Update existing redis values when parsing pages

If we're parsing a page for a symbol that's out of the cache
and encounter a symbol that was already cached we can update that symbol
to keep it up to date without additional requests

2 files changed, 25 insertions, 6 deletions

diff --git a/bot/exts/info/doc/_cog.py b/bot/exts/info/doc/_cog.py
index 67a21ed72..678134f3c 100644
--- a/bot/exts/info/doc/_cog.py
+++ b/bot/exts/info/doc/_cog.py
@@ -36,6 +36,8 @@ FORCE_PREFIX_GROUPS = (
 WHITESPACE_AFTER_NEWLINES_RE = re.compile(r"(?<=\n\n)(\s+)")
 NOT_FOUND_DELETE_DELAY = RedirectOutput.delete_delay
 
+doc_cache = DocRedisCache(namespace="Docs")
+
 
 class DocItem(NamedTuple):
     """Holds inventory symbol information."""
@@ -116,7 +118,9 @@ class CachedParser:
         while self._queue:
             item, soup = self._queue.pop()
             try:
-                self._results[item] = get_symbol_markdown(soup, item)
+                markdown = get_symbol_markdown(soup, item)
+                await doc_cache.set_if_exists(item, markdown)
+                self._results[item] = markdown
             except Exception:
                 log.exception(f"Unexpected error when handling {item}")
             else:
@@ -161,8 +165,6 @@ class CachedParser:
 class DocCog(commands.Cog):
     """A set of commands for querying & displaying documentation."""
 
-    doc_cache = DocRedisCache()
-
     def __init__(self, bot: Bot):
         self.base_urls = {}
         self.bot = bot
@@ -174,7 +176,7 @@ class DocCog(commands.Cog):
         self.scheduled_inventories = set()
 
         self.bot.loop.create_task(self.init_refresh_inventory())
-        self.bot.loop.create_task(self.doc_cache.delete_expired())
+        self.bot.loop.create_task(doc_cache.delete_expired())
 
     async def init_refresh_inventory(self) -> None:
         """Refresh documentation inventory on cog initialization."""
@@ -292,12 +294,12 @@ class DocCog(commands.Cog):
             return None
         self.bot.stats.incr(f"doc_fetches.{symbol_info.package.lower()}")
 
-        markdown = await self.doc_cache.get(symbol_info)
+        markdown = await doc_cache.get(symbol_info)
         if markdown is None:
             log.debug(f"Redis cache miss for symbol `{symbol}`.")
             markdown = await self.item_fetcher.get_markdown(self.bot.http_session, symbol_info)
             if markdown is not None:
-                await self.doc_cache.set(symbol_info, markdown)
+                await doc_cache.set(symbol_info, markdown)
             else:
                 markdown = "Unable to parse the requested symbol."
 
diff --git a/bot/exts/info/doc/_redis_cache.py b/bot/exts/info/doc/_redis_cache.py
index c617eba49..2230884c9 100644
--- a/bot/exts/info/doc/_redis_cache.py
+++ b/bot/exts/info/doc/_redis_cache.py
@@ -28,6 +28,23 @@ class DocRedisCache(RedisObject):
             )
 
     @namespace_lock
+    async def set_if_exists(self, item: DocItem, value: str) -> None:
+        """
+        Set markdown `value` for `key` if `key` exists.
+
+        Keys expire after a week to keep data up to date.
+        """
+        expiry_timestamp = datetime.datetime.now().timestamp() + 7 * 24 * 60 * 60
+
+        with await self._get_pool_connection() as connection:
+            if await connection.hexists(f"{self.namespace}:{item.package}", self.get_item_key(item)):
+                await connection.hset(
+                    f"{self.namespace}:{item.package}",
+                    self.get_item_key(item),
+                    pickle.dumps((value, expiry_timestamp))
+                )
+
+    @namespace_lock
     async def get(self, item: DocItem) -> Optional[str]:
         """Get markdown contents for `key`."""
         with await self._get_pool_connection() as connection: