-- Recommendation observability (#796 phase 4). Per-source play outcomes so the
-- operator can see whether each recommendation surface is landing and tune the
-- taste weights. Source is stamped on play_events when a play is launched from
-- a system-playlist surface ('for_you' | 'discover' | the discovery mixes);
-- NULL for library / radio / user-playlist plays, which are excluded here.

-- name: RecommendationSourceMetricsForUser :many
-- $1 user_id, $2 window_days. plays/skips are counts; avg_completion is the
-- mean completion ratio over plays that recorded one (0 when none did).
SELECT
    pe.source,
    count(*)::bigint AS plays,
    count(*) FILTER (WHERE pe.was_skipped)::bigint AS skips,
    COALESCE(
        avg(pe.completion_ratio) FILTER (WHERE pe.completion_ratio IS NOT NULL),
        0)::float8 AS avg_completion
FROM play_events pe
WHERE pe.user_id = $1
  AND pe.source IS NOT NULL
  AND pe.started_at > now() - ($2::float8 * INTERVAL '1 day')
GROUP BY pe.source
ORDER BY plays DESC;