using Godot;
using System;

using Rokojori.Extensions;
namespace Rokojori
{
  /** Which scalar a mask texture's pixel is reduced to.

      Int values are switched on in TextureStack.gdshaderinc - do not renumber.
  */
  public enum TextureStackMaskChannel
  {
    Red        = 0,
    Green      = 1,
    Blue       = 2,
    Alpha      = 3,
    Luminance  = 4
  }

  /** One mask on a TextureStackLayer.

      A mask reduces its texture to a single 0-1 value and multiplies it into
      the layer's effective opacity. Several masks on one layer multiply
      together, which is how the outline's masked-decal example is authored
      without any nesting: a circle-gradient texture and a noise texture as two
      masks on one layer.

      texture takes any Texture2D, so a TextureStackTexture2D goes straight in
      and a mask can itself be a composited stack.

      The transform is applied around the centre of the layer's placement rect
      and is independent of the layer's own content UV transform. Its UV space
      is rect-local: on a full-texture layer that is the whole texture, on a
      decal it is the decal, which is what makes a mask follow a stamp.

      Levels remap the sampled value before invert: everything at or below
      levelsMin becomes 0, everything at or above levelsMax becomes 1. Leave at
      0/1 for no remapping. This is the "one noise texture, many hardnesses"
      control.

      Mask count per layer is capped by the blit source ceiling - see
      TextureStackLayer.MaxMasks.

      Every value is a property that emits changed, so editing a mask
      recomposites the stack that reads it - see TextureStackChangeSource.
  */
  [Tool]
  [GlobalClass]
  public partial class TextureStackMask:Resource
  {
    Texture2D _texture;

    [Export]
    public Texture2D texture
    {
      get => _texture;
      set { _texture = value; TextureStackNotify.Changed( this ); }
    }

    TextureSettings _textureSettings;

    /** Sampling and colour space for the mask texture. Empty means Linear
        sampling and no conversion - see TextureSettings.

        This is the slot that matters most in the whole system: a mask is
        usually authored small, a gradient or a 64px noise, and stretched across
        the whole output, so Nearest here is the difference between a smooth
        falloff and visible banding.
    */
    [Export]
    public TextureSettings textureSettings
    {
      get => _textureSettings;
      set { _textureSettings = value; TextureStackNotify.Changed( this ); }
    }

    TextureStackMaskChannel _channel = TextureStackMaskChannel.Red;

    [Export]
    public TextureStackMaskChannel channel
    {
      get => _channel;
      set { _channel = value; TextureStackNotify.Changed( this ); }
    }

    bool _invert = false;

    [Export]
    public bool invert
    {
      get => _invert;
      set { _invert = value; TextureStackNotify.Changed( this ); }
    }

    [ExportGroup( "Transform" )]

    Vector2 _offset = Vector2.Zero;

    [Export]
    public Vector2 offset
    {
      get => _offset;
      set { _offset = value; TextureStackNotify.Changed( this ); }
    }

    Vector2 _scale = Vector2.One;

    [Export]
    public Vector2 scale
    {
      get => _scale;
      set { _scale = value; TextureStackNotify.Changed( this ); }
    }

    float _rotationDegrees = 0;

    [Export]
    public float rotationDegrees
    {
      get => _rotationDegrees;
      set { _rotationDegrees = value; TextureStackNotify.Changed( this ); }
    }

    bool _repeat = false;

    /** Off: the mask is transparent (value 0) outside its own 0-1 range, so a
        scaled-down mask hides everything around itself. On: it tiles.
    */
    [Export]
    public bool repeat
    {
      get => _repeat;
      set { _repeat = value; TextureStackNotify.Changed( this ); }
    }

    [ExportGroup( "Levels" )]

    float _levelsMin = 0;

    [Export( PropertyHint.Range, "0,1" )]
    public float levelsMin
    {
      get => _levelsMin;
      set { _levelsMin = value; TextureStackNotify.Changed( this ); }
    }

    float _levelsMax = 1;

    [Export( PropertyHint.Range, "0,1" )]
    public float levelsMax
    {
      get => _levelsMax;
      set { _levelsMax = value; TextureStackNotify.Changed( this ); }
    }

    public bool isUsable => texture != null;

    /** offset.xy / scale.xy, as the composite shader expects it. */
    public Vector4 packedTransform
    {
      get
      {
        var s = new Vector2(
          Mathf.IsZeroApprox( scale.X ) ? 0.0001f : scale.X,
          Mathf.IsZeroApprox( scale.Y ) ? 0.0001f : scale.Y
        );

        return new Vector4( offset.X, offset.Y, s.X, s.Y );
      }
    }

    /** rotation in radians / repeat as 0-1 / levelsMin / levelsMax. */
    public Vector4 packedParameters
    {
      get
      {
        var min = levelsMin;
        var max = levelsMax;

        // A collapsed or inverted range would divide by zero in the shader.
        if ( max - min < 0.0001f )
        {
          max = min + 0.0001f;
        }

        return new Vector4( Mathf.DegToRad( rotationDegrees ), repeat ? 1 : 0, min, max );
      }
    }
  }
}