import 'dart:ui' as ui;

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

/// Filters live pixels beneath the glass; symbols above it remain undistorted.
class GlassRefraction extends StatefulWidget {
  const GlassRefraction({
    super.key,
    required this.strength,
    this.blurSigma = 2,
    required this.child,
  });
  final double strength;

  /// Optical softness in logical pixels, independent of display density.
  final double blurSigma;
  final Widget child;
  @override
  State<GlassRefraction> createState() => _GlassRefractionState();
}

class _GlassRefractionState extends State<GlassRefraction> {
  static Future<ui.FragmentProgram>? _program;
  static ui.FragmentProgram? _loadedProgram;
  ui.FragmentShader? _shader;
  @override
  void initState() {
    super.initState();
    if (ui.ImageFilter.isShaderFilterSupported) _load();
  }

  Future<void> _load() async {
    try {
      final program = _loadedProgram ??= await (_program ??=
          ui.FragmentProgram.fromAsset('shaders/liquid_glass.frag'));
      if (mounted) setState(() => _shader = program.fragmentShader());
    } catch (error) {
      _program = null;
      _loadedProgram = null;
      debugPrint('Glass refraction unavailable: $error');
    }
  }

  @override
  void dispose() {
    _shader?.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) => _shader == null
      ? BackdropFilter(
          filter: ui.ImageFilter.blur(
            sigmaX: widget.blurSigma,
            sigmaY: widget.blurSigma,
            tileMode: TileMode.clamp,
          ),
          child: widget.child,
        )
      : _LiveGlassFilter(
          shader: _shader!,
          strength: widget.strength,
          blurSigma: widget.blurSigma,
          pixelRatio: MediaQuery.devicePixelRatioOf(context),
          child: widget.child,
        );
}

class _LiveGlassFilter extends SingleChildRenderObjectWidget {
  const _LiveGlassFilter({
    required this.shader,
    required this.strength,
    required this.blurSigma,
    required this.pixelRatio,
    required super.child,
  });
  final ui.FragmentShader shader;
  final double strength, blurSigma, pixelRatio;
  @override
  _RenderLiveGlass createRenderObject(BuildContext context) =>
      _RenderLiveGlass(shader, strength, blurSigma, pixelRatio);
  @override
  void updateRenderObject(
    BuildContext context,
    _RenderLiveGlass renderObject,
  ) => renderObject.update(shader, strength, blurSigma, pixelRatio);
}

class _RenderLiveGlass extends RenderProxyBox {
  _RenderLiveGlass(
    this._shader,
    this._strength,
    this._blurSigma,
    this._pixelRatio,
  );
  ui.FragmentShader _shader;
  double _strength, _blurSigma, _pixelRatio;
  final _layer = LayerHandle<BackdropFilterLayer>();
  void update(
    ui.FragmentShader shader,
    double strength,
    double blurSigma,
    double pixelRatio,
  ) {
    _shader = shader;
    _strength = strength;
    _blurSigma = blurSigma;
    _pixelRatio = pixelRatio;
    markNeedsPaint();
  }

  @override
  bool get alwaysNeedsCompositing => child != null;
  @override
  void paint(PaintingContext context, Offset offset) {
    if (child == null) return;
    // Sample coordinates are physical pixels. Resolve the actual transform
    // during paint so the glass also follows the Dock's hide/show animation.
    final origin = localToGlobal(Offset.zero) * _pixelRatio;
    _shader
      ..setFloat(2, origin.dx)
      ..setFloat(3, origin.dy)
      ..setFloat(4, size.width * _pixelRatio)
      ..setFloat(5, size.height * _pixelRatio)
      ..setFloat(6, _strength);
    _layer.layer ??= BackdropFilterLayer();
    // Refract the original backdrop first, then diffuse it with the engine's
    // separable Gaussian blur. Keeping the shader inside the composition also
    // keeps its source texture coordinates independent of blur padding.
    _layer.layer!.filter = ui.ImageFilter.compose(
      outer: ui.ImageFilter.blur(
        sigmaX: _blurSigma,
        sigmaY: _blurSigma,
        tileMode: TileMode.clamp,
      ),
      inner: ui.ImageFilter.shader(_shader),
    );
    context.pushLayer(_layer.layer!, super.paint, offset);
  }

  @override
  void dispose() {
    _layer.layer = null;
    super.dispose();
  }
}