// ***********************************************************************
// Assembly         : FCS.Lib.Utility
// Author          : fhdk
// Created          : 2022 12 17 13:33
// 
// Last Modified By: fhdk
// Last Modified On : 2023 03 14 09:16
// ***********************************************************************
// <copyright file="GuidGenerator.cs" company="FCS">
//     Copyright (C) 2022-2023 FCS Frede's Computer Services.
//     This program is free software: you can redistribute it and/or modify
//     it under the terms of the GNU Affero General Public License as
//     published by the Free Software Foundation, either version 3 of the
//     License, or (at your option) any later version.
// 
//     This program is distributed in the hope that it will be useful,
//     but WITHOUT ANY WARRANTY; without even the implied warranty of
//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//     GNU Affero General Public License for more details.
// 
//     You should have received a copy of the GNU Affero General Public License
//     along with this program.  If not, see [https://www.gnu.org/licenses]
// </copyright>
// <summary></summary>
// ***********************************************************************

using System;
using System.Text;

namespace FCS.Lib.Utility;

/// <summary>
/// Used for generating UUID based on RFC 4122.
/// </summary>
/// <seealso href="http://www.ietf.org/rfc/rfc4122.txt">RFC 4122 - A Universally Unique IDentifier (UUID) URN Namespace</seealso>
public static class GuidGenerator
{
    /// <summary>
    /// number of bytes in guid
    /// </summary>
    public const int ByteArraySize = 16;

    /// <summary>
    /// multiplex variant info - variant byte
    /// </summary>
    public const int VariantByte = 8;

    /// <summary>
    /// multiplex variant info - variant byte mask
    /// </summary>
    public const int VariantByteMask = 0x3f;

    /// <summary>
    /// multiplex variant info - variant byte shift
    /// </summary>
    public const int VariantByteShift = 0x80;

    /// <summary>
    /// multiplex version info - version byte
    /// </summary>
    public const int VersionByte = 7;

    /// <summary>
    /// multiplex version info - version byte mask
    /// </summary>
    public const int VersionByteMask = 0x0f;

    /// <summary>
    /// multiplex version info version byte shift
    /// </summary>
    public const int VersionByteShift = 4;

    // indexes within the uuid array for certain boundaries
    private const byte TimestampByte = 0;
    private const byte GuidClockSequenceByte = 8;
    private const byte NodeByte = 10;

    // offset to move from 1/1/0001, which is 0-time for .NET, to gregorian 0-time of 10/15/1582
    private static readonly DateTimeOffset GregorianCalendarStart = new(1582, 10, 15, 0, 0, 0, TimeSpan.Zero);

    static GuidGenerator()
    {
        DefaultClockSequence = new byte[2];
        DefaultNode = new byte[6];

        var random = new Random();
        random.NextBytes(DefaultClockSequence);
        random.NextBytes(DefaultNode);
    }


    /// <summary>
    /// Default clock sequence
    /// </summary>
    public static byte[] DefaultClockSequence { get; set; }

    /// <summary>
    /// Default node
    /// </summary>
    public static byte[] DefaultNode { get; set; }

    /// <summary>
    /// Set default node
    /// </summary>
    /// <param name="nodeName"></param>
    public static void SetDefaultNode(string nodeName)
    {
        var x = nodeName.GetHashCode();
        var node = $"{x:X}";
        DefaultNode = Encoding.UTF8.GetBytes(node.ToCharArray(), 0, 6);
    }

    /// <summary>
    /// Get version
    /// </summary>
    /// <param name="guid"></param>
    /// <returns><see cref="GuidVersion"/></returns>
    public static GuidVersion GetVersion(this Guid guid)
    {
        var bytes = guid.ToByteArray();
        return (GuidVersion)((bytes[VersionByte] & 0xFF) >> VersionByteShift);
    }

    /// <summary>
    /// Get date time offset from guid
    /// </summary>
    /// <param name="guid"></param>
    /// <returns><see cref="DateTimeOffset"/></returns>
    public static DateTimeOffset GetDateTimeOffset(Guid guid)
    {
        var bytes = guid.ToByteArray();

        // reverse the version
        bytes[VersionByte] &= VersionByteMask;
        bytes[VersionByte] |= (byte)GuidVersion.TimeBased >> VersionByteShift;

        var timestampBytes = new byte[8];
        Array.Copy(bytes, TimestampByte, timestampBytes, 0, 8);

        var timestamp = BitConverter.ToInt64(timestampBytes, 0);
        var ticks = timestamp + GregorianCalendarStart.Ticks;

        return new DateTimeOffset(ticks, TimeSpan.Zero);
    }

    /// <summary>
    /// get date time from guid
    /// </summary>
    /// <param name="guid"></param>
    /// <returns><see cref="DateTime"/></returns>
    public static DateTime GetDateTime(Guid guid)
    {
        return GetDateTimeOffset(guid).DateTime;
    }

    /// <summary>
    /// get local date time from guid
    /// </summary>
    /// <param name="guid"></param>
    /// <returns><see cref="DateTime"/></returns>
    public static DateTime GetLocalDateTime(Guid guid)
    {
        return GetDateTimeOffset(guid).LocalDateTime;
    }

    /// <summary>
    /// get utc date time from guid
    /// </summary>
    /// <param name="guid"></param>
    /// <returns><see cref="DateTime"/></returns>
    public static DateTime GetUtcDateTime(Guid guid)
    {
        return GetDateTimeOffset(guid).UtcDateTime;
    }

    /// <summary>
    /// Generate time based guid
    /// </summary>
    /// <returns><see cref="Guid"/></returns>
    public static Guid GenerateTimeBasedGuid()
    {
        return GenerateTimeBasedGuid(DateTimeOffset.UtcNow, DefaultClockSequence, DefaultNode);
    }

    /// <summary>
    /// Generate time based guid providing a NodeName string
    /// </summary>
    /// <param name="nodeName"></param>
    /// <returns><see cref="Guid"/></returns>
    public static Guid GenerateTimeBasedGuid(string nodeName)
    {
        var x = nodeName.GetHashCode();
        var node = $"{x:X}";
        var defaultNode = Encoding.UTF8.GetBytes(node.ToCharArray(), 0, 6);
        return GenerateTimeBasedGuid(DateTimeOffset.UtcNow, DefaultClockSequence, defaultNode);
    }

    /// <summary>
    /// Generate time based guid providing a valid DateTime object
    /// </summary>
    /// <param name="dateTime"></param>
    /// <returns><see cref="Guid"/></returns>
    public static Guid GenerateTimeBasedGuid(DateTime dateTime)
    {
        return GenerateTimeBasedGuid(dateTime, DefaultClockSequence, DefaultNode);
    }

    /// <summary>
    /// Generate time base guid providing a valid DateTimeOffset object
    /// </summary>
    /// <param name="dateTime"></param>
    /// <returns><see cref="Guid"/></returns>
    public static Guid GenerateTimeBasedGuid(DateTimeOffset dateTime)
    {
        return GenerateTimeBasedGuid(dateTime, DefaultClockSequence, DefaultNode);
    }

    /// <summary>
    /// Generate time based guid providing a date time, byte array for clock sequence and node
    /// </summary>
    /// <param name="dateTime"></param>
    /// <param name="clockSequence"></param>
    /// <param name="node"></param>
    /// <returns><see cref="Guid"/></returns>
    public static Guid GenerateTimeBasedGuid(DateTime dateTime, byte[] clockSequence, byte[] node)
    {
        return GenerateTimeBasedGuid(new DateTimeOffset(dateTime), clockSequence, node);
    }

    /// <summary>
    /// Generate time based guid providing a valid DateTimeOffset Object and byte arrays for clock sequence and node
    /// </summary>
    /// <param name="dateTime"></param>
    /// <param name="clockSequence"></param>
    /// <param name="node"></param>
    /// <returns><see cref="Guid"/></returns>
    /// <exception cref="ArgumentNullException"></exception>
    /// <exception cref="ArgumentOutOfRangeException"></exception>
    public static Guid GenerateTimeBasedGuid(DateTimeOffset dateTime, byte[] clockSequence, byte[] node)
    {
        if (clockSequence == null)
            throw new ArgumentNullException(nameof(clockSequence));

        if (node == null)
            throw new ArgumentNullException(nameof(node));

        if (clockSequence.Length != 2)
            throw new ArgumentOutOfRangeException(nameof(clockSequence), "The clockSequence must be 2 bytes.");

        if (node.Length != 6)
            throw new ArgumentOutOfRangeException(nameof(node), "The node must be 6 bytes.");

        var ticks = (dateTime - GregorianCalendarStart).Ticks;
        var guid = new byte[ByteArraySize];
        var timestamp = BitConverter.GetBytes(ticks);

        // copy node
        Array.Copy(node, 0, guid, NodeByte, Math.Min(6, node.Length));

        // copy clock sequence
        Array.Copy(clockSequence, 0, guid, GuidClockSequenceByte, Math.Min(2, clockSequence.Length));

        // copy timestamp
        Array.Copy(timestamp, 0, guid, TimestampByte, Math.Min(8, timestamp.Length));

        // set the variant
        guid[VariantByte] &= VariantByteMask;
        guid[VariantByte] |= VariantByteShift;

        // set the version
        guid[VersionByte] &= VersionByteMask;
        guid[VersionByte] |= (byte)GuidVersion.TimeBased << VersionByteShift;

        return new Guid(guid);
    }
}