refa: download video (#1737)

* opt: save pb danmaku

* refa: download video

* opt: replaceAll

* fix: wait delete

* opt: remove completer

* fix: index.json

* tweaks

Signed-off-by: bggRGjQaUbCoE <githubaccount56556@proton.me>

---------

Co-authored-by: bggRGjQaUbCoE <githubaccount56556@proton.me>

lib/utils/em.dart

@@ -1,5 +1,6 @@
 abstract class Em {
   static final _exp = RegExp('<[^>]*>([^<]*)</[^>]*>');
+  static final _htmlRegExp = RegExp(r'&(lt|gt|quot|apos|nbsp|amp);');
 
   static String regCate(String origin) {
     Iterable<Match> matches = _exp.allMatches(origin);
@@ -17,14 +18,21 @@ abstract class Em {
       },
       onNonMatch: (String str) {
         if (str != '') {
-          str = str
-              .replaceAll('&lt;', '<')
-              .replaceAll('&gt;', '>')
-              .replaceAll('&quot;', '"')
-              .replaceAll('&apos;', "'")
-              .replaceAll('&nbsp;', " ")
-              .replaceAll('&amp;', "&");
-          res.add((isEm: false, text: str));
+          res.add((
+            isEm: false,
+            text: str.replaceAllMapped(
+              _htmlRegExp,
+              (m) => switch (m.group(1)) {
+                'lt' => '<',
+                'gt' => '>',
+                'quot' => '"',
+                'apos' => "'",
+                'nbsp' => ' ',
+                'amp' => '&',
+                _ => m.group(0)!,
+              },
+            ),
+          ));
         }
         return '';
       },

lib/utils/extension.dart

@@ -260,6 +260,14 @@ extension DirectoryExt on Directory {
       await delete(recursive: recursive);
     } catch (_) {}
   }
+
+  Future<bool> lengthGte(int length) async {
+    int count = 0;
+    await for (var _ in list()) {
+      if (++count == length) return true;
+    }
+    return false;
+  }
 }
 
 extension SizeExt on Size {

lib/utils/path_utils.dart

@@ -16,6 +16,8 @@ abstract final class PathUtils {
   static const _fileExt = '.m4s';
   static const audioNameType2 = 'audio$_fileExt';
   static const videoNameType2 = 'video$_fileExt';
+  static const coverName = 'cover.jpg';
+  static const danmakuName = 'danmaku.pb';
   static const downloadDir = 'download';
 
   static String buildShadersAbsolutePath(