#region Copyright notice and license

// Copyright 2015 gRPC authors.
//
// 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.

#endregion

using System.Collections.Generic;
using System.Collections.ObjectModel;

using Grpc.Core.Internal;
using Grpc.Core.Utils;

namespace Grpc.Core
{
    /// <summary>
    /// Client-side call credentials. Provide authorization with per-call granularity.
    /// </summary>
    public abstract class CallCredentials
    {
        /// <summary>
        /// Composes multiple <c>CallCredentials</c> objects into
        /// a single <c>CallCredentials</c> object.
        /// </summary>
        /// <param name="credentials">credentials to compose</param>
        /// <returns>The new <c>CompositeCallCredentials</c></returns>
        public static CallCredentials Compose(params CallCredentials[] credentials)
        {
            return new CompositeCallCredentials(credentials);
        }

        /// <summary>
        /// Creates a new instance of <c>CallCredentials</c> class from an
        /// interceptor that can attach metadata to outgoing calls.
        /// </summary>
        /// <param name="interceptor">authentication interceptor</param>
        public static CallCredentials FromInterceptor(AsyncAuthInterceptor interceptor)
        {
            return new AsyncAuthInterceptorCredentials(interceptor);
        }

        /// <summary>
        /// Populates call credentials configurator with this instance's configuration.
        /// End users never need to invoke this method as it is part of internal implementation.
        /// </summary>
        public abstract void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object state);

        private class CompositeCallCredentials : CallCredentials
        {
            readonly IReadOnlyList<CallCredentials> credentials;

            public CompositeCallCredentials(CallCredentials[] credentials)
            {
                GrpcPreconditions.CheckArgument(credentials.Length >= 2, "Composite credentials object can only be created from 2 or more credentials.");
                this.credentials = new List<CallCredentials>(credentials).AsReadOnly();
            }

            public override void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object state)
            {
                configurator.SetCompositeCredentials(state, credentials);
            }
        }

        private class AsyncAuthInterceptorCredentials : CallCredentials
        {
            readonly AsyncAuthInterceptor interceptor;

            public AsyncAuthInterceptorCredentials(AsyncAuthInterceptor interceptor)
            {
                this.interceptor = GrpcPreconditions.CheckNotNull(interceptor);
            }

            public override void InternalPopulateConfiguration(CallCredentialsConfiguratorBase configurator, object state)
            {
                configurator.SetAsyncAuthInterceptorCredentials(state, interceptor);
            }
        }
    }
}