using Godot;
using System;

using Rokojori.Extensions;
namespace Rokojori
{
  /** How a HeightMapGeneratorLayer combines with what is already in the map.

      All three are <marked>native</marked> BlitMaterial blend modes, so a layer
      costs one content blit into a scratch buffer plus one hardware-blended blit
      onto the map - no ping-pong buffer and no accumulation read anywhere.

      The int values are passed to HeightMapShape.gdshader as shape_blend_mode,
      which decides whether the falloff goes into RGB (Add/Subtract, premultiplied
      so the hardware just sums it) or into alpha (Replace, so Mix crossfades to
      the layer's height across the falloff). Do not renumber without updating the
      shader.
  */
  public enum HeightMapBlendMode
  {
    /** Adds the layer's height on top of what is underneath. The default, and
        the one that makes a stack of layers read as constructive.
    */
    Add       = 0,

    /** Subtracts it - craters, trenches, cut-outs. */
    Subtract  = 1,

    /** Overwrites with the layer's height, fading back to what is underneath
        across the falloff. The layer's height value is an <marked>absolute</marked>
        world height here, not a delta - plateaus and flattened build sites.
    */
    Replace   = 2
  }

  public static class HeightMapBlendModeX
  {
    public static BlitMaterial.BlendModeEnum ToBlitBlendMode( this HeightMapBlendMode mode )
    {
      switch ( mode )
      {
        case HeightMapBlendMode.Add:      return BlitMaterial.BlendModeEnum.Add;
        case HeightMapBlendMode.Subtract: return BlitMaterial.BlendModeEnum.Sub;
        case HeightMapBlendMode.Replace:  return BlitMaterial.BlendModeEnum.Mix;
      }

      return BlitMaterial.BlendModeEnum.Add;
    }

    /** True when the layer's height value means "this world height", false when
        it means "this much height on top of what is there".
    */
    public static bool IsAbsolute( this HeightMapBlendMode mode )
    {
      return mode == HeightMapBlendMode.Replace;
    }
  }
}