packages/flutter/lib/src/material/bottom_app_bar.dart

// Copyright 2018 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/foundation.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';

import 'material.dart';
import 'scaffold.dart';
import 'theme.dart';

// Examples can assume:
// Widget bottomAppBarContents;

/// A container that is typically used with [Scaffold.bottomNavigationBar], and
/// can have a notch along the top that makes room for an overlapping
/// [FloatingActionButton].
///
/// Typically used with a [Scaffold] and a [FloatingActionButton].
///
/// ## Sample code
///
/// ```dart
/// new Scaffold(
///   bottomNavigationBar: new BottomAppBar(
///     color: Colors.white,
///     child: bottomAppBarContents,
///   ),
///   floatingActionButton: new FloatingActionButton(onPressed: null),
/// )
/// ```
///
/// See also:
///
///  * [ComputeNotch] a function used for creating a notch in a shape.
///  * [ScaffoldGeometry.floatingActionBarComputeNotch] the [ComputeNotch] used to
///    make a notch for the [FloatingActionButton]
///  * [FloatingActionButton] which the [BottomAppBar] makes a notch for.
///  * [AppBar] for a toolbar that is shown at the top of the screen.
class BottomAppBar extends StatefulWidget {
  /// Creates a bottom application bar.
  ///
  /// The [color] and [elevation] arguments must not be null.
  const BottomAppBar({
    Key key,
    this.color,
    this.elevation = 8.0,
    this.shape,
    this.notchMargin = 4.0,
    this.child,
  }) : assert(elevation != null),
       assert(elevation >= 0.0),
       super(key: key);

  /// The widget below this widget in the tree.
  ///
  /// {@macro flutter.widgets.child}
  ///
  /// Typically this the child will be a [Row], with the first child
  /// being an [IconButton] with the [Icons.menu] icon.
  final Widget child;

  /// The bottom app bar's background color.
  ///
  /// When null defaults to [ThemeData.bottomAppBarColor].
  final Color color;

  /// The z-coordinate at which to place this bottom app bar. This controls the
  /// size of the shadow below the bottom app bar.
  ///
  /// Defaults to 8, the appropriate elevation for bottom app bars.
  final double elevation;

  /// The notch that is made for the floating action button.
  ///
  /// If null the bottom app bar will be rectangular with no notch.
  final NotchedShape shape;

  /// The margin between the [FloatingActionButton] and the [BottomAppBar]'s
  /// notch.
  ///
  /// Not used if [shape] is null.
  final double notchMargin;

  @override
  State createState() => new _BottomAppBarState();
}

class _BottomAppBarState extends State<BottomAppBar> {
  ValueListenable<ScaffoldGeometry> geometryListenable;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    geometryListenable = Scaffold.geometryOf(context);
  }

  @override
  Widget build(BuildContext context) {
    final CustomClipper<Path> clipper = widget.shape != null
      ? new _BottomAppBarClipper(
        geometry: geometryListenable,
        shape: widget.shape,
        notchMargin: widget.notchMargin,
      )
      : const ShapeBorderClipper(shape: const RoundedRectangleBorder());
    return new PhysicalShape(
      clipper: clipper,
      elevation: widget.elevation,
      color: widget.color ?? Theme.of(context).bottomAppBarColor,
      child: new Material(
        type: MaterialType.transparency,
        child: widget.child == null
          ? null
          : new SafeArea(child: widget.child),
      ),
    );
  }
}

class _BottomAppBarClipper extends CustomClipper<Path> {
  const _BottomAppBarClipper({
    @required this.geometry,
    @required this.shape,
    @required this.notchMargin,
  }) : assert(geometry != null),
       assert(shape != null),
       assert(notchMargin != null),
       super(reclip: geometry);

  final ValueListenable<ScaffoldGeometry> geometry;
  final NotchedShape shape;
  final double notchMargin;

  @override
  Path getClip(Size size) {
    final Rect appBar = Offset.zero & size;
    if (geometry.value.floatingActionButtonArea == null) {
      return new Path()..addRect(appBar);
    }

    // button is the floating action button's bounding rectangle in the
    // coordinate system that origins at the appBar's top left corner.
    final Rect button = geometry.value.floatingActionButtonArea
      .translate(0.0, geometry.value.bottomNavigationBarTop * -1.0);

    return shape.getOuterPath(appBar, button.inflate(notchMargin));
  }

  @override
  bool shouldReclip(_BottomAppBarClipper oldClipper) => oldClipper.geometry != geometry;
}