using System.Reflection;

namespace AcDream.App.Rendering.Gpu.Gl;

/// <summary>
/// The single source of truth mapping each <see cref="GpuPushConstants"/>
/// field to the GLSL uniform name the GL backend binds it to — the names
/// documented on the fields themselves. <see cref="GlGpuPushConstantBinder"/>
/// reads these constants (not string literals of its own) when it calls
/// <c>GL.GetUniformLocation</c>, and <see cref="AssertMapsEveryField"/> lets a
/// test prove the table cannot silently drop a field that a later slice adds
/// to the shared struct.
/// </summary>
internal static class GlPushConstantUniformNames
{
    public const string ViewProjection = "uViewProjection";
    public const string DrawIdOffset = "uDrawIDOffset";
    public const string LightingMode = "uLightingMode";
    public const string RenderPass = "uRenderPass";
    public const string LightDebug = "uLightDebug";
    public const string TextureIndexA = "uTextureIndexA";
    public const string TextureIndexB = "uTextureIndexB";
    public const string ParamA = "uParamA";
    public const string ParamB = "uParamB";

    /// <summary>
    /// Field name (as declared on <see cref="GpuPushConstants"/>) to GLSL
    /// uniform name, built from the same constants the binder applies with —
    /// so the binder and this completeness table can never disagree.
    /// </summary>
    public static IReadOnlyDictionary<string, string> ByFieldName { get; } =
        new Dictionary<string, string>
        {
            [nameof(GpuPushConstants.ViewProjection)] = ViewProjection,
            [nameof(GpuPushConstants.DrawIdOffset)] = DrawIdOffset,
            [nameof(GpuPushConstants.LightingMode)] = LightingMode,
            [nameof(GpuPushConstants.RenderPass)] = RenderPass,
            [nameof(GpuPushConstants.LightDebug)] = LightDebug,
            [nameof(GpuPushConstants.TextureIndexA)] = TextureIndexA,
            [nameof(GpuPushConstants.TextureIndexB)] = TextureIndexB,
            [nameof(GpuPushConstants.ParamA)] = ParamA,
            [nameof(GpuPushConstants.ParamB)] = ParamB,
        };

    /// <summary>
    /// Throws if <see cref="GpuPushConstants"/> declares a public instance
    /// field this table does not map — the drift guard the campaign spec asks
    /// for. Called from a unit test, not from production code.
    /// </summary>
    internal static void AssertMapsEveryField()
    {
        FieldInfo[] fields = typeof(GpuPushConstants).GetFields(
            BindingFlags.Public | BindingFlags.Instance);
        foreach (FieldInfo field in fields)
        {
            if (!ByFieldName.ContainsKey(field.Name))
            {
                throw new InvalidOperationException(
                    $"GpuPushConstants.{field.Name} has no mapped GLSL uniform name in " +
                    $"{nameof(GlPushConstantUniformNames)}.");
            }
        }

        if (ByFieldName.Count != fields.Length)
        {
            throw new InvalidOperationException(
                $"{nameof(GlPushConstantUniformNames)} maps {ByFieldName.Count} names but " +
                $"{nameof(GpuPushConstants)} declares {fields.Length} fields — a stale entry " +
                "survives a field rename or removal.");
        }
    }
}