-- 004_event_triggers.sql — event-driven schedule triggers.
--
-- Until now schedules only supported cron. This migration adds:
--   * trigger_kind = 'event' schedules, powered by a CEL expression over
--     the event bus. Example: players_online == 0
--   * optional sustained-state: fire only after the condition has been
--     continuously true for N seconds. Enables "idle shutdown if 0 players
--     for 30m" without firing every 60s when the polled player count is 0.
--
-- cron_spec becomes nullable so event triggers can exist with NULL there.
-- Exactly one of cron_spec / event_spec is populated; the application
-- enforces this.

ALTER TABLE schedules ALTER COLUMN cron_spec DROP NOT NULL;

ALTER TABLE schedules
    ADD COLUMN event_spec             TEXT,
    ADD COLUMN event_sustained_seconds INTEGER NOT NULL DEFAULT 0;

CREATE INDEX idx_schedules_trigger_kind ON schedules(trigger_kind);