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

// adapted from Flutter `_PopupMenuRouteLayout` in `/material/popup_menu.dart`
class QuickChooserRouteLayout extends SingleChildLayoutDelegate {
  final RelativeRect triggerRect;
  final PopupMenuPosition menuPosition;
  final EdgeInsets padding;
  final Set<Rect> avoidBounds;

  static const double _kMenuScreenPadding = 8.0;

  QuickChooserRouteLayout(
    this.triggerRect,
    this.menuPosition,
    this.padding,
    this.avoidBounds,
  );

  @override
  BoxConstraints getConstraintsForChild(BoxConstraints constraints) {
    return BoxConstraints.loose(constraints.biggest).deflate(
      const EdgeInsets.all(_kMenuScreenPadding) + padding,
    );
  }

  @override
  Offset getPositionForChild(Size size, Size childSize) {
    // size: The size of the overlay.
    // childSize: The size of the menu, when fully open, as determined by getConstraintsForChild.

    double y;
    switch (menuPosition) {
      case PopupMenuPosition.over:
        y = triggerRect.top - childSize.height;
        break;
      case PopupMenuPosition.under:
        y = triggerRect.bottom;
        break;
    }
    double x = (triggerRect.left + (size.width - triggerRect.right) - childSize.width) / 2;
    final wantedPosition = Offset(x, y);
    final originCenter = triggerRect.toRect(Offset.zero & size).center;
    final subScreens = DisplayFeatureSubScreen.subScreensInBounds(Offset.zero & size, avoidBounds);
    final subScreen = _closestScreen(subScreens, originCenter);
    return _fitInsideScreen(subScreen, childSize, wantedPosition);
  }

  Rect _closestScreen(Iterable<Rect> screens, Offset point) {
    Rect closest = screens.first;
    for (final Rect screen in screens) {
      if ((screen.center - point).distance < (closest.center - point).distance) {
        closest = screen;
      }
    }
    return closest;
  }

  Offset _fitInsideScreen(Rect screen, Size childSize, Offset wantedPosition) {
    double x = wantedPosition.dx;
    double y = wantedPosition.dy;
    // Avoid going outside an area defined as the rectangle 8.0 pixels from the
    // edge of the screen in every direction.
    if (x < screen.left + _kMenuScreenPadding + padding.left) {
      x = screen.left + _kMenuScreenPadding + padding.left;
    } else if (x + childSize.width > screen.right - _kMenuScreenPadding - padding.right) {
      x = screen.right - childSize.width - _kMenuScreenPadding - padding.right;
    }
    if (y < screen.top + _kMenuScreenPadding + padding.top) {
      y = _kMenuScreenPadding + padding.top;
    } else if (y + childSize.height > screen.bottom - _kMenuScreenPadding - padding.bottom) {
      y = screen.bottom - childSize.height - _kMenuScreenPadding - padding.bottom;
    }

    return Offset(x, y);
  }

  @override
  bool shouldRelayout(QuickChooserRouteLayout oldDelegate) {
    return triggerRect != oldDelegate.triggerRect || padding != oldDelegate.padding || !setEquals(avoidBounds, oldDelegate.avoidBounds);
  }
}