Fix API calls by all workers

Quite a complex commit by GPT. I'll rewrite it somewhen

blueprints/risdeveau/modules/api/lb.py

@@ -11,6 +11,9 @@ from apscheduler.triggers.interval import IntervalTrigger
 import requests
 from flask import Flask, jsonify
 
+from .scheduler_guard import should_start_scheduler
+from .shared_cache import atomic_write_json, cache_file, load_json_if_newer
+
 
 @dataclass
 class Cache:
@@ -18,6 +21,7 @@ class Cache:
     last_updated = time()
     status = None
 
+
 data = {
     "caches": {
         "now": Cache(),
@@ -27,6 +31,55 @@ data = {
     "etag": ""
 }
 
+_IS_WRITER = should_start_scheduler()
+_CACHE_PATH = cache_file("listenbrainz")
+_CACHE_MTIME = 0.0
+
+
+def refresh_cache() -> None:
+    """Refresh in-memory cache from the shared JSON file (for non-writer workers)."""
+    global _CACHE_MTIME
+    if _IS_WRITER:
+        return
+
+    payload, mtime = load_json_if_newer(_CACHE_PATH, _CACHE_MTIME)
+    if payload is None:
+        return
+
+    try:
+        data["etag"] = payload.get("etag", data.get("etag", ""))
+        data["last_updated"] = payload.get("last_updated", data.get("last_updated", time()))
+        caches = payload.get("caches", {})
+        for key, cache in data.get("caches", {}).items():
+            if isinstance(caches, dict) and key in caches and isinstance(caches[key], dict):
+                c = caches[key]
+                cache.data = c.get("data", cache.data)
+                cache.last_updated = c.get("last_updated", cache.last_updated)
+                cache.status = c.get("status", cache.status)
+    finally:
+        _CACHE_MTIME = mtime
+
+
+def _persist_cache() -> None:
+    """Persist current cache state to the shared JSON file (writer worker only)."""
+    if not _IS_WRITER:
+        return
+
+    payload = {
+        "etag": data.get("etag", ""),
+        "last_updated": data.get("last_updated", time()),
+        "caches": {
+            k: {
+                "data": v.data,
+                "last_updated": v.last_updated,
+                "status": v.status,
+            }
+            for k, v in data.get("caches", {}).items()
+        },
+    }
+    atomic_write_json(_CACHE_PATH, payload)
+
+
 def yt_cover(youtube_url):
     parsed_url = urlparse(youtube_url)
 
@@ -42,6 +95,7 @@ def yt_cover(youtube_url):
 
     return f"https://img.youtube.com/vi/{video_id}/2.jpg"
 
+
 def parse_listens(json: dict) -> dict:
     cover_replacing = {
         "1e699948-c7c8-4bb2-9f8b-62e14b882a5d": "ca464c1d-5848-45bb-b92d-b1e4b00f9d65",
@@ -86,7 +140,11 @@ def parse_listens(json: dict) -> dict:
 
     return new_json
 
+
 def api_request(url: str, cache: Cache):
+    changed = False
+    prev_status = cache.status
+
     try:
         response = requests.get(url, timeout=10)
         if response.status_code == 200:
@@ -100,24 +158,36 @@ def api_request(url: str, cache: Cache):
                 data['etag'] = md5(''.join(
                     ( dumps(data['caches'][x].data) for x in data['caches'] )
                 ).encode()).hexdigest()
+                changed = True
         else:
             cache.status = f'error: {response.status_code}'
     except Exception as e:
         cache.status = f'error: {str(e)}'
 
-scheduler = BackgroundScheduler()
-scheduler.add_job(
-    func=lambda: api_request("https://api.listenbrainz.org/1/user/risdeveau/listens?count=5", data['caches']['listens']),
-    trigger=IntervalTrigger(minutes=1),
-    id='risdeveau.listenbrainz.listens',
-    replace_existing=True
-)
-scheduler.add_job(
-    func=lambda: api_request("https://api.listenbrainz.org/1/user/risdeveau/playing-now", data['caches']['now']),
-    trigger=IntervalTrigger(seconds=15),
-    id='risdeveau.listenbrainz.playing-now',
-    replace_existing=True
-)
-scheduler.start()
+    if prev_status != cache.status:
+        changed = True
 
-atexit.register(lambda: scheduler.shutdown())
+    if changed:
+        _persist_cache()
+
+
+scheduler = BackgroundScheduler()
+
+if _IS_WRITER:
+    scheduler.add_job(
+        func=lambda: api_request("https://api.listenbrainz.org/1/user/risdeveau/listens?count=5", data['caches']['listens']),
+        trigger=IntervalTrigger(minutes=1),
+        id='risdeveau.listenbrainz.listens',
+        replace_existing=True
+    )
+    scheduler.add_job(
+        func=lambda: api_request("https://api.listenbrainz.org/1/user/risdeveau/playing-now", data['caches']['now']),
+        trigger=IntervalTrigger(seconds=15),
+        id='risdeveau.listenbrainz.playing-now',
+        replace_existing=True
+    )
+    _persist_cache()
+    scheduler.start()
+    atexit.register(lambda: scheduler.shutdown())
+else:
+    refresh_cache()