the-mews/app/lib/presentation/reader/reader_screen.dart

import 'dart:io' show Process;

import 'package:flutter/foundation.dart'
    show defaultTargetPlatform, TargetPlatform;
import 'package:url_launcher/url_launcher.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart' show ScrollDirection;
import 'package:flutter/services.dart' show LogicalKeyboardKey;
import 'package:signals/signals_flutter.dart' show SignalBuilder;

import '../../application/controllers/browser_controller.dart'
    show
        BrokenPage,
        CertificateChanged,
        ClientCertificateRequired,
        LoadFailed,
        ProtocolFailure,
        RedirectLoop,
        UnsupportedPage;
import '../../database/database.dart' show ClientCertificate;
import '../../application/pages/mews_urls.dart';
import '../../mews/document.dart';
import '../../mews/parser.dart' show mewsPlainText;
import '../app.dart';
import 'address_bar.dart';
import 'mews_page_view.dart';
import 'palettes.dart';
import 'swipe_navigator.dart';

/// The whole v1 UI: an address bar that hides on scroll, the page reader with
/// swipe back/forward, and error states that never guess.
class ReaderScreen extends StatefulWidget {
  const ReaderScreen({super.key});

  @override
  State<ReaderScreen> createState() => _ReaderScreenState();
}

class _ReaderScreenState extends State<ReaderScreen> {
  final _scroll = ScrollController();
  final _addressFocus = FocusNode();

  /// The address bar is on screen from the start, hidden while the reader
  /// scrolls down, back on any upward scroll. A pointer host with a keyboard
  /// has room to spare and keys to reach the bar, so it never hides.
  bool _chromeVisible = true;
  bool _showBrokenText = false;
  final _checkedSubscriptions = <String>{};

  /// Touch devices navigate with gestures; the others are pointer hosts
  /// whose readers reach the chrome with the mouse and the keyboard.
  static bool get _isTouch => switch (defaultTargetPlatform) {
        TargetPlatform.android || TargetPlatform.iOS => true,
        _ => false,
      };

  @override
  void initState() {
    super.initState();
    _scroll.addListener(_onScroll);
  }

  @override
  void dispose() {
    _scroll.removeListener(_onScroll);
    _scroll.dispose();
    _addressFocus.dispose();
    super.dispose();
  }

  void _onScroll() {
    // On a pointer host the bar stays on screen, so scrolling changes
    // nothing about it.
    if (!_isTouch) return;
    if (!_scroll.hasClients) return;
    final position = _scroll.position;

    // The bar hides when the reader scrolls down and comes back on any
    // upward scroll; it is always visible at the top of the page.
    final wantVisible = position.pixels <= 0 ||
        position.userScrollDirection == ScrollDirection.forward;

    if (wantVisible != _chromeVisible) {
      setState(() => _chromeVisible = wantVisible);
    }
  }

  @override
  Widget build(BuildContext context) {
    final deps = AppScope.of(context).deps;

    final reader = Scaffold(
      body: Column(
        children: [
          AnimatedSlide(
            offset: _chromeVisible ? Offset.zero : const Offset(0, -1),
            duration: const Duration(milliseconds: 200),
            curve: Curves.easeOut,
            child: AnimatedSize(
              duration: const Duration(milliseconds: 200),
              curve: Curves.easeOut,
              alignment: Alignment.topCenter,
              child: _chromeVisible
                  ? AddressBar(focusNode: _addressFocus)
                  : const SizedBox(width: double.infinity),
            ),
          ),
          Expanded(
            child: SignalBuilder(builder: (context) {
              final browser = deps.browser;
              final page = browser.currentPage.value;
              // The swipe peek uses the current page's palette when there is
              // one, so the neighbor slides in on matching paper.
              final peekBackground = page == null
                  ? Theme.of(context).scaffoldBackgroundColor
                  : paletteFor(
                      pageVariant: page.variant,
                      readerVariant: deps.settings.variant.value,
                      dark: Theme.of(context).brightness == Brightness.dark,
                      url: page.url,
                    ).background;

              // The 40em column plus its padding: swipes are accepted
              // anywhere in the margin beside it.
              final contentWidth =
                  42 * 17.0 * deps.settings.fontScale.value;

              return SwipeNavigator(
                canGoBack: browser.canGoBack,
                canGoForward: browser.canGoForward,
                backView: _neighborView(browser.backPage.value),
                forwardView: _neighborView(browser.forwardPage.value),
                backTitle: browser.backPage.value?.title,
                forwardTitle: browser.forwardPage.value?.title,
                background: peekBackground,
                contentWidth: page == null ? null : contentWidth,
                onBack: browser.back,
                onForward: browser.forward,
                child: Stack(
                  children: [
                    Positioned.fill(child: _body(context, page)),
                    if (browser.loading.value)
                      const Positioned(
                        top: 8,
                        left: 0,
                        right: 0,
                        child: LinearProgressIndicator(minHeight: 2),
                      ),
                  ],
                ),
              );
            }),
          ),
        ],
      ),
    );

    // A pointer host drives the reader from the keyboard as well: the bar
    // takes an address (Ctrl or Cmd+L, which selects what is in it), the page
    // reloads (Ctrl or Cmd+R), and the walk goes back and forward
    // (Alt+Left/Right, or Cmd+Left/Right and Cmd+[ and Cmd+] on a Mac).
    // Touch hosts navigate with gestures instead.
    if (_isTouch) return reader;
    return CallbackShortcuts(
      bindings: {
        const SingleActivator(LogicalKeyboardKey.keyL, control: true):
            _addressFocus.requestFocus,
        const SingleActivator(LogicalKeyboardKey.keyL, meta: true):
            _addressFocus.requestFocus,
        const SingleActivator(LogicalKeyboardKey.keyR, control: true):
            deps.browser.reload,
        const SingleActivator(LogicalKeyboardKey.keyR, meta: true):
            deps.browser.reload,
        const SingleActivator(LogicalKeyboardKey.arrowLeft, alt: true):
            deps.browser.back,
        const SingleActivator(LogicalKeyboardKey.arrowRight, alt: true):
            deps.browser.forward,
        // The same walk, with the keys a Mac reader reaches for.
        const SingleActivator(LogicalKeyboardKey.arrowLeft, meta: true):
            deps.browser.back,
        const SingleActivator(LogicalKeyboardKey.arrowRight, meta: true):
            deps.browser.forward,
        const SingleActivator(LogicalKeyboardKey.bracketLeft, meta: true):
            deps.browser.back,
        const SingleActivator(LogicalKeyboardKey.bracketRight, meta: true):
            deps.browser.forward,
      },
      // Key events reach only the focused branch, and a session starts with
      // nothing focused; this node gives them a place to arrive. Tapping the
      // address field or a control moves the focus deeper in, where the
      // shortcuts still apply.
      child: Focus(autofocus: true, skipTraversal: true, child: reader),
    );
  }

  Widget _body(BuildContext context, MewsPage? page) {
    final deps = AppScope.of(context).deps;

    if (page == null) {
      return SignalBuilder(builder: (context) {
        final error = deps.browser.error.value;
        return switch (error) {
          BrokenPage(:final source) => _errorPage(context, source),
          LoadFailed() => _errorPage(context, null),
          // A protocol status carries the site's own words for what went
          // wrong.
          ProtocolFailure(:final message) =>
            _plainErrorPage(context, 'error-protocol-failed', detail: message),
          // A certificate request is a choice, not a failure: the reader
          // presents one of their identities, or none. A refused or invalid
          // certificate is a failure the reader cannot fix by choosing again.
          ClientCertificateRequired(:final status, :final meta) => status == 60
              ? _identityPickerPage(context, meta)
              : _plainErrorPage(
                  context,
                  status == 61
                      ? 'error-certificate-not-authorized'
                      : 'error-certificate-invalid',
                  detail: meta),
          RedirectLoop() => _plainErrorPage(context, 'error-redirect-loop'),
          UnsupportedPage() => _plainErrorPage(context, 'error-unsupported-type'),
          CertificateChanged() => _certificateErrorPage(context),
          null => _emptyPage(context),
        };
      });
    }

    _checkSubscription(context, page);
    _showBrokenText = false;

    return SignalBuilder(builder: (context) {
      final settings = deps.settings;
      final font = settings.font.value;
      final fontScale = settings.fontScale.value;
      final variant = settings.variant.value;
      final visited = deps.browser.visitedUrls.value;

      final palette = paletteFor(
        pageVariant: page.variant,
        readerVariant: variant,
        dark: Theme.of(context).brightness == Brightness.dark,
        url: page.url,
      );
      return MewsPageView(
        key: ValueKey(page.url),
        page: page,
        ownPage: MewsUrls.isInternal(page.url),
        palette: palette,
        fontFamily: font,
        fontScale: fontScale,
        visitedUrls: visited,
        onLinkTap: (url) => deps.browser.open(url),
        onFormSubmit: (form, values) =>
            deps.browser.submitForm(form.action, form.method, values),
        fetchImageBytes: deps.browser.fetchImageBytes,
        scrollController: _scroll,
      );
    });
  }

  /// Renders a neighboring page for the swipe peek, non-interactive: it is a
  /// look ahead, and committing the navigation brings the real thing.
  Widget? _neighborView(MewsPage? page) {
    if (page == null) return null;
    final deps = AppScope.of(context).deps;
    final settings = deps.settings;
    final palette = paletteFor(
      pageVariant: page.variant,
      readerVariant: settings.variant.value,
      dark: Theme.of(context).brightness == Brightness.dark,
      url: page.url,
    );
    return ColoredBox(
      color: palette.background,
      child: MewsPageView(
        page: page,
        ownPage: MewsUrls.isInternal(page.url),
        palette: palette,
        fontFamily: settings.font.value,
        fontScale: settings.fontScale.value,
        visitedUrls: deps.browser.visitedUrls.value,
        onLinkTap: (_) {},
        onFormSubmit: (_, _) {},
      ),
    );
  }

  Widget _emptyPage(BuildContext context) {
    // No page yet: the address bar is the whole UI.
    return const SizedBox.expand();
  }

  /// An error page that says [messageId], optionally the site's own words
  /// under it, and offers to try again.
  Widget _plainErrorPage(BuildContext context, String messageId, {String? detail}) {
    final strings = AppScope.of(context).strings;
    final deps = AppScope.of(context).deps;
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(24),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text(strings.t(messageId), textAlign: TextAlign.center),
            if (detail != null && detail.isNotEmpty) ...[
              const SizedBox(height: 8),
              Text(detail, textAlign: TextAlign.center),
            ],
            const SizedBox(height: 16),
            FilledButton(
              onPressed: () => deps.browser.reload(),
              child: Text(strings.t('error-try-again')),
            ),
          ],
        ),
      ),
    );
  }

  /// The choice a certificate request asks for: one of the reader's
  /// identities, presented from now on to the site that asked.
  Widget _identityPickerPage(BuildContext context, String meta) {
    final strings = AppScope.of(context).strings;
    final deps = AppScope.of(context).deps;
    return FutureBuilder<List<ClientCertificate>>(
      future: deps.db.allClientCertificates(),
      builder: (context, snapshot) {
        final held = snapshot.data ?? const <ClientCertificate>[];
        return Center(
          child: SingleChildScrollView(
            child: Padding(
              padding: const EdgeInsets.all(24),
              child: Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  Text(strings.t('certificates-choose'), textAlign: TextAlign.center),
                  if (meta.isNotEmpty) ...[
                    const SizedBox(height: 8),
                    Text(meta, textAlign: TextAlign.center),
                  ],
                  const SizedBox(height: 16),
                  if (held.isEmpty)
                    FilledButton(
                      onPressed: () => deps.browser.open(MewsUrls.certificates),
                      child: Text(strings.t('certificates-add')),
                    )
                  else
                    for (final certificate in held)
                      Padding(
                        padding: const EdgeInsets.only(bottom: 8),
                        child: FilledButton.tonal(
                          onPressed: () => deps.browser.chooseCertificate(certificate.id),
                          child: Text(certificate.name),
                        ),
                      ),
                  const SizedBox(height: 8),
                  OutlinedButton(
                    onPressed: () => deps.browser.reload(),
                    child: Text(strings.t('error-try-again')),
                  ),
                ],
              ),
            ),
          ),
        );
      },
    );
  }

  /// A changed certificate is the reader's choice to make or refuse, so the
  /// error page carries both: trust what was presented, or try again.
  Widget _certificateErrorPage(BuildContext context) {
    final strings = AppScope.of(context).strings;
    final deps = AppScope.of(context).deps;
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(24),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text(strings.t('error-certificate-changed'), textAlign: TextAlign.center),
            const SizedBox(height: 16),
            FilledButton(
              onPressed: () => deps.browser.trustPresentedCertificate(),
              child: Text(strings.t('error-certificate-trust')),
            ),
            const SizedBox(height: 8),
            OutlinedButton(
              onPressed: () => deps.browser.reload(),
              child: Text(strings.t('error-try-again')),
            ),
          ],
        ),
      ),
    );
  }

  /// Hands [url] to the system's web browser. The reader does not watch
  /// what happens to it there, and a system with no browser answers nothing
  /// rather than failing here.
  ///
  /// The launcher asks GIO on Linux, which can fail to see the session's
  /// browser from the environment the app runs in, and a binary built before
  /// the launcher was added answers not at all; in both cases xdg-open asks
  /// the session directly.
  Future<void> _openOutside(String url) async {
    final uri = Uri.tryParse(url);
    if (uri == null) return;

    var opened = false;
    try {
      opened = await launchUrl(uri, mode: LaunchMode.externalApplication);
    } on Exception {
      // No answer; the fallback below asks the session itself.
    }
    if (opened) return;

    if (defaultTargetPlatform == TargetPlatform.linux) {
      final result = await Process.run('xdg-open', [url]);
      // A missing xdg-open or a session without a browser answers with an
      // error; nothing more to do but stay where we are.
      if (result.exitCode != 0) return;
    }
  }

  Widget _errorPage(BuildContext context, String? brokenSource) {
    final strings = AppScope.of(context).strings;
    final deps = AppScope.of(context).deps;

    // A web address can be shown by the system's browser, so a page that
    // will not load here can leave; a protocol page has nowhere else to go,
    // so only trying again is offered there.
    final failed = deps.browser.currentAddress;
    final failedScheme = Uri.tryParse(failed)?.scheme;
    final canOpenOutside =
        brokenSource == null && (failedScheme == 'http' || failedScheme == 'https');

    Widget content;
    if (brokenSource == null) {
      content = Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          Text(strings.t('error-load-failed'), textAlign: TextAlign.center),
          const SizedBox(height: 16),
          FilledButton(
            onPressed: () => deps.browser.reload(),
            child: Text(strings.t('error-try-again')),
          ),
          if (canOpenOutside) ...[
            const SizedBox(height: 8),
            OutlinedButton(
              onPressed: () => _openOutside(failed),
              child: Text(strings.t('error-open-in-browser')),
            ),
          ],
        ],
      );
    } else if (_showBrokenText) {
      content = Column(
        children: [
          Text(strings.t('error-broken-page-text-title'),
              style: Theme.of(context).textTheme.titleMedium),
          const SizedBox(height: 8),
          Expanded(child: SingleChildScrollView(child: Text(mewsPlainText(brokenSource)))),
        ],
      );
    } else {
      content = Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          Text(strings.t('error-broken-page'), textAlign: TextAlign.center),
          const SizedBox(height: 16),
          FilledButton(
            onPressed: () => setState(() => _showBrokenText = true),
            child: Text(strings.t('error-broken-page-show-text')),
          ),
        ],
      );
    }

    return Center(
      child: Padding(
        padding: const EdgeInsets.all(24),
        child: content,
      ),
    );
  }

  /// Records the posts of a subscribed page once per page load, so what is new
  /// shows up on the subscriptions and posts pages (spec 6.1). The controller
  /// no-ops for a page the reader is not subscribed to.
  void _checkSubscription(BuildContext context, MewsPage page) {
    if (_checkedSubscriptions.contains(page.url)) return;
    _checkedSubscriptions.add(page.url);
    final deps = AppScope.of(context).deps;
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (mounted) deps.subscriptions.refreshSite(page);
    });
  }
}