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

using System;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using Microsoft.AspNetCore.Cryptography.Cng;
using Microsoft.AspNetCore.DataProtection.Test.Shared;
using Microsoft.AspNetCore.Testing.xunit;
using Xunit;

namespace Microsoft.AspNetCore.DataProtection.Cng
{
    public class GcmAuthenticatedEncryptorTests
    {
        [ConditionalFact]
        [ConditionalRunTestOnlyOnWindows]
        public void Encrypt_Decrypt_RoundTrips()
        {
            // Arrange
            Secret kdk = new Secret(new byte[512 / 8]);
            GcmAuthenticatedEncryptor encryptor = new GcmAuthenticatedEncryptor(kdk, CachedAlgorithmHandles.AES_GCM, symmetricAlgorithmKeySizeInBytes: 256 / 8);
            ArraySegment<byte> plaintext = new ArraySegment<byte>(Encoding.UTF8.GetBytes("plaintext"));
            ArraySegment<byte> aad = new ArraySegment<byte>(Encoding.UTF8.GetBytes("aad"));

            // Act
            byte[] ciphertext = encryptor.Encrypt(plaintext, aad);
            byte[] decipheredtext = encryptor.Decrypt(new ArraySegment<byte>(ciphertext), aad);

            // Assert
            Assert.Equal(plaintext, decipheredtext);
        }

        [ConditionalFact]
        [ConditionalRunTestOnlyOnWindows]
        public void Encrypt_Decrypt_Tampering_Fails()
        {
            // Arrange
            Secret kdk = new Secret(new byte[512 / 8]);
            GcmAuthenticatedEncryptor encryptor = new GcmAuthenticatedEncryptor(kdk, CachedAlgorithmHandles.AES_GCM, symmetricAlgorithmKeySizeInBytes: 256 / 8);
            ArraySegment<byte> plaintext = new ArraySegment<byte>(Encoding.UTF8.GetBytes("plaintext"));
            ArraySegment<byte> aad = new ArraySegment<byte>(Encoding.UTF8.GetBytes("aad"));
            byte[] validCiphertext = encryptor.Encrypt(plaintext, aad);

            // Act & assert - 1
            // Ciphertext is too short to be a valid payload
            byte[] invalidCiphertext_tooShort = new byte[10];
            Assert.Throws<CryptographicException>(() =>
            {
                encryptor.Decrypt(new ArraySegment<byte>(invalidCiphertext_tooShort), aad);
            });

            // Act & assert - 2
            // Ciphertext has been manipulated
            byte[] invalidCiphertext_manipulated = (byte[])validCiphertext.Clone();
            invalidCiphertext_manipulated[0] ^= 0x01;
            Assert.Throws<CryptographicException>(() =>
            {
                encryptor.Decrypt(new ArraySegment<byte>(invalidCiphertext_manipulated), aad);
            });

            // Act & assert - 3
            // Ciphertext is too long
            byte[] invalidCiphertext_tooLong = validCiphertext.Concat(new byte[] { 0 }).ToArray();
            Assert.Throws<CryptographicException>(() =>
            {
                encryptor.Decrypt(new ArraySegment<byte>(invalidCiphertext_tooLong), aad);
            });

            // Act & assert - 4
            // AAD is incorrect
            Assert.Throws<CryptographicException>(() =>
            {
                encryptor.Decrypt(new ArraySegment<byte>(validCiphertext), new ArraySegment<byte>(Encoding.UTF8.GetBytes("different aad")));
            });
        }

        [ConditionalFact]
        [ConditionalRunTestOnlyOnWindows]
        public void Encrypt_KnownKey()
        {
            // Arrange
            Secret kdk = new Secret(Encoding.UTF8.GetBytes("master key"));
            GcmAuthenticatedEncryptor encryptor = new GcmAuthenticatedEncryptor(kdk, CachedAlgorithmHandles.AES_GCM, symmetricAlgorithmKeySizeInBytes: 128 / 8, genRandom: new SequentialGenRandom());
            ArraySegment<byte> plaintext = new ArraySegment<byte>(new byte[] { 0, 1, 2, 3, 4, 5, 6, 7 }, 2, 3);
            ArraySegment<byte> aad = new ArraySegment<byte>(new byte[] { 7, 6, 5, 4, 3, 2, 1, 0 }, 1, 4);

            // Act
            byte[] retVal = encryptor.Encrypt(
                plaintext: plaintext,
                additionalAuthenticatedData: aad,
                preBufferSize: 3,
                postBufferSize: 4);

            // Assert

            // retVal := 00 00 00 (preBuffer)
            //         | 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F (keyModifier)
            //         | 10 11 12 13 14 15 16 17 18 19 1A 1B (nonce)
            //         | 43 B6 91 (encryptedData)
            //         | 8D 0D 66 D9 A1 D9 44 2D 5D 8E 41 DA 39 60 9C E8 (authTag)
            //         | 00 00 00 00 (postBuffer)

            string retValAsString = Convert.ToBase64String(retVal);
            Assert.Equal("AAAAAAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaG0O2kY0NZtmh2UQtXY5B2jlgnOgAAAAA", retValAsString);
        }
    }
}