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

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        colorSchemeSeed: Colors.blue,
      ),
      home: const ZoomViewMvp(),
    );
  }
}

class ZoomViewMvp extends StatefulWidget {
  const ZoomViewMvp({super.key});

  @override
  State<ZoomViewMvp> createState() => _ZoomViewMvpState();
}

class _ZoomViewMvpState extends State<ZoomViewMvp> {

  final controller = ScrollController();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ZoomView(
        controller: controller,
        child: ListView.builder(
          controller: controller,
          itemBuilder: (context, index) {
            return Center(child: Text("simple text ${index.toString()}"));
          },
        )
      ),
    );
  }
}


///Allows a ListView or other Scrollables that implement ScrollPosition and
///jumpTo(offset) in their controller to be zoomed and scrolled.
class ZoomView extends StatefulWidget {
  const ZoomView({
    super.key,
    required this.child,
    required this.controller,
    this.maxScale = 4.0,
    this.minScale = 1.0,
    this.scrollAxis = Axis.vertical,
  });

  final Widget child;
  final ScrollController controller;

  ///scrollAxis must be set to Axis.horizontal if the Scrollable is horizontal
  final Axis scrollAxis;

  ///The maximum scale that the ZoomView can be zoomed to. Set to double.infinity to allow infinite zoom in
  final double maxScale;

  ///The minimum scale that the ZoomView can be zoomed to. Set to 0 to allow infinite zoom out
  final double minScale;

  @override
  State<ZoomView> createState() => _ZoomViewState();
}

class _ZoomViewState extends State<ZoomView> with TickerProviderStateMixin {
  @override
  void initState() {
    if (widget.scrollAxis == Axis.vertical) {
      _verticalController = widget.controller;
      _horizontalController = ScrollController();
    } else {
      _verticalController = ScrollController();
      _horizontalController = widget.controller;
    }

    super.initState();
  }

  ///The current scale of the ZoomView
  double _scale = 1;

  ///The scale of the ZoomView before the last scale update event
  double _lastScale = 1;

  late final ScrollController _verticalController;
  late final ScrollController _horizontalController;

  ///The focal point of pointers at the start of a scale event
  late Offset _localFocalPoint;

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (BuildContext context, BoxConstraints constraints) {
        double height = constraints.maxHeight;
        double width = constraints.maxWidth;
        return GestureDetector(
          behavior: HitTestBehavior.translucent,
          onScaleStart: (ScaleStartDetails details) {
            if (details.pointerCount != 1) {
              _localFocalPoint = details.localFocalPoint;
            }
          },
          onScaleUpdate: (ScaleUpdateDetails details) {
            if (details.pointerCount > 1) {
              final newScale = _lastScale / details.scale;
              final verticalOffset =
                  _verticalController.position.pixels + (_scale - newScale) * _localFocalPoint.dy;
              final horizontalOffset = _horizontalController.position.pixels +
                  (_scale - newScale) * _localFocalPoint.dx;
              //This is the main logic to actually perform the scaling
              setState(() {
                _scale = newScale;
              });
              _verticalController.jumpTo(verticalOffset);
              _horizontalController.jumpTo(horizontalOffset);
            } else {
              final correctedDelta = details.focalPointDelta * _scale;
              _verticalController.jumpTo(_verticalController.position.pixels - correctedDelta.dy);
              _horizontalController.jumpTo(_horizontalController.position.pixels - correctedDelta.dx);
            }
          },
          onScaleEnd: (ScaleEndDetails details) {
            _lastScale = _scale;
          },
          child: Column(
            children: [
              Expanded(
                //When scale decreases, the SizedBox will shrink and the FittedBox
                //will scale the child to fit the maximum constraints of the ZoomView
                child: FittedBox(
                  fit: BoxFit.fill,
                  child: SizedBox(
                    height: height * _scale,
                    width: width * _scale,
                    child: Center(
                      child: ScrollConfiguration(
                        behavior: const ScrollBehavior().copyWith(
                          overscroll: false,
                          //Disable all inputs on the list as we will handle them
                          //ourselves using the gesture detector and scroll controllers
                          dragDevices: <PointerDeviceKind>{},
                          scrollbars: false,
                        ),
                        child: ListView(
                          physics: const ClampingScrollPhysics(),
                          controller: widget.scrollAxis == Axis.vertical
                              ? _horizontalController
                              : _verticalController,
                          scrollDirection: widget.scrollAxis == Axis.vertical
                              ? Axis.horizontal
                              : Axis.vertical,
                          children: [
                            SizedBox(
                            width: widget.scrollAxis == Axis.vertical ? width : null,
                            height: widget.scrollAxis == Axis.vertical ? null : height,
                            child: widget.child,
                          ),
                          ],
                        ),
                      ),
                    ),
                  ),
                ),
              ),
            ],
          ),
        );
      },
    );
  }
}