// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using Microsoft.AspNet.Security.DataProtection.SafeHandles;

namespace Microsoft.AspNet.Security.DataProtection.Cng
{
    /// <summary>
    /// Provides cached CNG algorithm provider instances, as calling BCryptOpenAlgorithmProvider is expensive.
    /// Callers should use caution never to dispose of the algorithm provider instances returned by this type.
    /// </summary>
    internal static class CachedAlgorithmHandles
    {
        private static CachedAlgorithmInfo _aesCbc = new CachedAlgorithmInfo(() => GetAesAlgorithm(chainingMode: Constants.BCRYPT_CHAIN_MODE_CBC));
        private static CachedAlgorithmInfo _aesGcm = new CachedAlgorithmInfo(() => GetAesAlgorithm(chainingMode: Constants.BCRYPT_CHAIN_MODE_GCM));
        private static CachedAlgorithmInfo _hmacSha1 = new CachedAlgorithmInfo(() => GetHmacAlgorithm(algorithm: Constants.BCRYPT_SHA1_ALGORITHM));
        private static CachedAlgorithmInfo _hmacSha256 = new CachedAlgorithmInfo(() => GetHmacAlgorithm(algorithm: Constants.BCRYPT_SHA256_ALGORITHM));
        private static CachedAlgorithmInfo _hmacSha512 = new CachedAlgorithmInfo(() => GetHmacAlgorithm(algorithm: Constants.BCRYPT_SHA512_ALGORITHM));
        private static CachedAlgorithmInfo _pbkdf2 = new CachedAlgorithmInfo(GetPbkdf2Algorithm);
        private static CachedAlgorithmInfo _sha1 = new CachedAlgorithmInfo(() => GetHashAlgorithm(algorithm: Constants.BCRYPT_SHA1_ALGORITHM));
        private static CachedAlgorithmInfo _sha256 = new CachedAlgorithmInfo(() => GetHashAlgorithm(algorithm: Constants.BCRYPT_SHA256_ALGORITHM));
        private static CachedAlgorithmInfo _sha512 = new CachedAlgorithmInfo(() => GetHashAlgorithm(algorithm: Constants.BCRYPT_SHA512_ALGORITHM));
        private static CachedAlgorithmInfo _sp800_108_ctr_hmac = new CachedAlgorithmInfo(GetSP800_108_CTR_HMACAlgorithm);

        public static BCryptAlgorithmHandle AES_CBC
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _aesCbc);
            }
        }

        public static BCryptAlgorithmHandle AES_GCM
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _aesGcm);
            }
        }

        public static BCryptAlgorithmHandle HMAC_SHA1
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _hmacSha1);
            }
        }

        public static BCryptAlgorithmHandle HMAC_SHA256
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _hmacSha256);
            }
        }

        public static BCryptAlgorithmHandle HMAC_SHA512
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _hmacSha512);
            }
        }

        // Only available on Win8+.
        public static BCryptAlgorithmHandle PBKDF2
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _pbkdf2);
            }
        }

        public static BCryptAlgorithmHandle SHA1
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _sha1);
            }
        }

        public static BCryptAlgorithmHandle SHA256
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _sha256);
            }
        }

        public static BCryptAlgorithmHandle SHA512
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _sha512);
            }
        }

        public static BCryptAlgorithmHandle SP800_108_CTR_HMAC
        {
            get
            {
                return CachedAlgorithmInfo.GetAlgorithmHandle(ref _sp800_108_ctr_hmac);
            }
        }

        private static BCryptAlgorithmHandle GetAesAlgorithm(string chainingMode)
        {
            var algHandle = BCryptAlgorithmHandle.OpenAlgorithmHandle(Constants.BCRYPT_AES_ALGORITHM);
            algHandle.SetChainingMode(chainingMode);
            return algHandle;
        }

        private static BCryptAlgorithmHandle GetHashAlgorithm(string algorithm)
        {
            return BCryptAlgorithmHandle.OpenAlgorithmHandle(algorithm, hmac: false);
        }

        private static BCryptAlgorithmHandle GetHmacAlgorithm(string algorithm)
        {
            return BCryptAlgorithmHandle.OpenAlgorithmHandle(algorithm, hmac: true);
        }

        private static BCryptAlgorithmHandle GetPbkdf2Algorithm()
        {
            return BCryptAlgorithmHandle.OpenAlgorithmHandle(Constants.BCRYPT_PBKDF2_ALGORITHM, implementation: Constants.MS_PRIMITIVE_PROVIDER);
        }

        private static BCryptAlgorithmHandle GetSP800_108_CTR_HMACAlgorithm()
        {
            return BCryptAlgorithmHandle.OpenAlgorithmHandle(Constants.BCRYPT_SP800108_CTR_HMAC_ALGORITHM, implementation: Constants.MS_PRIMITIVE_PROVIDER);
        }

        // Warning: mutable struct!
        private struct CachedAlgorithmInfo
        {
            private WeakReference<BCryptAlgorithmHandle> _algorithmHandle;
            private readonly Func<BCryptAlgorithmHandle> _factory;

            public CachedAlgorithmInfo(Func<BCryptAlgorithmHandle> factory)
            {
                _algorithmHandle = null;
                _factory = factory;
            }

            public static BCryptAlgorithmHandle GetAlgorithmHandle(ref CachedAlgorithmInfo cachedAlgorithmInfo)
            {
                return WeakReferenceHelpers.GetSharedInstance(ref cachedAlgorithmInfo._algorithmHandle, cachedAlgorithmInfo._factory);
            }
        }
    }
}