import 'dart:io';

import 'package:path_provider/path_provider.dart';

/// 生图流程创建任务后，按接口返回的 `tree`（任务 id）将用户上传的压缩图存一份到本地；
/// Gallery 在接口未返回封面 URL 时可用其作为卡片底图。
abstract final class GalleryUploadCoverStore {
  static const String _subdir = 'gallery_upload_covers';
  static const String _fileExt = '.jpg';

  /// 本地封面最多保留时长，超时文件会在下次读/写前删除。
  static const Duration maxRetention = Duration(hours: 25);

  static Future<Directory> _directory() async {
    final base = await getApplicationSupportDirectory();
    final dir = Directory('${base.path}/$_subdir');
    if (!await dir.exists()) {
      await dir.create(recursive: true);
    }
    return dir;
  }

  static Future<Directory> _directoryAfterPurge() async {
    final dir = await _directory();
    await _purgeExpired(dir);
    return dir;
  }

  static Future<void> _purgeExpired(Directory dir) async {
    if (!await dir.exists()) return;
    final now = DateTime.now();
    try {
      await for (final entity in dir.list(followLinks: false)) {
        if (entity is! File) continue;
        final name = entity.uri.pathSegments.last;
        if (!name.endsWith(_fileExt)) continue;
        final stat = await entity.stat();
        if (now.difference(stat.modified) >= maxRetention) {
          try {
            await entity.delete();
          } catch (_) {}
        }
      }
    } catch (_) {}
  }

  static File _fileForTask(Directory dir, int taskId) =>
      File('${dir.path}/$taskId$_fileExt');

  /// [source] 一般为 [compressImageForUpload] 输出的待上传文件。
  static Future<void> saveForTask(int taskId, File source) async {
    if (taskId <= 0) return;
    if (!await source.exists()) return;
    final dir = await _directoryAfterPurge();
    final dest = _fileForTask(dir, taskId);
    await source.copy(dest.path);
  }

  static Future<String?> pathIfExists(int taskId) async {
    if (taskId <= 0) return null;
    final dir = await _directoryAfterPurge();
    final f = _fileForTask(dir, taskId);
    return await f.exists() ? f.path : null;
  }

  /// 仅查询 [ids] 中已有文件的 path，用于列表刷新后一次性填充状态。
  static Future<Map<int, String>> existingPathsForTaskIds(
    Iterable<int> ids,
  ) async {
    final dir = await _directoryAfterPurge();
    final out = <int, String>{};
    for (final id in ids) {
      if (id <= 0) continue;
      final f = _fileForTask(dir, id);
      if (await f.exists()) {
        out[id] = f.path;
      }
    }
    return out;
  }
}