The five discovery-mix producers (Deep Cuts, Rediscover, New for you,
On this day, First listens) were near-identical boilerplate that
differed only in (a) which SQL query they ran and (b) whether to
diversity-cap the result. Folded into one produceDiscoveryMix(spec)
factory + a per-mix discoveryMixSpec slice. The registry composes the
factory over the spec list so adding a new mix is one struct literal
+ a SQL query, never a new func.
Also fixes the user-reported bug that several mixes 'show the same
content from yesterday'. Audit of the SQL queries:
- Deep Cuts: ORDER BY md5(t.id::text || $2::text) → day-keyed
- On this day: ORDER BY w.c DESC, md5(...) → day-keyed
- Rediscover: ORDER BY tier, c DESC, id → invariant
- New for you: ORDER BY al.created_at DESC, disc, track → invariant
- First listens: ORDER BY tier, al.id, disc, track → invariant
The three invariant ones produced identical content day-over-day. The
unified spec carries a dailyRotate bool: when set, the producer
applies a daily-deterministic offset rotate-left of the candidate
pool BEFORE diversify+truncate. Rotation (not shuffle) preserves
contiguous-block ordering inside each day's slice — matters for First
listens which is album-coherent.
Set on Rediscover + First listens (where same-content-every-day is
clearly a bug). Left off New for you because 'newest album first
regardless of day' is the intended UX for that surface — daily
rotation there would feel wrong.
Daily rotation seed: rand.New(NewSource(int64(userIDHash(userID,
dateStr)))) — same primitive used by For-You's pickHeadAndTail
sampling so behavior is consistent across the system playlist family.
No test file referenced the deleted produceXxx functions directly,
only the registry, so this is a closed refactor.
bvandeusen
7473e98d91