packages/devtools_app/lib/src/debugger/hover.dart

// Copyright 2021 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

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

import '../theme.dart';
import '../ui/utils.dart';

/// Regex for valid Dart identifiers.
final _identifier = RegExp(r'^[a-zA-Z0-9]|_|\$');

/// Returns the word in the [line] for the provided hover [dx] offset given
/// the [line]'s [textStyle].
String wordForHover(double dx, TextSpan line) {
  String word = '';
  final hoverIndex = _hoverIndexFor(dx, line);
  final lineText = line.toPlainText();
  if (hoverIndex >= 0 && hoverIndex < lineText.length) {
    final hoverChar = lineText[hoverIndex];
    word = '$word$hoverChar';
    if (_identifier.hasMatch(hoverChar) || hoverChar == '.') {
      // Merge trailing valid identifiers.
      int charIndex = hoverIndex + 1;
      while (charIndex < lineText.length) {
        final character = lineText[charIndex];
        if (_identifier.hasMatch(character)) {
          word = '$word$character';
        } else {
          break;
        }
        charIndex++;
      }

      // Merge preceding characters including those linked by a `.`.
      charIndex = hoverIndex - 1;
      while (charIndex >= 0) {
        final character = lineText[charIndex];
        if (_identifier.hasMatch(character) || character == '.') {
          word = '$character$word';
        } else {
          break;
        }
        charIndex--;
      }
    }
  }

  return word;
}

/// Returns the index in the Textspan's plainText for which the hover offset is
/// located.
int _hoverIndexFor(double dx, TextSpan line) {
  int hoverIndex = -1;
  final length = line.toPlainText().length;
  for (var i = 0; i < length; i++) {
    final painter = TextPainter(
      text: truncateTextSpan(line, i + 1),
      textDirection: TextDirection.ltr,
    )..layout();
    if (dx <= painter.width) {
      hoverIndex = i;
      break;
    }
  }
  return hoverIndex;
}

const _hoverCardBorderWidth = 2.0;
const _hoverYOffset = 10;

/// A card to display content while hovering over a widget.
///
/// This widget will automatically remove itself after the mouse has entered
/// and left its region.
///
/// Note that if a mouse has never entered, it will not remove itself.
class HoverCard {
  HoverCard({
    @required BuildContext context,
    @required PointerHoverEvent event,
    @required String title,
    @required Widget contents,
    @required double width,
  }) {
    final overlayState = Overlay.of(context);
    final colorScheme = Theme.of(context).colorScheme;
    final focusColor = Theme.of(context).focusColor;
    final hoverHeading = colorScheme.hoverTitleTextStyle;
    final position = event.position;

    _overlayEntry = OverlayEntry(builder: (context) {
      return Positioned(
        left: position.dx - (width / 2.0),
        top: position.dy + _hoverYOffset,
        child: MouseRegion(
          onExit: (_) {
            remove();
          },
          onEnter: (_) {
            _hasMouseEntered = true;
          },
          child: Container(
            padding: const EdgeInsets.all(denseSpacing),
            decoration: BoxDecoration(
              color: colorScheme.defaultBackgroundColor,
              border: Border.all(
                color: focusColor,
                width: _hoverCardBorderWidth,
              ),
              borderRadius: BorderRadius.circular(defaultBorderRadius),
            ),
            width: width,
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                SizedBox(
                  width: width,
                  child: Text(
                    title,
                    overflow: TextOverflow.ellipsis,
                    style: hoverHeading,
                    textAlign: TextAlign.center,
                  ),
                ),
                Divider(color: colorScheme.hoverTextStyle.color),
                contents,
              ],
            ),
          ),
        ),
      );
    });
    overlayState.insert(_overlayEntry);
  }

  OverlayEntry _overlayEntry;

  bool _isRemoved = false;

  bool _hasMouseEntered = false;

  /// Attempts to remove the HoverCard from the screen.
  ///
  /// The HoverCard will not be removed if the mouse is currently inside the
  /// widget.
  void maybeRemove() {
    if (!_hasMouseEntered) remove();
  }

  /// Removes the HoverCard even if the mouse is in the corresponding mouse
  /// region.
  void remove() {
    if (!_isRemoved) _overlayEntry.remove();
    _isRemoved = true;
  }
}