Add a scheduled task to end open sessions

[yakkomajuri]

Documenting for myself

[mariusandra]

Actually... we could use the new retry queue system to schedule tasks to be run in the future. So we could schedule something to retry every 30min to check if a session has ended.

Assuming that PR is merged and we also have a fetchUser method, this could be the entire plugin:

export function processEvent(event, { storage, retry, fetchUser }) {
    if (!(await fetchUser(event.distinct_id))) {
        posthog.capture("session start")
        retry('checkIfSessionOver', { distinct_id: event.distinct_id }, 30 * 60) // in 30 min
    }
    storage.set('session_ping_' + event.distinct_id, new Date().valueOf())
}

export function onRetry(type, { distinct_id }, { retry }) {
    if (type === 'checkIfSessionOver') {
        const ping = await storage.get('session_ping_' + distinct_id, null)
        if (ping && new Date().valueOf() - ping > 30 * 60 * 1000) {
            storage.set('session_ping_' + event.distinct_id, undefined)
            posthog.capture("session end")
        } else if (ping) {
            retry('checkIfSessionOver', { distinct_id }, 30 * 60) // in another 30 min
        }
    }
}

[mariusandra]

NOTE: this is a whiteboard draft, not real plugin code

Rewritten to use cache

export function processEvent(event, { cache, retry, fetchUser }) {
    if ((await cache.incr(`session_${event.distinct_id}`)) === 0) {
        posthog.capture("session start")
        retry('checkIfSessionOver', { distinct_id: event.distinct_id }, 30 * 60) // in 30 min
    }
    cache.expire(`session_${event.distinct_id}`, 30 * 60)
}

export function onRetry(type, { distinct_id }, { cache, retry }) {
    if (type === 'checkIfSessionOver') {
        const ping = await cache.get(`session_${distinct_id}`, null)
        if (!ping) {
            posthog.capture("session end")
        } else {
            retry('checkIfSessionOver', { distinct_id }, 5 * 60) // check again in 5 min
        }
    }
}