// Copyright 2005-2010 Gallio Project - http://www.gallio.org/
// Portions Copyright 2000-2004 Jonathan de Halleux
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//     http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

using System;

namespace Gallio.Runtime.Extensibility
{
    /// <summary>
    /// Specifies the result of an attempt to resolve a dependency.
    /// </summary>
    public struct DependencyResolution
    {
        private readonly bool isSatisfied;
        private readonly object value;

        private DependencyResolution(bool isSatisfied, object value)
        {
            this.isSatisfied = isSatisfied;
            this.value = value;
        }

        /// <summary>
        /// Creates a result object that represents a satisfied dependency.
        /// </summary>
        /// <param name="value">The value provided for the dependency.</param>
        /// <returns>The result object.</returns>
        public static DependencyResolution Satisfied(object value)
        {
            return new DependencyResolution(true, value);
        }

        /// <summary>
        /// Creates a result object that represents an unsatisfied dependency.
        /// </summary>
        /// <returns>The result object.</returns>
        public static DependencyResolution Unsatisfied()
        {
            return new DependencyResolution(false, null);
        }

        /// <summary>
        /// Returns true if the dependency was satisfied.
        /// </summary>
        public bool IsSatisfied
        {
            get { return isSatisfied; }
        }

        /// <summary>
        /// Returns the value used to satisfy the dependency.
        /// </summary>
        /// <exception cref="InvalidOperationException">Thrown if the dependency was not satisfied.</exception>
        public object Value
        {
            get
            {
                if (!isSatisfied)
                    throw new InvalidOperationException("The dependency was not satisfied.");
                return value;
            }
        }
    }
}
