json

job_thread/main.py

@@ -1,7 +1,8 @@
+import json
 import logging
-import sqlite3
+from copy import deepcopy
 from dataclasses import dataclass
-from os import environ
+from os import environ, fsync
 from time import time
 
 import feedparser
@@ -11,7 +12,7 @@ SECONDS_IN_WEEK = 60 * 60 * 24 * 7
 
 
 class Config:
-    DB_PATH = "posts.db"
+    DB_PATH = "db.json"
     SUBREDDIT = "developersindia"
 
     POST_FLAIR = "Hiring"
@@ -34,34 +35,79 @@ Stay tuned for updates on the latest job openings, and apply for the ones that i
     FEED_URL = "https://developersindia.in/?feed=job_feed"
 
 
-class Database:
+@dataclass
-    def __init__(self, db_path):
+class Post:
-        self.conn = sqlite3.connect(db_path)
+    post_id: str
-        self.conn.row_factory = sqlite3.Row
+    epoch: int
 
-        self.cur = self.conn.cursor()
+
+def dict_raise_or_set(d, key, value):
+    if d.get(key) is not None:
+        raise ValueError(f"Key {key} already present in dictionary")
+
+    d[key] = value
+
+
+class Database:
+    POSTS = "postid_epoch"
+    COMMENTS = "jobid_commentid"
+
+    def __init__(self, db_path):
+        try:
+            self._fp = open(db_path, "r+")
+            self._db = json.loads(self._fp.read() or "{}")
+        except FileNotFoundError:
+            self._fp = open(db_path, "w")
+            self._db = {}
+
+        self._copy = None
 
         self._create()
 
+    def __enter__(self):
+        self._copy = deepcopy(self._db)
+
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        # We re-write the DB on each transaction as we cannot guarantee "atomicity"
+        # when dealing with external APIs. Eg, we can locally roll back a transaction
+        # inserting multiple posts into the DB in case of an exception, but the
+        # posts obviously won't be deleted on the reddit side. So we write
+        # as much as possible incrementally to prevent losing track of already created
+        # posts, preventing their re-creation server side in case of a crash.
+        if exc_type:
+            self._db = self._copy
+        # If a change was actually made
+        elif self._db != self._copy:
+            self._fp.seek(0)
+            self._fp.write(json.dumps(self._db, indent=4))
+            self._fp.truncate()  # Trim the file to the desired size
+            fsync(self._fp)
+
+        self._copy = None
+
     def _create(self):
-        with self.conn:
+        with self:
-            self.cur.execute(
+            self._db.setdefault(self.POSTS, {})
-                "CREATE TABLE IF NOT EXISTS Posts"
+            self._db.setdefault(self.COMMENTS, {})
-                "(post_id TEXT PRIMARY KEY, time INTEGER NOT NULL DEFAULT(UNIXEPOCH()))"
-            )
 
-    def get_latest_post(self):
+    def get_latest_post(self) -> Post | None:
-        self.cur.execute("SELECT post_id, time from Posts ORDER BY time DESC")
+        # {"id": 1234, "id2": "5678"} -> ("id2", "5678") (Descending)
+        try:
+            result = sorted(
+                self._db[self.POSTS].items(),
+                key=lambda item: item[1],
+                reverse=True,
+            )[0]
+        except IndexError:
+            return None
 
-        if (result := self.cur.fetchone()) is not None:
+        return Post(post_id=result[0], epoch=result[1])
-            return dict(result)
 
-    def insert_post(self, post_id: str, timestamp: int):
+    def insert_post(self, post: Post):
-        with self.conn:
+        with self:
-            self.cur.execute(
+            dict_raise_or_set(self._db[self.POSTS], post.post_id, post.epoch)
-                "INSERT INTO Posts (post_id, time) VALUES ((?), (?))",
-                (post_id, timestamp),
-            )
 
 
 @dataclass
@@ -94,14 +140,14 @@ def get_job_entries(feed_url):
     ]
 
 
-def should_create_new_post(latest_post):
+def should_create_new_post(latest_post: Post) -> bool:
     if latest_post is not None:
-        return (time() - latest_post["time"]) >= SECONDS_IN_WEEK
+        return (time() - latest_post.epoch) >= SECONDS_IN_WEEK
 
     return True
 
 
-def create_job_post(subreddit):
+def create_job_post(subreddit) -> Post:
     # https://old.reddit.com/r/redditdev/comments/ovte4q/praw_flair_a_post/h7doqmd/?context=3
     flair = next(
         filter(
@@ -117,7 +163,7 @@ def create_job_post(subreddit):
     )
     submission.mod.sticky()
 
-    return submission
+    return Post(post_id=submission.id, epoch=submission.created_utc)
 
 
 def main():
@@ -141,24 +187,22 @@ def main():
     if should_create_new_post(maybe_old_post):
         # Un-stick/pin the old post
         if maybe_old_post is not None:
-            logging.info(f"Un-pinning old post")
+            logging.info(f"Un-pinning old post {maybe_old_post}")
 
             try:
-                reddit.submission(maybe_old_post["post_id"]).mod.sticky(
+                reddit.submission(maybe_old_post.post_id).mod.sticky(
                     state=False
                 )
             except Exception:
                 logging.warning(f"Failed to un-pin post!", exc_info=True)
 
-        new_submission = create_job_post(subreddit)
+        new_post = create_job_post(subreddit)
 
-        logging.info(
+        logging.info(f"Created new post {new_post}")
-            f"Created new post {new_submission.id} at {new_submission.created_utc}"
-        )
 
-        db.insert_post(new_submission.id, new_submission.created_utc)
+        db.insert_post(new_post)
 
-    submission = reddit.submission(db.get_latest_post()["post_id"])
+    submission = reddit.submission(db.get_latest_post().post_id)
 
     logging.info(f"Fetched latest submission {submission.id}")