using System.Collections.Generic;
using Godot;
using System;

using Rokojori.Extensions;
namespace Rokojori
{
  /** One Resource a TextureStackTexture2D has to listen to, and which layer an
      edit to it should redraw from.

      Exists because the change tree is deeper than the compositing tree. A
      composite walks layers; staying in sync means also watching every mask,
      every TextureSettings, every stamp set, every nested stack and every plain
      Texture2D sitting in a slot. All of those report the draw index of the
      layer that owns them, so an edit three levels down still becomes an
      incremental redraw from the right place rather than a full recomposite.

      Why this is needed at all: <marked>Godot does not emit `changed` on a
      scripted Resource when the inspector edits a plain [Export] field.</marked>
      Built-in resources emit it by hand from their setters - that is why
      Gradient, Curve and BaseMaterial3D all call emit_changed() in every
      setter. So every resource in this system does the same, and this is how
      they are found and subscribed.
  */
  public struct TextureStackChangeSource
  {
    public Resource resource;

    /** Draw index of the owning layer - 0 is the bottom layer. */
    public int drawIndex;

    /** Adds unless it is null or already in the list. The same resource
        reachable from two layers keeps the lower draw index, because a redraw
        has to start from the lowest layer the edit can affect.
    */
    public static void Add( List<TextureStackChangeSource> into, Resource resource, int drawIndex )
    {
      if ( resource == null || into == null )
      {
        return;
      }

      for ( var i = 0; i < into.Count; i++ )
      {
        if ( into[ i ].resource != resource )
        {
          continue;
        }

        if ( drawIndex < into[ i ].drawIndex )
        {
          var existing = into[ i ];
          existing.drawIndex = drawIndex;
          into[ i ] = existing;
        }

        return;
      }

      into.Add( new TextureStackChangeSource(){ resource = resource, drawIndex = drawIndex } );
    }
  }
}