Compute Available Offers per User

You are given a set of promotional offers and a CSV event stream read from standard input.

Each Offer has the following fields:

• name : string
• start_at : timestamp
• end_at : timestamp
• user_max_redemption_count : integer

Each OfferEvent row has:

• user_id : string
• offer_name : string
• event_time : timestamp

Each event represents one redemption attempt by a user for an offer.

Process the events in the order they appear. An event should be counted only if all of the following are true:

1. the referenced offer exists,
2. the event time is within the offer's validity window, inclusive: start_at <= event_time <= end_at ,
3. before applying the event, that user has redeemed the offer fewer than user_max_redemption_count times.

You are also given a PROCESSING_DATE.

After all events are processed, compute the offers that are still available to each user. An offer is available to a user on PROCESSING_DATE if:

• the offer is still active on that date: start_at <= PROCESSING_DATE <= end_at , and
• the user's counted redemptions for that offer are still below user_max_redemption_count .

Return a mapping from each user to the list of currently available offer names. If a user appears in the input but has no available offers, return an empty list for that user.

Example output:

{
  'user1': ['Offer_1', 'Offer_2'],
  'user2': ['Offer_1']
}

For deterministic output, sort each user's offer list lexicographically.