using System;
using System.Linq;
using System.Text;

namespace System.Security.Cryptography
{
    /// <summary>
    /// 对称加密算法 - AES
    /// </summary>
    public static class AESUtils
    {
        #region 创建 Aes 实例

        /// <summary>
        /// 创建 <see cref="Aes"/> 实例
        /// </summary>
        /// <param name="keySize">密钥大小，默认192</param>
        /// <param name="padding">填充</param>
        /// <param name="mode">模式</param>
        /// <returns></returns>
        public static Aes Create(int keySize = 192, PaddingMode padding = PaddingMode.PKCS7, CipherMode mode = CipherMode.CBC)
            => new AesCryptoServiceProvider
            {
                KeySize = keySize,
                Padding = padding,
                Mode = mode,
            };

        /// <summary>
        /// 通过 <see cref="AesParameters"/>(ByteArray) 创建 <see cref="Aes"/> 实例
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public static Aes Create(byte[] data) => Parameters.Create(data).Create();

        /// <summary>
        /// 通过 <see cref="AesParameters"/>(ByteArray) 创建 <see cref="Aes"/> 实例
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public static Aes? Create_Nullable(byte[]? data)
        {
            if (data == default) return default;
            return Create(data);
        }

        /// <summary>
        /// 通过 <see cref="AesParameters"/>(String) 创建 <see cref="Aes"/> 实例
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public static Aes Create(string data) => Parameters.Create(data).Create();

        /// <summary>
        /// 通过 <see cref="AesParameters"/>(String) 创建 <see cref="Aes"/> 实例
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public static Aes? Create_Nullable(string? data)
        {
            if (data == default) return default;
            return Create(data);
        }

        #endregion

        #region 从 Aes 实例中获取密钥

        /// <summary>
        /// 将 <see cref="Aes"/> 实例中的 [密钥,向量,模式,填充] 转换为可传输的模型类对象。
        /// </summary>
        /// <param name="aes"></param>
        /// <returns></returns>
        internal static Parameters ToParams(this Aes aes) => new Parameters(aes.Key, aes.IV, aes.Mode, aes.Padding);

        /// <summary>
        /// 将 <see cref="Aes"/> 实例中的密钥转换为可传输的字符串。
        /// </summary>
        /// <param name="aes"></param>
        /// <returns></returns>
        public static string ToParamsString(this Aes aes) => aes.ToParams().ToString();

        /// <summary>
        /// 将 <see cref="Aes"/> 实例中的密钥转换为可传输的 <see cref="byte"/>[] 。
        /// </summary>
        /// <param name="aes"></param>
        /// <returns></returns>
        public static byte[] ToParamsByteArray(this Aes aes) => aes.ToParams().ToByteArray();

        #endregion

        #region 加密(Encrypt)

        /// <summary>
        /// AES加密(ByteArray → ByteArray)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static byte[] Encrypt(this Aes aes, byte[] data)
        {
            using var transform = aes.CreateEncryptor();
            return transform.TransformFinalBlock(data, 0, data.Length);
        }

        /// <summary>
        /// AES加密(ByteArray → ByteArray)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static byte[]? Encrypt_Nullable(this Aes aes, byte[]? data)
        {
            if (data == default) return default;
            return Encrypt(aes, data);
        }

        /// <summary>
        /// AES加密(String → ByteArray)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></retu
        public static byte[] EncryptToByteArray(this Aes aes, string text)
        {
            var data = Encoding.UTF8.GetBytes(text);
            return Encrypt(aes, data);
        }

        /// <summary>
        /// AES加密(String → ByteArray)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></returns>
        public static byte[]? EncryptToByteArray_Nullable(this Aes aes, string? text)
        {
            if (text == default) return default;
            return EncryptToByteArray(aes, text);
        }

        /// <summary>
        /// AES加密(String → String)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string Encrypt(this Aes aes, string text)
        {
            var result = EncryptToByteArray(aes, text);
            return result.Base64UrlEncode();
        }

        /// <summary>
        /// AES加密(String → String)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string? Encrypt_Nullable(this Aes aes, string? text)
        {
            if (text == default) return default;
            return Encrypt(aes, text);
        }

        /// <summary>
        /// AES加密(ByteArray → String)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static string EncryptToString(this Aes aes, byte[] data)
        {
            var result = Encrypt(aes, data);
            return result.Base64UrlEncode();
        }

        /// <summary>
        /// AES加密(ByteArray → String)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static string? EncryptToString_Nullable(this Aes aes, byte[]? data)
        {
            if (data == default) return default;
            return EncryptToString(aes, data);
        }

        #endregion

        #region 解密(Decrypt)

        /// <summary>
        /// AES解密(ByteArray → ByteArray)
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static byte[] Decrypt(this Aes aes, byte[] data)
        {
            using var transform = aes.CreateDecryptor();
            return transform.TransformFinalBlock(data, 0, data.Length);
        }

        /// <summary>
        /// (解密) ByteArray → ByteArray
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static byte[]? Decrypt_Nullable(this Aes aes, byte[]? data)
        {
            if (data == default) return default;
            return Decrypt(aes, data);
        }

        /// <summary>
        /// (解密) String → ByteArray
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></returns>
        public static byte[] DecryptToByteArray(this Aes aes, string text)
        {
            var data = text.Base64UrlDecodeToByteArray();
            return Decrypt(aes, data);
        }

        /// <summary>
        /// (解密) String → ByteArray
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></returns>
        public static byte[]? DecryptToByteArray_Nullable(this Aes aes, string? text)
        {
            if (text == default) return default;
            return DecryptToByteArray(aes, text);
        }

        /// <summary>
        /// (解密) String → String
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string Decrypt(this Aes aes, string text)
        {
            var result = DecryptToByteArray(aes, text);
            return Encoding.UTF8.GetString(result);
        }

        /// <summary>
        /// (解密) String → String
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string? Decrypt_Nullable(this Aes aes, string? text)
        {
            if (text == default) return default;
            return Decrypt(aes, text);
        }

        /// <summary>
        /// (解密) ByteArray → String
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static string DecryptToString(this Aes aes, byte[] data)
        {
            var result = Decrypt(aes, data);
            return Encoding.UTF8.GetString(result);
        }

        /// <summary>
        /// (解密) ByteArray → String
        /// </summary>
        /// <param name="aes"></param>
        /// <param name="data"></param>
        /// <returns></returns>
        public static string? DecryptToString_Nullable(this Aes aes, byte[]? data)
        {
            if (data == default) return default;
            return DecryptToString(aes, data);
        }

        #endregion

        /// <summary>
        /// <see cref="Aes"/> [密钥,向量,模式,填充] 模型类
        /// <para>使用内置函数序列化此模型，不可使用 JSON 或 MessagePack 处理此类</para>
        /// <para>String: <see cref="ToString"/> / <see cref="Create(string)"/></para>
        /// <para>ByteArray: <see cref="ToByteArray"/> / <see cref="Create(byte[])"/></para>
        /// </summary>
        internal sealed class Parameters
        {
            Parameters(CipherMode mode, PaddingMode padding)
            {
                _mode = mode;
                _padding = padding;
                OnPropertyChanged();
            }

            Parameters(Flags flags)
            {
                OnPropertyChanged(flags);
            }

            public Parameters(string key, string iv, CipherMode mode = CipherMode.CBC, PaddingMode padding = PaddingMode.PKCS7) : this(mode, padding)
            {
                Key = key;
                IV = iv;
            }

            public Parameters(byte[] key, byte[] iv, CipherMode mode = CipherMode.CBC, PaddingMode padding = PaddingMode.PKCS7) : this(mode, padding)
            {
                KeyByteArray = key;
                IVByteArray = iv;
            }

            public Parameters(string key, string iv, Flags flags) : this(flags)
            {
                Key = key;
                IV = iv;
            }

            public Parameters(byte[] key, byte[] iv, Flags flags) : this(flags)
            {
                KeyByteArray = key;
                IVByteArray = iv;
            }

            [Flags]
            public enum Flags
            {
                CipherMode_CBC = 2,

                /// <summary>
                /// ECB模式已被定义为不安全的，除非对接第三方服务要求使用之外，否则不应使用！
                /// </summary>
                [Obsolete("low safety.")] CipherMode_ECB = 16,

                //[Obsolete("target .NET Standard 1.4 is not supported.")]
                CipherMode_OFB = 32,

                //[Obsolete("target .NET Standard 1.4 is not supported.")]
                CipherMode_CFB = 64,

                CipherMode_CTS = 512,
                PaddingMode_None = 4096,
                PaddingMode_PKCS7 = 8,
                PaddingMode_Zeros = 1024,

                //[Obsolete("target .NET Standard 1.4 is not supported.")]
                PaddingMode_ANSIX923 = 2048,

                //[Obsolete("target .NET Standard 1.4 is not supported.")]
                PaddingMode_ISO10126 = 4
            }

            string? _key;
            byte[]? _keyByteArray;
            string? _iv;
            byte[]? _ivByteArray;
            CipherMode _mode;
            PaddingMode _padding;
            Flags _flags;

            /// <summary>
            /// 模式与填充
            /// </summary>
            public Flags ModeAndPadding
            {
                get => _flags;
                set
                {
                    if (value != _flags)
                    {
                        OnPropertyChanged(value);
                    }
                }
            }

            /// <summary>
            /// 密钥(String)
            /// </summary>
            public string? Key
            {
                get => _key;
                set
                {
                    _key = value;
                    _keyByteArray = value.Base64UrlDecodeToByteArray_Nullable();
                }
            }

            /// <summary>
            /// 密钥(ByteArray)
            /// </summary>
            public byte[]? KeyByteArray
            {
                get => _keyByteArray;
                set
                {
                    _keyByteArray = value;
                    _key = value.Base64UrlEncode_Nullable();
                }
            }

            /// <summary>
            /// 向量(String)
            /// </summary>
            public string? IV
            {
                get => _iv;
                set
                {
                    _iv = value;
                    _ivByteArray = value.Base64UrlDecodeToByteArray_Nullable();
                }
            }

            /// <summary>
            /// 向量(ByteArray)
            /// </summary>
            public byte[]? IVByteArray
            {
                get => _ivByteArray;
                set
                {
                    _ivByteArray = value;
                    _iv = value.Base64UrlEncode_Nullable();
                }
            }

            /// <summary>
            /// 模式
            /// </summary>
            public CipherMode Mode
            {
                get => _mode;
                set
                {
                    if (value != _mode)
                    {
                        _mode = value;
                        OnPropertyChanged();
                    }
                }
            }

            /// <summary>
            /// 填充
            /// </summary>
            public PaddingMode Padding
            {
                get => _padding;
                set
                {
                    if (value != _padding)
                    {
                        _padding = value;
                        OnPropertyChanged();
                    }
                }
            }

            void OnPropertyChanged()
            {
                var mode = Flags.CipherMode_CBC;
                var padding = Flags.PaddingMode_PKCS7;
#pragma warning disable CS0618 // 类型或成员已过时
                switch (_mode)
                {
                    case CipherMode.ECB:
                        mode = Flags.CipherMode_ECB;
                        break;

                    case CipherMode.OFB:
                        mode = Flags.CipherMode_OFB;
                        break;

                    case CipherMode.CFB:
                        mode = Flags.CipherMode_CFB;
                        break;

                    case CipherMode.CTS:
                        mode = Flags.CipherMode_CTS;
                        break;
                }
                switch (_padding)
                {
                    case PaddingMode.None:
                        padding = Flags.PaddingMode_None;
                        break;

                    case PaddingMode.Zeros:
                        padding = Flags.PaddingMode_Zeros;
                        break;

                    case PaddingMode.ANSIX923:
                        padding = Flags.PaddingMode_ANSIX923;
                        break;

                    case PaddingMode.ISO10126:
                        padding = Flags.PaddingMode_ISO10126;
                        break;
                }
#pragma warning restore CS0618 // 类型或成员已过时
                _flags = mode | padding;
            }

            void OnPropertyChanged(Flags flags)
            {
#pragma warning disable CS0618 // 类型或成员已过时
                if ((flags & Flags.CipherMode_CBC) == Flags.CipherMode_CBC)
                    _mode = CipherMode.CBC;
                else if ((flags & Flags.CipherMode_CTS) == Flags.CipherMode_CTS)
                    _mode = CipherMode.CTS;
                else if ((flags & Flags.CipherMode_OFB) == Flags.CipherMode_OFB)
                    _mode = CipherMode.OFB;
                else if ((flags & Flags.CipherMode_CFB) == Flags.CipherMode_CFB)
                    _mode = CipherMode.CFB;
                else if ((flags & Flags.CipherMode_ECB) == Flags.CipherMode_ECB)
                    _mode = CipherMode.ECB;

                if ((flags & Flags.PaddingMode_PKCS7) == Flags.PaddingMode_PKCS7)
                    _padding = PaddingMode.PKCS7;
                else if ((flags & Flags.PaddingMode_Zeros) == Flags.PaddingMode_Zeros)
                    _padding = PaddingMode.Zeros;
                else if ((flags & Flags.PaddingMode_ANSIX923) == Flags.PaddingMode_ANSIX923)
                    _padding = PaddingMode.ANSIX923;
                else if ((flags & Flags.PaddingMode_ISO10126) == Flags.PaddingMode_ISO10126)
                    _padding = PaddingMode.ISO10126;
                else if ((flags & Flags.PaddingMode_None) == Flags.PaddingMode_None)
                    _padding = PaddingMode.None;
#pragma warning restore CS0618 // 类型或成员已过时

                _flags = flags;
            }

            public static Parameters Create(byte[] data)
            {
                var uint16 = BitConverter.ToUInt16(data, 0);
                var flags = (Flags)uint16;
                var IVByteArray = data.Skip(2).Take(16).ToArray();
                var KeyByteArray = data.Skip(18).Reverse().ToArray();
                return new Parameters(KeyByteArray, IVByteArray, flags);
            }

            public static Parameters Create(string data)
            {
                var bytes = data.Base64UrlDecodeToByteArray();
                return Create(bytes);
            }

            public byte[] ToByteArray()
            {
                if (IVByteArray == null) throw new NullReferenceException(nameof(IVByteArray));
                if (KeyByteArray == null) throw new NullReferenceException(nameof(KeyByteArray));
                return BitConverter.GetBytes((ushort)ModeAndPadding)
                    .Concat(IVByteArray)
                    .Concat(KeyByteArray.Reverse())
                    .ToArray();
            }

            public new string ToString() => ToByteArray().Base64UrlEncode();

            public Aes Create()
            {
                if (IVByteArray == null) throw new NullReferenceException(nameof(IVByteArray));
                if (KeyByteArray == null) throw new NullReferenceException(nameof(KeyByteArray));
                return new AesCryptoServiceProvider
                {
                    Key = KeyByteArray,
                    IV = IVByteArray,
                    Mode = Mode,
                    Padding = Padding
                };
            }

            public bool Equals(Parameters? other)
            {
                if (other == null) return false;
                return Mode == other.Mode &&
                    Padding == other.Padding &&
                    KeyByteArray.SequenceEqual_Nullable(other.KeyByteArray) &&
                    IVByteArray.SequenceEqual_Nullable(other.IVByteArray);
            }
        }
    }
}