import 'dart:math';
import 'dart:typed_data';

enum FeedbackKind { problem, development }

class FeedbackException implements Exception {
  const FeedbackException(this.message);
  final String message;
  @override
  String toString() => message;
}

class FeedbackDeliveryUncertain extends FeedbackException {
  const FeedbackDeliveryUncertain(this.submissionId) : super(instructions);
  final String submissionId;
  static const instructions =
      '邮件可能已经发送，但结果尚未确认。请先联系开发者按提交编号核对收件箱；确认前请勿修改内容后重新提交或创建新反馈。';
}

abstract interface class FeedbackSender {
  /// Completes only when the server confirms acceptance. Use [FeedbackSubmission.id]
  /// as the server's idempotency key so retrying a timed-out request is safe.
  Future<void> send(FeedbackSubmission submission);
}

class UnconfiguredFeedbackSender implements FeedbackSender {
  const UnconfiguredFeedbackSender();
  static const message = '反馈服务暂未配置，暂时无法提交。你的填写内容已保留，请稍后再试。';
  @override
  Future<void> send(FeedbackSubmission submission) async {
    throw const FeedbackException(message);
  }
}

class FeedbackLimits {
  const FeedbackLimits({
    this.maxAttachments = 3,
    this.maxFileBytes = 8 * 1024 * 1024,
    this.maxTotalBytes = 20 * 1024 * 1024,
  });
  final int maxAttachments;
  final int maxFileBytes;
  final int maxTotalBytes;
  static const defaults = FeedbackLimits();
}

class FeedbackAttachment {
  FeedbackAttachment._(this.filename, this.contentType, Uint8List bytes)
    : bytes = bytes.asUnmodifiableView();

  final String filename;
  final String contentType;
  final Uint8List bytes;
  int get size => bytes.length;

  static const supportedTypes = {
    'jpg': 'image/jpeg',
    'jpeg': 'image/jpeg',
    'png': 'image/png',
    'gif': 'image/gif',
    'webp': 'image/webp',
    'heic': 'image/heic',
    'mp4': 'video/mp4',
    'mov': 'video/quicktime',
    'm4v': 'video/x-m4v',
    'webm': 'video/webm',
  };

  static Future<FeedbackAttachment> read({
    required String name,
    required Stream<List<int>> stream,
    int maxBytes = 8 * 1024 * 1024,
  }) async {
    final basename = name.replaceAll('\\', '/').split('/').last;
    final safeName = basename
        .replaceAll(RegExp(r'[\x00-\x1f\x7f<>:"/\\|?*]'), '')
        .trim();
    final extension = safeName.split('.').last.toLowerCase();
    final type = supportedTypes[extension];
    if (type == null || safeName.length > 150) {
      throw const FeedbackException('请选择受支持的图片或视频，文件名应少于 150 个字符');
    }
    final buffer = BytesBuilder(copy: false);
    var count = 0;
    await for (final chunk in stream) {
      count += chunk.length;
      if (count > maxBytes) {
        throw FeedbackException('单个附件不能超过 ${_megabytes(maxBytes)} MB');
      }
      buffer.add(chunk);
    }
    if (count == 0) throw const FeedbackException('不能添加空文件');
    return FeedbackAttachment._(safeName, type, buffer.takeBytes());
  }
}

class FeedbackSubmission {
  FeedbackSubmission._({
    required this.id,
    required this.kind,
    this.message,
    this.contact,
    this.school,
    this.attachments = const [],
    this.diagnosticLog,
  });

  factory FeedbackSubmission.problem({
    required String id,
    required String message,
    String? contact,
    List<FeedbackAttachment> attachments = const [],
    FeedbackLimits limits = FeedbackLimits.defaults,
    Uint8List? diagnosticLog,
  }) {
    final text = message.trim();
    if (text.isEmpty) throw const FeedbackException('请填写问题或建议');
    if (text.length > 5000) throw const FeedbackException('问题或建议不能超过 5000 个字符');
    _validateContact(contact);
    validateAttachments(attachments, limits);
    if (diagnosticLog != null &&
        (diagnosticLog.isEmpty || diagnosticLog.length > 256 * 1024)) {
      throw const FeedbackException('日志附件不能超过256 KB');
    }
    return FeedbackSubmission._(
      id: id,
      kind: FeedbackKind.problem,
      message: text,
      contact: _optional(contact),
      attachments: List.unmodifiable(attachments),
      diagnosticLog: diagnosticLog == null
          ? null
          : Uint8List.fromList(diagnosticLog).asUnmodifiableView(),
    );
  }

  factory FeedbackSubmission.development({
    required String id,
    required String school,
    required String contact,
  }) {
    final schoolName = school.trim();
    if (schoolName.isEmpty) throw const FeedbackException('请填写学校');
    if (schoolName.length > 200) {
      throw const FeedbackException('学校名称不能超过 200 个字符');
    }
    if (contact.trim().isEmpty) throw const FeedbackException('请填写联系方式');
    _validateContact(contact);
    return FeedbackSubmission._(
      id: id,
      kind: FeedbackKind.development,
      school: schoolName,
      contact: contact.trim(),
    );
  }

  final String id;
  final FeedbackKind kind;
  final String? message;
  final String? contact;
  final String? school;
  final List<FeedbackAttachment> attachments;
  final Uint8List? diagnosticLog;

  static String newId() {
    final random = Random.secure();
    return List.generate(
      16,
      (_) => random.nextInt(256).toRadixString(16).padLeft(2, '0'),
    ).join();
  }

  static void validateAttachments(
    List<FeedbackAttachment> files,
    FeedbackLimits limits,
  ) {
    if (files.length > limits.maxAttachments) {
      throw FeedbackException('最多添加 ${limits.maxAttachments} 个附件');
    }
    if (files.any((file) => file.size > limits.maxFileBytes)) {
      throw FeedbackException('单个附件不能超过 ${_megabytes(limits.maxFileBytes)} MB');
    }
    if (files.fold<int>(0, (total, file) => total + file.size) >
        limits.maxTotalBytes) {
      throw FeedbackException(
        '附件总大小不能超过 ${_megabytes(limits.maxTotalBytes)} MB',
      );
    }
  }

  static String? _optional(String? value) =>
      value == null || value.trim().isEmpty ? null : value.trim();
  static void _validateContact(String? contact) {
    if ((contact?.trim().length ?? 0) > 200) {
      throw const FeedbackException('联系方式不能超过 200 个字符');
    }
  }
}

String _megabytes(int bytes) => (bytes / (1024 * 1024)).toStringAsFixed(0);