TagesByte/lib/services/summarizer.dart

import '../models/article.dart';
import '../models/briefing.dart';
import '../models/source.dart';

class SummarizerException implements Exception {
  SummarizerException(this.message);

  final String message;

  @override
  String toString() => message;
}

/// Something that can turn articles into summaries. Implemented by the
/// direct Claude API client and by the n8n webhook bridge.
abstract class Summarizer {
  String get name;

  Future<String> summarizeArticle(Article article, String text, SourceLanguage language);

  Future<DailyBriefing> createBriefing(List<Article> articles, SourceLanguage language);
}

/// Shared prompt material and response mapping for all summarizers.
class BriefingInput {
  BriefingInput(List<Article> articles)
      : byId = {for (var i = 0; i < articles.length; i++) 'a${i + 1}': articles[i]};

  /// Short ids keep the prompt compact and are easy for the model to cite.
  final Map<String, Article> byId;

  static const excerptChars = 220;

  String toPromptList() {
    final buffer = StringBuffer();
    byId.forEach((id, a) {
      final excerpt = a.excerpt.length > excerptChars
          ? '${a.excerpt.substring(0, excerptChars)}…'
          : a.excerpt;
      buffer.writeln('[$id] (${a.source.name}) ${a.title}'
          '${excerpt.isEmpty ? '' : ' — $excerpt'}');
    });
    return buffer.toString();
  }

  List<Map<String, dynamic>> toJsonList() => [
        for (final e in byId.entries)
          {
            'id': e.key,
            'title': e.value.title,
            'url': e.value.link,
            'source': e.value.source.name,
            'language': e.value.source.language.name,
            'published': e.value.published?.toIso8601String(),
            'excerpt': e.value.excerpt,
          }
      ];

  /// Maps `{intro, topics: [{title, summary, article_ids}]}` onto a briefing.
  DailyBriefing toBriefing(Map<String, dynamic> json, String generatedBy) {
    final topics = (json['topics'] as List? ?? []).map((t) {
      final topic = t as Map<String, dynamic>;
      final ids = (topic['article_ids'] as List? ?? []).cast<String>();
      return BriefingTopic(
        title: topic['title'] as String? ?? '',
        summary: topic['summary'] as String? ?? '',
        sources: [
          for (final id in ids)
            if (byId[id] != null)
              ArticleRef(
                title: byId[id]!.title,
                url: byId[id]!.link,
                sourceName: byId[id]!.source.name,
              ),
        ],
      );
    }).toList();
    return DailyBriefing(
      createdAt: DateTime.now(),
      intro: json['intro'] as String? ?? '',
      topics: topics,
      generatedBy: generatedBy,
    );
  }
}

String languageName(SourceLanguage language) =>
    language == SourceLanguage.de ? 'German' : 'English';