import 'dart:convert';

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:shared_preferences/shared_preferences.dart';

const String _llmDiagnosticsLogKey = 'llm_diagnostics_log_v1';
const int _maxLlmDiagnosticsEvents = 40;
const int _maxLlmDiagnosticsDetailChars = 8000;

class LlmDiagnosticsEvent {
  const LlmDiagnosticsEvent({
    required this.at,
    required this.stage,
    required this.message,
    this.details,
  });

  factory LlmDiagnosticsEvent.fromJson(Map<String, dynamic> json) {
    return LlmDiagnosticsEvent(
      at: DateTime.parse(
        json['at'] as String? ?? DateTime.now().toUtc().toIso8601String(),
      ).toLocal(),
      stage: json['stage'] as String? ?? 'unknown',
      message: json['message'] as String? ?? '',
      details: json['details'] as String?,
    );
  }

  final DateTime at;
  final String stage;
  final String message;
  final String? details;

  Map<String, dynamic> toJson() {
    return <String, dynamic>{
      'at': at.toUtc().toIso8601String(),
      'stage': stage,
      'message': message,
      if (details != null) 'details': details,
    };
  }
}

class LlmDiagnosticsLog {
  const LlmDiagnosticsLog();

  Future<List<LlmDiagnosticsEvent>> read() async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    final String? raw = prefs.getString(_llmDiagnosticsLogKey);
    if (raw == null || raw.isEmpty) {
      return const <LlmDiagnosticsEvent>[];
    }
    try {
      final List<dynamic> items = jsonDecode(raw) as List<dynamic>;
      return items
          .whereType<Map<String, dynamic>>()
          .map(LlmDiagnosticsEvent.fromJson)
          .toList(growable: false);
    } on FormatException {
      return const <LlmDiagnosticsEvent>[];
    }
  }

  Future<void> record(String stage, String message, {String? details}) async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    final List<LlmDiagnosticsEvent> current = await read();
    final List<LlmDiagnosticsEvent> next = <LlmDiagnosticsEvent>[
      LlmDiagnosticsEvent(
        at: DateTime.now(),
        stage: stage,
        message: message,
        details: _compactDetails(details),
      ),
      ...current,
    ].take(_maxLlmDiagnosticsEvents).toList(growable: false);
    await prefs.setString(
      _llmDiagnosticsLogKey,
      jsonEncode(
        next
            .map((LlmDiagnosticsEvent event) => event.toJson())
            .toList(growable: false),
      ),
    );
  }

  Future<void> clear() async {
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.remove(_llmDiagnosticsLogKey);
  }

  String exportText(List<LlmDiagnosticsEvent> events) {
    if (events.isEmpty) {
      return 'No LLM diagnostics recorded.';
    }
    return events
        .map((LlmDiagnosticsEvent event) {
          final String details = event.details == null
              ? ''
              : '\n${event.details}';
          return '[${event.at.toIso8601String()}] ${event.stage}: ${event.message}$details';
        })
        .join('\n\n');
  }
}

final Provider<LlmDiagnosticsLog> llmDiagnosticsLogProvider =
    Provider<LlmDiagnosticsLog>((Ref ref) => const LlmDiagnosticsLog());

String? _compactDetails(String? value) {
  final String? trimmed = value?.trim();
  if (trimmed == null || trimmed.isEmpty) {
    return null;
  }
  if (trimmed.length <= _maxLlmDiagnosticsDetailChars) {
    return trimmed;
  }
  return '${trimmed.substring(0, _maxLlmDiagnosticsDetailChars)}\n[truncated]';
}