Popular Picks: fix empty result for deezer (popularity threshold scale mismatch)

The discovery pool synthesizes deezer popularity onto a 0-100 score (base 45 + bonuses, capped at 100), but _get_popularity_thresholds had deezer on the raw-rank scale (500000/100000). So Popular Picks' 'popularity >= 500000' matched nothing — empty for every deezer-primary user — while Hidden Gems' '< 100000' caught the whole pool. Deezer thresholds now sit on the 0-100 scale (60/50, like Spotify's 60/40). Tested.

core/personalized_playlists.py

@@ -111,7 +111,10 @@ class PersonalizedPlaylistsService:
         Either value can be None to skip that filter for that source.
 
         - Spotify: 60 / 40 (the existing 0-100 popularity scale)
-        - Deezer:  500000 / 100000 (rank values — ballpark from real data)
+        - Deezer:  60 / 50 (ALSO 0-100 — the discovery pool SYNTHESIZES deezer popularity to a
+          0-100 score at scan time, capped at 100; it is NOT Deezer's raw rank. The old
+          500000/100000 rank thresholds matched nothing, so Popular Picks came back empty for
+          deezer users while Hidden Gems' < 100000 caught the whole pool.)
         - iTunes / others: None / None (no popularity data; fall back to no
           threshold filter, just diversity-on-random)
 
@@ -121,7 +124,7 @@ class PersonalizedPlaylistsService:
         if normalized == 'spotify':
             return 60, 40
         if normalized == 'deezer':
-            return 500_000, 100_000
+            return 60, 50
         # iTunes, hydrabase, anything else — no usable popularity data
         return None, None
 

tests/test_popularity_thresholds.py

@@ -0,0 +1,37 @@
+"""Popular Picks was empty for deezer users — wrong popularity-threshold scale.
+
+The discovery pool synthesizes deezer popularity onto a 0-100 score (base 45 + bonuses, capped
+at 100), but _get_popularity_thresholds had deezer on the raw-rank scale (500000/100000). So
+`popularity >= 500000` matched nothing (Popular Picks empty) while `< 100000` matched the whole
+pool (Hidden Gems caught everything). Thresholds must stay on the 0-100 scale.
+"""
+
+from __future__ import annotations
+
+from core.personalized_playlists import PersonalizedPlaylistsService
+
+
+def _svc():
+    return PersonalizedPlaylistsService(database=None)
+
+
+def test_deezer_thresholds_are_on_the_0_100_scale():
+    popular_min, hidden_max = _svc()._get_popularity_thresholds('deezer')
+    assert (popular_min, hidden_max) == (60, 50)         # was (500000, 100000) — unreachable
+    assert 0 < popular_min <= 100 and 0 < hidden_max <= 100
+    assert popular_min > hidden_max                       # popular tier sits above the hidden tier
+
+
+def test_spotify_thresholds_unchanged():
+    assert _svc()._get_popularity_thresholds('spotify') == (60, 40)
+
+
+def test_case_insensitive():
+    assert _svc()._get_popularity_thresholds('Deezer') == (60, 50)
+    assert _svc()._get_popularity_thresholds('SPOTIFY') == (60, 40)
+
+
+def test_sources_without_popularity_skip_the_filter():
+    assert _svc()._get_popularity_thresholds('itunes') == (None, None)
+    assert _svc()._get_popularity_thresholds('musicbrainz') == (None, None)
+    assert _svc()._get_popularity_thresholds('') == (None, None)