import 'dart:convert';

/// Reassembles SSE / text lines that TCP may split across chunks.
Stream<String> splitSseLines(Stream<String> input) async* {
  final buf = StringBuffer();
  await for (final chunk in input) {
    buf.write(chunk);
    var text = buf.toString();
    final parts = text.split('\n');
    buf
      ..clear()
      ..write(parts.removeLast());
    for (final part in parts) {
      yield part.endsWith('\r') ? part.substring(0, part.length - 1) : part;
    }
  }
  if (buf.isNotEmpty) {
    final rest = buf.toString();
    yield rest.endsWith('\r') ? rest.substring(0, rest.length - 1) : rest;
  }
}

/// Pulls visible assistant text out of one SSE `data:` payload.
String? extractSseContent(String data) {
  final trimmed = data.trim();
  if (trimmed.isEmpty || trimmed == '[DONE]' || trimmed == 'null') return null;
  if (trimmed.startsWith('[DONE]')) return null;

  dynamic decoded;
  try {
    decoded = jsonDecode(trimmed);
  } catch (_) {
    // Plain-text SSE (Yqcloud / TeachAnything style).
    if (looksLikeJson(trimmed)) return null;
    return trimmed;
  }

  if (decoded is String) {
    return decoded.isEmpty ? null : decoded;
  }
  if (decoded is! Map) return null;

  final map = Map<String, dynamic>.from(decoded);
  if (map['action'] == 'error' || map['error'] != null) {
    final err = map['error'] ?? map['type'] ?? map['message'];
    throw Exception('SSE error: $err');
  }

  // Duck.ai
  final duck = map['message'];
  if (duck is String && duck.isNotEmpty && map['role'] != 'user') {
    return duck;
  }

  // OpenAI chat.completions streaming
  final choices = map['choices'];
  if (choices is List && choices.isNotEmpty) {
    final choice = choices.first;
    if (choice is Map) {
      final delta = choice['delta'];
      if (delta is Map) {
        final content = delta['content'];
        if (content is String && content.isNotEmpty) return content;
      }
      final message = choice['message'];
      if (message is Map) {
        final content = message['content'];
        if (content is String && content.isNotEmpty) return content;
      }
      final text = choice['text'];
      if (text is String && text.isNotEmpty) return text;
    }
  }

  // GLM / z.ai
  if (map['type'] == 'chat:completion') {
    final inner = map['data'];
    if (inner is Map) {
      final err = inner['error'];
      if (err != null) {
        throw Exception('SSE error: $err');
      }
      final phase = inner['phase'];
      if (phase == 'thinking') return null;
      final delta = inner['delta_content'];
      if (delta is String && delta.isNotEmpty && phase != 'thinking') {
        return delta;
      }
      final edit = inner['edit_content'];
      if (edit is String && edit.isNotEmpty) {
        return edit.split('\n</details>\n').last;
      }
    }
  }

  final content = map['content'];
  if (content is String && content.isNotEmpty) return content;

  return null;
}

String? extractOpenAiMessage(String body) {
  final trimmed = body.trim();
  if (trimmed.isEmpty) return null;
  try {
    final decoded = jsonDecode(trimmed);
    if (decoded is Map) {
      if (decoded['error'] != null) {
        throw Exception('API error: ${decoded['error']}');
      }
      final choices = decoded['choices'];
      if (choices is List && choices.isNotEmpty) {
        final choice = choices.first;
        if (choice is Map) {
          final message = choice['message'];
          if (message is Map && message['content'] is String) {
            return message['content'] as String;
          }
          if (choice['text'] is String) return choice['text'] as String;
        }
      }
      if (decoded['output_text'] is String) {
        return decoded['output_text'] as String;
      }
    }
  } catch (e) {
    if (e.toString().startsWith('Exception: API error')) rethrow;
  }
  return null;
}

bool looksLikeJson(String text) {
  final t = text.trimLeft();
  return t.startsWith('{') || t.startsWith('[');
}

/// Parses a full SSE document (e.g. WebView returning response.text()).
Iterable<String> extractAllSseContent(String raw) sync* {
  for (final line in raw.split(RegExp(r'\r?\n'))) {
    final trimmed = line.trim();
    if (trimmed.isEmpty) continue;
    if (trimmed.startsWith('event:')) continue;
    String data = trimmed;
    if (trimmed.startsWith('data:')) {
      data = trimmed.substring(5).trim();
    }
    final content = extractSseContent(data);
    if (content != null && content.isNotEmpty) yield content;
  }
}