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

/// The floating nav bar used to slide off the bottom of the screen as the rider
/// moved down a list and come back when he reversed. That buys 66pt of list and
/// costs him the ability to change tab at all until he scrolls the other way —
/// on a long Activity list the only route out is a gesture he has to know
/// about. A control that vanishes is not a smaller control; it is a missing one.
///
/// It compacts instead: labels collapse, icons draw in, the pill narrows and
/// shortens, and every target stays on screen. This is Instagram's iOS tab bar.
///
/// `BottomPage` builds four real tab pages (Get controllers, SharedPreferences,
/// Geolocator, live fetches) and cannot be pumped in a unit test, so — as in
/// `card_stripe_layout_test.dart` — these pin the *idiom* rather than the
/// widget. Two halves, only one of them obvious:
///
///  • A `NotificationListener<ScrollNotification>` accumulates `scrollDelta`
///    from `ScrollUpdateNotification`. Deliberately not `UserScrollNotification`:
///    that fires when a drag *begins*, when `metrics.pixels` has barely moved,
///    so a distance threshold measured there compares an offset against itself
///    and never fires at all.
///
///  • The label collapses via `Align(heightFactor:)` inside a `ClipRect`, not a
///    fade. Fading alone leaves the label's height behind, so the bar cannot
///    actually get shorter — it shrinks around a blank line.
void main() {
  const barKey = ValueKey('nav');
  const labelKey = ValueKey('label');

  const double resting = 66;
  const double compactHeight = 46;

  /// The shell shape, with the same wiring `BottomPage` uses.
  Widget shell({
    required ValueNotifier<double> compact,
    required ValueNotifier<double> accum,
    bool scrollable = true,
  }) {
    return MaterialApp(
      home: ValueListenableBuilder<double>(
        valueListenable: compact,
        builder: (context, k, _) => Scaffold(
          body: NotificationListener<ScrollNotification>(
            onNotification: (n) {
              if (n.metrics.axis != Axis.vertical) return false;
              if (n.metrics.maxScrollExtent <= 0) {
                accum.value = 0;
                compact.value = 0;
                return false;
              }
              if (n is! ScrollUpdateNotification) return false;
              final delta = n.scrollDelta ?? 0;
              if (delta == 0) return false;
              accum.value =
                  (accum.value * delta > 0) ? accum.value + delta : delta;
              if (delta > 0 && compact.value == 0 && accum.value > 24) {
                accum.value = 0;
                compact.value = 1;
              } else if (delta < 0 && compact.value == 1 && accum.value < -6) {
                accum.value = 0;
                compact.value = 0;
              }
              return false;
            },
            child: ListView(
              children: [SizedBox(height: scrollable ? 3000 : 10)],
            ),
          ),
          bottomNavigationBar: SizedBox(
            key: barKey,
            height: resting + (compactHeight - resting) * k,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              mainAxisSize: MainAxisSize.min,
              children: [
                const Icon(Icons.home_rounded, size: 21),
                ClipRect(
                  child: Align(
                    alignment: Alignment.topCenter,
                    heightFactor: (1 - k).clamp(0.0, 1.0),
                    child: Opacity(
                      opacity: (1 - k * 1.8).clamp(0.0, 1.0),
                      child: const Text('Home', key: labelKey),
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }

  double barHeight(WidgetTester tester) =>
      tester.getSize(find.byKey(barKey)).height;

  testWidgets('scrolling down shrinks the bar; scrolling back restores it',
      (tester) async {
    final compact = ValueNotifier(0.0);
    final accum = ValueNotifier(0.0);
    addTearDown(compact.dispose);
    addTearDown(accum.dispose);
    await tester.pumpWidget(shell(compact: compact, accum: accum));

    expect(barHeight(tester), resting);

    // Finger bottom → up: the list scrolls forward, the bar draws in.
    await tester.drag(find.byType(ListView), const Offset(0, -300));
    await tester.pumpAndSettle();
    expect(barHeight(tester), compactHeight);

    // Finger top → down: he is heading back, so it returns to full size.
    await tester.drag(find.byType(ListView), const Offset(0, 300));
    await tester.pumpAndSettle();
    expect(barHeight(tester), resting);
  });

  testWidgets('the bar never leaves — the rider can always change tab',
      (tester) async {
    // This is the whole reason the behaviour changed. Whatever the rider does
    // with his thumb, the tab targets stay on screen and stay tappable.
    final compact = ValueNotifier(0.0);
    final accum = ValueNotifier(0.0);
    addTearDown(compact.dispose);
    addTearDown(accum.dispose);
    await tester.pumpWidget(shell(compact: compact, accum: accum));

    for (final drag in const [-300.0, -600.0, -1200.0]) {
      await tester.drag(find.byType(ListView), Offset(0, drag));
      await tester.pumpAndSettle();
      expect(barHeight(tester), greaterThanOrEqualTo(compactHeight),
          reason: 'the bar must never collapse past its compact height');
      expect(find.byType(Icon), findsOneWidget,
          reason: 'and its icons must stay on screen');
    }
  });

  testWidgets('the label collapses rather than merely fading', (tester) async {
    // A fade alone leaves the label's height behind, so the bar would shrink
    // around a blank line and never reach its compact height.
    final compact = ValueNotifier(0.0);
    final accum = ValueNotifier(0.0);
    addTearDown(compact.dispose);
    addTearDown(accum.dispose);
    await tester.pumpWidget(shell(compact: compact, accum: accum));

    final labelled = tester.getSize(find.byKey(labelKey)).height;
    expect(labelled, greaterThan(0));

    await tester.drag(find.byType(ListView), const Offset(0, -300));
    await tester.pumpAndSettle();

    // The Align is what gives the room back; the Text keeps its own size and is
    // clipped, so measuring the Text would report the same height either way.
    final align = tester.getSize(
      find.ancestor(of: find.byKey(labelKey), matching: find.byType(Align)).first,
    );
    expect(align.height, lessThan(1),
        reason: 'the label must hand its height back, not just go invisible');
  });

  testWidgets('a page too short to scroll never compacts the bar',
      (tester) async {
    final compact = ValueNotifier(0.0);
    final accum = ValueNotifier(0.0);
    addTearDown(compact.dispose);
    addTearDown(accum.dispose);
    await tester
        .pumpWidget(shell(compact: compact, accum: accum, scrollable: false));

    await tester.drag(find.byType(ListView), const Offset(0, -300));
    await tester.pumpAndSettle();
    expect(barHeight(tester), resting);
  });

  testWidgets('a horizontal scroll leaves the bar alone', (tester) async {
    // Tab strips and carousels scroll sideways; the nav bar is not theirs.
    final compact = ValueNotifier(0.0);
    addTearDown(compact.dispose);

    await tester.pumpWidget(
      MaterialApp(
        home: Scaffold(
          body: NotificationListener<ScrollNotification>(
            onNotification: (n) {
              if (n.metrics.axis != Axis.vertical) return false;
              compact.value = 1;
              return false;
            },
            child: ListView(
              scrollDirection: Axis.horizontal,
              children: [Container(width: 3000)],
            ),
          ),
        ),
      ),
    );

    await tester.drag(find.byType(ListView), const Offset(-300, 0));
    await tester.pumpAndSettle();
    expect(compact.value, 0);
  });
}