movie_item.dart

// Copyright 2022, the Chromium project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

// ignore_for_file: avoid_print

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'movie.dart';

/// A single movie row.
class MovieItem extends StatelessWidget {
  MovieItem(this.movie, this.reference, {Key? key}) : super(key: key);

  final Movie movie;
  final MovieDocumentReference reference;

  /// Returns the movie poster.
  Widget get poster {
    return SizedBox(
      width: 100,
      child: Image.network(movie.poster),
    );
  }

  /// Returns movie details.
  Widget get details {
    return Padding(
      padding: const EdgeInsets.only(left: 8, right: 8),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          title,
          metadata,
          genres,
          Likes(
            reference: reference,
            currentLikes: movie.likes,
          ),
        ],
      ),
    );
  }

  /// Return the movie title.
  Widget get title {
    return Text(
      '${movie.title} (${movie.year})',
      style: const TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
    );
  }

  /// Returns metadata about the movie.
  Widget get metadata {
    return Padding(
      padding: const EdgeInsets.only(top: 8),
      child: Row(
        children: [
          Padding(
            padding: const EdgeInsets.only(right: 8),
            child: Text('Rated: ${movie.rated}'),
          ),
          Text('Runtime: ${movie.runtime}'),
        ],
      ),
    );
  }

  /// Returns a list of genre movie tags.
  List<Widget> get genreItems {
    return [
      for (final genre in movie.genre ?? <String>[])
        Padding(
          padding: const EdgeInsets.only(right: 2),
          child: Chip(
            backgroundColor: Colors.lightBlue,
            label: Text(
              genre,
              style: const TextStyle(color: Colors.white),
            ),
          ),
        ),
    ];
  }

  /// Returns all genres.
  Widget get genres {
    return Padding(
      padding: const EdgeInsets.only(top: 8),
      child: Wrap(
        children: genreItems,
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.only(bottom: 4, top: 4),
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          poster,
          Flexible(child: details),
        ],
      ),
    );
  }
}

/// Displays and manages the movie 'like' count.
class Likes extends StatefulWidget {
  /// Constructs a new [Likes] instance with a given [DocumentReference] and
  /// current like count.
  Likes({
    Key? key,
    required this.reference,
    required this.currentLikes,
  }) : super(key: key);

  /// The reference relating to the counter.
  final MovieDocumentReference reference;

  /// The number of current likes (before manipulation).
  final int currentLikes;

  @override
  // ignore: library_private_types_in_public_api
  _LikesState createState() => _LikesState();
}

class _LikesState extends State<Likes> {
  /// A local cache of the current likes, used to immediately render the updated
  /// likes count after an update, even while the request isn't completed yet.
  late int _likes = widget.currentLikes;

  Future<void> _onLike() async {
    final currentLikes = _likes;

    // Increment the 'like' count straight away to show feedback to the user.
    setState(() {
      _likes = currentLikes + 1;
    });

    try {
      // Update the likes using a transaction.
      // We use a transaction because multiple users could update the likes count
      // simultaneously. As such, our likes count may be different from the likes
      // count on the server.
      final newLikes = await FirebaseFirestore.instance
          .runTransaction<int>((transaction) async {
        final movie = await widget.reference.transactionGet(transaction);

        if (!movie.exists) {
          throw Exception('Document does not exist!');
        }

        final updatedLikes = movie.data!.likes + 1;
        widget.reference.transactionUpdate(
          transaction,
          likes: updatedLikes,
        );
        return updatedLikes;
      });

      // Update with the real count once the transaction has completed.
      setState(() => _likes = newLikes);
    } catch (e, s) {
      print(s);
      print('Failed to update likes for document! $e');

      // If the transaction fails, revert back to the old count
      setState(() => _likes = currentLikes);
    }
  }

  @override
  void didUpdateWidget(Likes oldWidget) {
    super.didUpdateWidget(oldWidget);
    // The likes on the server changed, so we need to update our local cache to
    // keep things in sync. Otherwise if another user updates the likes,
    // we won't see the update.
    if (widget.currentLikes != oldWidget.currentLikes) {
      _likes = widget.currentLikes;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        IconButton(
          iconSize: 20,
          onPressed: _onLike,
          icon: const Icon(Icons.favorite),
        ),
        Text('$_likes likes'),
      ],
    );
  }
}