// -----------------------------------------------------------------------------
// 让 .NET 开发更简单，更通用，更流行。
// Copyright © 2020-2021 Furion, 百小僧, Baiqian Co.,Ltd.
//
// 框架名称：Furion
// 框架作者：百小僧
// 框架版本：2.7.9
// 源码地址：Gitee： https://gitee.com/dotnetchina/Furion
//          Github：https://github.com/monksoul/Furion
// 开源协议：Apache-2.0（https://gitee.com/dotnetchina/Furion/blob/master/LICENSE）
// -----------------------------------------------------------------------------

using System;
using System.Security.Cryptography;

namespace HT.Cloud.Code
{
	/// <summary>
	/// 连续 GUID ID 生成器
	/// <para>代码参考自：https://github.com/PomeloFoundation/Pomelo.EntityFrameworkCore.MySql/blob/ebe011a6f1b2a2a9709fe558cfc7ed3215b55c37/src/EFCore.MySql/ValueGeneration/Internal/MySqlSequentialGuidValueGenerator.cs </para>
	/// </summary>
	public class SequentialGuidIDGenerator : IDistributedIDGenerator
	{
		/// <summary>
		/// 随机数生成器
		/// </summary>
		private static readonly RandomNumberGenerator _rng = RandomNumberGenerator.Create();

		/// <summary>
		/// 生成逻辑
		/// </summary>
		/// <param name="idGeneratorOptions"></param>
		/// <returns></returns>
		public object Create(object idGeneratorOptions = null)
		{
			// According to RFC 4122:
			// dddddddd-dddd-Mddd-Ndrr-rrrrrrrrrrrr
			// - M = RFC version, in this case '4' for random UUID
			// - N = RFC variant (plus other bits), in this case 0b1000 for variant 1
			// - d = nibbles based on UTC date/time in ticks
			// - r = nibbles based on random bytes

			var options = (idGeneratorOptions ?? new SequentialGuidSettings()) as SequentialGuidSettings;

			var randomBytes = new byte[7];
			_rng.GetBytes(randomBytes);
			var ticks = (ulong)options.TimeNow.Ticks;

			var uuidVersion = (ushort)4;
			var uuidVariant = (ushort)0b1000;

			var ticksAndVersion = (ushort)((ticks << 48 >> 52) | (ushort)(uuidVersion << 12));
			var ticksAndVariant = (byte)((ticks << 60 >> 60) | (byte)(uuidVariant << 4));

			if (options.LittleEndianBinary16Format)
			{
				var guidBytes = new byte[16];
				var tickBytes = BitConverter.GetBytes(ticks);
				if (BitConverter.IsLittleEndian)
				{
					Array.Reverse(tickBytes);
				}

				Buffer.BlockCopy(tickBytes, 0, guidBytes, 0, 6);
				guidBytes[6] = (byte)(ticksAndVersion << 8 >> 8);
				guidBytes[7] = (byte)(ticksAndVersion >> 8);
				guidBytes[8] = ticksAndVariant;
				Buffer.BlockCopy(randomBytes, 0, guidBytes, 9, 7);

				return new Guid(guidBytes);
			}

			var guid = new Guid((uint)(ticks >> 32), (ushort)(ticks << 32 >> 48), ticksAndVersion,
				ticksAndVariant,
				randomBytes[0],
				randomBytes[1],
				randomBytes[2],
				randomBytes[3],
				randomBytes[4],
				randomBytes[5],
				randomBytes[6]);

			return guid;
		}
	}
}