import 'package:flutter/material.dart';
import 'package:infinite_lazy_2d_grid/utils/conversions.dart';

// ------------------------------ Public Types -------------------------------

typedef WidgetBuilder = Widget Function();

// ------------------------------ Private Types ------------------------------

// some simple exceptions
// ignore: non_constant_identifier_names
final _ChildNotFoundException = Exception('Child with the given ID does not exist');

class _CanvasItem {
  Offset gsPosition;
  final WidgetBuilder builder;

  _CanvasItem({required this.gsPosition, required this.builder});
}

// ------------------------------ Controller ------------------------------

/// Every canvas view needs one and this handles the positioning logic
class CanvasController with ChangeNotifier {
  int _nextId = 0; // surely we won't run out of IDs, Clueless
  Offset _gsTopLeftOffset = Offset.zero;
  final Map<int, _CanvasItem> _children = {}; // int for IDs

  // -------------------- public functions --------------------

  // -------- child manip --------

  int addChild(Offset position, WidgetBuilder builder) {
    _children[_nextId] = _CanvasItem(gsPosition: position, builder: builder);
    return _nextId++;
  }

  void removeChild(int id) {
    _children.remove(id);
  }

  int updatePosition(int id, Offset newPosition) {
    if (_children.containsKey(id)) {
      _children[id]!.gsPosition = newPosition;
      return id;
    } else {
      throw _ChildNotFoundException;
    }
  }

  Offset getPosition(int id) {
    if (_children.containsKey(id)) {
      return _children[id]!.gsPosition;
    } else {
      throw _ChildNotFoundException;
    }
  }

  // -------- gesture handling --------
  void handleGesture(ScaleUpdateDetails details) {
    // handle gestures like pinch to zoom, pan, etc.

    // convention is that if I drag from right to left, dx is negative
    // for top to bottom, dy is postive ( so usual display conventions and final vector postion - initial vector position )
    final delta = details.focalPointDelta;

    _gsTopLeftOffset -= delta;

    notifyListeners();
  }

  List<(Offset, Widget)> widgetsWithScreenPositions() {
    return _children.values.map((item) {
      final ssPosition = gsToSs(item.gsPosition, _gsTopLeftOffset);
      return (ssPosition, item.builder());
    }).toList();
  }
}