-- =============================================================
-- Attendance statistics view for GM analytics
-- Returns per-player aggregated metrics for a given game group.
-- NOTE: waitlist count reflects CURRENT registration_status only.
--       Full historical waitlist tracking will come with #15.
-- =============================================================

CREATE OR REPLACE FUNCTION get_group_attendance_stats(p_group_id UUID)
RETURNS TABLE (
    player_id           UUID,
    display_name        VARCHAR,
    telegram_username   VARCHAR,
    total_sessions      BIGINT,
    confirmed_count     BIGINT,
    declined_count      BIGINT,
    no_response_count   BIGINT,
    waitlisted_count    BIGINT,
    cancellation_affected_count BIGINT,
    attendance_rate     NUMERIC
) AS $$
BEGIN
    RETURN QUERY
    WITH player_sessions AS (
        SELECT
            sp.player_id,
            s.id                AS session_id,
            sp.rsvp_status,
            sp.registration_status,
            s.status            AS session_status,
            s.scheduled_at
        FROM session_participants sp
        JOIN sessions s ON s.id = sp.session_id
        WHERE s.group_id = p_group_id
    ),
    player_totals AS (
        SELECT
            ps.player_id,
            COUNT(*) FILTER (WHERE ps.session_status <> 'Cancelled')                      AS total_sessions,
            COUNT(*) FILTER (WHERE ps.rsvp_status = 'Confirmed' AND ps.session_status <> 'Cancelled') AS confirmed_count,
            COUNT(*) FILTER (WHERE ps.rsvp_status = 'Declined' AND ps.session_status <> 'Cancelled')  AS declined_count,
            COUNT(*) FILTER (WHERE ps.rsvp_status = 'Pending' AND ps.scheduled_at < NOW() AND ps.session_status <> 'Cancelled') AS no_response_count,
            COUNT(*) FILTER (WHERE ps.registration_status = 'Waitlisted' AND ps.session_status <> 'Cancelled') AS waitlisted_count,
            COUNT(*) FILTER (WHERE ps.session_status = 'Cancelled')                        AS cancellation_affected_count
        FROM player_sessions ps
        GROUP BY ps.player_id
    )
    SELECT
        pt.player_id,
        p.display_name,
        COALESCE(p.external_username, p.telegram_username) AS telegram_username,
        pt.total_sessions,
        pt.confirmed_count,
        pt.declined_count,
        pt.no_response_count,
        pt.waitlisted_count,
        pt.cancellation_affected_count,
        ROUND(
            100.0 * pt.confirmed_count
            / NULLIF(pt.total_sessions, 0),
            1
        ) AS attendance_rate
    FROM player_totals pt
    JOIN players p ON p.id = pt.player_id
    ORDER BY pt.confirmed_count DESC, pt.total_sessions DESC;
END;
$$ LANGUAGE plpgsql STABLE;
