using Editor.Prism.Core;

namespace Editor.Prism.Compiler.Backends;

/// <summary>
/// What a backend can express.
/// <para>
/// Consulted during <em>validation</em>, not at emit time, so the user is told "this graph uses a
/// loop, which the strict-HLSL dialect cannot express" long before anything is written to disk.
/// </para>
/// </summary>
public sealed record BackendCapabilities(
	ShaderModel MaxShaderModel,
	StageMask Stages,
	bool Loops,
	bool RealBranching,
	bool StructMethods,
	bool Interpolators,
	bool Combos,
	int MaxVaryingSlots,
	int MaxSamplers )
{
	/// <summary>True when the backend can emit this stage.</summary>
	public bool Supports( ShaderStage stage ) => Stages.Contains( stage );

	/// <summary>True when the backend can provide a capability at its maximum shader model.</summary>
	public bool Supports( Capability capability )
	{
		if ( Capabilities.MinShaderModel( capability ) > MaxShaderModel ) return false;

		return capability switch
		{
			Capability.Loops => Loops,
			Capability.DynamicBranching => RealBranching,
			Capability.StructMethods => StructMethods,
			Capability.Interpolators => Interpolators,
			Capability.Combos => Combos,
			_ => true
		};
	}

	/// <summary>
	/// The s&amp;box VFX target: SM 6.0 Vulkan, no hull or domain stage (the engine's block parser
	/// throws on those), everything else available.
	/// </summary>
	public static readonly BackendCapabilities Sbox = new(
		ShaderModel.Sm6_0,
		StageMask.Vertex | StageMask.Pixel | StageMask.Geometry | StageMask.Compute,
		Loops: true,
		RealBranching: true,
		StructMethods: true,
		Interpolators: true,
		Combos: true,
		MaxVaryingSlots: PrismConstants.MaxVaryingSlots,
		MaxSamplers: PrismConstants.MaxSamplers );

	/// <summary>The portable Slang target: no engine combos, no engine interpolator budget.</summary>
	public static readonly BackendCapabilities Slang = new(
		ShaderModel.Sm6_5,
		StageMask.All,
		Loops: true,
		RealBranching: true,
		StructMethods: true,
		Interpolators: true,
		Combos: false,
		MaxVaryingSlots: 32,
		MaxSamplers: 32 );
}