************************
// Copyright 2007, Charlie Poole
// This is free software licensed under the NUnit license. You may
// obtain a copy of the license at http://nunit.org/?p=license&r=2.4
// ****************************************************************

using System;

namespace NUnit.Framework.Constraints
{
    /// <summary>
    /// TypeConstraint is the abstract base for constraints
    /// that take a Type as their expected value.
    /// </summary>
    public abstract class TypeConstraint : Constraint
    {
        /// <summary>
        /// The expected Type used by the constraint
        /// </summary>
        protected Type expectedType;

        /// <summary>
        /// Construct a TypeConstraint for a given Type
        /// </summary>
        /// <param name="type"></param>
        public TypeConstraint(Type type)
        {
            this.expectedType = type;
        }

        /// <summary>
        /// Write the actual value for a failing constraint test to a
        /// MessageWriter. TypeCOnstraints override this method to write
        /// the name of the type.
        /// </summary>
        /// <param name="writer">The writer on which the actual value is displayed</param>
		public override void WriteActualValueTo(MessageWriter writer)
		{
			writer.WriteActualValue( actual == null ? null : actual.GetType() ); 
		}
	}

    /// <summary>
    /// ExactTypeConstraint is used to test that an object
    /// is of the exact type provided in the constructor
    /// </summary>
    public class ExactTypeConstraint : TypeConstraint
    {
        /// <summary>
        /// Construct an ExactTypeConstraint for a given Type
        /// </summary>
        /// <param name="type"></param>
        public ExactTypeConstraint(Type type) : base( type ) { }

        /// <summary>
        /// Test that an object is of the exact type specified
        /// </summary>
        /// <param name="actual"></param>
        /// <returns></returns>
        public override bool Matches(object actual)
        {
            this.actual = actual;
            return actual != null && actual.GetType() == this.expectedType;
        }

        /// <summary>
        /// Write the description of this constraint to a MessageWriter
        /// </summary>
        /// <param name="writer"></param>
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            writer.WriteExpectedValue(expectedType);
        }
    }

    /// <summary>
    /// InstanceOfTypeConstraint is used to test that an object
    /// is of the same type provided or derived from it.
    /// </summary>
    public class InstanceOfTypeConstraint : TypeConstraint
    {
        /// <summary>
        /// Construct an InstanceOfTypeConstraint for the type provided
        /// </summary>
        /// <param name="type"></param>
        public InstanceOfTypeConstraint(Type type) : base(type) { }

        /// <summary>
        /// Test whether an object is of the specified type or a derived type
        /// </summary>
        /// <param name="actual"></param>
        /// <returns></returns>
        public override bool Matches(object actual)
        {
            this.actual = actual;
            return actual != null && expectedType.IsInstanceOfType(actual);
        }

        /// <summary>
        /// Write a description of this constraint to a MessageWriter
        /// </summary>
        /// <param name="writer"></param>
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            writer.WritePredicate("instance of");
            writer.WriteExpectedValue(expectedType);
        }
	}

    /// <summary>
    /// AssignableFromConstraint is used to test that an object
    /// can be assigned from a given Type.
    /// </summary>
    public class AssignableFromConstraint : TypeConstraint
    {
        /// <summary>
        /// Construct an AssignableFromConstraint for the type provided
        /// </summary>
        /// <param name="type"></param>
        public AssignableFromConstraint(Type type) : base(type) { }

        /// <summary>
        /// Test whether an object can be assigned from the specified type
        /// </summary>
        /// <param name="actual"></param>
        /// <returns></returns>
        public override bool Matches(object actual)
        {
			this.actual = actual;
            return actual != null && actual.GetType().IsAssignableFrom( expectedType );
        }

        /// <summary>
        /// Write a description of this constraint to a MessageWriter
        /// </summary>
        /// <param name="writer"></param>
        public override void WriteDescriptionTo(MessageWriter writer)
        {
            writer.WritePredicate("Type assignable from");
            writer.WriteExpectedValue(expectedType);
        }
    }
}