import 'dart:typed_data';

import 'package:desktop_drop/desktop_drop.dart';
import 'package:file_selector/file_selector.dart' as fs;
import 'package:flutter/foundation.dart' show kIsWeb;
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:pdf_signature/l10n/app_localizations.dart';

import '../../pdf/view_model/view_model.dart';
import '../../preferences/widgets/settings_screen.dart';

// Abstraction to make drop handling testable without constructing
// platform-specific DropItem types in widget tests.
abstract class DropReadable {
  String get name;
  String? get path; // may be null on some platforms
  Future<Uint8List> readAsBytes();
}

class _DropReadableFromDesktop implements DropReadable {
  final DropItemFile inner;
  _DropReadableFromDesktop(this.inner);
  @override
  String get name => inner.name;
  @override
  String? get path => inner.path;
  @override
  Future<Uint8List> readAsBytes() => inner.readAsBytes();
}

// Allow injecting Riverpod's read function from either WidgetRef or ProviderContainer
typedef Reader = T Function<T>(ProviderListenable<T> provider);

// Select first .pdf file (case-insensitive) or fall back to first entry.
Future<void> handleDroppedFiles(
  Reader read,
  Iterable<DropReadable> files,
) async {
  if (files.isEmpty) return;
  final pdf = files.firstWhere(
    (f) => (f.name.toLowerCase()).endsWith('.pdf'),
    orElse: () => files.first,
  );
  Uint8List? bytes;
  try {
    bytes = await pdf.readAsBytes();
  } catch (_) {
    bytes = null;
  }
  final String path = pdf.path ?? pdf.name;
  read(pdfProvider.notifier).openPicked(path: path, bytes: bytes);
  read(signatureProvider.notifier).resetForNewPage();
}

class WelcomeScreen extends ConsumerStatefulWidget {
  const WelcomeScreen({super.key});

  @override
  ConsumerState<WelcomeScreen> createState() => _WelcomeScreenState();
}

class _WelcomeScreenState extends ConsumerState<WelcomeScreen> {
  bool _dragging = false;

  Future<void> _pickPdf() async {
    final typeGroup = const fs.XTypeGroup(label: 'PDF', extensions: ['pdf']);
    final file = await fs.openFile(acceptedTypeGroups: [typeGroup]);
    if (file != null) {
      Uint8List? bytes;
      try {
        bytes = await file.readAsBytes();
      } catch (_) {
        bytes = null;
      }
      ref.read(pdfProvider.notifier).openPicked(path: file.path, bytes: bytes);
      ref.read(signatureProvider.notifier).resetForNewPage();
    }
  }

  @override
  Widget build(BuildContext context) {
    final l = AppLocalizations.of(context);
    final content = Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        Icon(
          Icons.picture_as_pdf,
          size: 64,
          color: Theme.of(context).hintColor,
        ),
        const SizedBox(height: 12),
        Text(
          l.noPdfLoaded,
          style: Theme.of(context).textTheme.titleMedium,
          textAlign: TextAlign.center,
        ),
        const SizedBox(height: 16),
        OutlinedButton.icon(
          key: const Key('btn_open_pdf_welcome'),
          onPressed: _pickPdf,
          icon: const Icon(Icons.folder_open),
          label: Text(l.openPdf),
        ),
      ],
    );

    // Use desktop_drop on desktop and mobile; web drag&drop not handled here
    final dropZone = DropTarget(
      enable: !kIsWeb,
      onDragEntered: (_) => setState(() => _dragging = true),
      onDragExited: (_) => setState(() => _dragging = false),
      onDragDone: (details) async {
        final desktopFiles = details.files.whereType<DropItemFile>();
        final adapters = desktopFiles.map<DropReadable>(
          (f) => _DropReadableFromDesktop(f),
        );
        await handleDroppedFiles(ref.read, adapters);
      },
      child: AnimatedContainer(
        duration: const Duration(milliseconds: 150),
        padding: const EdgeInsets.all(24),
        decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(12),
          border: Border.all(
            color:
                _dragging
                    ? Theme.of(context).colorScheme.primary
                    : Theme.of(context).dividerColor,
            width: 2,
          ),
          color:
              _dragging
                  ? Theme.of(context).colorScheme.primary.withOpacity(0.05)
                  : Colors.transparent,
        ),
        child: content,
      ),
    );

    return Scaffold(
      appBar: AppBar(
        title: Text(l.appTitle),
        actions: [
          IconButton(
            tooltip: l.settings,
            onPressed:
                () => showDialog<bool>(
                  context: context,
                  builder: (_) => const SettingsDialog(),
                ),
            icon: const Icon(Icons.settings),
          ),
        ],
      ),
      body: Center(
        child: ConstrainedBox(
          constraints: const BoxConstraints(maxWidth: 560),
          child: dropZone,
        ),
      ),
    );
  }
}