// Copyright 2014 The Flutter 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 'dart:math' as math;
import 'package:flutter/widgets.dart';

/// A [CupertinoMagnifier] used for magnifying text in cases where a user's
/// finger may be blocking the point of interest, like a selection handle.
///
/// Delegates styling to [CupertinoMagnifier] with its position depending on
/// [magnifierOverlayInfoBearer].
///
/// Specifically, the [CupertinoTextMagnifier] follows the following rules.
/// [CupertinoTextMagnifier]:
/// - is positioned horizontally inside the screen width, with [horizontalScreenEdgePadding] padding.
/// - is hidden if a gesture is detected [hideBelowThreshold] units below the line
///   that the magnifier is on, shown otherwise.
/// - follows the x coordinate of the gesture directly (with respect to rule 1).
/// - has some vertical drag resistance; i.e. if a gesture is detected k units below the field,
///   then has vertical offset [dragResistance] * k.
class CupertinoTextMagnifier extends StatefulWidget {
  /// Constructs a [RawMagnifier] in the Cupertino style, positioning with respect to
  /// [magnifierOverlayInfoBearer].
  ///
  /// The default constructor parameters and constants were eyeballed on
  /// an iPhone XR iOS v15.5.
  const CupertinoTextMagnifier({
    super.key,
    this.animationCurve = Curves.easeOut,
    required this.controller,
    this.dragResistance = 10.0,
    this.hideBelowThreshold = 48.0,
    this.horizontalScreenEdgePadding = 10.0,
    required this.magnifierOverlayInfoBearer,
  });

  /// The curve used for the in / out animations.
  final Curve animationCurve;

  /// This magnifier's controller.
  ///
  /// The [CupertinoTextMagnifier] requires a [MagnifierController]
  /// in order to show / hide itself without removing itself from the
  /// overlay.
  final MagnifierController controller;

  /// A drag resistance on the downward Y position of the lens.
  final double dragResistance;

  /// The difference in Y between the gesture position and the caret center
  /// so that the magnifier hides itself.
  final double hideBelowThreshold;

  /// The padding on either edge of the screen that any part of the magnifier
  /// cannot exist past.
  ///
  /// This includes any part of the magnifier, not just the center; for example,
  /// the left edge of the magnifier cannot be outside the [horizontalScreenEdgePadding].v
  ///
  /// If the screen has width w, then the magnifier is bound to
  /// `_kHorizontalScreenEdgePadding, w - _kHorizontalScreenEdgePadding`.
  final double horizontalScreenEdgePadding;

  /// [CupertinoTextMagnifier] will determine its own positioning
  /// based on the [MagnifierOverlayInfoBearer] of this notifier.
  final ValueNotifier<MagnifierOverlayInfoBearer>
      magnifierOverlayInfoBearer;

  /// The duration that the magnifier drags behind its final position.
  static const Duration _kDragAnimationDuration = Duration(milliseconds: 45);

  @override
  State<CupertinoTextMagnifier> createState() =>
      _CupertinoTextMagnifierState();
}

class _CupertinoTextMagnifierState extends State<CupertinoTextMagnifier>
    with SingleTickerProviderStateMixin {
  // Initalize to dummy values for the event that the inital call to
  // _determineMagnifierPositionAndFocalPoint calls hide, and thus does not
  // set these values.
  Offset _currentAdjustedMagnifierPosition = Offset.zero;
  double _verticalFocalPointAdjustment = 0;
  late AnimationController _ioAnimationController;
  late Animation<double> _ioAnimation;

  @override
  void initState() {
    super.initState();
    _ioAnimationController = AnimationController(
      value: 0,
      vsync: this,
      duration: CupertinoMagnifier._kInOutAnimationDuration,
    )..addListener(() => setState(() {}));

    widget.controller.animationController = _ioAnimationController;
    widget.magnifierOverlayInfoBearer
        .addListener(_determineMagnifierPositionAndFocalPoint);

    _ioAnimation = Tween<double>(
      begin: 0.0,
      end: 1.0,
    ).animate(CurvedAnimation(
      parent: _ioAnimationController,
      curve: widget.animationCurve,
    ));
  }

  @override
  void dispose() {
    widget.controller.animationController = null;
    _ioAnimationController.dispose();
    widget.magnifierOverlayInfoBearer
        .removeListener(_determineMagnifierPositionAndFocalPoint);
    super.dispose();
  }

  @override
  void didUpdateWidget(CupertinoTextMagnifier oldWidget) {
    if (oldWidget.magnifierOverlayInfoBearer != widget.magnifierOverlayInfoBearer) {
      oldWidget.magnifierOverlayInfoBearer.removeListener(_determineMagnifierPositionAndFocalPoint);
      widget.magnifierOverlayInfoBearer.addListener(_determineMagnifierPositionAndFocalPoint);
    }
    super.didUpdateWidget(oldWidget);
  }

  @override
  void didChangeDependencies() {
    _determineMagnifierPositionAndFocalPoint();
    super.didChangeDependencies();
  }

  void _determineMagnifierPositionAndFocalPoint() {
    final MagnifierOverlayInfoBearer textEditingContext =
        widget.magnifierOverlayInfoBearer.value;

    // The exact Y of the center of the current line.
    final double verticalCenterOfCurrentLine =
        textEditingContext.caretRect.center.dy;

    // If the magnifier is currently showing, but we have dragged out of threshold,
    // we should hide it.
    if (verticalCenterOfCurrentLine -
            textEditingContext.globalGesturePosition.dy <
        -widget.hideBelowThreshold) {
      // Only signal a hide if we are currently showing.
      if (widget.controller.shown) {
        widget.controller.hide(removeFromOverlay: false);
      }
      return;
    }

    // If we are gone, but got to this point, we shouldn't be: show.
    if (!widget.controller.shown) {
      _ioAnimationController.forward();
    }

    // Never go above the center of the line, but have some resistance
    // going downward if the drag goes too far.
    final double verticalPositionOfLens = math.max(
        verticalCenterOfCurrentLine,
        verticalCenterOfCurrentLine -
            (verticalCenterOfCurrentLine -
                    textEditingContext.globalGesturePosition.dy) /
                widget.dragResistance);

    // The raw position, tracking the gesture directly.
    final Offset rawMagnifierPosition = Offset(
      textEditingContext.globalGesturePosition.dx -
          CupertinoMagnifier.kDefaultSize.width / 2,
      verticalPositionOfLens -
          (CupertinoMagnifier.kDefaultSize.height -
              CupertinoMagnifier.kMagnifierAboveFocalPoint),
    );

    final Rect screenRect = Offset.zero & MediaQuery.of(context).size;

    // Adjust the magnifier position so that it never exists outside the horizontal
    // padding.
    final Offset adjustedMagnifierPosition = MagnifierController.shiftWithinBounds(
      bounds: Rect.fromLTRB(
          screenRect.left + widget.horizontalScreenEdgePadding,
          // iOS doesn't reposition for Y, so we should expand the threshold
          // so we can send the whole magnifier out of bounds if need be.
          screenRect.top -
              (CupertinoMagnifier.kDefaultSize.height +
                  CupertinoMagnifier.kMagnifierAboveFocalPoint),
          screenRect.right - widget.horizontalScreenEdgePadding,
          screenRect.bottom +
              (CupertinoMagnifier.kDefaultSize.height +
                  CupertinoMagnifier.kMagnifierAboveFocalPoint)),
      rect: rawMagnifierPosition & CupertinoMagnifier.kDefaultSize,
    ).topLeft;

    setState(() {
      _currentAdjustedMagnifierPosition = adjustedMagnifierPosition;
      // The lens should always point to the center of the line.
      _verticalFocalPointAdjustment =
          verticalCenterOfCurrentLine - verticalPositionOfLens;
    });
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedPositioned(
      duration: CupertinoTextMagnifier._kDragAnimationDuration,
      curve: widget.animationCurve,
      left: _currentAdjustedMagnifierPosition.dx,
      top: _currentAdjustedMagnifierPosition.dy,
      child: CupertinoMagnifier(
        inOutAnimation: _ioAnimation,
        additionalFocalPointOffset: Offset(0, _verticalFocalPointAdjustment),
      ),
    );
  }
}

/// A [RawMagnifier] used for magnifying text in cases where a user's
/// finger may be blocking the point of interest, like a selection handle.
///
/// [CupertinoMagnifier] is a wrapper around [RawMagnifier] that handles styling
/// and transitions.
///
/// {@macro flutter.widgets.magnifier.intro}
///
/// See also:
///
/// * [RawMagnifier], the backing implementation.
/// * [CupertinoTextMagnifier], a widget that positions [CupertinoMagnifier] based on
/// [MagnifierOverlayInfoBearer].
/// * [MagnifierController], the controller for this magnifier.
class CupertinoMagnifier extends StatelessWidget {
  /// Creates a [RawMagnifier] in the Cupertino style.
  ///
  /// The default constructor parameters and constants were eyeballed on
  /// an iPhone XR iOS v15.5.
  const CupertinoMagnifier({
    super.key,
    this.size = kDefaultSize,
    this.borderRadius = const BorderRadius.all(Radius.elliptical(60, 50)),
    this.additionalFocalPointOffset = Offset.zero,
    this.shadows = const <BoxShadow>[
      BoxShadow(
        color: Color.fromARGB(25, 0, 0, 0),
        blurRadius: 11,
        spreadRadius: 0.2,
      ),
    ],
    this.borderSide =
        const BorderSide(color: Color.fromARGB(255, 232, 232, 232)),
    this.inOutAnimation,
  });

  /// The shadows displayed under the magnifier.
  final List<BoxShadow> shadows;

  /// The border, or "rim", of this magnifier.
  final BorderSide borderSide;

  /// The vertical offset that the magnifier is along the Y axis above
  /// the focal point.
  @visibleForTesting
  static const double kMagnifierAboveFocalPoint = -26;

  /// The default size of the magnifier.
  ///
  /// This is public so that positioners can choose to depend on it, although
  /// it is overrideable.
  @visibleForTesting
  static const Size kDefaultSize = Size(80, 47.5);

  /// The duration that this magnifier animates in / out for.
  ///
  /// The animation is a translation and a fade. The translation
  /// begins at the focal point, and ends at [kMagnifierAboveFocalPoint].
  /// The opacity begins at 0 and ends at 1.
  static const Duration _kInOutAnimationDuration = Duration(milliseconds: 150);

  /// The size of this magnifier.
  final Size size;

  /// The border radius of this magnifier.
  final BorderRadius borderRadius;

  /// This [RawMagnifier]'s controller.
  ///
  /// Since [CupertinoMagnifier] has no knowledge of shown / hidden state,
  /// this animation should be driven by an external actor.
  final Animation<double>? inOutAnimation;

  /// Any additional focal point offset, applied over the regular focal
  /// point offset defined in [kMagnifierAboveFocalPoint].
  final Offset additionalFocalPointOffset;

  @override
  Widget build(BuildContext context) {
    Offset focalPointOffset =
        Offset(0, (kDefaultSize.height / 2) - kMagnifierAboveFocalPoint);
    focalPointOffset.scale(1, inOutAnimation?.value ?? 1);
    focalPointOffset += additionalFocalPointOffset;

    return Transform.translate(
      offset: Offset.lerp(
        const Offset(0, -kMagnifierAboveFocalPoint),
        Offset.zero,
        inOutAnimation?.value ?? 1,
      )!,
      child: RawMagnifier(
        size: size,
        focalPointOffset: focalPointOffset,
        decoration: MagnifierDecoration(
          opacity: inOutAnimation?.value ?? 1,
          shape: RoundedRectangleBorder(
            borderRadius: borderRadius,
            side: borderSide,
          ),
          shadows: shadows,
        ),
      ),
    );
  }
}
