CollisionGroupRegistry.cs

using Newtonsoft.Json;
 
namespace Gondwana.Physics.Collisions;

public sealed class CollisionGroupRegistry
{
    [JsonProperty("groups")]
    private readonly Dictionary<string, int> _groups;
 
    [JsonProperty("nextBit")]
    private int _nextBit;

    public CollisionGroupRegistry()
    {
        _groups = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
 
        Define("WorldStatic");
        Define("Actors");
        Define("Projectiles");
        Define("Triggers");
    }

#pragma warning disable IDE0051 // Used by Newtonsoft.Json via reflection.
    [JsonConstructor]
    private CollisionGroupRegistry(Dictionary<string, int> groups, int nextBit)
    {
        _groups = new Dictionary<string, int>(groups ?? throw new ArgumentNullException(nameof(groups)),
                                              StringComparer.OrdinalIgnoreCase);
        _nextBit = nextBit;
    }
 
#pragma warning restore IDE0051

    public int Define(string name)
    {
        if (string.IsNullOrWhiteSpace(name))
            throw new ArgumentException("Group name cannot be empty.", nameof(name));
 
        if (_groups.TryGetValue(name, out var existing))
            return existing;
 
        if (_nextBit >= 31)
            throw new InvalidOperationException("Max 31 collision groups exceeded for int masks.");
 
        int value = 1 << _nextBit++;
        _groups.Add(name, value);
        return value;
    }

    public int Get(string name)
    {
        if (!_groups.TryGetValue(name, out var value))
            throw new KeyNotFoundException($"Collision group '{name}' not defined.");
 
        return value;
    }

    public int GetMask(IEnumerable<string> names)
    {
        ArgumentNullException.ThrowIfNull(names);
 
        int mask = CollisionMasks.None;
        foreach (var name in names)
            mask |= Get(name);
 
        return mask;
    }

    public IReadOnlyCollection<string> GetGroupNames() => _groups.Keys.ToArray();

    public int WorldStatic => _groups["WorldStatic"];

    public int Actors => _groups["Actors"];

    public int Projectiles => _groups["Projectiles"];

    public int Triggers => _groups["Triggers"];
}