relatica/lib/riverpod_controllers/networking/link_preview_services.dart

import 'dart:convert';

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:html/parser.dart';
import 'package:result_monad/result_monad.dart';
import 'package:riverpod_annotation/riverpod_annotation.dart';

import '../../models/exec_error.dart';
import '../../models/link_preview_data.dart';
import '../rp_provider_extension.dart';
import 'network_services.dart';

part 'link_preview_services.g.dart';

const ogTitleKey = 'og:title';
const ogDescriptionKey = 'og:description';
const ogSiteNameKey = 'og:site_name';
const ogImageKey = 'og:image';

@riverpod
Future<Result<LinkPreviewData, ExecError>> linkPreview(
    Ref ref, String url) async {
  return await ref.read(_openGraphDataProvider(url).future).transform((ogData) {
    final title = ogData.getValue(ogTitleKey);
    final description = ogData.getValue(ogDescriptionKey);
    final siteName = ogData.getValue(ogSiteNameKey);
    final availableImageUrls = ogData.getValues(ogImageKey);
    final selectedImageUrl =
        availableImageUrls.isEmpty ? '' : availableImageUrls.first;
    return LinkPreviewData(
      link: url,
      title: title,
      description: description,
      siteName: siteName,
      availableImageUrls: availableImageUrls,
      selectedImageUrl: selectedImageUrl,
    );
  }).execErrorCastAsync();
}

@riverpod
Future<Result<List<MapEntry<String, String>>, ExecError>> _openGraphData(
    Ref ref, String url) async {
  ref.cacheFor(const Duration(minutes: 5));
  final headers = ref.watch(userAgentHeaderProvider);
  final request = NetworkRequest(Uri.parse(url), headers: headers);
  return await ref
      .read(httpGetRawBytesProvider(request).future)
      .transform((bodyBytes) {
    final rawHtml = utf8.decode(bodyBytes);
    final htmlDoc = parse(rawHtml);
    final openGraphTags = htmlDoc.head
        ?.querySelectorAll("[property*='og:']")
        .map((p) {
          final key = p.attributes['property'] ?? '';
          final value = p.attributes['content'] ?? '';
          return MapEntry(key, value);
        })
        .where((e) => e.key.isNotEmpty)
        .toList();
    return openGraphTags ?? [];
  }).mapError((error) {
    final type = error is ExecError ? error.type : ErrorType.serverError;
    final message = error is ExecError
        ? 'Error getting link preview: ${error.message}'
        : 'Error getting link preview';
    return ExecError(type: type, message: message);
  });
}

extension OpenGraphFinders on List<MapEntry<String, String>> {
  String getValue(String key) {
    return firstWhere(
      (e) => e.key == key,
      orElse: () => const MapEntry('', ''),
    ).value;
  }

  List<String> getValues(String key) {
    return where((e) => e.key == key).map((e) => e.value).toList();
  }
}