// 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 'package:flutter/cupertino.dart';

/// Implements a single iOS application page's layout.
///
/// The scaffold lays out the navigation bar on top and the content between or
/// behind the navigation bar.
///
/// When tapping a status bar at the top of the IsekaiPageScaffold, an
/// animation will complete for the current primary [ScrollView], scrolling to
/// the beginning. This is done using the [PrimaryScrollController] that
/// encloses the [ScrollView]. The [ScrollView.primary] flag is used to connect
/// a [ScrollView] to the enclosing [PrimaryScrollController].
///
/// {@tool dartpad}
/// This example shows a [IsekaiPageScaffold] with a [ListView] as a [child].
/// The [CupertinoButton] is connected to a callback that increments a counter.
/// The [backgroundColor] can be changed.
///
/// ** See code in examples/api/lib/cupertino/page_scaffold/cupertino_page_scaffold.0.dart **
/// {@end-tool}
///
/// See also:
///
///  * [CupertinoTabScaffold], a similar widget for tabbed applications.
///  * [CupertinoPageRoute], a modal page route that typically hosts a
///    [IsekaiPageScaffold] with support for iOS-style page transitions.
class IsekaiPageScaffold extends StatefulWidget {
  /// Creates a layout for pages with a navigation bar at the top.
  const IsekaiPageScaffold({
    super.key,
    this.navigationBar,
    this.bottomNavigationBar,
    this.backgroundColor,
    this.resizeToAvoidBottomInset = false,
    required this.child,
  })  : assert(child != null),
        assert(resizeToAvoidBottomInset != null);

  /// The [navigationBar], typically a [CupertinoNavigationBar], is drawn at the
  /// top of the screen.
  ///
  /// If translucent, the main content may slide behind it.
  /// Otherwise, the main content's top margin will be offset by its height.
  ///
  /// The scaffold assumes the navigation bar will account for the [MediaQuery]
  /// top padding, also consume it if the navigation bar is opaque.
  // TODO(xster): document its page transition animation when ready
  final ObstructingPreferredSizeWidget? navigationBar;

  /// The [bottomNavigationBar], typically a [CupertinoNavigationBar], is drawn at the
  /// bottom of the screen.
  ///
  /// If translucent, the main content may slide behind it.
  /// Otherwise, the main content's bottom margin will be offset by its height.
  ///
  /// The scaffold assumes the navigation bar will account for the [MediaQuery]
  /// bottom padding, also consume it if the navigation bar is opaque.
  final ObstructingPreferredSizeWidget? bottomNavigationBar;

  /// Widget to show in the main content area.
  ///
  /// Content can slide under the [navigationBar] when they're translucent.
  /// In that case, the child's [BuildContext]'s [MediaQuery] will have a
  /// top padding indicating the area of obstructing overlap from the
  /// [navigationBar].
  final Widget child;

  /// The color of the widget that underlies the entire scaffold.
  ///
  /// By default uses [CupertinoTheme]'s `scaffoldBackgroundColor` when null.
  final Color? backgroundColor;

  /// Whether the [child] should size itself to avoid the window's bottom inset.
  ///
  /// For example, if there is an onscreen keyboard displayed above the
  /// scaffold, the body can be resized to avoid overlapping the keyboard, which
  /// prevents widgets inside the body from being obscured by the keyboard.
  ///
  /// Defaults to true and cannot be null.
  final bool resizeToAvoidBottomInset;

  @override
  State<IsekaiPageScaffold> createState() => _IsekaiPageScaffoldState();
}

class _IsekaiPageScaffoldState extends State<IsekaiPageScaffold> {
  void _handleStatusBarTap() {
    final ScrollController? primaryScrollController =
        PrimaryScrollController.of(context);
    // Only act on the scroll controller if it has any attached scroll positions.
    if (primaryScrollController != null && primaryScrollController.hasClients) {
      primaryScrollController.animateTo(
        0.0,
        // Eyeballed from iOS.
        duration: const Duration(milliseconds: 500),
        curve: Curves.linearToEaseOut,
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    Widget paddedContent = widget.child;

    final MediaQueryData existingMediaQuery = MediaQuery.of(context);

    final double topPadding;
    final bool topFullObstruction;
    if (widget.navigationBar != null) {
      // Propagate top padding and include viewInsets if appropriate
      topPadding = widget.navigationBar!.preferredSize.height +
          existingMediaQuery.padding.top;

      topFullObstruction = widget.navigationBar!.shouldFullyObstruct(context);
    } else {
      // Propagate bottom padding and include viewInsets if appropriate
      topPadding = existingMediaQuery.padding.top;

      topFullObstruction = false;
    }

    final double bottomPadding;
    final bool bottomFullObstruction;
    if (widget.bottomNavigationBar != null) {
      // Propagate bottom padding and include viewInsets if appropriate
      bottomPadding = widget.bottomNavigationBar!.preferredSize.height +
          existingMediaQuery.padding.bottom;

      bottomFullObstruction =
          widget.bottomNavigationBar!.shouldFullyObstruct(context);
    } else {
      // Propagate bottom padding and include viewInsets if appropriate
      bottomPadding = existingMediaQuery.padding.bottom;

      bottomFullObstruction = false;
    }

    final EdgeInsets newViewInsets = existingMediaQuery.viewInsets;

    var fixedExistingMediaQuery = existingMediaQuery.removePadding(
      removeTop: widget.navigationBar != null && topFullObstruction,
      removeBottom: widget.bottomNavigationBar != null && bottomFullObstruction,
    );
    paddedContent = MediaQuery(
      data: fixedExistingMediaQuery.copyWith(
        padding: fixedExistingMediaQuery.padding.copyWith(
          top: topFullObstruction ? null : topPadding,
          bottom: bottomFullObstruction ? null : bottomPadding,
        ),
        viewInsets: newViewInsets,
      ),
      child: Padding(
        padding: EdgeInsets.only(
          top: (widget.navigationBar == null)
              ? 0
              : (topFullObstruction ? topPadding : 0),
          bottom: (widget.bottomNavigationBar == null)
              ? 0
              : (bottomFullObstruction ? bottomPadding : 0),
        ),
        child: paddedContent,
      ),
    );

    return DecoratedBox(
      decoration: BoxDecoration(
        color: CupertinoDynamicColor.maybeResolve(
                widget.backgroundColor, context) ??
            CupertinoTheme.of(context).scaffoldBackgroundColor,
      ),
      child: Stack(
        children: <Widget>[
          // The main content being at the bottom is added to the stack first.
          paddedContent,
          if (widget.navigationBar != null)
            Positioned(
              top: 0.0,
              left: 0.0,
              right: 0.0,
              child: widget.navigationBar!,
            ),
          if (widget.bottomNavigationBar != null)
            Positioned(
              bottom: 0.0,
              left: 0.0,
              right: 0.0,
              child: widget.bottomNavigationBar!,
            ),
          // Add a touch handler the size of the status bar on top of all contents
          // to handle scroll to top by status bar taps.
          Positioned(
            top: 0.0,
            left: 0.0,
            right: 0.0,
            height: existingMediaQuery.padding.top,
            child: GestureDetector(
              excludeFromSemantics: true,
              onTap: _handleStatusBarTap,
            ),
          ),
        ],
      ),
    );
  }
}