using System.Runtime.CompilerServices;

namespace OECS;

/// <summary>
/// Registry of component types discovered at compile time by the
/// OECS.SourceGen incremental generator. The consuming project's
/// generated code populates this via a module initializer, so no
/// manual registration is needed.
/// </summary>
public static class ComponentRegistry
{
    private static ComponentDescriptor[]? _descriptors;
    private static Dictionary<string, ComponentDescriptor>? _byTypeName;

    /// <summary>
    /// All discovered component descriptors. Populated automatically
    /// by the source generator at module initialization.
    /// </summary>
    public static ComponentDescriptor[] Descriptors =>
        _descriptors ?? Array.Empty<ComponentDescriptor>();

    /// <summary>
    /// Lookup by assembly-qualified type name. Populated automatically
    /// by the source generator at module initialization.
    /// </summary>
    public static IReadOnlyDictionary<string, ComponentDescriptor> ByTypeName
    {
        get
        {
            if (_byTypeName == null)
            {
                var dict = new Dictionary<string, ComponentDescriptor>();
                foreach (var desc in Descriptors)
                    dict[desc.TypeName] = desc;
                _byTypeName = dict;
            }
            return _byTypeName;
        }
    }

    /// <summary>
    /// Called by generated code to register discovered component types.
    /// Must be called before any serialization occurs.
    /// </summary>
    public static void Initialize(ComponentDescriptor[] descriptors)
    {
        _descriptors = descriptors;
        _byTypeName = null; // Rebuild on next access.
    }
}