Implement LAST, NEXT commands

lib/nntp/tiny/session.py

@@ -191,6 +191,60 @@ class Session():
 
         return self.respond(ResponseCode.NNTP_GROUP_LISTING, text)
 
+    def _cmd_last(self):
+        if self.newsgroup is None:
+            return self.respond(ResponseCode.NNTP_NEWSGROUP_NOT_SELECTED)
+
+        if self.article_id is None:
+            return self.respond(ResponseCode.NNTP_ARTICLE_INVALID_NUMBER)
+
+        sql = """
+            select
+                max(id)
+            from
+                newsgroup_message
+            where
+                newsgroup_id = ?
+                and id < ?
+        """
+
+        cr  = self.db.execute(sql, (self.newsgroup.id, self.article_id))
+        row = cr.fetchone()
+
+        if row is None or row[0] is None:
+            return self.respond(ResponseCode.NNTP_ARTICLE_NO_PREVIOUS)
+
+        self.article_id = row[0]
+
+        return self.respond(ResponseCode.NNTP_ARTICLE_STAT_RESPONSE)
+
+    def _cmd_next(self):
+        if self.newsgroup is None:
+            return self.respond(ResponseCode.NNTP_NEWSGROUP_NOT_SELECTED)
+
+        if self.article_id is None:
+            return self.respond(ResponseCode.NNTP_ARTICLE_INVALID_NUMBER)
+
+        sql = """
+            select
+                min(id)
+            from
+                newsgroup_message
+            where
+                newsgroup_id = ?
+                and id > ?
+        """
+
+        cr  = self.db.execute(sql, (self.newsgroup.id, self.article_id))
+        row = cr.fetchone()
+
+        if row is None or row[0] is None:
+            return self.respond(ResponseCode.NNTP_ARTICLE_NO_NEXT)
+
+        self.article_id = row[0]
+
+        return self.respond(ResponseCode.NNTP_ARTICLE_STAT_RESPONSE)
+
     def _newsgroup_summary(self, newsgroup: Newsgroup) -> str:
         sql = """
             select
@@ -587,6 +641,8 @@ class Session():
         'CAPABILITIES': _cmd_capabilities,
         'MODE':         _cmd_mode,
         'GROUP':        _cmd_group,
+        'LAST':         _cmd_last,
+        'NEXT':         _cmd_next,
         'LISTGROUP':    _cmd_listgroup,
         'LIST':         _cmd_list,
         'NEWNEWS':      _cmd_newnews,