-- Session Analysis -- split each user's event stream into sessions based on
-- inactivity gap, then aggregate per session.
--
-- Required parameters (clickhouse.Named):
--   workspace_id    : String
--   from            : DateTime64(3,'UTC')
--   to              : DateTime64(3,'UTC')
--   timeout_seconds : UInt32
--   limit           : UInt32
--   offset          : UInt32
--
-- Optional parameters (template-driven):
--   user_id : String   (when .HasUserID)
SELECT
    user_id,
    session_index                              AS session_id,
    min(timestamp)                             AS started_at,
    max(timestamp)                             AS ended_at,
    count()                                    AS events,
    dateDiff('second', min(timestamp), max(timestamp)) AS duration_seconds
FROM (
    SELECT
        user_id,
        timestamp,
        sum(is_new_session) OVER (PARTITION BY user_id ORDER BY timestamp) AS session_index
    FROM (
        SELECT
            user_id,
            timestamp,
            if(
                dateDiff(
                    'second',
                    lagInFrame(timestamp) OVER (PARTITION BY user_id ORDER BY timestamp),
                    timestamp
                ) > {timeout_seconds:UInt32},
                1,
                0
            ) AS is_new_session
        FROM events_track
        WHERE workspace_id = {workspace_id:String}
          AND received_at >= {from:DateTime64(3,'UTC')}
          AND received_at <  {to:DateTime64(3,'UTC')}
          AND user_id != ''
{{- if .HasUserID }}
          AND user_id = {user_id:String}
{{- end }}
    )
)
GROUP BY user_id, session_index
ORDER BY started_at DESC
LIMIT {limit:UInt32}
OFFSET {offset:UInt32}