SPT-Server-Build/Libraries/SPTarkov.Server.Core/Models/Common/MongoId.cs

using System.Text.RegularExpressions;

namespace SPTarkov.Server.Core.Models.Common;

public readonly partial struct MongoId : IEquatable<MongoId>
{
    private readonly string _stringId;

    public MongoId(string id)
    {
        if (string.IsNullOrWhiteSpace(id) || id.Length != 24)
        {
            // TODO: Items.json root item has an empty parentId property
            Console.WriteLine($"Critical MongoId error: Incorrect length. id: {id}");
        }

        if (!IsValidMongoId(id))
        {
            Console.WriteLine(
                $"Critical MongoId error: Incorrect format. Must be a hexadecimal [a-f0-9] of 24 characters. id: {id}"
            );
        }

        _stringId = string.Intern(id);
    }

    public MongoId()
    {
        _stringId = Generate();
    }

    /// <summary>
    /// Create a 24 character MongoId
    /// </summary>
    /// <returns>24 character objectId</returns>
    private static string Generate()
    {
        // Allocate a span directly onto the stack, will dispose whenever we finished running
        // Span is recommended to work with stackalloc + we use stackalloc here because we don't do anything with this afterwards
        Span<byte> objectId = stackalloc byte[12];

        // Time stamp (4 bytes)
        var timestamp = (int)DateTimeOffset.UtcNow.ToUnixTimeSeconds();
        // Convert to big-endian
        objectId[0] = (byte)(timestamp >> 24);
        objectId[1] = (byte)(timestamp >> 16);
        objectId[2] = (byte)(timestamp >> 8);
        objectId[3] = (byte)timestamp;

        // Random value (5 bytes)
        var rand = new Random();
        rand.NextBytes(objectId.Slice(4, 5));

        // Incrementing counter (3 bytes)
        // 24-bit counter
        var counter = rand.Next(0, 16777215);
        objectId[9] = (byte)(counter >> 16);
        objectId[10] = (byte)(counter >> 8);
        objectId[11] = (byte)counter;

        return Convert.ToHexStringLower(objectId);
    }

    public override string ToString()
    {
        return _stringId ?? string.Empty;
    }

    public bool Equals(MongoId? other)
    {
        if (other is null)
        {
            return other == this;
        }

        return other.ToString().Equals(ToString(), StringComparison.InvariantCultureIgnoreCase);
    }

    public bool Equals(string? other)
    {
        if (other is null)
        {
            return other == this;
        }

        return other.Equals(ToString(), StringComparison.InvariantCultureIgnoreCase);
    }

    public static bool IsValidMongoId(string stringToCheck)
    {
        return MongoIdRegex().IsMatch(stringToCheck);
    }

    public static implicit operator string(MongoId mongoId)
    {
        return mongoId.ToString();
    }

    public static implicit operator MongoId(string mongoId)
    {
        return new MongoId(mongoId);
    }

    public bool Equals(MongoId other)
    {
        return _stringId == other._stringId;
    }

    public override bool Equals(object? obj)
    {
        return obj is MongoId other && Equals(other);
    }

    public static bool operator ==(MongoId left, MongoId right)
    {
        return left.Equals(right);
    }

    public static bool operator !=(MongoId left, MongoId right)
    {
        return !left.Equals(right);
    }

    public override int GetHashCode()
    {
        return _stringId.GetHashCode();
    }

    public MongoId Empty()
    {
        return new MongoId("000000000000000000000000");
    }

    [GeneratedRegex("^[a-fA-F0-9]{24}$")]
    private static partial Regex MongoIdRegex();
}