import 'dart:async';

import '../print/backend.dart';
import '../print/cups_backend.dart' show noopLog;
import '../utils/command_runner.dart';
import 'protocol.dart';

/// 打印队列中的单个任务运行时状态。
class PrintQueueTask {
  PrintQueueTask({required this.taskId, required this.request});

  final String taskId;
  final PrintRequest request;

  /// printing / done / error
  String state = 'printing';
  int status = 0;
  String error = '';
  DateTime? finishedAt;
}

/// 串行打印队列：打印机物理上一次只能打一张卡，任务逐个执行。
///
/// 任务状态存内存字典供前端轮询；完成后保留 30 分钟（对齐 C# 版 PrintQueue）。
class PrintQueue {
  PrintQueue(this._backend, {void Function(String line)? onLog}) : _log = onLog ?? noopLog {
    _cleanupTimer = Timer.periodic(const Duration(minutes: 5), (_) => _cleanupOld());
  }

  final PrintBackend _backend;
  final void Function(String line) _log;

  final _tasks = <String, PrintQueueTask>{};
  Future<void> _tail = Future.value();
  Timer? _cleanupTimer;
  int _seq = 0;

  /// 提交打印任务，立即返回 taskId。
  String submit(PrintRequest request) {
    if (request.front == null || request.front!.color.isEmpty) {
      throw ArgumentError('缺少正面卡面图（front.color）');
    }
    final task = PrintQueueTask(taskId: 't${++_seq}', request: request);
    _tasks[task.taskId] = task;
    // 串行链：每个任务等前一个完成后执行，异常在 _run 内消化，链条不中断
    _tail = _tail.then((_) => _run(task));
    return task.taskId;
  }

  PrintTaskDto? get(String taskId) {
    final task = _tasks[taskId];
    if (task == null) return null;
    return PrintTaskDto(taskId: task.taskId, state: task.state, status: task.status, statusText: task.error);
  }

  Future<void> _run(PrintQueueTask task) async {
    _log('[${task.taskId}] 开始打印（份数 ${task.request.copies}）');
    try {
      await _backend.printOneCard(task.request);
      task.state = 'done';
      _log('[${task.taskId}] 打印完成');
    } catch (e) {
      task.state = 'error';
      task.error = errorMessageOf(e);
      _log('[${task.taskId}] 打印失败：${task.error}');
    } finally {
      task.finishedAt = DateTime.now();
    }
  }

  /// 清掉已完成/失败超 30 分钟的任务，避免内存常驻增长。
  void _cleanupOld() {
    final now = DateTime.now();
    _tasks.removeWhere((_, task) =>
        task.finishedAt != null && now.difference(task.finishedAt!).inMinutes > 30);
  }

  void dispose() {
    _cleanupTimer?.cancel();
    _cleanupTimer = null;
  }

  /// 从任意异常里提取可读文案（前端 statusText 直接展示）。
  static String errorMessageOf(Object e) {
    if (e is CommandException) return e.message;
    try {
      final dynamic err = e;
      final msg = err.message;
      if (msg is String && msg.isNotEmpty) return msg;
    } catch (_) {}
    return e.toString();
  }
}