feat: allow to remember read news items

The state is stored in $XDG_STATE_HOME/ruyi/news.read.txt. The stored
data is just plain text, with one alphabetically-sorted news item ID per
line.

ruyi/config/__init__.py

@@ -7,6 +7,7 @@
 from xdg import BaseDirectory
 
 from .. import log, argv0
+from .news import NewsReadStatusStore
 
 
 DEFAULT_REPO_URL = "https://mirror.iscas.ac.cn/git/ruyisdk/packages-index.git"
@@ -33,6 +34,8 @@ def __init__(self) -> None:
         self.override_repo_branch: str | None = None
         self.include_prereleases = False
 
+        self._news_read_status_store: NewsReadStatusStore | None = None
+
     def apply_config(self, config_data: GlobalConfigRootType) -> None:
         if pkgs_cfg := config_data.get("packages"):
             self.include_prereleases = pkgs_cfg.get("prereleases", False)
@@ -45,6 +48,19 @@ def cache_root(self) -> str:
     def data_root(self) -> str:
         return os.path.join(BaseDirectory.xdg_data_home, self.resource_name)
 
+    @property
+    def state_root(self) -> str:
+        return os.path.join(BaseDirectory.xdg_state_home, self.resource_name)
+
+    @property
+    def news_read_status(self) -> NewsReadStatusStore:
+        if self._news_read_status_store is not None:
+            return self._news_read_status_store
+
+        filename = os.path.join(self.ensure_state_dir(), "news.read.txt")
+        self._news_read_status_store = NewsReadStatusStore(filename)
+        return self._news_read_status_store
+
     def get_repo_dir(self) -> str:
         return self.override_repo_dir or os.path.join(self.cache_root, "packages-index")
 
@@ -82,6 +98,10 @@ def ensure_config_dir(cls) -> str:
     def ensure_cache_dir(cls) -> str:
         return BaseDirectory.save_cache_path(cls.resource_name)
 
+    @classmethod
+    def ensure_state_dir(cls) -> str:
+        return BaseDirectory.save_state_path(cls.resource_name)
+
     @classmethod
     def get_config_file(cls) -> str | None:
         # TODO: maybe allow customization of config root

ruyi/config/news.py

@@ -0,0 +1,29 @@
+class NewsReadStatusStore:
+    def __init__(self, path: str) -> None:
+        self._path = path
+        self._status = set()
+        self._orig_status = set()
+
+    def load(self) -> None:
+        try:
+            with open(self._path, "r") as fp:
+                for l in fp:
+                    self._orig_status.add(l.strip())
+        except FileNotFoundError:
+            return
+
+        self._status = self._orig_status.copy()
+
+    def __contains__(self, key: str) -> bool:
+        return key in self._status
+
+    def add(self, id: str) -> None:
+        return self._status.add(id)
+
+    def save(self) -> None:
+        if self._status == self._orig_status:
+            return
+
+        content = "".join(f"{id}\n" for id in self._status)
+        with open(self._path, "w", encoding="utf-8") as fp:
+            fp.write(content)