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

using Rokojori.Extensions;
namespace Rokojori
{
  /** A TextureStack that lives on disk.

      The user's answer to open question 4, built as asked: it behaves like a
      TextureStackTexture2D, but it <marked>defines a file as its target and
      always writes its result there</marked>.

      The difference from TextureStackTexture2D is where the pixels are, and it
      changes what each one is for:

        - TextureStackTexture2D is a DrawableTexture2D. Its pixels only exist on
          the GPU, so they have to be recomposited every single time the resource
          loads - in the editor and in a shipped game alike. That is the price of
          being live: edit a layer and it recomposites.
        - BakedTexture2D is an ImageTexture. It composites once, when something
          asks it to, and from then on it loads a file like any other texture.
          No compositing at load, no GPU buffers held, no stack cost in a
          shipped build - and the stack is still there as the editable source.

      So: author with a TextureStackTexture2D, ship with a BakedTexture2D, or
      use one directly for anything heavy enough that recompositing on load is
      not wanted. <code>bakeOnChange</code> makes it behave like the live one
      while authoring, at the cost of a disk write per edit.

      The file is a normal project asset, so Godot imports, compresses and
      mipmaps it the way it does any other texture. That is the main practical
      reason to bake: a composited DrawableTexture2D is always uncompressed
      RGBA8 in VRAM.
  */
  [Tool]
  [GlobalClass]
  public partial class BakedTexture2D:ImageTexture
  {
    TextureStack _stack;

    [Export]
    public TextureStack stack
    {
      get => _stack;
      set { _stack = value; OnChanged(); }
    }

    string _path = "";

    /** Where the result is written, and read back from afterwards. A project
        path with an image extension - .png, .exr for HDR, .webp or .jpg.
        Textures.Save picks the encoder off the extension.
    */
    [Export( PropertyHint.SaveFile, "*.png,*.exr,*.webp,*.jpg" )]
    public string path
    {
      get => _path;
      set { _path = value; OnChanged(); }
    }

    int _width = 1024;

    [Export]
    public int width
    {
      get => _width;
      set { _width = value; OnChanged(); }
    }

    int _height = 1024;

    [Export]
    public int height
    {
      get => _height;
      set { _height = value; OnChanged(); }
    }

    /** Rgba8 by default, same as TextureStackTexture2D and for the same reason
        - see the note on its format property.
    */
    TextureStackFormat _format = TextureStackFormat.Rgba8;

    [Export]
    public TextureStackFormat format
    {
      get => _format;
      set { _format = value; OnChanged(); }
    }

    Color _clearColor = new Color( 0, 0, 0, 0 );

    [Export]
    public Color clearColor
    {
      get => _clearColor;
      set { _clearColor = value; OnChanged(); }
    }

    bool _mipmaps = true;

    /** Mipmaps on the baked image. The imported texture's own mipmap setting
        takes over once the file exists, so this only matters for the image this
        writes.
    */
    [Export]
    public bool mipmaps
    {
      get => _mipmaps;
      set { _mipmaps = value; OnChanged(); }
    }

    [ExportToolButton( "Bake" )]
    public Callable BakeButton => Callable.From( () => Bake() );

    [ExportToolButton( "Load Baked" )]
    public Callable LoadButton => Callable.From( () => LoadBaked() );

    [ExportGroup( "Baking" )]

    bool _bakeOnChange = false;

    /** On: every edit to the stack rebakes and rewrites the file, so it behaves
        like a live TextureStackTexture2D. Off - the default - only the Bake
        button and the BakeTextureStack Action write anything, and a change just
        reloads whatever is on disk.

        Off by default because a bake is a disk write and a reimport, which is
        not something to do per slider pixel.
    */
    [Export]
    public bool bakeOnChange
    {
      get => _bakeOnChange;
      set { _bakeOnChange = value; OnChanged(); }
    }

    float _quality = 1;

    /** For the lossy formats only - jpg and webp. png and exr ignore it; 1
        makes webp lossless.
    */
    [Export( PropertyHint.Range, "0,1" )]
    public float quality
    {
      get => _quality;
      set { _quality = value; }
    }

    [ExportGroup( "Info" )]

    [Export]
    public string info = "";


    public Vector2I size => new Vector2I( Mathf.Max( 1, _width ), Mathf.Max( 1, _height ) );

    bool _loaded = false;

    /** True once an image is in here, baked or loaded. */
    public bool isLoaded => _loaded;


    /** Composites the stack, writes it to path, and shows the result. */
    public bool Bake()
    {
      if ( _stack == null || _stack.numLayers == 0 )
      {
        info = "Nothing to bake - no stack.";
        return false;
      }

      var image = TextureStackBaker.Render( _stack, size, _format, _clearColor, _mipmaps );

      if ( image == null )
      {
        info = "Composite failed.";
        return false;
      }

      if ( _mipmaps )
      {
        image.GenerateMipmaps();
      }

      Apply( image );

      if ( string.IsNullOrEmpty( _path ) )
      {
        info = size.X + "x" + size.Y + " " + _format + ", baked in memory - no path set.";
        return true;
      }

      TextureStackBaker.Save( image, _path, _quality );

      info = size.X + "x" + size.Y + " " + _format + ", baked to " + _path;

      return true;
    }

    /** Reads the file back without compositing anything. What a load does. */
    public bool LoadBaked()
    {
      var image = TextureStackBaker.Load( _path );

      if ( image == null )
      {
        return false;
      }

      Apply( image );

      info = image.GetWidth() + "x" + image.GetHeight() + ", loaded from " + _path;

      return true;
    }

    /** SetImage handles both cases - it creates the texture when there is none
        yet and replaces the RID when there is. It also emits changed, which
        collapses the inspector; unavoidable here and not worth avoiding, since
        the pixels really are a new texture and a bake is always explicit.
    */
    void Apply( Image image )
    {
      SetImage( image );

      _loaded = true;
    }


    /* SCHEDULING
       --------------------------------------------------------------------------
       Same deferred-setter mechanism as TextureStackTexture2D, and for the same
       reason: there is no resource-load callback to hook, so every property
       setter schedules and a flag coalesces the burst of writes a .tres load
       produces.

       What runs at the end of it differs. A TextureStackTexture2D has to
       composite, because its pixels do not survive being saved. This one only
       has to <marked>load its file</marked>, which is the whole point - unless
       bakeOnChange asks for the live behaviour.
    */

    bool _scheduled = false;

    void OnChanged()
    {
      if ( _scheduled )
      {
        return;
      }

      _scheduled = true;

      // By name, not from a lambda - a delegate Callable does not survive a C#
      // assembly reload. See the change-hooks note below.
      CallDeferred( MethodName.Flush );
    }

    /** Public and named because it is called by name through CallDeferred. */
    public void Flush()
    {
      _scheduled = false;

      if ( ! GodotObject.IsInstanceValid( this ) )
      {
        return;
      }

      if ( _bakeOnChange )
      {
        Bake();
        return;
      }

      LoadBaked();

      EnsureChangeHooks();
    }


    /* CHANGE HOOKS
       --------------------------------------------------------------------------
       Only needed for bakeOnChange, and only then - without it an edit to a
       layer changes nothing about this texture until someone bakes. Same
       mechanism and the same reasons as TextureStackTexture2D's, including
       connecting by method name rather than from a lambda, because a delegate
       Callable's GCHandle is released by a C# assembly reload. See the note
       there and on TextureStackChangeSource.

       No draw index is bound here: a bake is a full composite into a throwaway
       target, so there is no accumulation to replay from and nothing an
       incremental index could do.
    */

    bool _hooked = false;
    readonly List<Resource> _hookedResources = new List<Resource>();
    readonly List<Callable> _hookedCallables = new List<Callable>();
    readonly List<TextureStackChangeSource> _changeSources
      = new List<TextureStackChangeSource>();

    void EnsureChangeHooks()
    {
      if ( _hooked || _stack == null )
      {
        return;
      }

      ClearChangeHooks();

      _hooked = true;

      Hook( _stack );

      _changeSources.Clear();
      _stack.CollectChangeSources( _changeSources );

      for ( var i = 0; i < _changeSources.Count; i++ )
      {
        Hook( _changeSources[ i ].resource );
      }

      _changeSources.Clear();
    }

    void Hook( Resource resource )
    {
      if ( resource == null || _hookedResources.Contains( resource ) )
      {
        return;
      }

      var callable = new Callable( this, MethodName.OnChangeSourceChanged );

      if ( ! resource.IsConnected( Resource.SignalName.Changed, callable ) )
      {
        resource.Connect( Resource.SignalName.Changed, callable );
      }

      _hookedResources.Add( resource );
      _hookedCallables.Add( callable );
    }

    /** Called by name from the `changed` signal of everything in the stack.
        Public because Godot calls it; the name is part of the connection.
    */
    public void OnChangeSourceChanged()
    {
      _hooked = false;

      OnChanged();
    }

    void ClearChangeHooks()
    {
      for ( var i = 0; i < _hookedResources.Count; i++ )
      {
        var resource = _hookedResources[ i ];

        if ( resource == null || ! GodotObject.IsInstanceValid( resource ) )
        {
          continue;
        }

        var callable = _hookedCallables[ i ];

        if ( resource.IsConnected( Resource.SignalName.Changed, callable ) )
        {
          resource.Disconnect( Resource.SignalName.Changed, callable );
        }
      }

      _hookedResources.Clear();
      _hookedCallables.Clear();
    }
  }
}